Preparation of ferrous sulfate by dissolution and crystallization of NdFeB secondary waste

Aiming at the problems of complex operation and high energy consumption when recovering iron from NdFeB secondary waste, this paper used ferrous sulfate solution to simulate the acid leaching reduction solution of waste, and adopted the soluble crystallization method to recover ferrous sulfate in the solution. The solubility of ferrous sulfate in pure water and ethanol-aqueous solution was measured, respectively. The data were fitted by the Apelblat equation to confirm the feasibility of the experiment. Ethanol was selected as the elution agent, and the effects of the amount of ethanol, the initial concentration of ferrous sulfate, the temperature, the stirring speed, the way of adding ethanol, and the aging time on the crystallization rate were investigated, respectively. When the volume ratio of ethanol to ferrous sulfate solution was 1∶1, the initial ferrous sulfate concentration 200 g/L, the temperature of 283.15 K, the added seed crystals of about 1% of the solute mass, the rate of continuous addition of ethanol 10 mL/min, the stirring speed 150 r/min and the aging time 60 min, the crystallization rate reached 95.28%. This method was used to recover ferrous sulfate from real secondary-waste reducing solution, and the products were characterized by ICP-AES, XRD, TGA and SEM. The results show that the ferrous sulfate products prepared by the anti-solvent crystallization method has high purity and low impurity content.