Study on the Influence of Citric Acid Dosage and pH Value on the Leaching Rate of Rare Earth and Aluminum during Ammonium Sulfate Leaching of Ion-Type Rare Earth
Utilizing the chelation reaction between citrate ions and rare earth and aluminum ions,as well as the buffering effect of citrate salts on pH value,the leaching rate of rare earth is increased while the leaching rate of aluminum is decreased.In this study,under constant amounts of ammonium sulfate and trisodium citrate,column leaching experiments were conducted by varying the dosage of citric acid and pH value.Based on the changes in the concentrations of rare earth ions and aluminum ions,as well as the pH value in the leaching solution,the effect of citric acid dosage on the leaching rates of rare earth and aluminum,and its relationship with pH value,were investigated.The distribution of RE3+,Al3+,C6H5O73-and SO42-was simulated using Visual MINTEQ software at pH values ranging from 3 to 6 to discuss the influencing mechanism.The results showed that as the citric acid dosage decreased,the concentrations of RE3+and Al3+in the leaching solution both decreased.However,the ratio of the total leached rare earth to the total leached aluminum exhibited a peak value,reaching a maximum of 4.45.This is because at pH values between 4.0 and 4.5,over 90%of the rare earth ions formed stable complexes with citrate ions,enhancing the leaching rate of rare earth.Meanwhile,0 to 10%of Al3+hydrolyzed to form Al(OH)3 precipitates,reducing the impurity leaching rate.
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