Recovery of Rare Earth Elements From Rare Earth Calcium Thermal Reduction Slag by Calcium Oxide Fixation Fluorine Roasting and Hydrochloric Acid Leaching
Rare earth and calcium fluoride were recovered from rare earth calcium thermal reduction slag by calcium ox-ide fixation fluorine roasting and hydrochloric acid leaching.The transformation mechanism of the reduction slag during calcium oxide roasting,the thermodynamic analysis of leaching process and the leaching rule of rare earth under different conditions were studied.Thermodynamic analysis showed that increasing temperature can promote the reaction of calcium oxide and rare earth fluoride to produce rare earth oxide and calcium fluoride.The presence of CaF2 inhibits the leaching of rare earth ele-ments,while the high concentration of Ca2+reduces the leaching of F-and promotes the leaching of rare earth elements.The leaching test results showed that the leaching temperature,leaching time,hydrochloric acid concentration and liquid-solid ratio can promote the leaching of rare earth elements in a certain range.The optimum test conditions were:roasting temperature of 800 ℃,roasting time of 1.5 h,mass ratio of calcium oxide to reduction slag of 1∶1,pellet diameter of 10 mm,grinding time of roasting slag of 3 min,leaching temperature of 40 ℃,leaching time of 1.5 h,hydrochloric acid concentration of 4 mol/L,liq-uid-solid ratio of 10∶1 mL/g.Under the below suitable conditions,the leaching rate of rare earth reached 95.44％.The grade of CaF2 in the leaching residue is 97.02％with the recovery rate of 97.88％,and thus the comprehensive utilization of the reduc-tion residue is realized.
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