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Characterization, Cleanup, and Revitalization of Mining Sites

Cleanup Technologies

A range of traditional and innovative technologies may be appropriate for remediation at current and former mining sites. EPA's Office of Research and Development's Engineering Technical Support Center (ETSC) provides assistance to EPA regional offices, states, and communities on the design, function, and application of these technologies. ETSC scientists and engineers work closely with the Superfund program and other EPA programs that address remediation of mining sites, and also collaborate with state governments, universities, and private entities to develop new approaches and remediation technologies for mining wastes.

A resource, Review of Peer Reviewed Documents on Treatment Technologies Used at Mining Waste SitesAdobe PDF Logo, by EPA's Office of Superfund Remediation and Technology Innovation, provides a comprehensive evaluation of mine treatment technologies used to remediate waste rock, tailings, pit lakes, water from adits, underground workings, leachate, groundwater and surface water. The guide includes a description of each technology, detailed case study evaluation(s), costs, limitations, lessons learned, and provides references to find additional information on a given technology. Pre-and post-treatment data collected from peer-reviewed case studies for several treatment technologies is provided in the Appendices of the guide to allow users to further assess the effectiveness of various treatment technologies.

EPA's Office of Superfund Remediation and Technology Innovation's 2014 report, Reference Guide to Treatment Technologies for Mining-Influenced WaterAdobe PDF Logo, highlights select mining-influenced water (MIW) treatment technologies used or piloted as part of remediation efforts at mine sites. The report includes short descriptions of treatment technologies and information on the contaminants treated, pre-treatment requirements, long-term maintenance needs, performance, and costs. Sample sites illustrate considerations associated with selecting a technology. Website links and sources for more information on each topic are also included. Appendix A of the guide summarizes the technologies discussed in the body of the report, as well as additional technologies or products designed as passive or low-cost treatment options.

The Interstate Technology and Regulatory Council's (ITRC) web-based technical and regulatory guidance site, Mining Waste Treatment Technology Selection, is a tool for selecting an applicable technology or suite of technologies for remediation of mining sites. The guidance uses a series of questions to point users to a set of treatment technologies that may be applicable to a particular site. The website provides an overview of each technology with information about its applicability, advantages, limitations, performance, stakeholder and regulatory considerations, and lessons learned, as well as links to applicable case studies.

The EPA Abandoned Mine Site Characterization and Cleanup Handbook (2000)Adobe PDF Logo provides a compendium of information gained during many years of experience on mine site cleanup projects. Chapter 10 summarizes several conventional and innovative (as of 2000) treatment technologies; collection, diversion, and containment technologies; reuse, recycle, and reclamation; and institutional controls.

The technology information below is adapted from the technology overviews on ITRC's Mining Waste Technology Selection site, with a link to the entry for each technology.

Mining Solid Waste

Capping, Covers, and Grading — Capping, or covering of solid mining waste, is an effective treatment technology that can be used as a short-term, interim measure or as a long-term or final action. Installation of a cap or cover on solid mining waste can reduce or eliminate erosion, fugitive dust emissions, and infiltration of water to prevent the migration of contaminants. A variety of materials is available and the technology can be modified to adapt to site-specific conditions. Caps and covers can be used alone or with other treatment technologies. The cap or cover must be maintained to ensure its effectiveness. Institutional controls also may be required.

  • The Ridgeway TMF Cover System After 20 Years of Atmospheric Forcing. What We Knew Then and NowAdobe PDF Logo
    Meiers, G., Z. Kenyon, P. Butsavage, and M. Pernito. | Proceedings of the 16th International Conference on Mine Closure, 2-5 October, Reno, NV, 2023
    The Rio Tinto, Kennecott Ridgeway Mining Company tailings management facility (TMF) was reclaimed with a dry cover system and is a unique case study spanning over 20 years of closure performance. The TMF contains ~60 million tonnes of potentially acid-generating tailings (PAG). After mining operations ceased, the TMF was reclaimed with a hydraulically-placed saprolite clay water store-and-release cover system. A key performance objective of the cover system is maintaining high saturation in the cover and tailings, thereby limiting oxygen ingress and providing geochemical stability to the potentially acid-generating tailings. Vegetation on the cover is primarily Bermuda grasses, millet, and sericea lespedeza. The vegetation was originally mowed to maintain the grassland but was discontinued later, allowing woody brush species to colonize the landform. Vegetation management was implemented in 2022 to return the cover to the original grassland vegetation. The cover system design was supported by numerical simulations of water balance to evaluate performance under varying climatic conditions. A field response numerical simulation model was developed to gain further insight into the predicted performance of the cover system. A cover system assessment program was implemented to obtain multiple lines of evidence to support the performance of the cover system following 22 years of atmospheric forcing, including an in situ sampling and characterization program to assess vegetation characteristics and geotechnical and geochemical properties of the tailings and cover material. The oxygen ingress rate through the cover system was estimated to be 1-5 mol/m2/yr, suggesting that vegetation management could reduce the oxygen ingress rate. The degree of saturation in the tailings and cover material ranged from 68%-100%, supporting the estimated oxygen ingress.
  • Design and Regulatory Approval of a Novel In-Situ Salt Cap for Final Closure of Contaminated Wastewater Ponds at a Brine Mining OperationAdobe PDF Logo
    Lundmark, K., D. Abranovic, and A. Kafle.
    Proceedings of the 16th International Conference on Mine Closure, 2-5 October, Reno, NV, 2023
    A novel cap closure technology was developed to close a series of large (over 4 sq km) earthen evaporation ponds at a brine mining operation adjacent to the Great Salt Lake in Utah. The cap design included in situ precipitation of a salt cap (primarily NaCl) to prevent contact between humans and wildlife with contaminated sediments and mine wastes contained in the facility's wastewater evaporation ponds. The nature-based salt cap is designed to mimic naturally occurring salt beds present regionally in the Great Basin and is preferable over traditional closure approaches because 1) saturated wastes and sediments in the ponds are not suitable for traditional earthwork equipment operation; 2) long haul distances for waste disposal or importing cap materials; and 3) the size of the wastewater evaporation ponds and large volume of wastes/sediments. Salt cap design parameters, including annual salt deposition rates (in cm), brine requirements, and salt weathering rates were estimated through a multi-year field-scale pilot test at a salt accumulation test cell constructed within the footprint of one of the wastewater evaporation ponds. Pilot testing also evaluated the effects of brine sources on salt deposition rates, where brine was obtained either from Great Salt Lake or from solar evaporation ponds brine feedstock for the mining operations. Key technical challenges addressed during salt cap design included the construction of interior partitions, irregular/sloping beds, and groundwater discharge areas within the wastewater evaporation ponds; expected timeframe for construction; and potential for contaminant leaching upward into the salt cap. EPA approved the salt cap closure as the approach for final closure of the wastewater evaporation ponds under both Superfund and RCRA programs. This technology also uses sustainability best management practices to limit the use of natural resources and energy, reduce negative environmental impacts, and minimize or eliminate greenhouse gases to the greatest extent possible.
  • First Five-Year Review Report Holden Mine Site Okangan-Wenatchee National Forest Chelan County, WashingtonAdobe PDF Logo
    USDA, Forest Service, Pacific Northwest Region, 74 pp, 2018
    The Holden Mine produced about 200 million lbs of Cu, 40 million lbs of Zn, two million ounces of Ag, and 600,000 ounces of Au from ~10 million tons of ore. Excavation of 60 miles of underground tunnels produced 8.5 million tons of mill tailings placed on 90 acres of U.S. National Forest lands as well as 300,000 yd3 of waste rock piles. Direct release of hazardous materials from the mine, including acid mine drainage, heavy metals (Al, Cd, Cu, Fe, Pb, and Zn), and iron sulfide, affected about 125 acres of land. The remedy is being conducted in two phases. Phase 1, which began in 2013 with completion expected in 2018, includes regrading and capping the tailings and main waste rock piles, constructing a groundwater barrier wall and groundwater collection system around Tailings Pile 1 and the Lower West Area, constructing a new groundwater treatment facility, beginning in situ soil treatment (e.g., application of agricultural lime) in areas of interest, implementing institutional controls, and initiating performance verification monitoring. Phase 2 is expected to begin in 2023. In situ treatment is still under technical review and consideration for implementation due to environmental constraints, potential destruction of established forests and habitats, rough topography, and practicability of the remedy.

  • Cold Desert Evapotranspiration Cover System Design
    Bunting, L., J. Keller, M. Milczarek, C. Jim, and K. Bansah.
    Proceedings of the 16th International Conference on Mine Closure, 2-5 October, Reno, NV, 2023
    The effectiveness of 0.3 m, 0.9 m, and 1.5 m thick monolayer evapotranspiration (ET) cover systems was evaluated at the Round Mountain Gold Corporation mine in central Nevada to minimize net percolation of precipitation into underlying potential acid-generating waste rock. Each test plot is ~200 m2 and includes three cover system performance monitoring stations with sensors placed at ~0.6 m intervals along a vertical profile in the cover and waste rock to 2.4 m max depths. The sensors measure soil matric potential, temperature, water content, and direct net percolation water flux. Soil water content and matric potential data were used to evaluate the cover systems' capacity to store infiltrated precipitation and to remove water via ET. Direct net percolation flux measurements were collected below the estimated depth of ET to provide a point estimate of net percolation flux into the waste rock. The site-specific seed mix applied to the test plots did not establish, so vegetation primarily comprises invasive annuals. Annual precipitation from 2012 to 2021 represented long-term average precipitation conditions. Wetting was observed to a max depth of 1.2 m at the 0.3 m and 1.5 m ET plots. The deepest wetting (1.8 m) was observed in the 0.9 m ET plot due to focused run-on at two monitoring stations. Soil profile drying occurred in late spring and early summer at all plots in response to decreased precipitation and increased ET. The average annual net percolation flux over the monitoring period was 0 for the 0.3 and 1.5 m ET cover systems and 0.1% of precipitation for the 0.9 m cover system, most likely due to run-on to the test plot. Results indicate no difference in the effectiveness of 0.3 m, 0.9 m, and 1.5 m ET cover systems in minimizing net percolation of precipitation into underlying waste rock.
  • Design and Construction of a Combination Soil and Water Cover on a Tailings Storage Facility in Tasmania
    Cahill, C., R. Longey, and D. Tonks.
    Mine Waste and Tailings Conference, 13-14 July, Brisbane, Australia, 11 pp, 2023
    The Main Creek Tailings Dam (MCTD), located at the Savage River Mine in northwest Tasmania is transitioning from an upstream-constructed operational tailing storage facility (TSF) to closure. Tailings stored in the MCTD are potentially acid-forming (PAF), requiring careful management through operation and closure to minimize the risk of Acid and Metalliferous Drainage (AMD) forming in the TSF. The site is situated on Tasmania's west coast, with rainfall significantly exceeding evaporation. While a water cover would typically be most suitable, due to the upstream constructed embankments, a soil cover was required adjacent to embankments to meet long-term stability requirements. During operations, three trial covers were constructed to monitor the performance over several years. Data obtained was used to evaluate cover performance and calibrate numerical transient seepage models. Based on the trial cover performance, the preferred cover was a combination of clay and rock fill cover that maintained a high degree of saturation in the clay, minimizing oxygen ingress to the underlying tailings and reducing the likelihood of AMD formation. The preferred clay and rock combination cover was assessed and optimized during the detailed design phase by undertaking 2-dimensional transient unsaturated seepage modeling in SVFlux, considering a conservative climate scenario. The construction process, challenges, and QA/QC are described in the article.
  • Mine Rock Stockpile Reclamation Trial, Detour Lake Mine: Design, Construction, and Lessons LearnedAdobe PDF Logo
    Cash, A.E., C.A. Mendoza, J. Straker, V. Raizman, K. Lyle, and G. McKenna.
    British Columbia Mine Reclamation Symposium, 19-22 September, Kimberly, BC, 13 pp, 2022
    A large-scale (10 ha) Test Cover Trial on waste rock stockpiles during the early stages of mining is being designed, established, monitored, and evaluated at Detour Lake Mine. Results will be used to develop guidance for beneficial strategies for landform design and progressive reclamation. The design included 13 cover trial treatments with varying characteristics to consider geotechnical aspects (i.e., constructability, stability, erodibility), ecological aspects (i.e., plant and root development, habitat development), and hydrological aspects (i.e., partitioning water between evapotranspiration, surface runoff, net percolation). The available cover materials were silt rich with variable amounts of peat. Design variables for the trial included ranges in waste rock slope angles, reclamation cover thickness, composition, surface grading, and revegetation treatments to accommodate the unique and challenging properties of these materials. Design modifications were required during construction to accommodate operational challenges and site conditions. Modifications were also necessary to decrease cover density, account for minimal to variable peat content, and compensate for reduced planting densities while maintaining the design intent. Insights into operational-scale construction methods and techniques gained throughout the construction process are being applied to ongoing progressive reclamation at the mine. Monitoring results are described in a companion paper. Companion paper:
  • Laboratory and Field-Based Assessment of the Effects of Sediment Capping Materials on Zinc Flux, Bioabailability, and ToxicityAdobe PDF Logo
    Cervi, E.C., K. Thiamkeelakul, M. Hudson, A. Rentschler, S. Nedrich, S.S. Brown, et al.
    Environmental Toxicology and Chemistry 39(1)240-249(2020)
    A former mining site was remediated and restored with a focus on disconnecting mine spoils from groundwater and managing the quantity and quality of runoff. However, a remaining task is to ensure that concentrations of Zn in the stream outflow of a pit lake are reduced below water quality standards. The efficacy of AquaBlok™, limestone, and limestone-bone char capping materials for decreasing Zn dissolution from sediments under natural and reasonable worst-case conditions (pH = 5.5) was evaluated. Field exposures were conducted in situ in limnocorrals and ex situ in core tube mesocosms. Simultaneous in situ and ex situ toxicity tests were conducted using Daphnia magna, Hyalella azteca, and Chironomus dilutus exposed to surficial sediments, caps, and hypolimnetic overlying waters for 4 d. No differences in responses between treatments involving sediment capping materials in both in situ and ex situ tests were observed, likely due to dissolved Zn in surface water being below the hardness-adjusted threshold effects levels (164 µg/L). Both studies provided site-specific data to select an effective remedy with reduced uncertainty compared to laboratory and chemistry-only approaches.

  • Conversion of an Evapotranspiration Soil Cover to a Geosynthetic Cover for a Waste Rock Facility Closure Adobe PDF Logo
    Yuan, P.H., G. Zhan, A. Jones, and R. Hufford.
    Proceedings of the 16th International Conference on Mine Closure, 2-5 October, Reno, NV, 2023
    This article presents a case study, where parts of an existing evapotranspiration (ET) cover were replaced with a geomembrane overlain by a geocomposite drainage material to achieve low percolation rates at the Rain Mine in northern Idaho. The ET cover was constructed in 2002 on a waste rock facility (WRF), 2,020 m above mean sea level where annual precipitation, primarily snow, is estimated at 442 mm. Mature vegetation was established by 2011. Estimated percolation through the WRF was ~12% of annual average precipitation (2011-2019). The high percolation rate occurs because accumulated snow is difficult to manage with an ET cover in a snowmelt hydrology setting. Existing ET cover soils were salvaged and placed on the geosynthetic cover. The geosynthetic cover system was constructed on the part of the WRF that receives most wind-drifted snowfall deposits. The case study summarizes a performance evaluation of the ET soil cover, characterization data collected, and geotechnical analyses performed to support the new cover design. Construction experience learned from the execution of the project and performance data of the new cover system collected to date are also presented. Preliminary results indicate that the seepage rate from the WRF was significantly reduced after installation of the new cover.
  • Evapotranspiration Covers at Uranium Mill Sites
    Caldwell, T.G., S. Tabatabai, J.M. Huntington, G.E. Davies, and M. Fuhrmann.
    Vadose Zone Journal 21(5):e20222(2022)
    This update reviews the current state of the science regarding evapotranspiration (ET) covers and considerations for long-term applications. Waste isolation is a key strategy to mitigate risk from municipal solid waste (MSW) and hazardous waste streams. Conventional covers at MSW facilities are designed for a 30-yr post-closure period where compacted soils and geosynthetics are used to minimize percolation into buried waste. ET covers have shown beneficial use for MSW management by encouraging infiltration, storage, and precipitation transpiration to minimize percolation. Uranium Mill Tailings Radiation Control Act sites were covered by a clay radon barrier, creating tortuous flow paths that allow radioactive decay and attenuation of short-lived, 222Rn gas. An ET-radon cover may provide greater resilience for long-term waste isolation by exploiting natural processes instead of resisting them.
  • Global Cover System Design: Technical Guidance DocumentAdobe PDF Logo
    International Network for Acid Prevention (INAP), 216 pp, 2017
    Designed primarily for those investigating the use of cover systems on mine sites, this document offers a "best practice" summary to assist mine operators, designers, and regulators to address the role cover systems play over the life of the mine, from early conceptualization to long-term performance monitoring. A conceptual model illuminates how cover system designs might affect contaminant and acidity loading. The model attempts to determine when the varying roles of cover system design (e.g., control of net percolation or oxygen ingress) might influence loadings. Acknowledgment of these unique relationships provides an opportunity to optimize cost-effective management of metal loading and acid rock drainage. The cover system design tool walks users through relevant climatic factors to optimize cover system design alternatives and meet desired performance design criteria.

Chemical Stabilization Using Phosphate and Biosolids Treatment — This technology addresses soil, sediment, or mine tailings at remote, rural, and urban locations and can be used for small and large volumes of wastes. Phosphate treatment can be used by itself or with other technologies as an interim or final remedy. Ex situ treatment is more widely used than in situ and frequently is applied in conjunction with off-site disposal. In situ treatment has proven effective at reducing the bioavailability of lead and other heavy metals and providing a relatively nontoxic growth medium for previously barren mine/mill waste. In situ treatment has been used in mines as a coating on exposed ore surfaces but the technology has not been widely used to stabilize lead-contaminated soil in residential settings. Chemical phosphate treatments use a variety of phosphate species, but phosphoric acid has been demonstrated to be the most effective. Organic sources of phosphate such as biosolids or composted animal wastes also are used to stabilize, reclaim, and revegetate barren mine and mill wastes.

  • Restoration and Risk Reduction of Lead Mining Waste by Phosphate-Enriched Biosolid AmendmentsAdobe PDF Logo
    Li, N., X. Tang, J. Yang, and Z. Sun. | Scientific Reports 11:8965(2021)
    A field study was conducted to stabilize Pb using six phosphate (P)-enriched biosolid amendments in contaminated mining wastes (average of 1004 mg Pb/kg) at the Jasper County Superfund site in Missouri. The six amendments were Mizzou doo compost (MD), spent mushroom compost (SMC), turkey litter compost (TLC), composted chicken litter (CCL), composted sewage sludge (CSS), and triple superphosphate (TSP). Kentucky tall fescue seeds were planted following the treatments, and soil and plant samples were collected and analyzed 8-10 years post-treatment. In all cases, the biosolid treatments resulted in significant reductions in bioaccessible Pb (96.5-97.5%), leachable Pb (95.0-97.1%), and plant tissue Pb (45.5-90.1%) in the treated wastes, as compared with the control. Treatments had no significantly toxicological effect on soil microbial community. Analysis of the Pb fractionation revealed that Pb risk reduction was accomplished by transforming labile Pb fractions to relatively stable species through the chemical stabilization reactions induced by the treatments. The solid-phase microprobe analysis confirmed the formation of pyromorphite or pyromorphite-like minerals after treatment. Among the six biosolid amendments examined, SMC and MD treatments were most effective in stabilizing and reducing Pb risk.
  • Bonita Peak Mining District Biocement-A Pilot StudyAdobe PDF Logo
    EPA Region 8, 2 pp, 2019
    Environmental Toxicology and Chemistry 39(1)240-249(2020)
    One of the leading sources of metals loading to nearby waterways originates from the runoff of contaminated soils from mine tailings in the Bonita Peak Mining District. To stabilize the solid media in source areas, EPA is implementing a BioCement pilot study on the north side of the former Kittimac Mill. BioCement technology provides an innovative erosion control strategy that uses "microbial induced calcite precipitation." to solidify loose soils into rock. Four 5' x 15' areas of the Kittimac site will be treated with BioCement over two months. If successful, this technology will be used to stabilize additional tailings and soil.

Electrokinetics — The electrokinetic remediation (ER) process is an in situ soil processing technology that separates and removes metals and organic contaminants from low-permeability soil, mud, sludge, and marine dredging. ER uses electrochemical and electrokinetic processes to desorb, and then remove, metals and polar organics. Targeted contaminants for electrokinetics are heavy metals, anions, and polar organics. Contaminant concentrations that can be treated range from a few parts per million (ppm) to tens of thousands ppm. There have been few commercial applications of electrokinetic remediation in the United States.

