Rare Earth Element Concentration and Recovery Trends in Coal, Mine Drainage, and Sludge

To evaluate the resource potential of rare earth elements (REEs) in mine drainage and sludge, the research trends on REE recovery from mine waste were investigated. The total average REE in coal and shale was analyzed to be 268 mg/kg and 283 mg/kg, respectively. The TREE (Total REE) concentration of the mine drainage was high in acidic drainage. The REE/NASE ratio displayed enriched middle REE patterns. As the mine drainage of the Daedeok Coal Mine was neutralized to pH 8.5, the REE component was reduced to <0.1 ppb and concentrated into sludge. The average TREE concentrations of sludge from coal and metal mines were quantified as 290 mg/kg and 532.6 mg/kg, respectively. The basket price of REE in 17 sludge sites was estimated to reach USD 790,493. Research on REE recovery is conducted widely to recover REE from raw water and sludge by adsorption and precipitation. A REE recovery system that considers the scattered location of closed mines is presented. It is a concept that primarily concentrates REE in individual mine drainage treatment facilities and subsequently produces high concentrations of REE in a facility with acid dissolution and solvent extraction processes.