Leaching Process and Mechanism of Weathered Crust Elution-Deposited Rare Earth Ore

Abstract

The leaching processes and mechanisms of weathered crust elution-deposited rare earth (RE) ores with ammonium sulfate were investigated for their high efficiency and low consumption exploitation. The leaching process is a typical reversible heterogeneous ion exchange reaction in liquid–solid systems. The raw ore and leached tailings were analyzed by SEM and FTIR. Results indicated that no dissolution or structural changes of the ores occurred during the leaching process. The migrations of RE3+, Al3+, and $$ {\mathrm{NH}}_4^{+} $$ in the leaching process were studied under various liquid–solid ratios. With increasing liquid–solid ratio, the content of $$ {\mathrm{NH}}_4^{+} $$ adsorbed on clay mineral by physical effect decreased, $$ {\mathrm{NH}}_4^{+} $$ adsorbed by ion-exchange increased, and the content of exchanged RE and Al increased until reaching equilibrium. The adsorption capacity of the RE ores for $$ {\mathrm{NH}}_4^{+} $$ remained about 0.61–0.63 mg/g. It was difficult to desorb $$ {\mathrm{NH}}_4^{+} $$ from RE ores with washing water alone. The leaching mechanism of Al was the same as RE, but the leaching of Al slightly lagged behind RE. At the optimal liquid–solid ratio of 0.4:1, the leaching efficiencies of RE and Al were 95.51% and 90.99%, respectively, and 56.65% of $$ {\mathrm{NH}}_4^{+} $$ remained in the leachate. After impurity removal and RE precipitation, the leachate can be reused by replenishing fresh leaching agent. The aim of this study is to enhance the leaching process of RE, restrain the leaching of impurities, and decrease the consumption of leaching agents.