  • Enhanced Remediation of CD-Contaminated Soil Using Electrokinetic Assisted by Permeable Reactive barrier with Lanthanum-Based Biochar Composite Filling Materials
    Li, S., Y. Wu, X. Li, Q. Liu, H. Li, W. Tu, X. Luo, and Y. Luo.
    Environmental Technology [Published online 4 March 2022 before print]
    Biochar and a novel lanthanum-based biochar composite (LaC) were synthesized from the malignant invasive plant Eupatorium adenophorum and used as inexpensive and environmentally benign permeable reactive barrier (PRB) filling material. The PRB was combined with electrokinetic remediation (EK) to remediate simulated and actual Cd-contaminated soil. During remediation, pH and residual Cd concentration in the simulated contaminated soil gradually increased from the anode to the cathode used to apply an electric field to the EK-PRB system. However, the soil conductivity changed in the opposite way; current density first increased and then decreased. For simulated contaminated soils with initial Cd concentrations of 34.9 and 100.6 mg/kg, the mean Cd removal rates achieved using LaC were 90.6% and 89.3%, respectively, significantly higher than those of biochar (P < 0.05). Similar results were achieved using natural soil from the mining area and contaminated farmland, with Cd removal rates of 66.9% and 72.0%, respectively. Fourier-transform infrared and X-ray photoelectron spectroscopy indicated many functional groups on the LaC surfaces. The removal mechanism of EK-PRB for Cd in contaminated soil includes electromigration, electroosmotic flow, surface adsorption, and ion exchange. Results indicated that LaC could be used in the EK-PRB technique to efficiently decontaminate heavy metals-contaminated soil.
  • In Situ Electrokinetic (EK) Remediation of the Total and Plant Available Cadmium (CD) in Paddy Agricultural Soil Using Low Voltage Gradients at Pilot and Full Scales
    Cao, Z., Y. Sun, Y. Deng, X. Zheng, S. Sun, M. Romantschuk, and A. Sinkkonen.
    Science of The Total Environment 785:147277(2021)
    A 14-day electrokinetic (EK) remediation was carried out in a field pilot (4 m2) test and a full-scale (200 m2) application at a Cd-contaminated paddy agricultural field near a mining area. A low voltage of 20 V was applied at both scales; the voltage gradients were 20 V/m (pilot) and 4 V/m (full scale). Samples were taken from near the anode and cathode, and in the middle of the electric field, in 0-10 cm, 10-20 cm, and 40-50 cm soil layers. After EK remediation, a significant portion of the total Cd was removed in all the layers at the pilot-scale, by 87%, 72%, and 54% from the top down; 74% was removed in the 0-10 cm layer at full scale. Significant removal (64%) of plant-available Cd was observed in the 0-10 cm layer at the pilot scale. The percentage reduction of the electrical conductivity and removal efficiency of the total Cd was higher near the anode than the cathode. The soil pH was elevated near the cathode but stayed below pH 6 due to the sufficient supply of lactic acid. After remediation, the concentration of the total Cd dropped below the 0.4 mg/kg dry wt soil hazard threshold for agricultural paddy fields in China. A total energy of 2 kW·h and 0.6 kW·h was consumed at the pilot and full scales, respectively.

  • Electrokinetic Remediation of Manganese and Zinc in Copper Mine Tailings
    Ortiz-Soto, R., D. Leal, C. Gutierrez, A. Aracena, A. Rojo, and H.K. Hansen.
    Journal of Hazardous Materials 365:905-911(2019)
    In an evaluation of the effect of initial acidity and electric field intensity on the electrokinetic remediation of Mn and Zn from mine tailings at a Chilean copper mine, experiments focused on the effect of the applied electric field (1 and 2 V/cm), the H2SO4 concentration during pretreatment (1 and 2 mol/L) and the interaction between these factors in Mn and Zn concentration. From the obtained results, Mn and Zn can be removed from the analyzed tailings, with maximum net removal of 31.88% and 17.95%, respectively. Electromigration enhancement was confirmed by an analysis of variance with a significance level of 10% for the soluble and total metal concentration in the cathodic zone, where total concentration was increased to 24% and 11% for Zn and Mn, respectively.
  • Acid Pond Sediment and Mine Tailings Contaminated with Metals: Physicochemical Characterization and Electrokinetic Remediation
    Karaca, O., C. Cameselle, and K.R. Reddy.
    Environmental Earth Sciences 76(12):[408](2017)
    Mine tailings and acid pond sediment from a former mining area in Canakkale (Turkey) were analyzed for physical (e.g., moisture content, particle size, specific gravity, and hydraulic conductivity) and chemical parameters (e.g., organic content, pH, ORP, and EC) as well as metal content and sequential extraction analysis in an attempt to evaluate their risk as a source of contaminants. Column tests demonstrated that Fe and Pb can be released to waterbodies in contact with the solid materials. Pb was released more easily than Fe due to its content in the more labile fractions in the sequential extraction analysis. When electrokinetic remediation was tested for metals removal from mine tailings and sediment, the technique removed 20% of Pb and Fe in 9 days of treatment at 1 VDC/cm. Metals removal efficiency was strongly affected by metal speciation. Electrokinetics removed metal fractions I-IV, especially in the closest section to the anode of the solid matrix, and the metals accumulated in the following sections. Results suggested that Fe and Pb could be removed from the mine tailings and sediment effectively if the advance of the acid front was favored and the treatment time increased, but considering the physicochemical characterization and electrokinetic treatment results, other green and more sustainable remedial strategies must be proposed for mitigation of environmental risks of former mining areas, such as metals immobilization and stabilization via phytocapping.

Excavation and Disposal — Excavation and disposal of contaminated soil, sediment, or tailings is an effective and proven technology that usually involves the removal of contaminated material with heavy equipment. This technology can be modified to adapt to site-specific conditions. Soil, sediment, or tailings can be removed so that the remaining contaminant concentrations meet cleanup goals. Excavated soil, sediment, or tailings can be disposed of either on-site (in an approved repository constructed for this purpose or another location where the exposure pathways allow the material to be beneficially reused) or off-site in a permitted disposal facility. Excavation and disposal can be used by itself as an interim or final remedy or with other technologies.

Soil Amendments — Cleanup treatments at mining sites may involve the addition of amendments to the contaminated soil. Soil amendments are materials added to soils to revitalize and make them suitable for sustaining plant life or development. Mining sites with contaminated or disturbed soils exhibit a variety of problems that often can be addressed effectively and directly through the use of soil amendments. Project managers could evaluate their effects in the subsurface, their potential for eventual transport to surface waters, and their possible subsequent adverse effects on plant and animal communities.

  • Can a Blend of Amendments Be An Important Component of a Rehabilitation Strategy for Surface Coal Mined Soils?
    Abraha, A.B., E.H. Tesfamariam, and W.F. Truter.
    Sustainability 11: 4297(2019)
    The role of different amendments to alleviate compaction problems in rehabilitated mine soils were quantified in this study using 5 single amendments and 3 different blends of amendments mixed thoroughly with degraded mine soil in a 1:3 (amendment:soil) ratio. Two additional unamended soils with different bulk densities (BD) were included as benchmarks. Amendment applications reduced BD by 4-20%, enhanced infiltration rate by 15-70%, increased porosity by 5-35% and increased plant available water (PAW) by 9-33% compared with the unamended soils. Between amendments, the blends of amendments reduced BD by 9-16%, enhanced infiltration rate by 17-59%, increased porosity by 6-32%, and PAW by 4-28% compared with single amendments. A blend of amendments had better soil restoration capacity through improving porosity, infiltration rate, and plant-available water. This article is Open Access at
  • Phytostabilization of ZN and CD in Mine Soil Using Corn in Combination with Biochars and Manure-Based Compost
    Sigua, G.C., J.M. Novak, D.W. Watts, J.A. Ippolito, T.F. Ducey, M.G. Johnson, et al.
    Environments 6(6):69(2019)
    The effect of biochar additions (BA) with or without manure-based compost (MBC) was evaluated on shoots biomass, roots biomass, uptake, and the bioconcentration factor (BCF) of Zn and Cd in corn (Zea mays L.) grown in mine soil. Biochar additions of beef cattle manure (BCM), poultry litter (PL), and lodgepole pine were applied at 0, 2.5, and 5.0% (w/w) in combination with different rates (0, 2.5, and 5.0%, w/w) of MBC, respectively. Shoots and roots uptake of Cd and Zn were significantly affected by BA, MBC, and the interaction of BA and MBC. Corn plants that received 2.5% PL and 2.5% BCM had the greatest Cd and Zn shoot uptake, respectively. Corn plants with 5% BCM had the greatest Cd and Zn root uptake. When averaged across BAs, the greatest BCF for Cd in the shoot (92.3) was from application of BCM and the least BCF was from application of PL (72.8). The incorporation of biochar enhanced phytostabilization of Cd and Zn. Concentrations of water-soluble Cd and Zn were lowest in soils amended with manure-based biochars, which improved the biomass productivity of corn. This article is Open Access at
  • Effects of Composted Biosolids and Manuer Applications for Prairie and Wetland Restoration on Remediated Mine Lands: Oronogo-Duenweg Mining Belt Site, Webb City, MOAdobe PDF Logo
    Nichols, J., S. Hamilton, D.E. Mosby, and E. Gramlich.
    Missouri Dept. of Natural Resources/U.S. Fish and Wildlife Service, 136 pp, 2017
    In a 2-year pilot study conducted to evaluate the potential environmental benefits and impacts of using composted manure products as a soil amendment on lead and zinc mine lands, different compost mixtures composed of cattle manure, poultry litter, municipal biosolids, wood chips, and conventional fertilizers were tested in both upland and wetland soils. Test plots established using the different compost mixtures were sampled to evaluate potential contaminants in stormwater runoff, changes in bioavailability and plant uptake of soil metals, and plant growth and diversity. Overall results of this study indicate that cattle manure-based composted soil amendments tended to perform better than the other amendments in terms of providing the best growth medium for the seeded native vegetation and producing relatively low levels of excess nutrients and metals in surface runoff. Few differences were observed in effects between the high (80 tons/acre) and low (40 tons/acre) application rates. The researchers concluded that application rates, within the range tested, could be scaled according to site-specific soil conditions without a significant increase in potential negative environmental impacts.
  • Using Organic Amendments to Restore Soil Physical and Chemical Properties of a Mine Site in Northeastern Oregon, USA Adobe PDF Logo
    Page-Dumroese, D.S., M.R. Ott, D.G. Strawn, and J.M. Tirocke.
    Applied Engineering in Agriculture 34(1):43-55(2018)
    The U.S. Department of Agriculture, Forest Service, in cooperation with the City of Bend, Oregon, initiated a mine tailing reclamation project in the Umatilla National Forest in northeastern Oregon to determine the benefits of surface-applied organic amendments. Researchers established a field study using organic amendments applied to gold dredgings capped with 10 cm of loam and showing little evidence of regeneration. Study plot applications consisted of biochar, biosolids, or wood chips singly or in combination. Each plot was divided in half, and one half was seeded with native grasses and forbs, and the other was planted with a combination of California brome and Jepson's blue wild rye. After two growing seasons, no significant differences were observed in plant cover between the planted or seeded plots, but soil properties were significantly altered by individual treatments. Combination treatments improved nutrient availability and soil moisture and grew up to twice as much plant cover as the control plots.

Mining-Influenced Water (MIW)

Aeration Treatment Systems — Aeration is a relatively simple and effective treatment process in which mechanical introduction of oxygen is used to enhance the oxidation and decrease the solubility of metals in MIW. Aeration can be used with other treatment technologies and often is applied together with acid-neutralizing agents, chemical oxidants, flocculants, and settling basins. The array of aeration technologies can be used at a broad range of sites that vary in site and flow conditions.

Anoxic Limestone Drains (ALD) — ALDs are low-cost, passive treatment systems that can be used to treat the acidity of MIW under specific geochemical conditions. ALDs are easy to construct and maintain, and consist of a buried bed of limestone engineered to intercept anoxic, acidic MIW and add alkalinity through dissolution of the limestone. ALDs can be used alone, but are more commonly used together with other treatment technologies such as constructed wetlands. They can be installed in remote locations and utilities are not required for implementation. The effectiveness of most ALD systems declines over time and they eventually require maintenance or replacement.

  • Review of Passive Systems for Acid Mine Drainage Treatment Adobe PDF Logo
    Skousen, J., C.E. Zipper, A. Rose, P.F. Ziemkiewicz, R. Nairn, L.M. McDonald, and R.L. Kleinmann.
    Mine Water Environment 36(1):133-153(2017)
    This paper reviews the current state of passive system technology development for the treatment of acid mine drainage, provides results for various system types, and offers guidance for system sizing and effective operation.
  • Passive Biological Treatment of Mine Water to Reduce Conductivity: Potential Designs, Challenges, and Research Needs Adobe PDF Logo
    Smyntek, P.M., R.C. Wagner, L.-A. Krometis, S.C. Sanchez, T. Wynn-Thompson, and W.H.J. Strosnider.
    Journal of Environmental Quality 46:1-9(2017)
    Passive biological treatment systems can be effective in removing acidity and metals from mine water, but review of current literature suggests that their ability to reduce conductivity appears somewhat limited. Some systems, particularly those that do not incorporate limestone into their construction materials, have been observed to reduce conductivity by 30-40%, which might prove useful as a pretreatment or finishing component of a larger treatment system, or in the treatment of legacy discharges. Design optimization will require identification of the ionic constituents responsible for primary conductivity constituents in various regions, long-term monitoring data of current systems that might not have been designed primarily to treat conductivity, and evaluation of the environmental factors governing underlying biogeochemical processes responsible for specific ion removals. Ideally, field-scale monitoring efforts will concurrently evaluate downstream impacts on aquatic ecology.

Biochemical Reactors — Passive treatment refers to processes that do not require frequent human intervention, operation, or maintenance, and typically employ natural construction materials, natural treatment media, and promote growth of natural vegetation. Biochemical reactors (BCRs) are an engineered passive treatment system that use microorganisms to remove contaminants from MIW. An organic substrate is typically used to promote microbial and chemical reactions that reduce concentrations of metals, acidity and sulfate. BCRs can be lower-maintenance treatment options for mining site cleanups and offer significant opportunities to reduce the environmental footprint associated with treatment of MIW.

Community Guide

  • Bioremediation for Acid Mine Drainage and Heavy Metals Contamination
    Uy, B. and L. Fairchok. Geo Engineer, April 21, 2021
    One method of remediating acid mine drainage includes the usage of bioreactors powered by sulfate-reducing bacteria (SRB). Sulfate-reducing bacteria are grown with some organic material, like cow manure or peat. These bacteria, in anaerobic conditions, use the organic carbon (CH2O) from these environments to reduce sulfate (SO42-) to sulfide (H2S), which reacts with the dissolved metal ions created by the reactions with pyrite and water to precipitate them. This decreases available concentrations of sulfate and dissolved metal ions from the original acid mine effluent, neutralizes pH from reduction of sulfate and removal of free hydronium (H3O+) ions, and additionally produces the pH buffer bicarbonate (HCO3-), which increases the pH of the acid mine effluent (produces alkalinity). By exposing this effluent to these bacteria, cleaner water can be discharged from mines. Case studies of Lilly and Orphan Boy Mine and Sure Thing Mine are presented and compared to understand the efficiencies of bioreactors with sulfate-reducing bacteria and the evolution in their designs. The mines are both located within similar regions in mountainous Montana, with similar climate, geology, and contaminants, but have very different methods of using sulfate-reducing bacteria in bioreactors. Because the remediation of Lilly and Orphan Boy Mine occurred before Sure Thing, the design ideology and lessons learned can be compared from one mine to the other.
  • Assessment of Bed Hydraulics and Metal Loadings in a Passive Vertical Flow Bioreactor in Commerce, Oklahoma
    Cremeans, M.M., J.F. Devlin, T.C. Osorno, and R.W. Nairn.
    Groundwater Monitoring & Remediation 39(3):40-47(2019)
    A passive vertical flow bioreactor (VFBR) engineered treatment pond was used to remediate groundwater contaminated from improperly abandoned, over-drilled, and cased legacy boreholes at the Mayer Ranch in Commerce, Oklahoma. The VFBR promoted metal sorption and precipitation as sulfides by established reducing conditions in the groundwater. To verify that operations were unhindered by nonuniform flow in the VFBR, a flow uniformity assessment was done using a streambed point velocity probe (SBPVP), which was independently validated with a water balance. The outflow calculated from the SBPVP data came within 30% of the value suggested by measured inflow rates to the pond, supporting the conclusion that flow through was occurring with a satisfactory level of uniformity. Water flow rates through the reactive bed were up to an order of magnitude greater than those employed in prior column testing, contributing to metal loading rates estimated to be 2 orders of magnitude greater than those tested in the columns. Rapid chemical reactions that likely occurred close to the pond water-sediment interface contributed to the treatment system achieving its design objectives. More information
  • Voluntary Reclamation and Remediation of the Former Garfield Vanadium Mine Site, Rifle, Colorado Part I: Remedial Investigation, Remedy Selection, and Reclamation
    Nielsen, B., C. Beul, J. Rusch, and L. Santisteban. | Technical Sessions: Smart Mining: Resources for a Connected World, 24-27 Feb 2019, Denver, Colorado. p 106 [plus Part II, p 107], 2019
    The Garfield Mine is a legacy vanadium mine in western Colorado. The site's multiple mine openings, waste rock piles, and adit seepages were voluntarily remediated through the Colorado Voluntary Cleanup Program (VCUP). The remediation process involved performing the site investigation under the supervision of a licensed radioactive materials handler while working with VCUP and the state's Radiation Management Unit. The remedial action objectives (RAOs) under VCUP included preventing direct human or biotic exposure to the waste rock and radiation emitting from the waste rock and maintaining the existing undeveloped character of the surrounding landscape. The site-wide design involved regrading, installation of an infiltration barrier and rock cover, a diversion channel, and a biologically based passive remediation water treatment system. The full-scale biologically based system, operational since 2017, was chosen to reduce metal concentrations and radionuclides in adit seepage (sulfate, Se, Zn, U, Ra, and gross alpha and beta particles) and prevent discharge from the site. The system consists of a sulfate-reducing biochemical reactor and post-treatment aerobic polishing cells that provide year-round operation and zero discharge of effluent. After 12 years of site investigations, the remedial action was completed in 2016 and 2017 with all RAOs met and a no-further-action determination granted in 2018.

