Leaching Behavior of Rare Earth Elements and Aluminum from Weathered Crust Elution-Deposited Rare Earth Ore with Ammonium Formate Inhibitor

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In situ leaching of weathered crust elution-deposited rare earth ore usually uses ammonium sulfate as the leaching agent, which poses challenges such as low mass transfer efficiency, high consumption of the leaching agent and long leaching periods. In order to intensify the leaching process of rare earth elements and reduce the impurity of leaching accompanying rare earth, ammonium sulfate and ammonium formate were mixed as a novel compound leaching agent to treat weathered crust elution-deposited rare earth ore. The effects of ammonium formate concentration, liquid/solid ratio, leaching agent pH and leaching temperature on the leaching process of rare earth (RE) and aluminum (Al) were investigated and evaluated using the chromatographic plate theory. Results showed that ammonium formate could effectively enhance the mass transfer efficiency of rare earth and significantly inhibit the mass transfer efficiency of aluminum. Leaching agent pH has a greater impact on the mass transfer efficiency of aluminum. A higher leaching temperature could enhance the mass transfer efficiency of rare earth and aluminum by providing a driving force to overcome the resistance of diffusion. The optimum conditions for leaching rare earth and aluminum are 0.1 mol/L ammonium sulfate compounded with 0.032 mol/L ammonium formate, pH 4–8 of the leaching agent, 0.8:1 liquid:solid (mL/g) ratio and room temperature. Under this condition, the mass transfer efficiency of rare earth was improved, and the mass transfer efficiency of aluminum was significantly inhibited.