(658h) Recovering Rare Earth Elements from Acid Mine Drainage Using Coal Combustion By-Products through Mine Reclamation

The demand of rare earth elements (REEs, including scandium, yttrium and a group of 15 lanthanides) in making critical parts for emerging technologies is projected to grow over the coming decades. Due to the significant instability of the market, finding alternative sources has become a critical issue for the United States and other countries. In the U.S., acid mine drainage (AMD) is considered a potential alternative source for REEs. Currently, the research team is developing a two-stage trap-and-concentrate (TAC) process to prepare a feedstock for producing rare earth oxides (REO feedstock). The TAC process first uses stabilized flue gas desulfurization material (sFGD) to capture REEs from AMD (AMD REEs) and then applies a sequential extraction procedure to produce a REO feedstock containing above 2 wt.% of total rare earth elements (T-REEe). sFGD material is a mixture of lime (CaO), calcium sulfite FGD by-product, and coal ash. The TAC process can be integrated with abandoned mine land (AML) reclamation to create an approach that can add economic incentives for AML reclamation, remediate AMD discharge, provide a long-term, high-volume beneficial use for coal combustion by-products, which otherwise needs to be disposed of in a landfill, and eliminate public safety hazards and threats to local environment and ecological systems posed by AMLs. The objectives of this DOE project are to (1) validate and understand the TAC process, (2) quantify the associated economic and environmental benefits, and (3) evaluate the full-scale application potential. So far, we have demonstrated that the sFGD material is effective in trapping AMD REEs. Over 99% of AMD T-REEe in contacted with sFGD material can be retained under a wide range of reaction conditions. A number sequential extraction approaches are tested to concentrate the retained REEs. The factors controlling the recovery of AMD REEs in the TAC process is investigated by using synchrotron-based analytical techniques to explore molecular-level understandings on the involved chemical mechanisms. The economic and environmental implications and the benefits of combining the TAC process with AMD mitigation as an integrated AML reclamation approach are also evaluated.