  • Construction of a Passive Sulfate Treatment SystemAdobe PDF Logo
    Robinson, J., I. Andrews, and J. Dodd. Mine Closure 2022: 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 367-374, 2022
    The third phase of a project to construct a passive sulfate reduction system with sulfur sequestering is reported in this paper. The tiered approach included bench- and pilot-scale systems to prove the feasibility of the system using a biochemical reactor (BCR) with different proportions of wood chips, straw, manure, limestone, and biochar to culture sulfate-reducing bacteria. The project also tested the use of a fixed-bed anaerobic bioreactor (FBAR), where alcohol was added to enhance the sulfate reducer activity. Three BCRs and two FBARs were set up for this stage of the assessment. The resulting treated leachate was passed through different media types to remove sulfur species generated by the bacteria, using an aerobic wetland to polish the effluent. The success of the bench-scale (Tier 1) project led to the construction of a pilot-scale system (Tier 2). The system operated continuously through 2021, with planning permission being awarded for the project, and construction (Tier 3) occurring in late 2022/early 2023.
  • Co-Remediation of Acid Mine Drainage and Industrial Effluent Using Passive Permeable Reactive Barrier Pre-Treatment and Active Co-Bioremediation
    Thisani, S.K., D.V. Von Kallon, and P. Byrne. | Minerals 12:565(2022)
    A study evaluated the performance of an active-passive process comprised of passive permeable reactive barrier acid mine drainage (AMD) pre-treatment and active anaerobic digestion AMD treatment using effluent as a carbon source. The bioreactor was operated for 24 days with peak chemical oxygen demand (COD) and sulfate loading rates of 6.6 kg COD/m3/day and 0.89 kg SO42-/m3/day, respectively. The AMD pre-treatment removed 99% of Fe, 94% of K, and 42% of Al concentrations. Biological treatment removed 89.7% of COD and 99% of sulfate concentrations. Cu, SO42-, and pH in treated wastewater were within South Africa's effluent discharge limits and potable water standards. Fe, Al, Mn, Ni, and Zn concentrations in the treated wastewater were marginally higher than the discharge and potable water limit, with all concentrations exceeding the limit by less than 0.65 mg/L. The remediation performance of the process was effective with limited operational inputs, which can enable low-cost co-remediation. This article is Open Access at
  • Passive Multi-Unit Field-Pilot for Acid Mine Drainage Remediation: Performance and Environmental Assessment of Post-Treatment Solid Waste
    Vasquez, Y., C.M. Neculita, G. Caicedo, J. Cubillos, J. Franco, M. Vasquez, A. Hernandez, and F. Roldan. | Chemosphere [Published online 23 November 2021 prior to print]
    The performance of a passive multi-unit field pilot to treat AMD from a coal mine in Colombia Andean Paramo was assessed. The multi-unit field-pilot combined a pre-treatment unit (550 L) filled with dispersed alkaline substrate and six passive biochemical reactors (PBRs; 220 L) under open (PBRs-A) and closed (PBRs-B) configurations to the atmosphere. The AMD quality was 1200 ± 91 mg/L Fe, 38.0 ± 1.3 mg/L Mn, 8.5 ± 1.6 mg/L Zn, and 3200 ± 183.8 mg/L SO42-, at pH 2.8. The input and output effluents were monitored to establish AMD remediation. Physicochemical stability of the post-treatment solids, including metals (Fe2+, Zn2+, and Mn2+) and sulfates for environmental contamination from reactive mixture post-treatment, was also assessed. A total removal of 74% SO42-, 63% Fe2+, and 48% Mn2+ in the PBRs-A, and 91% SO42, 80% Fe2+, and 66% Mn2+ removal was achieved in the PBRs-B. A 99% removal for Zn2+ was achieved in both without significant differences (p < 0.05). A study of the physicochemical stability of the post-treatment solids showed the PBRs could produce acidic leachates capable of releasing large quantities of Fe and Mn if they are disposed of under oxidizing conditions; contact with water or any other leaching solutions must be avoided. The different PBR configurations induced changes in the performance of the passive multi-unit field pilot during AMD remediation.
  • Successful Passive Treatment of Sulfate Rich Water Adobe PDF Logo
    Robinson, J., J. Dodd, I. Andrews, J. Gusek, L. Josslyn, and E. Clarke.
    Proceedings of the 14th IMWA Congress, Mine Water Management for Future Generations, 12-15 July, virtual, 8pp, 2021
    A passive sulfate reduction system with iron scrubbers was identified as the most viable option to treat elevated sulfate in landfill leachate. Bench-scale trials were conducted using a biochemical reactor with different proportions of wood chips, straw, manure, limestone, and biochar to culture sulfate-reducing bacteria. The concept of 'bugs on booze' was also trialed using a fixed bed anaerobic bioreactor, where alcohol was added to enhance the sulfate reducer activity. The resulting treated leachate was then passed through haematite, magnetite, and iron filings to remove sulfide generated by the bacteria, with an aerobic wetland used to polish the effluent. The success of the bench-scale project led to a pilot-scale system being constructed and monitored in Spring 2020. Results confirmed the success of the bench-scale testing and provided useful insights to manage the system, particularly in winter months.
  • Land Application Disposal System Design for Biochemical Reactor Treated Effluent
    Anton, N.R., D.T. Shanight, C.S. Storrar, M.J. Fischer, E.M. Janoviak, and B. Lala
    36th Annual Meeting of the American Society of Mining & Reclamation, 3-7 June, Big Sky, MT, 26 slides, 2019
    At the mine waste repository for the Upper Tenmile Creek Mining Area Superfund site, Montana, collected leachate water has been managed in an active water treatment plant and pilot biochemical reactor system, with disposal to a land application disposal (LAD) system since 2003. In 2018, the design was completed for a full-scale leachate passive treatment system utilizing parallel BCR cells, post-treatment settling, aeration, limestone channels, and a gravity-operated LAD system. The new system construction will begin in 2019, and the existing water treatment infrastructure will be decommissioned after the new system is operational and functional. The presentation includes the critical passive treatment design components and provides details of the pre-design investigation and design approach for the LAD system, including field siting for the LAD, test pits, soil lithology logging, permeability testing, soil metal sorption studies, metal sorption capacity and water balance calculations, and hydraulic design of the LAD.
    More information:
  • 2014 Treatability Study Date Evaluation: Barker-Hughesville Mining District Superfund Site Adobe PDF Logo
    U.S. EPA Region 8, 1050 pp, 2017
    In 2014, two treatability studies were conducted for the Barker-Hughesville Mining District Superfund Site as part of the remedial investigation/feasibility study process. Year 2 of the Danny T Adit study continued the 2013 year 1 field pilot study to evaluate various passive and semi-passive methods for treatment of the Danny T Mine adit water. The bench-scale study for the Tiger Mine was focused on potential in situ-based treatments that could be deployed inside the underground mine workings area. A representative mine discharge water (Tiger mine adit TI-AD004, the "Firehose" adit) was collected in bulk and analyzed at the treatability laboratory in batch container tests with various reagents. The report summarizes each of these studies, including their objectives, experimental and sampling procedures, results, conclusions, and recommendations.
  • Selenium, Uranium, and Nitrate: Treatment of Troublesome Contaminants in Mining Wastewaters - EBR Case Studies
    Opara, A., J. Adams, J. Fudyma, and J. Bowden.
    Journal of American Society of Mining and Reclamation 7(2):19-34(2018)
    This paper discusses an application of the electro-biochemical reactor (EBR) technology for Se, U, and NO3 bio-reduction and removal from mining wastewaters. Three case studies are presented, based on laboratory bench- and onsite pilot-scale trials with significantly different mining waters, each contaminated with varying concentrations of Se, U, and NO3. The EBR was demonstrated on all three sites to treat the waters to <0.5-3.2 µg/L Se, <0.1-0.8 µg/L U, and <0.02-<2 mg/L NO3-N.
  • Operation and Maintenance of Passive Treatment Systems
    Hedin, R.
    The 23rd British Columbia MEND Metal Leaching/Acid Rock Drainage Workshop, Vancouver. 32 slides, 2016
    Passive treatment of contaminated mine drainage is less costly than active treatment, but its reliability is sometimes questioned. A simple approach is presented that has been used to design effective passive treatment systems in Pennsylvania. Three systems that demonstrate commonly utilized passive technologies are described along with long-term monitoring data: (1) the Marchand system of oxidation/settling ponds and a constructed aerobic wetland; (2) the Anna S system of vertical flow ponds and aerobic wetlands; and (3) the Scootac system of a drainable limestone bed and settling pond. The systems have provided highly reliable and effective treatment for 3 to 18 years. The data demonstrate that properly designed, constructed, and maintained passive treatment systems are a highly cost-effective solution for contaminated mine discharges.
  • Year-Round Performance of a Passive Sulfate-Reducing Bioreactor that Usess Rice Bran as an Organic Carbon Source to Treat Acid Mine Drainage
    Sato, Y., T. Hamai, T. Hori, H. Habe, M. Kobayashi, and T. Sakata.
    Mine Water and the Environment [Publication online 2 Sep 2017 prior to print]
    The project objective was to demonstrate the stable operation of a sulfate-reducing bioreactor for at least a year in terms of continuous acid mine drainage (AMD) sulfate reduction and metal removal. The 35-L bioreactor contains sulfate-reducing bacteria (SRB) and a packed inoculum layer of a mixture of rice husks, limestone, and field soil covered with rice bran. During operation, the AMD input flow rate was adjusted to 11.7 mL/min (hydraulic retention time 50 h). Throughout the year, physicochemical analyses of system input and output AMD samples revealed that both pH and oxidation-reduction potential values remained consistent with the process of sulfate reduction by SRB, although this reduction was stronger in summer than in winter. Metal concentrations at the outlet port of <0.33 mg/L Zn, <0.08 mg/L Cu, and <0.005 mg/L Cd more than met Japan's national effluent standards. Illumina sequencing of 16S rRNA genes revealed the dominance of Desulfatirhabdium butyrativorans-related species within the bioreactor.
  • Closed Loop for AMD Treatment Waste Adobe PDF Logo
    Zamzow, K. and G. Miller. IMWA 2017: Mine Water & Circular Economy (Wolkersdorfer, C. et al., eds.). IMWA, Vol II:1103-1110(2017)
    The Leviathan is an abandoned former copper and sulfur mine located in the Sierra Nevada of the Western United States. Acid mine water at the site is addressed in four compost-free, open-pond, alcohol-based bioreactors that have operated since 2003, treating 11.4 to 15.1 million liters of drainage annually. To take advantage of a local opportunity, a manufacturing waste product rich in alcohols from biodiesel (BD) production at a nearby agricultural farm was used in a 55-day pilot study as a replacement for the ethanol usually used in the bioreactor system. Final results showed that although sulfate reduction was not as high as previous years, most metals were removed below effluent discharge requirements, particularly when appropriate hydraulic residence time was achieved. The investigators observed that cold climates may challenge consistent delivery of BD waste from storage tank to bioreactor.
  • Passive Treatment of Highly Contaminated Iron-Rich Acid Mine Drainage Adobe PDF Logo
    Neculita, C.M., T.V. Rakotonimaro, B. Bussiere, T. Genty, and G.J. Zagury.
    2017 National Meeting of the American Society of Mining and Reclamation, Morgantown, WV, 9-13 April. ASMR, Champaign, IL. 43 slides, 2017
    An investigation of the effectiveness of acid mine drainage treatment systems—DAS (dispersed alkalinity substrate) units, consisting of coarse organic matrix (wood chips) and neutralizing materials (calcite, magnesia), and a mixed treatment system comprising passive biochemical reactors (PBRs: wood waste-based and constructed wetlands)—compared the performance of a 2-yr lab study and two field treatment installations. In the lab, DAS-calcite, DAS-dolomite, or DAS-wood ash for iron pretreatment, prior to sulfate removal by PBR, was followed by a final polishing unit. In the field, a pilot tri-unit (two passive biochemical reactors separated by a wood-ash unit) system was installed on the Lorraine rehabilitated mine site and monitored over a 5-yr period. Up to 99% Fe removal occurred during lab testing (using two DAS-wood ash pretreatment units) relative to the field pilot (76% Fe removal). On East-Sullivan, a second rehabilitated mine site, a 14-yr monitoring dataset for a mixed treatment system showed the progressive improvement of water quality over time. Iron concentration declined 98%, and regulation requirements (Fe < 3 mg/L) were obtained in most of the discharge locations.

  • Anaerobic Bioreactor Technology (ABT) for the Treatment of Acid Mine Drainage (AMD)
    Bhavya, K., S. Begum, and A.G. Rao. Biotechnological Innovations in the Mineral-Metal Industry. ISBN 978-3-031-43624-6, ISBN 978-3-031-43627-7, Chapter 10:161-178(2024)
    Chapter 10 critically reviews the available aerobic and anaerobic bioreactor technologies, emphasizing anaerobic bioreactors to treat AMD. In the remediation of AMD, the anaerobic process is a biological remediation that neutralizes acidity and precipitates metal contaminants by natural microbial consortia, preferably sulfate-reducing bacteria (SRB). As the AMD is associated with low organic matter, an external factor carbon source is required to complete the remediation process. Anaerobic bioreactors, such as membrane bioreactors, continuous stirred tank reactors, bioelectrochemical systems, and up-flow sludge blanket reactors, are suitable bioreactor processes for the treatment of AMD wherein the syntrophic activity of both SRBs and other fermentative and few methane forming bacteria takes place. Through the application of SRBs, these anaerobic reactors are paving the way in treating AMD due to their efficacy and cost-effectiveness. However, the addition of external organic substances is required during the treatment of AMD with SRB, which could play a pivotal role in determining the cost of the technology. Comparing the passive and active SRB-based alternatives, their substrate choice, the recent advances in the anaerobic treatment of AMD, and future perspectives as an alternative to conventional techniques are discussed.

  • Performance of a Sulfidogenic Bioreactor Inoculated with Indigenous Acidic Communities for reating an Extremely Acidic Mine Water
    Gonzales, D., Y. Liu, D.V. Gomez, G. Southam, S. Hedrich, P. Galleguillos, C. Colipai, et al.
    Minerals Engineering 131:370:375(2019)
    This study tested the performance of a low pH sulfidogenic bioreactor inoculated with an indigenous microbial community to treat mine-impacted water. The inoculum was obtained from anaerobic sediments collected from an acidic river located in northern Chile. The sulfidogenic bioreactor system (2.3 L) was operated as a continuous flow mode unit for 99 days at 30°C and fed with synthetic water based on the chemical composition of the acidic river. The bioreactor pH was set to 4.5 initially and was increased in stages to pH 6.0 during the experiment. Results show that zinc concentrations in liquors draining the bioreactor were below the detection level in most of the samples analyzed. Increasing the glycerol concentration increased the removal of iron (70%), but generated acetic acid (from 1 to 5 mM). Microbial populations changed with varying operation parameters, and a known acetogenic sulfidogen (Desulfoporosinus acididurans) became more dominant over time.
  • Low-Cost Biological Treatment of Metal- and Sulphate-Contaminated Mine Water Adobe PDF Logo
    Neale, J.W., H.H. Muller, M. Gericke, and R. Meuhlbauer.
    Mine Water & Circular Economy (Wolkersdorfer, C. et al., eds.). IMWA, Vol I:453-461(2017)
    A passive biological sulfate reduction process was developed using a substrate mix comprising wood chips, wood shavings, hay, lucerne, and cow manure to address mine-affected water from a South African coal mine. The process achieved over 90% sulfate removal, raised the pH level above 7, and precipitated the metals. Operating parameters were optimized to increase process kinetics, and the results were used to design a pilot plant that will be operated at the mine to treat several hundred liters of water per day.
  • Passive Biological Treatment of Mine Water to Reduce Conductivity: Potential Designs, Challenges, and Research Needs Adobe PDF Logo
    Smyntek, P.M., R.C. Wagner, L.-A. Krometis, S.C. Sanchez, T. Wynn-Thompson, and W.H.J. Strosnider.
    Journal of Environmental Quality 46:1-9(2017)
    Passive biological treatment systems can be effective in removing acidity and metals from mine water, but review of current literature suggests that their ability to reduce conductivity appears somewhat limited. Some systems, particularly those that do not incorporate limestone into their construction materials, have been observed to reduce conductivity by 30-40%, which might prove useful as a pretreatment or finishing component of a larger treatment system, or in the treatment of legacy discharges. Design optimization will require identification of the ionic constituents responsible for primary conductivity constituents in various regions, long-term monitoring data of current systems that might not have been designed primarily to treat conductivity, and evaluation of the environmental factors governing underlying biogeochemical processes responsible for specific ion removals. Ideally, field-scale monitoring efforts will concurrently evaluate downstream impacts on aquatic ecology.

Chemical Precipitation — Chemical precipitation is a flexible, permanent technology used to treat MIW, including acid mine drainage, neutral drainage, and pit lake water. Chemical precipitation processes involve adding chemical reagents and then separating the precipitated solids from the cleaned water. Typically, the separation occurs in a clarifier, although separation by filtration or with ceramic or other membranes also is possible. When chemical precipitation is used in pit lakes or other water bodies, the precipitated solids can remain in the bottom of the pool. This technology can be used by itself or in conjunction with other treatments.

  • Comparison of Synthetic Rhamnolipids as Chemical Precipitants for PB, LA, AND MG
    McCawley, I.A., R.M. Maier, and D.E. Hogan
    Journal of Hazardous Materials 447:130801(2023)
    Research examined a novel approach to recovering metals from natural and contaminated aqueous systems based on rhamnolipid-facilitated chemical precipitation. Metal complex from solution, mixing only, and mixing followed by filtration or centrifugation were assessed to remove rhamnolipids. Recent advances in synthetically producing rhamnolipid surfactants allowed for the investigation of various rhamnolipid structures. Rhamnolipids with differing lengths and numbers of hydrophobic tails were assessed to remove Pb, La, and Mg from single metal solutions. Removal increased with increased rhamnolipid hydrophobicity and with adding an active removal step (filtration or centrifugation). Filtration removed ≤96% of all metals, while centrifugation removed ≤97% for Pb and La and 60% for Mg. Future studies in mixed-metal and real-world solutions will be needed to confirm the viability of these techniques in complex systems.
  • Pilot-Scale Feasibility Study for the Stabilization of Coal Tailings Via Microbially Induced Calcite Precipitation
    Rodin, S., P. Champagne, and V. Mann.
    Environmental Science and Pollution Research 30:8868-8882(2023)
    A study evaluated the physical and geochemical stabilization of coal tailings using microbially induced calcite precipitation at pilot scale. Three application techniques simulated commonly used agricultural approaches and equipment that could be deployed for field-scale treatment: spraying treatment solutions with irrigation sprinklers, mixing tailings and treatment solutions with a rototiller, and distributing treatment solutions via shallow trenches using an excavator ripper. Test cells containing 1.0×1.0×0.5 m of tailings were treated with ureolytic bacteria (Sporosarcina pasteurii) and cementation solutions composed of urea and calcium chloride for 28 days. Penetrometer tests were performed following incubation to evaluate the extent of cementation. The spray-on application method showed the greatest strength improvement, with an increase in surface strength of >50% for the 28-day testing period. The distribution of treatment solution using trenches was less effective, resulting in greater variability in particle size distribution of treated tailings, and is not recommended for field use. The use of rototilling equipment provided a homogenous distribution of treatment solution; however, disruption to the tailings material was less effective for facilitating effective cementation. Bacterial plate counts of soil samples indicated that S. pasteurii cultures remained viable in a tailings environment for 28 days at 18°C and near-neutral pH. The treatment also stabilized the pH of tailings porewater sampled over the incubation period, suggesting the potential for the treatment to provide short-term geochemical stability under unsaturated conditions.
  • Successive Alkali Diffusion Ceramic Reactor: Long-Term Removal of Acidity and Heavy Metals in Acid Mine Drainage
    Kim, M., Y. Yoon, N. Kamal, C.E. Choong, M. Jang, and G. Lee.
    Journal of Water Process Engineering 53:103858(2023)
    A novel alkali diffusion reactor using ceramic porous media (ceram-ADR) was developed to treat acidity and heavy metals in acid mine drainage (AMD) long-term without external energy. Batch and column tests were performed to investigate the neutralization capabilities of six alkaline chemicals (i.e., MgO, CaCO3, CaO, SiO2, Na2CO3, and NaHCO3) and the effects on pore size and hydraulic retention time (HRT) of ceram-ADRs. Among the chemicals, the ceram-ADR containing NaHCO3 yielded a suitable pH range for water quality guidelines (pH values from 5.0 to 9.5) with an HRT of 1-2 days and had the best efficiency in terms of consistent alkaline diffusion and long-term heavy metal removal (>99%). The precipitation process was a major mechanism in the removal of heavy metals. Based on the continuous column tests, ceram-ADR successfully treated three consecutive runs with ~340 bed volumes of AMD for neutralization and heavy metal removal, indicating that the ceram-ADR can be maintained for over three years without a lapse in performance.
  • Enhanced Decarbonation of Mine Drainage Using Iron OxidationAdobe PDF Logo
    Means, B. and R.L. Beam. | West Virginia Mine Drainage Task Force Symposium, 4-5 October, Morgantown, WV, 13 slides, 2022
    Ferruginous underground coal mine drainage in the Appalachian region contains elevated concentrations of inorganic carbon carbonic acid [H2CO3] or bicarbonate alkalinity [HCO3-] due to interactions between mine pools and alkaline recharge water. A novel strategy to minimize deprotonation of both carbonic acid and bicarbonate was implemented at two active treatment plants to promote ferrous iron oxidation and precipitation before, or in conjunction with, a decarbonation step. The acidity produced by iron hydrolysis serves to deprotonate bicarbonate, producing carbonic acid, which is then decarbonated before alkali addition. The process decreases bicarbonate and carbonate concentrations through transformation into carbonic acid before or during decarbonation, before pH adjustment. A 50% by wt. solution of H2O2 was used at one site to promote ferrous iron oxidization, while mechanical aeration was used at the other site. The strategy increased the removal of inorganic carbon from 26% to 56%, resulting in a net annual cost savings of 50%. Both sites were successfully geochemically modeled, indicating a cost analysis can be performed at sites to evaluate whether enhanced decarbonation, decarbonation or conventional alkali addition is most cost-effective.
  • Treatment of Mine Drainage with Significant Topographical Constraints: Case Study of the Bodennec Site (France)
    Jacob, J.C., M. Save, and Y. Menard. Mine Water and the Environment [Publication online 3 Mar 2018 prior to print]
    The Bodennec lead and zinc mine site produces circumneutral mine drainage that contains 8 mg/L of dissolved iron, whereas the Fe water quality objective is 3 mg/L at the outlet. The water treatment installation in use, based on three settling ponds, could not reach this objective, and the site lacked sufficient surface area to build additional ponds or a passive treatment plant. A pilot-scale NaOH system comprising a pump controlled by a flow meter was built on site to assess the feasibility of a low-maintenance system to effect treatment via injection of a small volume of concentrated NaOH solution into the water. A solar panel connected to a battery supplied the system with electricity. Given the stability of the pH in the drainage no pH probe was needed. A final water treatment plant based on this pilot was built in 2017.
  • Copper Mine Tailings Valorization Using Microbial Induced Calcium Carbonate Precipitation
    de Oliveira, D., E.J. Horn, and D.G. Randall.
    Journal of Environmental Management 298:113440(2021)
    The solidification of copper mine tailings was studied using microbial-induced calcium carbonate precipitation (MICP) to valorize the waste stream. The toxicity of copper on Sporosarcina pasteurii, the ureolytic bacteria which drives the MICP process, was investigated using bio-columns. The bio-columns produced from copper mine tailings had a compressive strength of 0.54 MPa, lower than bio-columns produced from beach sand (1.85 MPa). The low porosity of the copper mine tailings limited the depth to which the MICP reaction could successfully occur, resulting in the formation of a 1.8 mm ± 0.4 mm crust around the outer extremities of the bio-columns. Particle size was a key deciding factor, and, as a result, MICP is not suitable to produce 'thick' bio-cemented materials from small particles (<100 µm), such as mine tailings. However, the method could produce thinner materials such as bio titles or could potentially be used to cement together toxic dust particles that typically form on mine tailing heaps.

