Recovery of Rare Earth Elements (REE) from Acid Mine Drainage (AMD) Using Geotextile Tube Dewatering Technology
- Ben Lewis
- Feb 20
- 5 min read
Introduction:
Rare Earth Elements (REE) are a set of 17 elements crucial for modern industries, including electronics, defence, aerospace, and renewable energy. Global demand for REEs is increasing, but their mining is predominantly controlled by China, which produces over 99% of the world's supply. The United States, under strategic pressure to develop domestic REE sources, has initiated several research programs to explore alternative extraction methods.
Tom Stephens of TenCate Geosynthetics Americas, in collaboration with West Virginia University (WVU) and the Department of Environmental Protection (DEP), led a multi-year pilot study exploring the use of geotextile tubes for dewatering AMD and capturing REEs.
One such initiative is leveraging the environmental challenge of Acid Mine Drainage (AMD) in abandoned coal mines in Appalachia, turning it into an opportunity for REE recovery. AMD, a byproduct of the oxidation of sulphide minerals exposed during mining, leads to acidic, metal-laden water, which poses significant environmental hazards. Traditional treatment methods involve neutralizing the acidity and precipitating metals using alkaline chemicals, which results in large volumes of sludge that are difficult to manage. This sludge contains trace amounts of REEs, which are potentially recoverable.
Problem Context:
The Appalachian region has a long history of coal mining dating back to the 18th century. As mines were abandoned, AMD became a widespread issue, causing severe ecological damage. The U.S. Federal Clean Water Act (1972) required the treatment of AMD, leading to the creation of treatment ponds or lagoons lined with clay or geomembranes to collect the sludge. However, these ponds pose risks, including overflow and berm failures during heavy rains, necessitating better containment and dewatering technologies.
The West Virginia Department of Environmental Protection (DEP), in conjunction with West Virginia University (WVU), spearheaded a multi-year pilot project to explore the feasibility of using geotextile tube technology for AMD dewatering and REE recovery. This technology had previously shown success in smaller-scale projects, such as a Pennsylvania Department of Transportation (DOT) project along the I-99, which treated up to 250 m³/hr of AMD, making it a promising solution for large-scale mining applications.
Pilot Study at Omega Mine:
The Omega Mine Complex, located near Morgantown, West Virginia, was selected for the pilot project due to its large, continuous flow of AMD from three abandoned mines. The AMD flow, which ranges from 1 to 2 m³/min depending on the season, has a pH of 3.4 and contains approximately 0.2% solids. This AMD was collected from multiple points, pumped into an equalization tank, and treated with hydrated lime to raise the pH to 6.0. This process precipitated dissolved metals into solids, which were then further treated with an anionic polymer to aid in the agglomeration of solids.
The clarified slurry was pumped into geotextile tubes, which acted as containment units for the dewatering process. Each geotextile tube used in the study measured 13.7 meters in circumference and 74 meters in length, with the site capable of holding 16 tubes per layover of seven days; the solid content inside the geotextile tubes increased from 2% to approximately 45%. After 30 days, it reached 65% solids by weight. This significant reduction in water content allowed the slurry to become manageable and transportable for further processing.
Dewatering Process – Detailed Breakdown:
The geotextile tubes employed for this project were woven, high-strength fabrics designed to allow water to pass through the small pores while retaining the solid particles inside. The geotextile tube system at Omega operates 24/7 and handles consistent AMD flow rates. Here’s a breakdown of the process:
Collection: AMD was collected from three sources and pumped to a centralized location.
Chemical Treatment: Hydrated lime was injected into the equalization tank, raising the pH to 6.0 to precipitate metals. A small amount of anionic polymer was also added to enhance solid agglomeration.
Clarification: The AMD slurry entered a clarifier, where the precipitated solids settled to the conical bottom, forming a concentrated sludge.
Dewatering: The sludge was pumped into large geotextile tubes. The tubes retained the solid content while allowing water to drain out. Over time, the dewatered AMD inside the tubes solidified, reaching 65% solids content.
Effluent Management: The clear effluent from the dewatering process was treated and safely discharged back into the environment.
The setup is capable of managing the flow of AMD for 20 years without the need for additional geotextile tube layers. Furthermore, as AMD treatment using geotextile tubes proved successful at Omega, the West Virginia DEP expanded the approach, adding three more geotextile tube-based AMD management sites across the state.
REE Recovery Potential:
While the initial goal of the Omega project was to dewater AMD, it became apparent that REE recovery was also feasible. In 2017 the Research Institute launched a study to assess the REE content in AMD across 152 point sources in the Northern and Central Appalachian Basins. The findings revealed that the average concentration of REE in raw AMD water from the CAPP (Central Appalachian) region was 410.6 grams per ton (g/t) of dry solids.
At the Omega mine, dewatered solids retained within the geotextile tubes were found to contain 397 g/t of REEs, indicating a retention rate of 96.7%. This high capture efficiency demonstrates that geotextile tube technology not only dewaters AMD but also concentrates REEs for subsequent recovery.
Each geotextile tube at Omega was calculated to contain approximately 146 metric tons of dewatered solids, equating to about 58 kilograms of recoverable REE ore per tube. With the market value of Appalachian REEs estimated at $225/kg, each tube held an estimated $13,050 worth of REEs, making the recovery process economically viable and competitive with conventional REE extraction methods.
Economic and Environmental Impact:
The use of geotextile tubes in AMD treatment offers several advantages over traditional lagoon-based systems:
Cost-Efficiency: The initial installation costs of the geotextile tubes are offset by the potential revenue from REE recovery. At Omega, the process proved to be highly efficient, retaining over 90% of available REEs from the AMD flow.
Environmental Protection: Geotextile tubes provide a safer and more secure method of AMD containment, minimizing the risk of overflow or failure during extreme weather events. By reducing the volume of sludge in lagoons, they also decrease the likelihood of environmental contamination.
Scalability: The Omega site demonstrated that geotextile tube technology could handle large-scale operations. ThDEP'sDEThDEP'sDEP'snsionnthe system to additional sites with even larger flow rates (up to 10 times that of Omega) highlights its scalability for other AMD-impacted regions.
Conclusion:
Geotextile tube technology represents a promising and innovative solution for AMD dewatering and REE recovery. Not only does it mitigate the environmental impact of AMD, but it also opens the door to economically viable REE extraction from a previously untapped source. As demand for REEs continues to grow, especially in critical industries like defence and electronics, technologies like this could play a vital role in securing domestic supplies and reducing reliance on imports.
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