High sedimentation efficiency and enhanced rare earth recovery in the impurity removal process of rare earth leachate by flocculation system

The main impurity ion in rare earth (RE) leachate are aluminum ions, which can be effectively removed by precipitation in the form of aluminum hydroxides. The flocculent colloidal precipitation formed by aluminum ions has a loose structure and high liquid content, resulting in lower sedimentation efficiency and higher RE loss. The addition of flocculants in the impurity removal process of RE leachate is expected to solve this problem. The cationic polyacrylamide flocculant (CPAM) was screened as the flocculant to accelerate the sedimentation of the impurity removal process as well as to effectively improve the recovery of RE. The effects of CPAM concentration, dosage, stirring rate and stirring time on the flocculation process was investigated. The optimal flocculation effect could be obtained under conditions of dosage of 0.5 mL, concentration of 0.1%, stirring speed of 700 r/min and stirring time of 2 min. Under this condition, RE recovery efficiency was 97%, Al removal efficiency was 96%, and the sedimentation time of the flocs was 20 min. Compared with absence of flocculants in this process, Al removal efficiency remained almost unchanged, while RE recovery efficiency and the sedimentation time of flocs increased by 4% and shortened by 40 min, respectively. The flocculation mechanism was discussed by the theory of two-dimensional fractal dimension, and it was found that the flocculation was mainly based on the combined effect of bridge flocculation and electrical neutralization.