Constructed Treatment Wetlands — Constructed treatment wetlands are man-made biologically active systems such as bogs, swamps, or marshes with saturated soils and at least periodic surface or near-surface water designed specifically to treat contaminants in surface water, groundwater, or waste streams. This technology is a valid treatment option for a variety of waste streams, including MIW, remedial wastewaters, agriculture waste streams, and industrial waste streams. Constructed treatment wetlands have also been used for "wet capping" of solid wastes and are often called "capped mine wastes in a wetlands setting." Constructed treatment wetlands can be used with other technologies to extend the operational lifespan of the systems or enhance the removal performance of specific constituents of concern.

  • Influence of Sediment Quality and Microbial Community on the Functioning Capacity of a Constructed Wetland Treating Alkaline Leachate After 5.5 years in Operation
    Hudson. A., J.G. Murnane, T. O'Dwyer, M. Pawlett, and R. Courtney.
    Science of The Total Environment 867:161259(2023)
    A pilot-scale wetland was implemented to treat alkaline bauxite residue leachate and investigate the feasibility of constructed wetlands (CWs) to buffer alkaline pH. After 5.5 years, samples of supernatant water and sediment were collected at 0.5 m increments along the 11 m long wetland. Water samples were analyzed for pH, EC, and metal(loid) content, while the sediment was subjected to physicochemical assessment and element fractionation. Microbial biomass and community were assessed by phospholipid fatty acid analysis and functionality by the Rapid Automated Bacterial Impedance Technique. Results demonstrate that the CW effectively treated bauxite residue leachate, reducing influent pH from 11.5 to 7.8. Trace element analysis revealed an effective reduction in Al (94.9%), As (86.7%), and V (57.6%), with substrate analysis revealing a frontloading of elevated pH and trace element content in the first 5 m of the wetland. Sediment Al, As, and V were present mostly (>94% of the total) in recalcitrant forms. Sediment Na was mostly soluble (48-62%), but soils were not sodic (ESP<15%). Investigations into the microbial community revealed the greatest biomass in the first 5 m of the wetland, where pH, electrical conductivity, and metal contents were greatest. Microbial respiration using endemic Phragmites australis as a substrate demonstrates an ability to cycle recalcitrant carbon sources within a CW system.
  • Passive Treatment of Circumneutral Mine Drainage from the St. Louis Mine Tunnel, Rico CO: Part 3-Horizontal Wetlands Treatment Train Pilot StudyAdobe PDF Logo
    Sobolewski, A.B., A.C. Riese, T.J. Moore, and A.R. Brown.
    Mine Water and the Environment (2022)
    A study tested the performance of a demonstration-scale horizontal wetlands passive treatment train comprised of a settling basin, surface flow wetland, horizontal-flow anerobic wetland, aeration channel, and rock drain at the Rico-Argentine site. Mine drainage from the St Louis Tunnel is circumneutral most of the year, with spring freshets increasing flow, decreasing pH, and increasing metal concentrations. Total Zn, Cd, and Mn effluent concentrations met project treatment goals (PTGs) 75, 96.9, and 100% of the time, respectively, and 93.9, 100, and 100% of the time for the dissolved metals. Most PTG exceedances occurred during the freshet events. Most Zn and Cd attenuation was attributed to sulfide precipitation in the anaerobic cell and capture/filtration of suspended ZnS particles in the anaerobic wetland and rock drain. Manganese was attenuated in the aerobic portion of the anaerobic cell as Mn oxides and carbonates. Oxidation of Mn occurred in the rock drain as biogenically formed Mn oxides adhered to the rock matrix. Carryover of dissolved sulfides from the anaerobic cell limited the rock drain's Mn removal efficiency. Low temperatures did not significantly affect biological activity within the system; the effects of seasonal water quality were more important.
  • Effects of Cattails and Hydraulic Loading on Heavy Metal Removal from Closed Mine Drainage by Pilot Scale Constructed Wetlands
    T.T. Nguyen, S. Soda, A. Kanayama, and T. Hamai
    Water 13(14):1937(2021)
    Removal of heavy metals from neutral mine drainage of a closed mine in the Kyoto prefecture was demonstrated using pilot-scale constructed wetlands (CWs). The CWs were filled with loamy soil and limestone and were planted with or without cattails. The hydraulic retention time (HRT) in the CWs was shortened gradually from 3.8 to 1.2 days during 3.5-months of operation. A short HRT of 1.2 days in the CWs was sufficient to achieve the effluent standard for Cd (0.03 mg/L). The CWs planted with or without cattails reduced the average Cd concentrations from 0.031 to 0.01 and 0.005 mg/L, Zn from 0.52 to 0.14 and 0.08 mg/L, Cu from 0.07 to 0.04 and 0.03 mg/L, and As from 0.011 to 0.006 and 0.006 mg/L. Heavy metals were removed mainly by adsorption to the soil in both CWs. The biological concentration factors in cattails were >2 for Cd, Zn, and Cu. The translocation factors of cattails for all metals ranged from 0.5 to 0.81. Sulfate-reducing bacteria (SRB) were detected only from soil in the planted CW. Although cattails were a minor sink, the plants contributed to metal removal by rhizofiltration and incubation of SRB and may have produced sulfide precipitates in the rhizosphere.
  • The Treatment of Acid Mine Drainage Using Vertically Flowing Wetland: Insights into the Fate of Chemical Species
    Nguegang, B., V. Masindi, T.A.M. Msagati, and M. Tekere.
    Minerals 11:477(2021)
    Acid mine drainage (AMD) was treated in a vertically flowing wetland enriched with Vetiveria zizanioides as a decontaminating media and soil as the substrate. Water percolated through the substrate was collected and characterized every five days for 30 days. Results revealed a tolerant index of 1.03 for Vetiveria zizanioides and a net reduction of metals and sulfate. The removal efficacy of chemical species was observed to obey the following order: Fe (71.25%) > Zn (70.40%) > Mn (62%) > Al (56.68%) > SO4 2− (55.18%) > Ni (35%) > Cu (18.83%). The removal of chemical species was further aided by the used substrate, which could be attributed to the accumulation of chemical species on the soil through precipitation, adsorption, and phytoretention. Substrate plays a significant role in removing metals, while the grass and external factors accounted for the remaining chemical species attenuation. The distribution of chemical species was predominantly in the roots, except manganese, which was transferred in the shoot (67%). AMD chemical species present in the substrate and the grass components confirmed that the plants played a huge role in removing contaminants. The PH REdox EQuilibrium geochemical model confirmed that metals existed as di-and-trivalent complexes in AMD. Available metals were precipitated as metals hydroxides and oxy-hydrosulfates by the substrate. Results indicate that vertically flowing wetland can be used for passive treatment of AMD, particularly at active and abandoned mines.
    This article is Open Access at
  • Case Study: Performance of the Operating Demonstration-Scale Constructed Wetland Treatment System at Minto Mine
    Bouchard, E., C. Prentice, R. Herbert, R. Martz, B. Eisner, V. Friesen, and M. Simair.
    41st British Columbia Mine Reclamation Symposium, 17-20 September, Williams Lake, BC, 2018
    The Minto Mine is following a phased approach for the design and implementation of a Constructed Wetland Treatment System (CWTS) for water treatment at closure. The CWTS is currently in the demonstration-scale and optimization stage preceding full-scale implementation. The CWTS has successfully treated constituents of potential concern in the mine site's sub-arctic continental climate. Carex aquatilis (aquatic sedge) and aquatic mosses (bryophytes) from natural wetlands onsite were used for planting, while water mine-impacted seepage water was used as feed water. The CWTS was designed to target specific physicochemical parameters for treatment (confirmed and refined through off-site pilot-scale testing), which enable denitrifying selenium- and sulfate-reducing bacteria to treat nutrients, metals, and metalloids in the water. The CWTS treated targeted constituents of potential concern in the following extents and percentages: cadmium 80% (from 0.0261 µg/L to 0.0092 µg/L), copper 65% (from 49.1 µg/L to 17.3 µg/L), molybdenum 58% (from 6.3 µg/L to 2.7 µg/L), selenium 89% (from 4.0 µg/L to 0.5 µg/L), zinc 98% (from 49.2 µg/L to 1.9 µg/L), and nitrate as N 97% (from 6.5 mg/L to 0.19 mg/L). Continued trials were underway in 2018 to investigate treatment under a wider range of operational conditions.
  • Operation and Maintenance of Passive Treatment Systems
    Hedin, R.
    The 23rd British Columbia MEND Metal Leaching/Acid Rock Drainage Workshop, Vancouver. 32 slides, 2016
    Passive treatment of contaminated mine drainage is less costly than active treatment, but its reliability is sometimes questioned. A simple approach is presented that has been used to design effective passive treatment systems in Pennsylvania. Three systems that demonstrate commonly utilized passive technologies are described along with long-term monitoring data: (1) the Marchand system of oxidation/settling ponds and a constructed aerobic wetland; (2) the Anna S system of vertical flow ponds and aerobic wetlands; and (3) the Scootac system of a drainable limestone bed and settling pond. The systems have provided highly reliable and effective treatment for 3 to 18 years. The data demonstrate that properly designed, constructed, and maintained passive treatment systems are a highly cost-effective solution for contaminated mine discharges.
    Slides: Adobe PDF Logo
    Paper: Adobe PDF Logo
  • Constructed Wetland Design and Optimization for Metal and Metalloid Treatment at the Minto Mine in the Yukon, Canada
    Haakensen, M., V. Friesen, and R. Herbert.
    Technical Program: The 12th International Symposium on Mining with Backfill, 19-22 February 2018, Denver, CO.
    A 2-year site-specific demonstration of a constructed wetland treatment system was conducted for Capstone Mining Corporation's Minto Mine (Yukon). Biogeochemical technologies such as microbial community profiling were used to guide system design in a site-specific context. Pilot-scale tests enabled selection of the optimal full-scale demonstration design from several options and tested different predicted closure water chemistries. The selected design treats the water for Cd, Cu, and Se, with polishing achieved for several additional metals. Removal rate coefficients were developed for modeling and sizing of full-scale systems. The Government of Yukon recognized the project with the 2017 Robert E. Leckie Award for responsible and innovative exploration and mining practices to Capstone subsidiary Minto Explorations Ltd. See the details of this demonstration project in the report, Minto Mine Constructed Wetland Treatment Research Program: Demonstration-Scale 2017, at

  • Acid Mine Drainage Remediation with Small Scale Constructed Wetlands in Ancash Highlands - PeruAdobe PDF Logo
    Leon, V., K. Aguirre, A. Gonzales, N. Herrera, A. Leon, D. Osorio, A. Quijano, and E. Palacios.
    Proceedings of the 8th World Congress on New Technologies (NewTech'22), 3-5 August, Prague, Czech Republic, 2022
    Four small-scale constructed wetlands (SS-CWs) were constructed (0.59 m x 0.38 m x 0.24 m) and were continuously fed with acid mine drainage (AMD) collected from mining sites in the Ancash region, the main Cu (20.6%), Zn (38.0%), and Ag (19.6%) producer in Peru. The flow rate and hydraulic retention time were 5 L/d and 3.1 d, respectively. From bottom to top, the SS-CWs were composed of limestone, organic matter (40% compost, 40% animal manure, and 20% peat), and macrophytes (Juncus imbricatus) for SSCW 1, limestone and organic matter for SS-CW 2, limestone, organic matter, macrophytes and reducing sulfate bacteria for SS-CW 3, and gravel 3/8", organic matter and macrophytes for SS-CW 4. Influent AMD had a pH of 2.3 ± 0.1 (N=10), electrical conductivity of 3018 ± 257.7 mS/cm (N=10), and Fe concentration of 202.3 ± 34.6 mg/L (N=10). The effluent consisted of a pH of > 5.7, an electrical conductivity of > 2149.2 mS/cm, and Fe concentration of < 99.7 mg/L. A statistically significant pH difference (p-value: 0.022) existed between the four wetlands, though no statistically significant difference in Fe removal (p-value: 0.0733) was observed). The highest Fe removal efficiency occurred in SS-CW 3 (67.1% ± 8.7% [N=8]) followed by SS-CW 2 (64.1% ± 11.7% [N=9]), SSCW 4 (57.8% ± 8.4% [N=9]) and SS-CW 2 (51.4% ± 17.9% [N=9]). SS-CW 3 had all components of a constructed wetland and performed best, though the other SS-CWs also showed high efficiencies.
  • Effective Treatment of Acid Mine Drainage Using a Combination of MGO-Nanoparticles and a Series of Constructed Wetlands Planted with Vetiveria Zizanioides: A Hybrid and Stepwise Approach
    Nguegang, B., V. Masindi, T.A.M. Makudali, and M. Tekere.
    Journal of Environmental Management 310:114751(2022)
    Acid mine drainage (AMD) was treated in a study using a hybrid approach that combined a nano-and-biotic system synergistically integrated in a stepwise and modular fashion. The treatment chains were composed of different stages, including neutralization using activated magnesite or MgO-nanoparticles (NPs) (Stage 1) and polishing using a series of wetlands (Stage 2) in a stepwise connection. In Stage 1, actual AMD was treated with MgO-NPs at a ratio of 1:100 (1 g/100 mL – w/v ratio), 500 rpm of mixing speed, and 1 hour of hydraulic retention time (HRT). In Stage 2, the final water was fed into three interconnected constructed wetlands with different flow modalities [(subsurface vertical flow (SSVF-CW), free water surface flow (FWS-CW), and subsurface horizontal flow (SSHF-CW)], for further purification and polishing. The product water and substrate were collected daily at the outlet and bottom of each wetland. After treatment, the pH of the product water increased from 2.6 to 10.4. Significant removal of inorganic contaminants was observed in the following removal sequence: Fe (99.8%) ≥ Al (99.5%) ≥ Mn (99.24%) ≥ Zn (98.36%) ≥ Cu (97.38%) ≥ Ni (97.7%) ≥ SO42- (80.59%). Reduced electrical conductivity was also observed (86%). Step 1 partially removed the metals and sulfate while Step 2 effectively removed SO42- and EC levels, thus denoting stellar combination and complementary performance for the hybrid system in an integrated fashion. Analytical instruments underpin and succinct the fate of chemical species in raw and product MgO-NPs, substrates, and the grass. The product water conformed to the prescribed standards for effluent discharge, proving that the synergy of neutralization and bioremediation could yield the desired results in mine water management.
  • Remediation of Acid Mine Drainage-Impacted Wter by Vetiver Grass (Chrysopogon Zizanioides): A Multiscale Long-Term Study
    Kiiskila, J.D., D. Sarkar, S. Panja, S.V. Sahi, and R. Datta.
    Ecological Engineering 129:97-108(2019)
    The study developed a cost-efficient and sustainable floating treatment wetland system using vetiver grass (Chrysopogon zizanioides). Year-long large- and small-scale hydroponic experiments were used to determine the effectiveness of vetiver for treating acid mine drainage-impacted waters from the Tab-Simco mine site in southern Illinois. For the large-scale mesocosm study, vetiver rafts were suspended in 100-gal containers. Water quality was monitored every 28 days and at the end of the experiment (364 days); plant health was monitored by measuring changes in biomass and recording visual changes in root and shoot coloration and morphology. There was higher net removal of Fe (81%) and Pb (81%) with lower removal of Ni (38%), Zn (35%), SO42- (28%), Mn (27%), Cr (21%), Al (11%) and Cu (8.0%). Toxicity characteristic leaching procedure showed that vetiver biomass was not hazardous waste as a result of metal accumulation. From the small-scale experiment, there was near complete removal of SO42- (91%) and metals (90-100%) with the exception of Pb (15%) and Cu (0.0%).
  • A Preliminary Study to Design a Floating Treatment Wetland for Remediating Acid Mine Drainage-Impacted Water Using Vetiver Grass (Chrysopogon Zizanioides)
    Kiiskila, J.D., D. Sarkar, K.A. Feuerstein, and R. Datta.
    Environmental Science and Pollution Research 24(36):27985-27993(2017)
    A study is underway to develop a low-cost and sustainable floating wetland treatment (FWT) system for acid mine drainage (AMD) at the abandoned Tab-Simco coal mining site in Illinois using vetiver grass. Tab-Simco AMD is highly acidic (mean pH 2.64) and contains high levels of sulfate and metals. A 30-d greenhouse study conducted to screen and optimize the necessary parameters to design a FWT system showed significant sulfate removal, resulting in increased pH, particularly at higher planting densities. Vetiver also helped in metal removal: high amounts of Fe, Zn, and Cu were removed, with relatively lower amounts of Pb, Al, and Ni. Iron plaque formation on the root was observed, which increased metal stabilization in roots and lowered root-to-shoot metal translocation. Vetiver was tolerant of AMD, showing minimal change in biomass and plant growth. A large-scale mesocosm study is now in progress as the next step to develop a vetiver-based FTW system for AMD treatment.
  • Review of Passive Systems for Acid Mine Drainage Treatment Adobe PDF Logo
    Skousen, J., C.E. Zipper, A. Rose, P.F. Ziemkiewicz, R. Nairn, L.M. McDonald, and R.L. Kleinmann.
    Mine Water Environment 36(1):133-153(2017)
    This paper reviews the current state of passive system technology development for the treatment of acid mine drainage, provides results for various system types, and offers guidance for system sizing and effective operation.

Diversionary Structures — Diversionary structures are designed to prevent clean water from coming into contact with mining solid waste (net acid-producing materials) and to divert MIW to treatment or collection systems and away from sensitive environments. These include engineered channels, tunnels, pipelines, or other structures to divert surface water run-on or MIW runoff; engineered slurry walls, sheet pile walls, grouting, or other subsurface structures to divert or contain groundwater; and bulkheads and plugs in mine workings to control influx or discharge of MIW. Diversionary structures can be used to reduce the volume of, or exposure to, MIW. They also can be used to prevent erosion of mining waste and transport of soluble metals into surface water.

  • Faro Mine, Yukon Terroritory, Canada: A Case Study for Optimising Zinc Load Capture by Clean Water Diversion and Focused Contact Water CaptureAdobe PDF Logo
    Adams, B.M., K.H. Scully, J.T.C. Seto, and B. Harrison.
    Mine Closure 2022: 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 341-354, 2022
    Seepage from sulfidic waste stored in the Faro Mine waste rock dumps (WRDs) has variably impacted groundwater and surface water to the North Fork of Rose Creek (NFRC), a fish-bearing surface water body, which passes along the toe of the WRDs. Zinc is the primary parameter of concern, reaching several orders of magnitude higher than applicable water quality guidelines and previous yearly max concentrations. Intercepting contact water before reaching the NFRC is challenging due to the complex seepage patterns within the WRDs and the creek's proximity. Despite existing collection systems intercepting high-concentration seepage pathways, zinc concentrations in the creek remained elevated. The NFRC Realignment Project commenced to 'keep clean water clean' by diverting the NFRC into the non-contact water diversion channel (NCWDC) and allowing focused collection of WRD seepage in the remnant NFRC channel. The first phase of the contact water collection and conveyance system focused on the interception of shallow groundwater and surface flow in the remnant NFRC. Isolating the clean water through the NCWDC substantially reduced the surface water available for dilution. Both the uncertainty in capturing contact water before it reaches the creek and the inefficiency of capturing contact water once mixing occurred with creek flow were mitigated. A year after commissioning the NFRC Realignment Project, performance monitoring shows measured zinc concentrations in the NFRC ~2 orders of magnitude lower at the downstream monitoring station than realized by previous efforts.

Electrocoagulation — Electrocoagulation refers to a group of technologies that use an electrical current that coagulates organic constituents and suspended solids in water. The coagulated organics have the ability to adsorb certain ionic constituents, making it possible to separate a flocculent with most of the suspended organics and some of the ionic constituents removed. Another variant of this system oxidizes an iron or aluminum anode to form an iron or aluminum hydroxide flocculent that can co-adsorb/co-precipitate some ions. The electrocoagulation process is complex and site- and contaminant-specific. These systems may be effective in certain niche applications. Detailed bench and pilot studies are required before implementing the technique.

In Situ Treatment of Mine Pools and Pit Lakes — This emerging technology for treating MIW involves injecting or placing substances (including carbon sources such as molasses or alcohol with nutrients) or alkaline materials such as lime directly into the mine pool or pit lake to neutralize the MIW and produce anaerobic conditions to precipitate metals in place. The addition of a carbon source leads to the formation of a sulfate-reducing bioreactor. Some metals are less soluble in their reduced form, including selenium, chromium and uranium. These oxidized metals can be removed from the water as solids. In situ treatment of solid mining waste in the form of residual minerals in mine walls, tailings, or waste rock involves the application of amendments such as potassium permanganate, phosphate or biosolids, and carbon substrate to stabilize the metals in place and reduce the formation of leachate or inhibit the migration of metals.

