2026 Mohammadzadeh Hydrochloric acid leaching of apatite concentrate

Hydrochloric acid concentration plays a pivotal role in governing the dissolution behavior of apatite and the recovery of rare earth elements (REEs) during hydrometallurgical processing. In this study, the influence of hydrochloric acid concentration on the leaching of cerium (Ce), lanthanum (La), and neodymium (Nd) from an apatite concentrate derived from iron ore processing waste was comprehensively investigated by correlating microstructural evolution with leaching performance. Response surface methodology (RSM) coupled with central composite design (CCD) was employed to evaluate the combined effects of hydrochloric acid concentration and leaching temperature on the recovery of cerium, lanthanum, and neodymium. Throughout the optimization study, the solid-to-liquid ratio (1:9) and leaching time (60 min) were maintained constant to isolate the influence of the selected variables and improve the reliability of the statistical model. Under the optimum conditions of 37 wt % HCl, a solid-to-liquid ratio of 1:9, a leaching time of 60 min, and a temperature of 65 °C, the recoveries of Ce, La, and Nd reached 94.19%, 86.33%, and 76.34%, respectively. SEM analysis of the leaching residues revealed a progressive transition from relatively smooth, well-preserved crystalline particles at low acid concentrations to severely corroded, fragmented, and porous structures at higher acid concentrations. These microstructural transformations provide direct evidence of enhanced apatite decomposition.