Mechanism and kinetics of enhancement of cerium dissolution from weathered residual rare earth ore by planetary ball milling

Abstract This study addressed the enhancement of cerium dissolution from weathered residual rare earth ore by mechanochemical activation by planetary ball milling. The activation mechanism was elucidated using cerium L III -edge x-ray absorption fine structure (XAFS) analysis to evaluate the effect of planetary ball milling on the crystal structure of the cerium minerals and phase composition of the ore. Leaching experiments were performed to investigate the influence of mechanochemical activation on leaching kinetics and extent of cerium dissolution. The leaching kinetics were performed using the shrinking core model in conjunction with an innovative approach based on cerium L III -edge XAFS analysis to resolve the independent leaching curves of tri- and tetravalent cerium. Planetary ball milling induced reduction of tetra- to trivalent cerium and resulted in increased cerium dissolution from weathered residual rare earth ore. Leaching results and specific surface area measurements highlighted that cerium dissolution was enhanced not only by the increase in surface area of the ore, but also by mechanochemical reaction. When the ore was grinding by planetary ball mill, the rate-determining process of leaching changed from chemical reaction to diffusion control and the leaching rate constants decreased, indicating the main mechanism of enhancement of cerium dissolution was reduction of tetravalent cerium.