  • Pit Lake Treatment at the Reclaimed Former Farley Mine
    Bonner, D., J. Forbort, J. Vogan, C. Leask, W. Nixdorf, O. Beruar, and R. Frost
    2020 Mine Design, Operation & Closure Conference, 18-20 August, virtual, 26 minutes, 2020
    The presentation details the reclamation, acid rock drainage management, and pit lake treatment approaches at a former mine in Manitoba. Reclamation involved consolidating sulfide mineral-bearing tailings and installing cover systems over the tailings, stormwater diversion systems, and an impermeable cover system over a waste rock stockpile. During reclamation activities, approximately 900 million gallons of ARD were treated using an interim ARD treatment system to create a freeboard for future ARD management and in situ treatment of ARD within the pit lake. The freeboard from this water treatment yielded storage for four years. A recent pit lake water treatment campaign was completed to create a freeboard, using an innovative approach to facilitate effective treatment by offloading quicklime directly from the bulk delivery trucks without the need for a slaker.
    See times 1:25-1:51:

  • The Use of Using Biological Treatment to Stabilize Schwartzwalder Mine and Reduce Long Term Water Treatment CostsAdobe PDF Logo
    Harrington, J. | CEMS Mining Mini-Conference, 11 May, virtual, 26 slides, 2021
    Source removal reclamation projects, including mine dewatering, active ex-situ mine water treatment using reverse osmosis (RO), and in-situ mine pool microbiological treatment, were implemented at the Schwartzwalder mine. Microbial food sources added to the mine pool initiated in-situ microbiological treatment and improved the effectiveness and sustainability of the overall water treatment processes, first by removing contaminants by >90%, then by preventing water quality degradation as the RO concentrates were returned to the mine pool. Pilot testing of a wetland approach that could be implemented in the former source areas of the mine to treat residual contamination by acting as a buffer between the mine and the adjacent stream and providing redundancy to in-situ microbiological treatment is ongoing. Microbiological treatment in the mine pool and/or in constructed wetlands may offer promise to achieve the pending requirements in Colorado SB19-1113, which requires new or amended permits to "demonstrate a reasonably foreseeable end date for any water quality treatment" with more than 50% cost reduction compared to active water treatment only.
  • In-Pit Batch Treatment of Arsenic: Laboratory Studies and Field TrialAdobe PDF Logo
    Mine Environment Neutral Drainage Program, 71 pp, 2019
    Lab and field studies were conducted to demonstrate in-pit batch treatment of arsenic-contaminated water in mine pits using ferric sulfate. The overall objective of the investigation was to demonstrate that in-pit batch treatment of arsenic represents a viable and economical alternative to traditional water treatment applications. Phase 1 was a bench-scale study to define the design criteria, including the attainable treatment efficiencies, the required reagent dosages, and the sludge production rates. Phase 2 was a field-scale treatment trial that evaluated the practicality and efficacy of in-pit batch treatment of arsenic within the Night Hawk Lake Mine open pit, as informed by the results in Phase 1. Total and dissolved arsenic concentrations at 3 depths were compared pre- and post-treatment in 3 sampling events at two stations (NHP 1 and NHP2). Immediately post-treatment, total arsenic concentration at the surface at NHP1 decreased from 0.6 mg/L to 0.01 mg/L total arsenic with a dissolved concentration <0.002 mg/L for a treatment efficiency of ~98 within the surface depths. The mid-depth samples for the same sampling event were ~0.03 and 0.01 mg/L for the total and dissolved arsenic concentrations, respectively. The arsenic concentrations at depth remained close to the initial concentrations before treatment.

  • Realizing Beneficial End Uses from Abandoned Pit LakesAdobe PDF Logo
    McCullough, C.D., M. Schultze, and J. Vandenberg.
    Minerals 10:133(2020)
    This publication reviews published case studies of abandoned mine pit lakes, including common attributes and reasons that led to successful repurposing as beneficial end uses. Recommendations are given for all stages of mine closure planning to prevent pit lake abandonment and to achieve successful closure with beneficial end uses.

Ion Exchange — Ion exchange is well-established treatment technology that involves the interchange (or exchange) of ions between a solid medium and MIW. The solid medium can be commercially produced or made from naturally occurring substances (e.g., peat or zeolites). Synthetic organic resins are used predominantly because their characteristics can be tailored to specific applications. Ion exchange can be applied to dissolved constituents, cations or anions to treat mine discharges with various flow rates and can be used as a stand-alone technology or with other treatment technologies. The ability to regenerate resin and recover metals provides a potential additional benefit of this approach.

Ion Flotation — Ion flotation is a common separation technology that concentrates metal ions from solution so they can be collected and disposed of or recycled. A surfactant with an opposite charge of the target ions is used to attract metal ions, and air bubbles carry the material to the surface of the solution. Ion flotation can be used to remove heavy metal ions from wastewater, but the process also is being studied to remove uranium from mine water by adding biological or synthetic rhannolipids, a type of biosurfactant. Biological or synthetic rhamnolipids can be made using sustainable production methods, and are biodegradable, recyclable and have low toxicity. As a separation process, ion flotation has low energy requirements, small space requirements, relatively low costs, and occurs quickly. The process is most effective when site-specific conditions, such as water chemistry, are considered.

  • New Technique Yields Promising Results for Uranium Removal in the Field Adobe PDF Logo
    National Institute of Environmental Health Sciences, Research Brief 326, 2 pp, 2022
    This Research Brief presents a new study using an ion flotation process to remove uranium from groundwater near abandoned mines. The performance of biologically derived and synthetic rhamnolipids was evaluated. Both forms of rhamnolipids were found to remove uranium via ion flotation for acidic solutions and will be most effective when site-specific conditions are considered.

Microbial Mats — A constructed microbial mat is an aquatic bioremediation system that uses naturally occurring, living organisms (primarily cyanobacteria) to rapidly remove metals from MIW. Cyanobacteria are photosynthetic and can be grown like plants, harvested, and dried until needed. Microbial mats grow rapidly, can survive harsh environmental conditions, and can tolerate high concentrations of compounds that are toxic to plants or algae. They are called "constructed" mats because they are grown using a standard technique that is inexpensive and requires minimal training. Microbial mats can be used as a stand-alone technology or with other technologies to treat dissolved organic and inorganic constituents, including a variety of metals, metalloids, radionuclides, and oxyanions, and can treat mine discharges collected in ponds and slow-flowing leachate. Sunlight intensity is an important requirement, and, like all biological systems, system performance decreases during winter seasons.

Passive Technologies — Passive treatment (passivation) of acid-generating material involves oxidizing or protecting the sulfide surface from water and oxygen. Techniques for reducing metal sulfide oxidation involve removing oxygen, water, bacteria, or the sulfide minerals, all of which contribute to the generation of acid mine drainage. All passivation technologies use a spray-on application, either as a solution (phosphate) or as a slurry (silica). It is one of the few treatment methods that can be used to treat exposed pit walls. Although laboratory and small-scale pilot data are available, this new technology has not been applied on a large scale and there are very limited data on long-term performance. In addition, several studies have indicated that there is an initial release of other constituents into the environment when passivation is applied. Techniques to control and possibly treat this release may be needed and regulatory approval obtained before releasing these constituents. This technology may be used alone or with other technologies.

  • Sustainable Treatment System Caps Off Cleanup at Elizabeth Mine Superfund Site
    EPA website, Published March 19, 2024
    Elizabeth Mine left ~80 acres of exposed waste rock and tailing after closure. These waste piles discharged contamination into local water bodies, affecting aquatic life in the West Branch of the Ompompanoosuc River. EPA added Elizabeth Mine to the NPL in 2001, identifying abandoned, highly toxic waste sites and prioritizing them for long-term cleanup from hazardous contamination. In 2001, EPA began implementing cleanup at Elizabeth Mine, including planned, time-critical action measures to stabilize and reinforce a local dam near the site was on the verge of collapse, including providing stand-by pumps to increase extra drainage capacity when snow melted. A major component of the cleanup was the Rotating Cylinder Treatment System (RCTS™), chosen due to its smaller footprint and lesser amounts of lime (calcium oxide) required to treat the high concentration of iron discharging from the tailing impoundment as compared to conventional lime treatment systems. By 2018, the iron concentration in the waste discharging from the tailing impoundment had been sufficiently decreased, allowing EPA to look for a more sustainable treatment method. EPA worked closely with the Vermont Department of Environmental Conservation and site consultants to develop an innovative passive treatment system that uses limestone beds, open settling ponds, vertical flow pond, and treatment wetlands to clean the water without any electrical power. The system has a level of redundancy that allows various components to be off-line and still achieve cleanup objectives. Data collected through June 2023 has shown that the passive treatment system effectively removes iron from the leachate to meet the state's water quality criterion.
  • Innovative Strategies for the Management of Metal Impacted Waters
    Mancini, S. | REMTECH 2021: The Remediation Technologies Symposium, Banff, AB, Canada, 13-15 October, 18 slides, 2021
    This presentation provides an overview of the development, design, and implementation of passive treatment technologies. Case studies on applying technologies, including in situ and ex situ treatment reactors such as Gravel Bed Reactors™ and bioreactors, phytotechnologies, constructed and engineered wetlands, pit lake in-pit treatment, and permeable reactive barriers are included. Deploying mobile treatment systems to mine sites, such as containerized columns and "wetlands on wheels," is also discussed as an important stage to facilitate treatability studies, regulatory approval, and advancement of technology application to full-scale. Each technology is discussed as a function of its implementability from a perspective of site-specific conditions, effectiveness, and expected impact on the local environment. Further, treatment system configurations, treatment mechanisms, and seasonality are explored to highlight the flexibility of their application in the context of various industry treatment needs.
  • Effect of an Extreme Flood Event on Solute Transport and Resilience of a Mine Water Treatment System in a Mineralised Catchment
    Mayes, W.M., M.T. Perks, A.R.G. Large, J.E. Davis, C.J. Gandy, P.A.H. Orme, and A.P. Jarvis.
    Science of The Total Environment 750:141693(2021)
    The Coledale Beck catchment contains the UK's first passive metal mine water treatment system. The catchment experienced an extreme rainfall event in December 2015 that equated to a 1 in 200-year event. The solute dynamics monitoring record for the site provided an opportunity to assess the effects of a major storm event on (1) catchment-scale solute transport and (2) the resilience of the new and novel passive treatment system to extreme events. Changes in system hydraulic efficiency explained a modest decline in treatment efficiency over time. There was no apparent flushing of the mine system during the storm event that could have compromised treatment system performance. Analysis of metal transport in the catchment downstream of the mine show the resilience of passive mine water treatment systems to extreme events and the importance of catchment-scale monitoring to ensure the continued effectiveness of treatment initiatives after major perturbation.
  • Passive Treatment of Acid-Mine Drainage
    Zipper, C., J. Skousen, and C. Jage.
    Virginia Cooperative Extension, Publication 460-133, 14 pp, 2018
    This publication presents guidance to design passive treatment systems for acid mine drainage. The mechanisms governing these systems' treatment effectiveness and performance are clearly described.
  • Performance of Passive Systems for Mine Drainage Treatment at Low Temperature and High Salinity: A Review
    Ali, H.E.B., C.M. Neculita, J.W. Molson, A. Maqsoud, G.J. Zagury.
    Minerals Engineering 134:325-344(2019)
    This paper reviews the principal parameters and processes that influence the quality of mine drainage (MD) and the performance of passive treatment of MD in cold climates. Major factors that affect treatment performance of passive systems are highlighted, such as low temperature, contamination level, and salinity. This review also discusses the effect of MD contamination level on passive biochemical reactor (PBR) efficiency. The effect of high salinity is discussed, with its potential to increase or decrease metal and sulfate removal depending on the major ions present. Reactive transport models used to predict long-term MD treatment efficiency are also considered. Further studies are needed to evaluate the simultaneous combined effect of these parameters on the performance of PBRs.
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  • Performance Review of a Passive Treatment System for FE, AS, MN at the Empire Mine State Historic Park
    Schipper, R., N. Gallagher, T. Rutkowski, S. Lofholm, and G. Leach. | Technical Sessions: Smart Mining: Resources for a Connected World, 24-27 Feb 2019, Denver, Colorado. p 76, 2019
    The Empire Mine State Historic Park contains 367 miles of now-flooded underground workings. Following closure, discharged mining-influenced water (MIW) contained arsenic, iron, and manganese in excess of federal and state standards. A full-scale passive treatment system (PTS), in operation since November 2011, was designed and constructed to treat the MIW and meet the permit limits. The PTS flowrate varies seasonally and has averaged 160 gpm with a peak near 1000 gpm. Metal removal results for the system have improved over time, corresponding with maturation of the PTS. Since February 2013, the PTS has provided effective removal of permitted metals to trace levels. In addition to metals removal, the PTS has also increased pH, increased dissolved oxygen, and reduced turbidity.
  • Toward Sustainability of Passive Treatment in Legacy Mining Watersheds: Operational Performance and System Maintenance
    Nairn, R.W., J.A. LaBar, L.R. Oxenford, N.L. Shepherd, B.K. Holzbauer-Schweitzer, J.G. Arango, Z. Tang, D.M. Dorman, C.A. Folz, J.I. McCann, J.D. Ingendorf, H.T. Stanfield, and R. C. Knox. | Proceedings from the postponed 14th IMWA Congress, "Mine Water Solutions," 2020
    A 12-year regular performance evaluation was conducted for a large, multi-process unit passive treatment system (PTS) at the Tar Creek Superfund site, which receives ≈1000 m3/day artesian-flow lead-zinc mine water. Since 2008, the PTS has consistently retained >95% of targeted metal mass. Regular, periodic, and rehabilitative maintenance commitments were also documented.
    See pages 123-128: PDF Logo
  • Twomile Run AMD Restoration Swamp Area Passive Treatment System Virtual Tour
    Wolfe, N. | 2021 PA Abandoned Mine Reclamation Conference, 27-28 October, Virtual, 37 minutes, 2021
    Restoration efforts of the Twomile Run watershed in western Clinton County, once impaired by abandoned coal mines, resulted in the recovery and reconnection of 6 miles of native brook trout stream. The largest and most significant of the nine treatment systems constructed is the Swamp passive treatment system due to its severe water quality and upstream position in the watershed. Design of the collection system was complicated by the presence of gas pipelines. Constructed in 2012, the treatment system includes settling ponds, vertical flow ponds in parallel with limestone and compost, and wetlands. Raw water entering the system averages 92 gal/min with pH 2.99, acidity 437 mg/L, Fe 54 mg/L, and Al 22 mg/L. The average effluent pH is 7.6 with 169 mg/L alkalinity, and both Fe and Al concentrations are < 1 mg/L. Though the water quality is considered high-risk, the system has performed reliably with minimal maintenance.

  • Development of a Novel Sizing Approach for Passive Mine Water Treatment Systems Based on Ferric iron Sedimentation Kinetics
    Opitz, J., M. Bauer, M. Alte, and S. Peiffer. | Water Research 233:119770(2023)
    A study evaluated Fe removal performance of a pilot-scale passive system operating in three identical, parallel lines to treat mining-influenced, ferruginous seepage water. The study determined and parameterized a robust, application-orientated model approach to size settling ponds and surface-flow wetlands. By systematically varying flow rates (and thus residence time), it was demonstrated that the sedimentation-driven removal of particulate hydrous ferric oxides in settling ponds might be approximated by a simplified first-order approach at low to moderate Fe levels. The first-order coefficient was found in the order of 2.1(±0.7) x 10-2 h-1, which corresponds well with previous lab studies. The sedimentation kinetics may be combined with the preceding Fe(II) oxidation kinetics to estimate the required residence time for pre-treatment of ferruginous mine water in settling ponds. In contrast, Fe removal in surface-flow wetlands is more complex due to the phytologic component; therefore, the study parameterized the underlying concentration dependency for polishing of pre-treated mine water. The quantitative results provide a novel, conservative approach for customized sizing of settling ponds and wetlands in integrated passive mine water treatment systems.
  • Passive Treatment of AMD Using a Full-Scale Up-Flow Mussel Shell Reactor, Bellvue Coal Mine, New ZealandAdobe PDF Logo
    Trumm, D., J. Pope, and H. Christenson.
    Proceedings of the 14th IMWA Congress, Mine Water Management for Future Generations, 12-15 July, virtual, 7 pp, 2021
    Results of the first full-scale up-flow mussel shell reactor to treat acid mine drainage (AMD) at the abandoned underground Bellvue Coal Mine are presented. The system consists of five 30,000-L plastic water tanks with associated alkathene piping and plastic valves to convey AMD from the adit and equally distribute it to the base of each tank. The water flows upwards through treatment media and is discharged into Cannel Creek. Each tank is filled with ~24 m3 of fresh mussel shells, broken into pieces ~5 cm long. The discharge piping is ~22 cm above the top of the shells to maintain a free water surface above the shells and ensure the reactor remains under reducing conditions. The tanks were filled with AMD and left static for 10 weeks before operation to allow reducing conditions to establish and iron-reducing and sulfate-reducing bacteria to populate the tanks. During site visits, field parameters were measured, and water samples were collected from the inlet and the system's outlet and Cannel Creek upstream and downstream of the confluence with the treated AMD. The system increased the pH from a median of 2.74 to a median of 6.94 and lowered metal concentrations by 97.2% (Fe), 99.8% (Al), 98.2% (Zn), and 97.0% (Ni).
  • Full-Scale Reducing and Alkalinity Producing System (RAPS) for the Passive Remediation of Polluted Mine Water from a Flooded Abandoned Underground Coal Mine, Carolina, South AfricaAdobe PDF Logo
    Dube, G.M., T. Mello, V. Vadapalli, H. Coetzee1, K. Tegegn, R. Lusunzi, S. Moja1, M. Malatji, M.E. Sinthumule, and R. Ramatsekisa.
    Proceedings of the 14th IMWA Congress, Mine Water Management for Future Generations, 12-15 July, virtual, 7 pp, 2021
    A reducing and alkalinity producing system (RAPS) named CaroRap was implemented to remediate coal mine water in South Africa. RAPS combines the mechanisms of anaerobic treatment wetlands and anoxic limestone drains to improve water quality by processes including calcite dissolution and sulfate reduction through sulfate-reducing bacteria (SRB). After four weeks of operation, the system, which included RAPS 1 and an oxidation pond, increased the pH to an average of 5.6 (from an average of 2.9) and increased alkalinity to ~35.8 mg/L. The increases were attributed to bicarbonate ions released from the dissolution of limestone. The system reduced total iron (Fe) by 92% and Al by 58.8%. There are limitations regarding adequate removal of Mn and SO4, and optimization measures will be explored further.
  • Full-Scale Demonstration Tests of Passive Treatment System by Jogmec in JapanAdobe PDF Logo
    Hayashi, K., T. Washio, Y. Masaki, T. Hamai, T. Sakata, M. Sakoda, M. Kobayashi, N. Masuda, and N. Sato.
    Proceedings from the postponed 14th IMWA Congress - "Mine Water Solutions," 2020
    Full-scale demonstration tests (flow rate 100 L/min) of a biological passive treatment system were conducted at an abandoned mine site in Japan to treat acid mine drainage (AMD) containing iron and zinc. Aerobic and anaerobic vertical-flow bioreactors utilized iron-oxidizing and sulfate-reducing bacteria (SRB). In the aerobic reactor, AMD containing 35 mg/L of Fe was treated to below the wastewater standards by using a water transfer method, such as a cascade. In the anaerobic process, the applicability of a process using ethanol or rice bran as organic resources of SRB was studied. See pages 106-109.
  • Neutralization and Uptake of Pollutant Cations from Acid Mine Drainage (AMD) Using Limestones and Zeolites in a Pilot-Scale Passive Treatment System
    Silva, D., C. Weber, and C. Oliveira. ǀ Minerals Engineering 170:107000(2021)
    A passive pilot-scale acid mine drainage treatment system was developed using open channels of calcitic (CL-I and CL-II) and dolomitic (DL-I and DL-II) limestone beds and mixtures with natural zeolites (NZ) and functionalized zeolites (FZ). Several parameters were examined, including pH, electrical conductivity, total acidity, total alkalinity, and concentrations of aluminum, iron, and manganese ions. DL-I, CL-II, and mixtures of CL-II/NZ and CL-II/FZ increased pH levels from 3.3 to 7.9, 8.2, 7.9, and 7.6, respectively; increased total alkalinity levels from 0 mg CaCO3/L to 20, 107, 42 and 34 mg CaCO3/L, respectively; and reduced total acidity levels by 95, 91, 90 and 90%, respectively. All beds promoted aluminum, iron, and manganese ion removal, but the CL-II/FZ mixture was the most efficient due to neutralization and a higher uptake of manganese ions (~99%). Results reveal ways to transform passive treatment systems using limestone beds and unconventional materials such as zeolites, combine neutralization and adsorption mechanisms in the same operation, ensure a simple maintenance and operational system and improve the economic and environmental sustainability of related processes.
  • 2014 Treatability Study Date Evaluation: Barker-Hughesville Mining District Superfund Site Adobe PDF Logo
    U.S. EPA Region 8, 1050 pp, 2017
    In 2014, two treatability studies were conducted for the Barker-Hughesville Mining District Superfund Site as part of the remedial investigation/feasibility study process. Year 2 of the Danny T Adit study continued the 2013 year 1 field pilot study to evaluate various passive and semi-passive methods for treatment of the Danny T Mine adit water. The bench-scale study for the Tiger Mine was focused on potential in situ-based treatments that could be deployed inside the underground mine workings area. A representative mine discharge water (Tiger mine adit TI-AD004, the "Firehose" adit) was collected in bulk and analyzed at the treatability laboratory in batch container tests with various reagents. The report summarizes each of these studies, including their objectives, experimental and sampling procedures, results, conclusions, and recommendations.

