Recovery of Light Rare Earth Elements from Coal Ash via Tartaric Acid and Magnesium Sulfate Leaching

Coal ash is a promising secondary resource for rare earth element (REE) recovery, yet efficient processing under environmentally benign conditions remains challenging. This study demonstrates that tartaric acid, when combined with MgSO4 as a salt additive, enables effective extraction of light REEs (La, Ce, Nd). REE recoveries improved from ~40% without salt to nearly 65% under optimized conditions. Kinetic modeling indicated a surface-reaction–controlled mechanism with activation energies of 20–22 kJ/mol, consistent with SEM evidence of particle erosion and size reduction. These findings highlight the potential of organic-salt leaching systems as alternatives to mineral acid processes, offering both effective REE recovery and reduced environmental impact.