Evaluation of pretreatment methods to enhance rare earth element recovery from coal ash via acid digestion

This study evaluates the effectiveness of different pretreatment methods to enhance the recovery of rare earth elements (REEs) from coal ash through acid digestion. Coal ash samples were characterized and subjected to a modified ASTM method C1345-96 using HF, HNO3 and H2O2 which achieved REE concentrations of up to 289 mg/kg in bottom ash and 279 mg/kg in fly ash. To reduce impurities and improve REE selectivity, two pretreatment strategies (magnetic separation and alkaline precipitation) were individually applied and compared. Magnetic separation effectively reduced Fe impurities, with a 66.65% removal observed in bottom ash, and resulted in a relative increase in REE concentration due to mass reduction. In contrast, alkaline precipitation was performed by adjusting the pH to approximately 2.5, resulting in over 96% Fe removal while minimizing REE loss. These results highlight a trade-o…