  • Passive Treatment of Metals-Impacted Water Using Sulfate-Mediated Metals Reduction (SMMR)
    Le, R. J. Smith, T. Carlson, M. Williams, D. Graves, S. Cronk, K. Cracchiola, and S. Dworatzek.
    2023 Bioremediation Symposium Proceedings, 8-11 May, Austin, TX, 21 slides, 2023
    The continuous removal of heavy metals, sulfate, fluoride, and total dissolved solids (TDS) from subsurface mine water at a copper mine was investigated in bench-scale up-flow anaerobic packed bed reactors over 8 weeks. The native sulfate-reducing community was stimulated using lactate as an electron donor and by maintaining anaerobic conditions (-0.5 V to 0.1 V), neutral pH, and a 24-hour hydraulic retention time. A sustainable source of hydroxyapatite was used as a sorption media in one of the three columns to enhance the sorption of heavy metals and fluoride. TDS, heavy metals, and sulfate removal were successfully achieved, along with the notable production of hydrogen sulfide in up-flow anaerobic packed bed reactors containing sulfate-reducing microbial communities. Fluoride removal was successfully achieved in the hydroxyapatite amended column. Findings from the bench-scale investigation are translatable to pilot- and full-scale implementations.
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    Longer abstract: PDF Logo

Permeable Reactive Barrier Systems — A permeable reactive barrier (PRB) is a continuous, in situ permeable treatment zone designed to intercept and remediate a contaminant plume. The treatment zone may be created directly using reactive materials such as iron or indirectly using materials designed to stimulate secondary processes, such as by adding carbon substrate and nutrients to enhance microbial activity. With most PRBs, the reactive material is in direct contact with the surrounding aquifer material. PRBs are designed to be more permeable than the surrounding aquifer materials, enabling contaminants to be treated while groundwater readily flows through. (ITRC 2005).

ITRC. 2005. Permeable Reactive Barriers: Lessons Learned/New Directions. PRB-4. Washington, D.C.: Interstate Technology — Regulatory Council, Permeable Reactive Barriers Team.

  • Pilot Test of the Permeable Reactive Barrier for Removing Uranium from the Flooded Gunnar Pit Adobe PDF Logo
    Kong, D., L. McGilp, A. Klyashtorin1, I. Wilson, and L.D. Wilson.
    Journal of Geoscience and Environment Protection 8:155-176(2020)
    Iron oxide coated sand (IOCS) media was applied in an experimental permeable reactive barrier to remove U contaminated floodwater from a mine pit. The mine pit contains ˜3.2 million m3 of water contaminated by dissolved U (1.2 mg/L), Ra-226 (0.4 Bq/L), and minor concentrations of other contaminants that is seeping over the pit rim into Lake Athabasca. Hydrous ferric oxide sorbents and their supported forms onto silica sands were prepared, characterized, and tested in bench-scale adsorption kinetic experiments in a field trial. A pilot permeable reactive barrier was fabricated and field-tested to provide technical data to design a full-scale permeable barrier employing the IOCS media.

  • A Review of Passive Acid Mine Drainage Treatment by PRB and LPB: From Design, Testing, to Construction
    Wang, Y., C. Wang, R. Feng, Y. Li, Z. Zhang, and S. Guo.
    Environmental Research 251(Part 1):118545(2024)
    This article comprehensively evaluates permeable reactive barrier systems utilized to remediate acid mine drainage. The concept of low permeability barriers, derived from site-contaminated groundwater management, is also introduced. Strategies for selecting materials, the physicochemical aspects influencing long-term efficacy, the intricacies of design and construction, and the challenges and prospects inherent in barrier technology are described.

  • A Permeable Reactive Barrier (PRB) for the Removal and Immobilization of Selenium in Seep Water and Shallow Groundwtater at a Phosphate Mine in Southern Idaho: Results of Bench Scale Testing
    Walker, W.J., D. Tooke, M. Wright, J. Hamilton, C. Schreier, and J. Peterson.
    Journal American Society of Mining and Reclamation 7(3):20-44(2018)
    A bench study was designed to determine the efficacy of a permeable reactive barrier (PRB) for removing elevated Se in groundwater and seep water at the toe of an overburden storage area at a phosphate mine in Idaho. The study consisted of three main parts: (1) characterization work designed to determine the basic chemistry of the site-water under consideration for treatment and the components of the proposed PRB, (2) batch leaching studies designed to assess the chemistry changes that each media component is expected to contribute to the overall water chemistry of the seep or groundwater in contact with the media, and (3) column studies consisting of vertical, 2-inch columns filled with the PRB media. Results indicated that the media proposed as components of the PRB posed no chemical changes of concern and resulted in rapid development of reducing conditions sufficient for Se reduction and immobilization. The groundwater Se, initially about 1 mg/L, was reduced to < 0.02 mg/L in the first 3 hours of column contact time, well below the 0.05 mg/L water quality goal.
  • Prospect for Treating Antimony-Laden Mine Wastewater Using Local Materials
    Ji, X., S. Liu, H. Juan, J. Jiang, A. He, E. Bocharnikova, and V. Matichenkov.
    Mine Water and the Environment 36(3):379-385(2017)
    Wastewater from the world's largest antimony mine (in Hunan, China) contains high levels of metal and metalloid contaminants (As, Cd, Hg, Pb, Se, and Sb). A study of the effectiveness of low-cost local industrial by-products [coal fly ash (CFA) and Ca-Si slag from the metals industry] and traditional agents [limestone, diatomaceous earth (DE), and zeolite] to treat the wastewater led to the ranking of their relative effectiveness: CFA > Ca-Si slag > DE > limestone > zeolite. CFA and Ca-Si slag removed 9.9 to 85.5% of As, Cd, Hg, Pb, Se, and Sb from wastewater. The CFA and Ca-Si slag could be employed as commercial filters or biogeochemical barriers to protect surface water and groundwater, and a similar approach might be used at other mines.

Pressure-Driven Membrane Separation Technologies — Pressure-driven membrane separation (PDMS) processes are tools used to separate media. Commonly used processes for treatment of MIW include reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. Any of these technologies can be used for surface and groundwater influenced by mining waste, but the particular tool used depends on the cleanup goal for the site. PDMS processes use semi-permeable membranes to reduce the concentration of the selected solutes in a feed solution. They produce a permeate stream containing materials that pass through the membrane, and a concentrate or waste stream that contains the materials filtered out of the feed solution. Passage through the membrane matrix is controlled by the application of a "driving force," which includes mechanical pressure, concentration or chemical potential, and temperature or electrical potential (Mortazavi 2008).

  • Mine-Affected Water Minimization Technology - 3 Years of Development Adobe PDF Logo
    Drak, A.
    Water in Mining Conference, 9-10 April, Toronto, ON, 34 slides, 2019
    The MaxH2O Desalter technology was pilot-tested to measure its effectiveness of treating acid mine drainage. The system removes sulfate ions by crystallization of calcium sulfate in the Crystalactor® while concentrating the wastewater in a reverse osmosis (RO) system. During the pilot, continuous crystallization of the calcium sulfate in the integrated salt precipitation unit maintained the saturation index in the range of 800%-1,200% during operation. The system operated without the addition of chemicals other than antiscalant and produced pellets of more than 90% dry solids content that do not require further sludge dewatering treatment. Depending on the effluent requirements, the obtained RO brine stream can be partially or completely blended with the RO product, further increasing the total recovery of the system.
  • Land Application Disposal System Design for Biochemical Reactor Treated EffluentAdobe PDF Logo
    Anton, N.R., D.T. Shanight, C.S. Storrar, M.J. Fischer, E.M. Janoviak, and B. Lala
    36th Annual Meeting of the American Society of Mining & Reclamation, 3-7 June, Big Sky, MT, 26 slides, 2019
    At the mine waste repository for the Upper Tenmile Creek Mining Area Superfund site, Montana, collected leachate water has been managed in an active water treatment plant and pilot biochemical reactor system, with disposal to a land application disposal (LAD) system since 2003. In 2018, the design was completed for a full-scale leachate passive treatment system utilizing parallel BCR cells, post-treatment settling, aeration, limestone channels, and a gravity-operated LAD system. The new system construction will begin in 2019, and the existing water treatment infrastructure will be decommissioned after the new system is operational and functional. The presentation includes the critical passive treatment design components and provides details of the pre-design investigation and design approach for the LAD system, including field siting for the LAD, test pits, soil lithology logging, permeability testing, soil metal sorption studies, metal sorption capacity and water balance calculations, and hydraulic design of the LAD.
    More information:

  • Membrane Technology Applied to Acid Mine Drainage From Copper Mining
    Ambiado, K., C. Bustos, A. Schwarz, and R. Borquez.
    Water Science and Technology 75(3):705-715(2017)
    The performance of two commercial spiral-wound membranes—NF99 and RO98pHt (Alfa Laval)—was compared in an evaluation of pilot-scale treatment by nanofiltration (NF) and reverse osmosis (RO) of high-strength acid mine drainage (AMD) from copper mining. Results showed high ion removal under optimum pressure conditions, which reached 92% for the NF99 membrane and 98% for the RO98pHt membrane. Sulfate removal reached 97% and 99% for NF99 and RO98pHt, respectively. Removal percentage for Cu, Al, Fe, and Mn surpassed 95% in both membranes. Although concentration polarization limited NF performance at higher pressures, permeate fluxes observed in NF were five times greater than those obtained by RO, with only slightly lower divalent ion rejection rates.
  • The Effect of Electro-Activation and Eggshell Powder on the Neutralization of Acid Mine Drainage
    Kastyuchik, A., A. Karam, and M. Aider.
    Journal of Sustainable Mining 16(3):73-82(2017)
    Acid neutralization and the precipitation of metals present in acid mine drainage (AMD) were carried out by electro-activation with ion-exchange membranes, which is based on the self-generation of necessary conditions for acid neutralization and metal precipitation. The treatment of sulfide mine tailings (SMT) was carried out using an electro-activation cell-generated alkaline solution in the cathode compartment. After 60 min of electro-activation, a pHcatholyte of 7.9-9.6 (depending on the experimental conditions) was obtained. The absence of Fe and other trace metal ions in the catholyte provide evidence that SMT electro-activation promotes the precipitation of insoluble trace metals in the cathode compartment. This approach can be applied to real conditions in combination with a pretreatment of SMT neutralization using biological calcareous amendments, such as eggshell powder. This paper is Open Access at

Mining-Influenced Water and Solid Waste

Backfilling and Subaqueous Disposal — Backfilling and subaqueous disposal technologies can be effective treatment alternatives for remediation of solid mining wastes and MIW. Subaqueous disposal involves removing surface material and placing it underground and underwater, thus eliminating direct contact exposures. Typically, subaqueous disposal is applied to sulfide-containing solid mining wastes to reduce oxidation, which limits acid generation and release of metals. Subaqueous disposal also is used to dispose of non-acid-generating solid mining wastes through backfilling. Solid mining wastes are disposed of into deep submarine environments, natural lakes, pit lakes, subsidence features, underground mines, and surface mines. Subaqueous disposal also includes injection of MIW and process waters into geologic formations below the depth of fresh groundwater, but this has not been widely practiced.

  • How to Assess Potential Biological Effects of Subaqueous Disposal of Mine Tailings: Literature Review and Recommended Tools and Methodologies
    Campbell, P.G.C. and W.A. Price.
    Mine Environment Neutral Drainage Program, MEND Report 2.19.1, 158 pp, 2018
    Subaqueous disposal (SAD) or flooding of sulfide-rich tailings in constructed facilities is a method used at some mine sites to mitigate the formation of acid mine drainage. The primary SAD mitigation mechanism is limitation of oxygen ingress into water-filled pores, which greatly reduces sulfide oxidation, minimizes metal leaching, and prevents acidic drainage development. The overall biological performance of such facilities is not well understood. In particular, a major gap in understanding relates to the biological colonization of such facilities, the health of biological communities that are established, and the influence of those communities on water and sediment geochemistry. This report contains an introduction, an extensive literature review (Sections 2-7), and a set of recommendations on tools and methodologies that might be used to assess the biological effects of submerged tailings.

In Situ Biological Treatment — In situ biological source treatment consists of isolating the source of MIW by establishing an in situ biological layer on exposed metal sulfide surfaces (Jin et al. 2008b). This is typically accomplished by injecting inoculum (e.g., wastewater effluent) and substrate into the subsurface material. The in situ biological source treatment can achieve satisfactory results without the cost of excavation and material handling. The process typically has two components: (a) developing an anaerobic environment through the injection and distribution of inoculums and substrates; and (b) forming and maintaining a biological film that impedes the release of products of iron reduction. A complete analysis of the MIW and the treatment material, including seasonal and formulation variations, must be completed before selecting an in situ biological source treatment system. Bench-scale tests exploring variations in the treatment material and the material to be treated are invaluable when determining whether an in situ biological source treatment system is applicable and the type of treatment material that is suitable for the site.

Jin, S., P. H. Fahlgren, J. M. Morris, and R. B. Gossard. 2008b. "Biological Source Treatment of Acid Mine Drainage Using Microbial and Substrate Amendments: Microcosm Studies," Mine Water and the Environment 27(1): 20-30.

  • Biological Treatment of uranium at the Historical Schwartzwalder Mine, Colorado, USAAdobe PDF Logo
    Gault, A.G., J.M. Harrington, E. Busby, R,M. Kleinberger, R. Martz, and V.P.M. Friesen.
    Proceedings of Mine Water Solution, 14-16 June, Vancouver, Canada, 2022
    The Schwartzwalder mine was dewatered to prevent seepage into Ralston Creek, as the mine water contained U levels up to 26 mg/L. Biological in situ treatment of the flooded mine workings (mine pool) involved injecting soluble organic carbon into the mine pool, creating strong reducing conditions, resulting in 80-90% U removal in situ. Before discharge to Ralston Creek, the pre-treated mine pool water is pumped to an ex situ reverse osmosis and ion exchange system. Although discharged water meets local water quality guidelines (< 0.03 mg/L), continued active water treatment is not sustainable for site closure. Pilot-scale trials for semi-passive and passive biological U treatment via bioreactors and constructed wetland treatment systems (CWTS) evaluated alternative long-term water treatment options to achieve reclamation targets without perpetual active treatment. Bioreactors supplemented with synthetic iron sulfide and ethanol, or ethanol and elevated phosphate, demonstrated ~83% and 96% dissolved U removal, respectively. Microbial community profiling of the bioreactor substrate identified a significant fraction of the bacteria population comprised of genera with known U- and sulfate-reducing functionality. Bulrush and water sedge plant species were tested in CWTS pilots for their ability to foster conditions to sequester U from mine discharge water. Bulrush and water sedge systems treated U to 0.6 to 4.2 mg/L (93 to 29% removal) and 0.01 to 0.5 mg/L (>99% to 93% removal), respectively, depending on the hydraulic residence time (HRT) of the CWTS. Water sedge systems treated to lower U concentrations than bulrush, including at a relatively short 5-day HRT.
  • Performance of Semi-Passive Systems for the Biological Treatment of High-As Acid Mine Drainage: Results from a Year of Monitoring at the Carnoules Mine (Southern France)
    Diaz-Vanegas, C., C. Casiot, L. Lin, L. De Windt, M. Hery, A. Desoeuvre, O. Bruneel, F. Battaglia-Brunet, and J. Jacob. | Mine Water and the Environment 41(3):679-694(2022)
    Two semi-passive treatment systems were installed and monitored for one year to treat As-enriched acid mine drainage (AMD) (≈ 1 g/L Fe(II) and 100 mg/L As(III)) at the Carnoules mine. Treatment was based on biological Fe and As oxidation by indigenous bacteria and subsequent As immobilization by ferric hydroxysulfates. Forced aeration and wood/pozzolana or plastic support were used for biofilm attachment. The system performance ranged from 86-98% for Fe oxidation, 30-60% for Fe removal, and 50-80% for As removal using a nine hr hydraulic retention time. No significant differences were measured between the two biofilm supports. The wood/pozzolana support had a shorter delay for performance recovery after interruptions. Iron oxidation rates were similar to those obtained in the Carnoules AMD stream and lab bioreactor, while As oxidation may have been enhanced. The sludge accumulated between 39 and 91 mg/g of As, mainly in the As(V) oxidation state; jarosite and amorphous ferric hydroxysulfate phases were the main Fe and As scavengers. Challenging environmental conditions during the long monitoring period confirm the robustness of the treatment units. The data will be useful in designing future full-scale treatment systems adapted to As-rich AMD.
  • Pilot Study of In Situ Biological Treatment at the Silver King Mine, Keno Hill, Yukon Adobe PDF Logo
    Gault, A.G., J.M. Harrington, C. Robertson, M.C. Simair, and V.P.M. Friesen.
    11th ICARD IMWA 2018 Annual Conference, September 10-14, Pretoria, South Africa. IMWA Proceedings (Volume I), 2018
    Part of closure planning for the United Keno Hill Mines site in central Yukon, Canada included evaluating options for long-term treatment of several flowing adits in which Cd and Zn are the principal contaminants of concern. A 3.5-year in situ pilot test conducted at the Silver King Mine was initiated to evaluate the potential closure strategy to treat Cd and Zn using in situ biological treatment. Pumped mine water was mixed with methanol or molasses as a carbon source and reinjected to create an environment ideal for sulfate-reducing bacteria to grow, precipitating Zn and Cd in the process. Four molasses injections were performed in 2015, each lasting between 24 and 42 days, and 2 additional injections of methanol followed in 2016, totaling 105 days. Genomic analysis confirmed the presence of sulfate-reducing bacteria dominated by members of the Desulfosporosinus genus. Following carbon injection, Zn and Cd concentrations declined by more than 90%. Despite rising slowly over time, Zn and Cd concentrations remained below both their pre-treatment concentrations and the effluent quality standards such that carbon injections on an annual basis may maintain low metal concentrations.

  • Treatment and Remediation of Metal-Contaminated Water and Groundwater in Mining Areas by Biological Sulfidogenic Processes: A Review
    Li, Y., Q. Zhao, M. Liu, J. Guo, J. Xia, J. Wang, Y. Qiu, J. Zou, W. He, and F. Jiang.
    Journal of Hazardous Materials 443(Part B):130377(2023)
    This review focuses on developments in the sulfur-reducing bacteria (SRB)-driven biological sulfidogenic process (BSP) for the treatment and remediation of metal-contaminated wastewater and groundwater. To identify the bottlenecks and to improve BSP performance, this paper reviews sulfidogenic bacteria presenting in metal-contaminated water and groundwater; highlights the critical factors for the metabolism of sulfidogenic bacteria during BSP; the ecological roles of sulfidogenic bacteria and the mechanisms of metal removal by sulfidogenic bacteria; and the application of sulfidogenic systems and their drawbacks. Research knowledge gaps, current process limitations, and future prospects are provided to improve the performance of BSP in the treatment and remediation of metal-contaminated wastewater and groundwater in mining areas.

