Sulfuric Acid Leaching of Ionic Rare Earth Magnesium Salt Enrichment and Removing Aluminum by MgO Precipitation

Abstract

Production of rare earth enrichment from the in situ leaching solution of ion-adsorbed rare earth ores greatly decreases the treatment scale and significantly reduces production energy consumption and cost. However, the generated rare earth enrichment has a high content of impurities. Further purification of rare earth is necessary. Therefore, a process comprised of sulfuric acid leaching and removing aluminum by the neutralization precipitation method to obtain the purified rare earth solution was proposed. The results of acid leaching revealed that at a sulfuric acid concentration of 1.75 mol/L, a temperature of 60 °C, a liquid–solid ratio of 5:1 mL/g, a leaching time of 0.5 h, and a stirring rate of 300 r/min, leaching efficiency of rare earth and magnesium reached 99.11% and 97.39%, respectively, while the leaching efficiencies of aluminum and silicon reached 72.91% and 55.26%, respectively. The comparison of different precipitants during the neutralization precipitation process showed that MgO was the best precipitant for the efficient removal of aluminum and low loss of rare earth. The results of removing aluminum revealed that when the final pH of the rare earth leaching solution was controlled to be 4.7, the reaction temperature was 25 °C, the slurry concentration of MgO was 0.3 mol/L, and the feeding rate of the MgO slurry was 0.5 mL/min, the removal rate of aluminum was 99.49%, and the loss rate of rare earth was 13.93%. The obtained purified rare earth solution contained 19 g/L of rare earth and less than 0.01 g/L of aluminum. Kinetic studies showed that the apparent activation energy of the aluminum removal process was 6.8 kJ/mol, indicating that the precipitation process was controlled by a mass transfer diffusion reaction.