Microwave-assisted deep eutectic solvent leaching for efficient and selective extraction of rare earth elements from coal fly ash.

Rare earth elements are strategic and critical materials for addressing the global energy crisis and advancing sustainable development goals. Coal fly ash, a major byproduct of coal-fired power plants, has emerged as a promising secondary source of REEs. However, conventional extraction methods suffer from low efficiency, high acid consumption, and significant environmental concerns. This study developed a microwave-assisted deep eutectic solvents leaching process for efficient and selective REE recovery from coal fly ash. Three DESs were synthesized using choline chloride as the hydrogen bond acceptor with p-toluenesulfonic acid, lactic acid, or formic acid as hydrogen bond donors. Among these, the ChCl-PTSA DES exhibited superior leaching performance due to its stronger acidity and higher ionization degree. Under optimized conditions, a REEs leaching efficiency of 89.16% was achieved. FT-IR and ¹H NMR analyses confirmed that DES formation is driven by hydrogen-bonding interactions, while the leaching mechanism involves synergistic protonation of the aluminosilicate matrix and coordination of liberated REE3+ ions with DES functional groups. This work establishes microwave-assisted DES leaching as a highly efficient, rapid, and sustainable strategy for REEs recovery from coal fly ash, offering a promising alternative to conventional hydrometallurgical processes.