  • The MnDRIVE Transdisciplinary Project Implementation of Smart Bioremediation Technology to Reduce Sulfate Concentrations in NE Minnesota Watersheds
    Hudak, G., L. Estepp, and P. Schoff.
    University of Minnesota Duluth, Natural Resources Research Institute. NRRI/TR-2017/17, 155 pp, 2017
    This MnDRIVE-supported project continues a long-running set of experiments to address issues associated with mining-impacted waters. Results to date show both promise and challenges for floating sulfate-reducing bacterial bioreactors as currently configured. Functional tests show that the bioremediation process can decrease aqueous sulfate concentrations in water substantially. The potential advantages of this bioremediation system include low power demand that can be satisfied by on-site solar photovoltaic panels, year-round operation with minimal need for human intervention, reasonable capital costs, low operating costs, and minimal waste production. In addition, the bioreactors used in this study are extremely flexible and adaptable; they have been designed as interchangeable modules that can operate in series or in parallel and will accommodate changes in flow rate. The bioreactor platform might be most useful as a preliminary stage to reduce sulfate concentrations in water prior to treatment by conventional energy- and material-intensive methods, such as reverse osmosis or ion exchange, both of which have limited efficiency in high-sulfate environments. The bacterially mediated reduction in sulfate could substantially decrease the burden on those more expensive systems and thus increase the cost-effectiveness of the remediation system as a whole. See more information on the problem of mining-related sulfate generation in Minnesota in a series of reports at
  • Attenuation of Acid Rock Drainage with a Sequential Injection of Compounds to Reverse Biologically Mediated Pyrite Oxidation in the Chattanooga Shale in Tennessee
    Byl, T.D., R. Oniszczak, D. Fall, P.K. Byl, D.E. Young, and M.W. Bradley.
    U.S. Geological Survey Karst Interest Group Proceedings, San Antonio, Texas, May 16-18, 2017: U.S. Geological Survey Scientific Investigations Report 2017-5023:37(2017)
    A study was conducted to disrupt chemolithotrophic bacteria responsible for acid rock drainage (ARD) associated with the Chattanooga Shale in Tennessee's karstic central basin. Researchers used chemical treatments to foster an environment favorable for competing microorganisms to attenuate the biologically induced ARD. Chemical treatments were injected into flow-through microcosms consisting of 501 grams of pyrite-rich shale pieces inoculated with ARD bacteria. Treatments included a sodium hydroxide-bleach mix, a sodium lactate solution, a sodium lactate-soy infant formula mix—each treatment with or without phosphate buffer, or injected sequentially with sodium hydroxide. The optimal treatment was a sequential injection of 1.5 g sodium hydroxide, followed by 0.75 g lactate and 1.5 g soy formula dissolved in 20 mL water. The pH of the discharge water rose to 6.0 within 10 days, dissolved-iron concentrations dropped <1 mg/L, the median alkalinity increased to 98 mg/L as CaCO3, and the stimulated sulfur-reducing and slime-producing bacteria populations exhibited an increase in estimated population counts. The ARD-attenuating benefits of the optimal treatment remained evident after 33 weeks. The other treatments provided ARD-attenuating effects but were tempered by problems such as high phosphate concentrations, short longevity, or other shortcomings.

Phytotechnologies — Phytotechnologies use plants to remediate various media impacted with different types of contaminants. There are six basic phytoremediation mechanisms that can be used to clean up mining-contaminated sites: phytoextraction, phytodegradation, phytovolatilization, rhizodegradation, phytosequestration, and phytohydraulics. These technologies can be applied to address certain issues associated with mining solid wastes and MIW, and also can stabilize tailings and act as a hydraulic control for drainage. Phytotechnologies are a common component of mining reclamation and restoration projects that establish a plant cover as a final remedy. Establishing phytotechnologies requires careful selection of plant species and soil amendments. Most phytotechnologies can be applied to both organic and inorganic contaminants and to soil/sediment, surface water, and groundwater. Phytotechnologies also can be applied simultaneously to various combinations of contaminant types and impacted media. Establishment of vegetation can be enhanced by using native soil or other amendments to offset the often poor growing conditions offered by the tailings material.

  • In Situ Restoration of Soil Ecological Function in a Coal Gangue Reclamation Area After 10 Years of Elm/Popular Phytoremediation
    Bai, D.-S., X. Yang, J.-L. Lai, Y.-W. Wang, Y. Zhang, and X.-G. Luo.
    Journal of Environmental Management 305:114400(2022)
    Soil ecological health risks and toxic effects of coal gangue accumulation were examined after 10 years of elm/poplar phytoremediation. Soil enzyme activities, ionome metabolism, and microbial community structure changes were analyzed at shallow (5-15 cm), intermediate (25-35 cm), and deep (45-55 cm) soil depths. Soil acid phosphatase activity in the restoration area increased by 4.36-7.18 fold. Soil concentrations of Cu, Pb, Ni, Co, Bi, U, Th, and the non-metallic element S were reduced. The repair effect was shallow > middle > deep. Redundancy analysis showed that S and Na are important driving forces for the microbial community distributions at shallow soil depths. The Kyoto Encyclopedia of Genes and Genomes (KEGG) function prediction indicated enhancement of the microbial function of the middle-depth soil layers in the restoration area. Phytoremediation enhanced the biotransformation of soil phosphorus in the coal gangue restoration area, reduced the soil content of metals, significantly changed the structure and function of the microbial community, and improved the overall soil ecological environment.

  • Arsenic Uptake by Pteris Vittata in a Subarctic Arsenic-Contaminated Agricultural Field in Japan: An 8-Year Study
    Kohda, Y. H.-T., G. Endo, N. Kitajima, K. Sugawara, M.-F. Chien, C. Inoue, and K. Miyauchi.
    Science of The Total Environment 831:154830(2022)
    The phytoremediation potential of tropical and subtropical As-hyperaccumulating fern Pteris vittata was investigated in an As-contaminated field near an abandoned goldmine in a subarctic area of northeast Japan. This study aimed to decrease the risk of water-soluble As in soil while nurturing the soil and respecting the plant life cycle for sustainable phytoremediation over eight years. The field was tilled and planted with new fern seedlings every spring, and grown ferns were harvested every autumn. Fronds, rhizomes, and roots of the fern were analyzed separately for biomass and As after harvesting each year. Frond biomass was significantly affected by the yearly change in weather conditions. As concentration in fronds was maintained at a 100-150 mg/kg dry weight. The accumulated As in P. vittata was higher than that of As-hyperaccumulator fern Pteris cretica, the native fern in the field trial area. Harvested biomass of P. vittata per plant was also higher than that of P. cretica. More than 43.5 g As/154 m2 (2.82 kg of As per hectare) was removed via phytoremediation during the experiment. Because of the short-term plant growth period and soil tilling process, total As in soil did not show significant depletion. However, the water-soluble As in the surface and deeper soil decreased to 10 µg/L (Japan Environmental Quality Standard for water-soluble As in soil).
  • Phytostabilization of Acidic Mine Tailings with Biochar, Biosolids, Lime, and Locally-Sourced Microbial Inoculum: Do Amendment Mixtures Influence Plant Growth, Tailing Chemistry, and Microbial Composition?
    Trippe, K.M., V.A. Manning, C.L.Reardon, A.M. Klein, C. Weidman, T.F. Ducey, J.M. Novak, D.W. Watts, H. Rushmiller, K.A. Spokas, J.A. Ippolito, and M.G. Johnsong.
    Applied Soil Ecology 165:103962(2021)
    Amendment mixtures composed of lime, biochar, biosolids (LBB), and locally sourced microbial inoculum (LSM) were evaluated to alleviate the constraints that hinder phytostabilization success in acid mine tailings. A greenhouse study that simulated in situ conditions to measure the influence of LBB-LSM amendment blends on plant growth, plant nutrients, metal concentrations, microbial function, and microbial community structure was conducted. Blue wildrye was grown in tailings collected from the Formosa mine site amended with various combinations of LBB-LSM. The above and belowground biomass of plants grown in mine tailings amended with LBB was 3-4 times larger than the biomass of plants grown in tailings amended with lime. Although the LSM addition did not influence immediate plant growth, it did affect nutrient content and altered the rhizosphere community composition.
  • Optimization of Combined Phytoremediation for Heavy Metal Contaminated Mine Tailings by a Field-Scale Orthogonal Experiment
    Li, X., X. Wang, Y. Chen, X. Yang, and Z. Cui.
    Ecotoxicology and Environmental Safety 168: 1-8(2019)
    The combined application of plant, microorganism, and amendment on the phytoremediation of heavy metals was optimized as a remediation technique for mine tailings by a field-scale orthogonal experiment aimed to achieve the maximum phytoremediation effect. Soybean, Mucor circinelloides, and A3 amendment were used as the plant, microorganism, and amendment materials. With the application, effective fractions of copper, zinc, lead, cadmium, and manganese were immobilized for decreased bioavailability, indicating the phytostabilization served as a major repair pathway. Plant length and biomass in the treatments were significantly higher than that in the control, indicating their phytoremediation potentials were enhanced. The final contents of heavy metals in soil were decreased, and the removal rates of soil heavy metals were in the order of Pb > Cd > Cu > Zn > Mn. Temporal variations of soil microorganism populations indicated that the abundance of soil microorganism in the treatments was significantly higher than that in the control, and bacteria became the dominant microbial species.
  • Dynamics of Bacterial Communities Mediating the Treatment of an As-rich Acid Mine Drainage in a Field Pilot
    Laroche, E., C. Casiot, L. Fernandez-Rojo, A. Desoeuvre, V. Tardy, O. Bruneel, et al.
    Frontiers in Microbiology 9:3169(2018)
    Bacterial diversity was characterized in a field-pilot bioreactor treating extremely arsenic (As)-rich acid mine drainage (AMD) in situ over a 6-month monitoring period. Over the monitoring period, iron (Fe)-oxidizing bacteria dominated the biogenic precipitate. Parameters that exerted a control on the bacterial communities potentially involved in the water treatment process included dissolved oxygen, temperature, pH, dissolved sulfates, arsenic and Fe(II) concentrations and redox potential. The ubiquity and the physiological diversity of the bacteria identified, as well as the presence of bacteria of biotechnological relevance, suggested that this treatment system could be applied to the treatment of other AMD. This article is Open Access at
  • Aided Phytostabilisation Reduces Metal Toxicity, Improves Soil Fertility and Enhances Microbial Activity in Cu-Rich Mine Tailings
    Touceda-Gonzalez, M., V. Alvarez-Lopez, A. Prieto-Fernandez, B. Rodriguez-Garrido, et al.
    Journal of Environmental Management 186(2):301-313(2017)
    A phytostabilization field trial was implemented in spring 2011 in Cu-rich mine tailings in NW Spain. The tailings were amended with composted municipal solids and planted with a grass (Agrostis capillaris) and with willow (Salix spp.) and poplar (Populus nigra L.) trees. Compost amendment improved soil properties, such as pH and fertility, and decreased soil Cu availability, leading to the establishment of a healthy vegetation cover. Both compost amendment and plant root activity stimulated soil enzyme activities and induced important shifts in the bacterial community structure over time. The beneficial effects of the phytostabilization process were maintained at least three years after treatment.

  • A Review on Remediation of Iron Ore Mine Tailings via Organic Amendments Coupled with Phytoremediation Adobe PDF Logo
    Sarathchandra, S.S., Z. Rengel, and Z.M. Solaiman.
    Plants 12:1871(2023)
    Existing physical, chemical, and amendment-assisted phytoremediation methods to rehabilitate mine tailings are compared from cost, reliability, and durability perspectives. The review concludes that amendment-assisted phytoremediation has received comparatively great attention; however, the selection of an appropriate phytoremediator is a critical step in the process. Moreover, phytoremediation efficiency is solely dependent on the amendment type and rate. Applying advanced plant improvement technologies, such as genetically engineered plants produced for this purpose, would be an alternative solution.
  • Distinguishing Reclamation, Revegetation and Phytoremediation, and the Importance of Geochemical Processes in the Reclamation of Sulfidic Mine Tailings: A Review
    Xie, L. and D. van Zyl.
    Chemosphere 252:126446(2020)
    Reclamation, revegetation, and phytoremediation concepts and relationships are clarified in this article to aid in the design of an appropriate reclamation plan during mine closure stage. Amended phytostabilization is the most promising technique to reduce metal (loid)s mobility in sulfidic tailings. The review stresses the importance of inorganic geochemical processes in the direct revegetation on sulfidic mine tailings and emphasizes their potential as an anticipated research direction in the near future.
  • Innovative and Sustainable Approach for Phytoremediation of Mine Tailings: A ReviewAdobe PDF Logo
    Punia, A.
    Waste Disposal & Sustainable Energy 1:169-176(2019)
    This review looks at innovating a sustainable solution to stabilize mine tailings using bioremediation and phytoremediation.

