Simultaneous and selective separation of fluorine and chlorine from zinc sulfate electrolyte by nanofiltration membrane

This study presents a novel nanofiltration membrane separation process for efficient removal of fluorine and chlorine from zinc sulfate electrolytes simultaneously. A nanofiltration device with a processing capacity of 2 m 3 /h was designed and used to treat the zinc sulfate electrolyte. The results revealed that the recovery rate of cleared solution and the retention rate increased with decreasing conductivity of raw solution. Diluting the zinc sulfate electrolyte is crucial for reducing the salt concentration in the raw solution, leading to a decrease in both the conductivity of raw solution and the membrane inlet pressure. Within the pH range of 3.7–5.8, the recovery rate of zinc ranged from 92.24 % to 98.74 %, while the recovery rate of sulfate ions varied from 92.38 % to 99.63 %. The removal rate of chlorine ranged from 51.52 % to 73.40 %, while the removal rate of fluorine varied from 35.71 % to 52.07 %. At a chloride concentration below 200 mg/L and a fluoride concentration below 50 mg/L, the raw solution maintained high removal efficiencies for both fluoride and chloride. Maintaining a pH between 4.0 and 5.9 is crucial for preventing the formation of precipitates and molecular forms. Nanofiltration is a potential and feasible approach for purification of zinc sulfate electrolytes.