Removal of Magnesium in Zinc Hydrometallurgical System via Freezing Crystallization: From Laboratory Experiments to Industrial Application

Abstract

Magnesium (Mg) is not only a typical impurity but also an important valuable metal in the zinc (Zn) hydrometallurgical process. This study proposed the use of freezing crystallization to recover Mg and reduce the Mg2+ concentration in waste electrolyte solutions, meeting the requirements of Zn hydrometallurgy. The experimental results indicated that the Mg2+ concentration decreased from 23.60 g/L to 14.28 g/L under optimal conditions at a temperature of 263.15 K, holding time of 90.00–120.00 min, H2SO4 concentration of 143.00 g/L, crystal seed addition of 50.00 g/L, and agitation speed of 300.00 rpm. The crystallization mother liquor was returned to the Zn hydrometallurgical process. The crystallization product was a mixture of MgSO4·7H2O and ZnSO4·7H2O with an aspect of 17. Notably, this method resulted in no discharge of waste gas, waste liquid, or waste residue. Additionally, during the industrial application process, the average removal efficiency of Mg2+ was 40.15%. The concentration of Mg2+ in waste electrolyte was reduced from 25.00–27.00 g/L to 13.00–15.00 g/L. These results indicated that the method effectively controlled the concentration of Mg2+ in the waste electrolyte and facilitated the recovery of Mg resources from Zn hydrometallurgy.