  • Dianthus Sylvestris Subsp. Sylvestris As a Promising Candidate for Phytostabilization of Cooper-Contaminated Post-Mining Sites in Alpine Ecosystems
    Poscic, F., F. Ginaldi, C. Ferfuia, I. Paskovic and A. Babst-Kostecka. Nordic Journal of Botany 2:e04199(2024)
    A study explored the potential of Dianthus sylvestris subsp. sylvestris to remediate post-mining sites contaminated with copper (Cu) at high altitudes, which is a challenging task for most management strategies. More than 1,300 mg Cu/kg in shoots were found in plants collected at the Monte Avanza legacy mine site, however, it was unclear whether the presence of copper was due to hyperaccumulation or foliar contamination. Field samples were washed with two different protocols to address the gap followed by a controlled Cu-tolerance test. Very high Cu concentrations exceeding the Cu hyperaccumulation threshold of 300 mg/kg were found in samples washed with water. Results for the plants cleaned with EDTA suggested a Cu exclusion strategy. Under controlled conditions, the plant showed Cu hypertolerance but did not hyperaccumulate Cu. D. sylvestris presents a Cu exclusion strategy rather than hyperaccumulation potential, making it a suitable candidate for Cu phytostabilization at high-altitude legacy mine sites.
  • Phytoremediation Potential of Native Plant Species in Mine Soils Polluted by Metal(loid)s and Rare Earth Elements Adobe PDF Logo
    Kushwaha, P., A. Tran, D. Quintero, M. Song, Q. Yu, R. Yu, M. Downes, R.M. Evans, A. Babst-Kostecka, J.I. Schroeder, and R.M. Maier.
    Science of The Total Environment 899:165667(2023)
    A study evaluated the contamination level of 29 metal(loid)s and rare earth elements (REEs) in two natural soils and four native plant species (Salsola oppositifolia, Stipa tenacissima, Piptatherum miliaceum and Artemisia herba-alba) growing in the vicinity of a Pb-(Ag)-Zn mine and assessed their phytoextraction and phytostabilization potential. Very high soil contamination was found for Zn, Fe, Al, Pb, Cd, As, Se, and Th, considerable to moderate contamination for Cu, Sb, Cs, Ge Ni, Cr, and Co, and low contamination for Rb, V, Sr, Zr, Sn, Y, Bi and U in the study area, dependent of sampling place. Available fraction of potentially toxic elements (PTEs) and REEs compared to total concentration showed a wide range from 0% for Sn to more than 10% for Pb, Cd, and Mn. Soil properties such as pH, electrical conductivity, and clay content affect the total, available, and water-soluble concentrations of different PTEs and REEs. Results from plant analysis showed that the concentration of PTEs in shoots could be at a toxicity level (Zn, Pb, and Cr), lower than toxic but more than sufficient or natural concentration accepted in plants (Cd, Ni, and Cu) or at an acceptable level (e.g., V, As, Co, and Mn). Accumulation of PTEs and REEs in plants and the translocation from root to shoot varied between plant species and sampling soils. A. herba-alba is the least efficient plant in the phytoremediation process; P. miliaceum was a good candidate for phytostabilization of Pb, Cd, Cu, V, and As, and S. oppositifolia for phytoextraction of Zn, Cd, Mn, and Mo. All plant species except A. herba-alba could be potential candidates for phytostabilization of REEs, while none of the plant species has the potential to be used for phytoextraction of REEs.
  • Zinc Accumulation in Atriplex Lentiformis is Driven by Plant Genes and the Soil Microbiome
    Kushwaha, P., A. Tran, D. Quintero, M. Song, Q. Yu, R. Yu, M. Downes, R.M. Evans, A. Babst-Kostecka, J.I. Schroeder, and R.M. Maier.
    Science of The Total Environment 899:165667(2023)
    A project aimed to identify relationships between tailings properties, the soil microbiome, and plant stress response genes during growth of Atriplex lentiformis in compost-amended (10 %, 15 %, 20 % w/w) mine tailings. Analyses included RNA-Seq for plant root gene expression, 16S rRNA amplicon sequencing for bacterial/archaeal communities, metal concentrations in both tailings and plant organs, and phenotypic measures of plant stress. Zn accumulation in A. lentiformis leaves varied with compost levels and was highest in the intermediate treatment (15 %, TC15). Microbial analysis identified Alicyclobacillus, Hydrotalea, and Pseudolabrys taxa with the highest relative abundance in TC15, which were strongly associated with Zn accumulation. The study identified 190 root genes with significant gene expression changes. The root genes were associated with different pathways, including abscisic acid and auxin signaling, defense responses, ion channels, metal ion binding, oxidative stress, transcription regulation, and transmembrane transport. The increasing levels of compost did not drive root gene expression changes. For example, 15 genes were up-regulated in TC15, whereas 106 genes were down-regulated in TC15. The variables analyzed explained 86% of the variance in Zn accumulation in A. lentiformis leaves. Zn accumulation was driven by shoot concentrations, leaf stress symptoms, plant root genes, and microbial taxa. Results suggest there are strong plant-microbiome associations that drive Zn accumulation in A. lentiformis and different plant gene pathways are involved in alleviating varying levels of metal stress.
  • Assessment of the Phytoremediation Effectiveness in the Restoration of Uranium Mine Tailings
    Madejona, P., M.T. Domínguez, I. Girona, P. Burgosa, M.T. Lopez-Fernandez, O.G, Porras, and E. Madejon. | Ecological Engineering 180:106669(2022)
    An assisted phytoremediation process was implemented at two U mine waste dumps (MWD) in the central-west of peninsular Spain. At each MWD, an area of ~10 ha was selected for sugar lime (SL) application at a rate of 75 T/ha. After SL addition, common grasses Cynodon dactylon, Secale cereale, and the leguminosae Vicia sativa were seeded. The evolution of soil physico-chemical properties and plant development were monitored for 69 months in top, medium and low areas of both MWDs. During the study pH values were maintained in the range of neutrality. Total concentrations of trace elements (including U) presented a high variability. Values were similar in the different areas of each MWD and did not change over time. In general, trace elements were higher than those found in non-contaminated soils. However, U and Mn availability and the accumulation of trace elements (especially U and Mn) decreased with time in the studied plants. Results indicated a positive effect of the amendment, improving the development of spontaneous and induced vegetation and the accumulation of soil organic matter.
  • Metal Lability and Mass Transfer Response to Direct-Planting Phytostabilization of Pyritic Mine Tailings
    Hammond, C.M., R.A. Root, R.M. Maier, and J. Chorover.
    Minerals 12(6):757(2022)
    Metal lability trends were investigated following a direct-planting phytostabilization trial at a Superfund mine tailings site in semi-arid central Arizona. Unamended tailings were characterized by high concentrations (mmol/kg) of Fe (2,100), S (3,100), As (41), Zn (39), and Pb (11), where As and Pb exceeded Arizona non-residential soil remediation levels. Phytostabilization treatments included a no-compost control, 100 g/kg compost with seed, and 200 g/kg compost with and without seed to the top 20 cm of the tailings profile. All plots received supplemental irrigation to double the mean annual precipitation. Tailings cores up to 90 cm were collected at planting and every summer for three years. The cores were sub-sectioned at 20 cm increments, then analyzed via total digestion and an operationally-defined sequential extraction for elemental analysis. Calculations of a mass transfer coefficient were normalized to Ti as an assigned immobile element. Pb was recalcitrant and relatively immobile in the tailings environment for the uncomposted control and composted treatments, with a maximum variation in the total concentration of 9-14 mmol/kg among all samples. Metal lability and translocation above the redox boundary (ca. 30 cm depth) were governed by acid generation, where surficial pH was measured as low as 2.7 ± 0.1 in and strongly correlated with the increased lability of Mn, Co, Ni, Cu, and Zn. There was no significant pH effect on V, Cr, or Pb availability. Translocation to depths was highest for Mn and Co though Zn, Ni, Cr, and Cu were also mobilized. Adding organic matter enhanced Cr mobilization from the near-surface to 40-60 cm depth (pH > 6) during the phytostabilization study compared to the control. Increased enrichment of some metals at 60-90 cm indicates that the long-term monitoring of elemental translocation is necessary to assess the efficacy of phytostabilization to contain subsurface metal contaminants and thereby protect the surrounding community from exposure. This article is Open Access at
  • Electrokinetic-Enhanced Phytoremediation of Uranium-Contaminated Soil Using Sunflower and Indian Mustard
    Larson, S.L., J.H. Ballard, J. Li, K. Guo, Z. Arslan, J.R. White, F.X. Han, J. Zhang, Y. Ma, and C.A. Waggoner, Army Corps of Engineers Document No. ERDC/EL MP-20-4, 14 pp, 2020
    Research examined the effects of electrokinetic treatments on plant uptake and bioaccumulation of uranium in soil from various sources, including mine tailings and ore wastes around abandoned mines and U redistribution in soils affected by planting and electrokinetic treatments. Soil was spiked with 100mg/kg UO2, UO3, and UO2(NO3)2. After sunflower and Indian mustard grew for 60 days, 1 voltage of direct current was applied across the soils for 9 days. U uptake in both plants was enhanced by electrokinetic treatments from soil spiked with UO3 or UO2(NO3)2. U accumulated more in roots than in shoots. Electrokinetic treatments were effective in lowering soil pH near the anode region. Overall, U removal efficiency reached 3.4-4.3% from soils with UO3 and uranyl with both plants, while efficiency in soil with UO2 was 0.7-0.8%. Electrokinetic remediation treatment enhanced U removal efficiency (5-6%) from soils with UO3 and uranyl but was 0.8-1.3% from soil spiked with UO2, indicating significant effects of U species and electrokinetic enhancement on U bioaccumulation.
  • Copper Phytoextraction and Phytostabilization Potential of Wild Plant Species Growing in the Mine Polluted Areas of Armenia
    Ghazaryan, K.A., H.S. Movsesyan, H.E. Khachatryan, N.P. Ghazaryan, T.M. Minkina, et al.
    Geochemistry: Exploration, Environment, Analysis 19(2):155-163(2018)
    The phytoremediation potential of 16 native wild plant species growing in Cu-contaminated soils of a mining region in Armenia was evaluated in this study. In roots of dominant plant species, Cu concentrations varied between 55 mg/kg (Hypericum perforatum) and 775 mg/kg (Thymus kotschyanus), and in shoots of plants in the range from 33 mg/kg (Teucrium orientale) and 243 mg/kg (Phleum pratense). The high contents of soil organic matter and clay in the soil facilitated the decrease of the ratio Cubioavailable/Cutotal and, as a result, the decrease of Cu accumulation capability of plants. Thymus kotschyanus, Phleum pratense and Achillea millefolium had the highest phytostabilization potential of all the studied species due to high bioconcentration factors of their roots and low translocation factors registered in these plants.
  • Effects of Vegetation Pattern and Spontaneous Succession on Remediation of Potential Toxic Metal-Polluted Soil in Mine Dumps
    Chen, F., Y. Yang, J. Mi, R. Liu, H. Hou and S. Zhang.
    Sustainability 11(2):397(2019)
    Plant growth, soil fertility, and the capacity of potential toxic metals (PTMs) using different vegetation patterns were investigated over 10 and 17 years to understand the role of vegetation pattern and spontaneous succession in the early phase of mine restoration projects. To do this, field and lab experiments on different vegetative patterns were conducted using combinations of rehabilitative plants (RP) and local plants (LP) at a metal mining dump in Sichuan, China. Phytoremediation using a simple vegetation pattern of RPs Agave sisalana and Neyraudia reynaudiana achieved a PTM pollution index of 9.28% lower, a soil fertility index of 21.86% lower, and biodiversity index of 73.69% lower than a complex vegetative pattern using RPs and LPs. Phytoremediation with a 10-year RP and LP pattern had a PTM pollution index 4.04% higher, a soil fertility index 4.48% lower, and a biodiversity index 12.49% lower than the 17-year RP and LP pattern. Results indicate the importance of choosing a suitable vegetation pattern to prevent spontaneous vegetation succession and ensure phytoremediation. This article is Open Access at
  • Phytostabilization of ZN and CD in Mine Soil Using Corn in Combination with Biochars and Manure-Based Compost
    Sigua, G.C., J.M. Novak, D.W. Watts, J.A. Ippolito, T.F. Ducey, M.G. Johnson, et al.
    Environments 6(6):69(2019)
    The effect of biochar additions (BA) with or without manure-based compost (MBC) was evaluated on shoots biomass, roots biomass, uptake, and the bioconcentration factor (BCF) of Zn and Cd in corn (Zea mays L.) grown in mine soil. Biochar additions of beef cattle manure (BCM), poultry litter (PL), and lodgepole pine were applied at 0, 2.5, and 5.0% (w/w) in combination with different rates (0, 2.5, and 5.0%, w/w) of MBC, respectively. Shoots and roots uptake of Cd and Zn were significantly affected by BA, MBC, and the interaction of BA and MBC. Corn plants that received 2.5% PL and 2.5% BCM had the greatest Cd and Zn shoot uptake, respectively. Corn plants with 5% BCM had the greatest Cd and Zn root uptake. When averaged across BAs, the greatest BCF for Cd in the shoot (92.3) was from application of BCM and the least BCF was from application of PL (72.8). The incorporation of biochar enhanced phytostabilization of Cd and Zn. Concentrations of water-soluble Cd and Zn were lowest in soils amended with manure-based biochars, which improved the biomass productivity of corn. This article is Open Access at
  • Remediation of Acid Mine Drainage-Impacted Wter by Vetiver Grass (Chrysopogon Zizanioides): A Multiscale Long-Term Study
    Kiiskila, J.D., D. Sarkar, S. Panja, S.V. Sahi, and R. Datta.
    Ecological Engineering 129:97-108(2019)
    The study developed a cost-efficient and sustainable floating treatment wetland system using vetiver grass (Chrysopogon zizanioides). Year-long large- and small-scale hydroponic experiments were used to determine the effectiveness of vetiver for treating acid mine drainage-impacted waters from the Tab-Simco mine site in southern Illinois. For the large-scale mesocosm study, vetiver rafts were suspended in 100-gal containers. Water quality was monitored every 28 days and at the end of the experiment (364 days); plant health was monitored by measuring changes in biomass and recording visual changes in root and shoot coloration and morphology. There was higher net removal of Fe (81%) and Pb (81%) with lower removal of Ni (38%), Zn (35%), SO42- (28%), Mn (27%), Cr (21%), Al (11%) and Cu (8.0%). Toxicity characteristic leaching procedure showed that vetiver biomass was not hazardous waste as a result of metal accumulation. From the small-scale experiment, there was near complete removal of SO42- (91%) and metals (90-100%) with the exception of Pb (15%) and Cu (0.0%).
  • A Combined Chemical and Phytoremediation Method for Reclamation of Acid Mine Drainage-Impacted Soils
    RoyChowdhury, A., D. Sarkar, and R. Datta.
    Environmental Science and Pollution Research [Publication online 13 March 2019 prior to print]
    This study utilized the metal-binding and acid-neutralizing capacity of an industrial by-product, drinking water treatment residuals (WTRs), and the extensive root system of a metal hyper-accumulating, fast-growing, non-invasive, high-biomass perennial grass, vetiver (Chrysopogon zizanioides L.) to prevent soil erosion. Aluminum-based and calcium-based WTRs were used to treat acid mine drainage (AMD)-impacted soil collected from the Tab-Simco coal mine in Carbondale, IL. A 4-month greenhouse column study performed using 5% and 10% w/w WTR application rates showed that soil erosion decreased in the soil-WTR-vetiver treatments. A scaled-up simulated field study was performed using 5% WTR application rate and vetiver. Soil pH increased from 2.69 to 7.2, and soil erosion indicators such as turbidity (99%) and total suspended solids (95%) in leachates were significantly reduced. See more on this study in A. RoyChowdhury's dissertation at
  • Phytoremediation of Selenium-Impacted Water by Aquatic Macrophytes
    Nattrass M., N.R. McGrew, J.I. Morrison, and B.S. Baldwin.
    Journal American Society of Mining and Reclamation 8(1):69-79(2019)
    The bioavailability of selenium (Se) chemical form and concentration on plant uptake were evaluated to determine the potential of aquatic macrophytes to improve water quality in a constructed wetland. The experiment was arranged as a 2x2 factorial nested within a split-split plot design replicated three times. Selenium treatments were applied to cattail (CT), duckweed (DWD), fanwort (CAB), soft rush (SR), muskgrass (MG), and unplanted controls (UNP) as a 4-L solution of either sodium selenite or sodium selenate to a total volume of 30 L at 0, 500, or 1000 µg/L Se. After six days, CT and MG-planted microcosms significantly decreased aqueous Se by 75 and 74%, respectively, compared to 61% for UNP. The aqueous fraction of microcosms planted to CAB, DWD, and SR were similar to UNP controls. Plant tissue Se content in CT was significantly less than CAB, DWD, or MG, suggesting CT has the potential to volatilize Se. Given its abundance and efficacy, CT is likely a suitable species for Se removal in constructed wetlands supplied with either selenite or selenate-impacted waters.
  • Mine Tailing Disposal Sites: Contamination Problems, Remedial Options and Phytocaps for Sustainable Remediation
    Karaca, O., C. Cameselle, and K.R. Reddy.
    Reviews in Environmental Science and Bio/Technology 17(1):205-228(2018)
    This review examines the use of phytocapping for the remediation of mine tailing deposits and abandoned mine areas. Phytocapping is a cost-effective technique that provides erosion control, landscape rehabilitation, improvement of soil properties for further colonization by more demanding vegetal species, reduction of metals leachability toward groundwater, and metals stabilization or immobilization. The most critical step in phytocapping is development of the initial vegetative cover because of the biotoxicity of the mine soil and mine tailings. Several amendment materials can be used to ameliorate soil conditions, serve as a source of nutrients, and create a favorable environment for plants to take root. Local fast-growing plant species are preferred because their adaptation to the soil and climate conditions favors their self-propagation. Available to view at
    [Note: It might be necessary to copy and paste the URL for direct access.]
  • Floating Wetland Treatment of Acid Mine Drainage Using Eichhorina Crassipes (Water Hyacinth)
    Palihakkara, C.R., S. Dassanayake, C. Jayawardena, and I.P. Senanayake.
    Journal of Health and Pollution 8(17):14-19(2018)
    The applicability of water hyacinth (Eichhornia crassipes), a tropical aquatic plant with reported heavy metal hyperaccumulation, was investigated in microcosm floating wetland treatment systems designed to remediate acid mine drainage with Cu and Cd concentrations exceeding threshold limits. Water hyacinth demonstrated the capability to reduce both Cu and Cd concentrations, except at an initial concentration of 4 mg/L of Cu, which was toxic to the plants; at 4 mg/L the plants had low metals accumulations and rapid dying was evident. This paper is Open Access at
  • Phytoremediation of Industrial Mines Wastewater Using Water Hyacinth
    Saha, P., O. Shinde, and S. Sarkar.
    International Journal of Phytoremediation 19(1):87-96(2017)
    For the Sukinda chromite mines area of Orissa, India, research is underway to develop a suitable phytoremediation technology for effective removal of Cr(VI) from mine wastewater using a water hyacinth species (Eichhornia crassipes). This plant was observed to remove 99.5% Cr(VI) of the processed water in 15 days, not only removing Cr(VI) but also reducing total dissolved solids, biological oxygen demand, chemical oxygen demand, and other elements of water. After an initial 5-L study, the same removal efficiency was achieved in a larger experiment performed using 100 L of mine wastewater. This paper is Open Access at Although water hyacinth is a problematic invasive species in the United States and other countries, researchers nonetheless are studying the potential for using its fast-growing, metal hyperaccumulating properties for water remediation under controlled conditions. See more at
  • Uranium Mine Waste Phytostabilization With Native Plants: A Case Study from Brazil
    Alves, L.J., F.C. Nunes, M.N.V. Prasad, P.A.O. Mangabeira, E. Gross, D.M. Loureiro, H.H.S. Medrado, and P.S.F. Bomfim.
    Bio-Geotechnologies for Mine Site Rehabilitation, Elsevier Inc. ISBN: 978-0-12-812986-9, Chapter 17:299-322(2018)
    This chapter presents the different techniques applied over the course of 14 years to the rehabilitation of a uranium mine in a semiarid climate with semiarid thorny scrub vegetation (Caatinga biome) in Brazil. The main rehabilitation strategies employed were the use of engineered blankets composed of plant fibers, the prospection of native grass species adapted to long periods of drought, and the use of legume species.
  • Phytoextration of Potentially Toxic Elements by Six Tree Species Growing on Hazardous Mining Sludge
    Mleczek, M., P. Golinski, M. Krzeslowska, M. Gasecka, Z. Magdziak, P. Rutkowski, S. Budzynska, B. Waliszewska, T. Kozubik, Z. Karolewski, and P. Niedzielski.
    Environmental Science and Pollution Research 24(28):22183-22195(2017)
    The phytoextraction abilities of six tree species—Acer platanoides L., Acer pseudoplatanus L., Betula pendula Roth, Quercus robur L., Tilia cordata Miller, Ulmus laevis Pall.— were compared following cultivation on mining sludge contaminated with As, Cd, Cu, Pb, Tl, and Zn. All six tree species survived on the unpromising substrate. With the exception of A. pseudoplatanus, the analyzed tree species showed a bioconcentration factor (BCF) > 1 for Tl, with the highest value for A. platanoides (1.41), although the translocation factor (TF) for this metal was < 1 in all the analyzed tree species. A. platanoides showed the highest BCF and a low TF and thus could be a promising species for Tl phytostabilization. This paper is Open Access at
  • Potential of Eucalyptus Camaldulensis for Phytostabilization and Biomonitoring of Trace-Element Contaminated Soils
    Madejon, P., T. Maranon, C.M. Navarro-Fernandez, M.T. Dominguez, J.M. Alegre, B. Robinson, and J.M. Murillo. PLoS ONE 12(6):e0180240(2017)
    In a study of the use of trees to immobilize trace metals (phytostabilization), researchers investigated the chemical composition of leaves and flower buds of Eucalyptus camaldulensis in seven sites along the Guadiamar River valley (SW Spain), an area contaminated by a mine spill in 1998. E. camaldulensis trees in the spill-affected area and adjacent non affected areas were growing on a variety of soils with pH from 5.6 to 8.1 at low concentration of plant nutrients. The spill-affected soils contained up to 1069 mg/kg As and 4086 mg/kg Pb. E. camaldulensis tolerated elevated trace metal concentrations in soil and had low trace metal concentrations in the aerial portions compared to other species growing in the same environment. Despite the relatively low concentration of trace metals in leaves, they were significantly correlated with the soil-extractable Cd, Mn, and Zn, but not Cu and Pb. This tree species generally is tolerant of impoverished and contaminated soils, grows fast, has a deep root system, and is suitable for phytostabilization of soils contaminated by trace metals owing to the low transfer of metals from soil to aboveground organs. Eucalyptus leaves also could be used for biomonitoring the soil extractability of Cd, Mn, and Zn (but not Cu or Pb). This paper is Open Access at

Reuse and Reprocess Technologies — Reuse and Reprocessing (R2) technologies are applicable where mining wastes can be put to cost-effective, beneficial use directly or following reprocessing or treatment, or where reprocessing of the waste will render it safe for permanent disposal at the mine site. R2 technologies can be used for remediation of many types of mine waste. Examples include direct use of chat-pile material as an asphalt component, reuse of contaminated soil as cover material for site remediation, or use of waste rock and leach-pad material as construction material, either directly or following treatment or reprocessing. R2 technologies can be employed almost anywhere and in any climate as long as a market exists for the beneficial product. The technologies usually are used with mine waste contaminated with metals, but waste containing other contaminants, such as radionuclides, cyanide, and certain organic chemicals, also may be suitable. R2 technologies can be applied alone, but often are applied with treatment technologies that address the contaminants in the material, making it safe for reuse or conversion into a usable form.

  • A New Application of Solvent Extraction to Separate Copper from Extreme Acid Mine Drainage Producing Solutions for Electrochemical and Biological Recovery ProcessesAdobe PDF Logo
    Nobahar, A., A.B. Melka, A. Pusta, J.P. Lourenco, J.D. Carlier, and M.C. Costa.
    Mine Water and the Environment 41(2):387-401(2022)
    Five extractants (Acorga M5640, LIX 54, LIX 622, LIX 622 N and LIX 864) diluted (15% [v/v]) in Shell GTL with 2.5% (v/v) octanol were compared and evaluated to recover Cu from an extreme AMD sample (5.3 ± 0.3 g/L Cu) collected at the inactive Sao Domingos Mine in Portugal. Acorga M5640 showed the best selective efficiency of the five extractants, extracting ≈ 96.0% of Cu from the AMD in one extraction step and the remaining Cu (to below detection) in three steps. Among the different stripping agents tested, 2 M sulfuric acid was the most efficient, stripping ≈ 99% of Cu. The recyclability of the organic phase was confirmed in five successive cycles of extraction and stripping. Contact time tests revealed that the extraction kinetics allows for ≈ 97% Cu transfer in 15 min. Aqueous-to-organic phase ratio tests demonstrated a maximum loading capacity of ≈ 16 g/L Cu in the organic phase. Raising the concentration of Cu in the stripping solution (2 M sulfuric acid) to ≈ 46 g/L through successive striping steps showed the potential to recover elemental Cu using traditional electrowinning. A biological approach to recover Cu from the stripping solution was evaluated by adding the supernatant of a sulfate-reducing bacteria culture to make different molar ratios of biogenic sulfide to copper; ratios over 1.75 resulted in precipitation of more than 95% of the Cu as covellite nanoparticles.
  • Resource Utilization of Acid Mine Drainage (AMD): A Review
    Yuan, J., Z. Ding, Y. Bi, J. Li, S. Wen, and S. Bai. | Water 14(15):2385(2022)
    This review provides updated information on sustainable treatments engaged in the literature on the resource utilization of AMD. The recovery and reuse of valuable resources (e.g., clean water, sulfuric acid, and metal ions) from AMD can offset the cost of AMD remediation. Iron oxide particles recovered from AMD can be applied as adsorbents to remove pollutants from wastewater and fabricate effective catalysts for heterogeneous Fenton reactions. Applying AMD in beneficiation fields, such as activating pyrite and chalcopyrite flotation, regulating pulp pH, and leaching copper-bearing waste rock, provides easy access to innovative AMD utilization. The review will help researchers understand the progress in research and identify the strengths and weaknesses of each treatment technology, which may help shape the direction of future research in this area. This article is Open Access at
  • High-Pressure Slurry Ablation: Novel Approach to Abandoned Mine Land Reclamation
    Lee, J. | The 43rd Annual Conference of the National Association of Abandoned Mine Land Programs, 16-20 October, Grand Junction, CO, abstract only, 2022
    The High-Pressure Slurry Ablation (HPSA) technology uses a mechanical process without chemicals to separate radioactive material from waste rock and produce higher concentration uranium ore to be used for recycling while minimizing mill waste tailings. HPSA further reduces the tailings waste volume generated by recycling the material at a uranium milling facility. HPSA technology can be highly valuable in remediating abandoned and inactive mine sites. The technology has demonstrated its exceptional ability to fulfill the specific need for the selective liberation of uranium and other valuable minerals in an energy-efficient manner, particularly when mineral-rich layers can easily be separated from the host rock. Evidence of HPSA's efficiency is best represented by how it processes uranium mine waste rock from uranium-hosted sandstone formations, where the soft mineral patina coatings of uranium can be easily separated (disassociated) from the harder sand grain. This disassociation concentrates uranium into the finer particle fraction of the material mass, making it more economically viable for physical and chemical separation (milling) downstream. The presentation covers work with Idaho National Lab, a treatability study conducted on the Navajo Nation, work done with other partners on abandoned uranium mines, and discusses other tailings re-processing. For more information on HPSA, see
  • Mine Water Use, Treatment, and Reuse in the United States: A Look at Current Industry Practices and Select Case Studies
    Miller, K.D., M.J. Bentley, J.N. Ryan, K.G. Linden, C. Larison, B.A. Kienzle, L.E. Katz, A.M. Wilson, J.T. Cox, P. Kurup, K.M. Van Allsburg, J. McCall, J.E. Macknick, M.S. Talmadge, A. Miara, K.A. Sitterley, A. Evans, K. Thirumaran, M. Malhotra, S.G. Gonzalez, J.R. Stokes-Draut, and S. Chellam. ǀ ACS ES&T Engineering [Published online 20 October 2021 before print]
    Current practices in mine water are identified, including how water is used in mining, influent, and effluent water quality, treatment technologies, and end uses to inform future research on implementable, reliable, and cost-effective advanced water treatment in the mining sector. Available literature was reviewed to evaluate mining in the U.S., and a techno-economic assessment on water use and disposal for three detailed case studies applicable to lithium, uranium, and copper mines was performed. Case studies highlight specific industry examples of distinct extraction methods, geographical regions, and mined commodities. Hypothetical scenarios based on case study baselines revealed potential impacts to mine water available for beneficial reuse using novel water treatment technologies and alternate water management strategies. The paper concludes by assessing national-level impacts resulting from the reuse of treated mine source water.
  • Efficient Methodologies in the Treatment of Acid Water from Mines with Recovery of Byproducts Adobe PDF Logo
    Aduvire1, O., M. Montesinos, and N. Loza.
    Proceedings of the 14th IMWA Congress, Mine Water Management for Future Generations, 12-15 July, virtual, 7 pp, 2021
    A staged acid-water treatment methodology is presented to make byproduct recovery economical and reduce contamination by diminishing the amount of non-usable slurry. Direct and staged treatment results are compared, including which byproducts were collected at different pH levels during staged treatment. Experimental neutralization and precipitation tests were conducted using various reagents and pH values to obtain the dosing of reagents and the treatment sequence. Based on the results of the tests and the hydrogeochemical characterization of the effluents, the processes and stages to consider are chosen in the design of the processing facility. These methodologies may reduce the costs of treating mine water, extend the life of waste deposits, reduce the discharge of solid and liquid waste into the environment, and allow the recovery and collection of by-products with potential economic use.