Role of initial moisture content on the leaching process of weathered crust elution-deposited rare earth ores

Abstract

Role of initial moisture content of ore was discussed to improve the leaching process of weathered crust elution-deposited rare earth ores, especially the difficult-to-permeate rare earth ores. Effects of the initial moisture content, the ammonium sulfate concentration and the liquid/solid ratio on the leaching efficiencies of rare earth and aluminum were investigated, and the leaching process under different initial moisture contents were further analyzed by the shrinking-core model and the chromatographic plate theory. The results showed that the ammonium sulfate concentration needs to be increased to 0.12 mol/L when the initial moisture content of ore is 20%, and a weak improvement on the leaching efficiency of rare earth can be investigated, where the leaching efficiency of rare earth is 95.35% and the aluminum is 94.75%, respectively. However, the leaching equilibrium time of rare earth and aluminum are significantly shorten from 853 min to 265 min for rare earth, and from 905 min to 350 min for aluminum, suggesting a great promotion of initial moisture content on the leaching rate of weathered crust elution-deposited rare earth ores. The leaching processes of weathered crust elution-deposited rare earth ores under different initial moisture contents are controlled by the inner particle diffusing according to the kinetic analysis. The reaction orders are 2.203 for rare earth and 1.980 for aluminum, respectively. The mass transfer discussion showed a smaller height equivalent to theoretical plate (HETP) corresponding to a higher initial moisture content indicating a better mass transfer of rare earth than aluminum. Therefore, the positive impact of initial moisture content of ore on the leaching process of weathered crust elution-deposited rare earth ores is confirmed by both the kinetic and the mass transfer discussions.