Optimization of rare earth carbonate reactive-crystallization process based on response surface method

Rare earth carbonate precipitation is mainly amorphous, of large volume and difficult to filter. To prepare crystalline rare earth carbonate, mother liquor of heavy rare earth was taken as research object, and the experimental scheme was designed based on the response surface central composite design (CCD) method. The concentration of mother liquor, aging time and seed crystal dosage were taken as independent variables, and the particle size of rare earth carbonate was taken as the response value to establish a quadratic polynomial numerical model to optimize the reactive-crystallization process of rare earth carbonate. The results show that these three factors have significant effect on the particle size of rare earth carbonate, and the influence order is mother liquid concentration > aging time > seed crystal dosage. Moreover, the interaction between mother liquor concentration and seed crystal dosage has a significant effect on the size of rare earth carbonate particles. The optimal parameters predicted by the model are as follows: the concentration of mother liquid is 1.75 g/L, seed crystal dosage is 13.56 wt%, and aging time is 8 h. Under these conditions, the predicted particle size is 28.74 μm, and the experiment particle size is 28.23 μm, between both, the relative error is 0.73%, which indicates that the established response surface model has a good prediction effect and a certain practical significance to guide the reactive-crystallization process of rare earth carbonate. The obtained rare earth carbonate has a crystallinity of 97.82%, uniform particles size, and low-hydrated crystals with a tengerite structure.