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Southern Research Institute and its project team will evaluate the feasibility of an innovative technology designed to concentrate rare earth elements (REEs) from coal fly ash (CFA). Project partner ArcSec has developed an alternating current graphite electrode plasma arc technology for CFA vitrification that will be utilized in this project. The thermal-based process proposed for this project utilizes plasma arc technology to concentrate REEs in fly ash. The technology has two options: a plasma smelting process and a plasma smelting process plus volatilization and sequential condensation. In option one the molten metal is collected and then tapped for further processing to concentrate the REEs. In option two, the molten metal pool is vaporized to apply sequential condensation to refine the concentration of the REEs into groups. The Phase 1 work will include sampling and characterization of coal fly ash from eight coal-fired power plants that utilize eastern bituminous coal (particularly eastern Kentucky coal) for REE content and a comprehensive feasibility study for the project. The team will conduct bench-scale experiments utilizing a plasma furnace to evaluate the fate of REEs in the separation between the top slag layer and the bottom molten metal layer. Evaluation of potential enhancements to promote the partitioning of REEs to the molten metal layer will be made and the plasma volatilization of the molten metal layer will be modeled, including sequential condensation of enriched REE material from the gas.
The proposed process aims to develop an economically viable domestic source of REEs from a waste stream. Since 2002, the United States has become almost 100% dependent on foreign sources of REEs. The proposed process also develops an additional beneficial use for coal fly ash. Over 27 million metric tons of coal fly ash were landfilled in 2013 in the United States. Developing a productive use for these materials would benefit the environment. When the proposed process is combined with vitrification, coal fly ash waste volumes can potentially be reduced by 68% per an ArcSec estimate. The proposed process is also unique as it is one of the few REE recovery strategies that does not include large-scale utilization of harsh chemicals in order to concentrate the elements from coal fly ash.