The effect of mechanical grinding and thermal treatment on the recovery of rare earth elements (REEs) from kaolinite

REE recovery from a kaolinite sample was conducted in the present study. The results of mineralogical analyses, salt leaching, and acid leaching tests confirmed that REEs predominantly existed as florencite (REEAl₃(PO₄)₂(OH)₆) in the material, and the proportion of ion-exchangeable and ion-substituted REEs was negligible. Mechanical grinding for 4 h completely destroyed the crystal structure of the material, but the recovery of total REEs was less than 20%, indicating that insufficient liberation of the REE-bearing particles is not the only factor leading to the low recovery. Thermal treatment of the raw material at 600 °C for 2 h largely enhanced the total REE recovery to as high as 92%. The improved recovery was ascribed to the thermal decomposition of crystallized florencite into an amorphous phase, which was proved through transmission electron microscopy - energy dispersive X-ray analysis. Findings from the study will contribute to REE recovery and comprehensive utilization of kaolinite.