Efficient Defluorination: Application of Calcium Sulfate Precipitation Method in Zinc Sulfate Solution

In the process of zinc hydrometallurgy, the content of fluorine in zinc sulfate solution directly affects the stripping of the zinc plate, which easily leads to the deterioration of working conditions. It not only has a serious impact on the entire zinc hydrometallurgical system but also causes huge economic losses. Especially in the process of zinc secondary resource utilization, the concentration of fluoride ions in the electrolyte exceeds the control standard of smelting enterprises, which has become a long-term technical challenge in the smelting industry. So far, no efficient and economical solution has been developed to effectively remove fluoride from a zinc sulfate solution with a high fluorine content. In view of this background, this study focuses on the application of the precipitation method, which stands out for its wide adaptability, simple operation, and cost advantages. The thermodynamic analysis of the purification and defluorination process of zinc sulfate solution was carried out, and the effects of different experimental conditions on the purification and defluorination of zinc sulfate solution were systematically explored. The results showed that when the solution was acidic, only a fluorite precipitated phase was formed in the system. In order to make the system only form a fluorite precipitated phase, the pH of the solution should be controlled below 7. Under the conditions of the molar ratio of Ca/F2 is 1, the reaction time is 45 min, the solution pH is 4.5, the reaction temperature is 24 °C, and the stirring speed of 900 r min –1, the fluorine removal rate can reach 83.19%, and the zinc loss rate is about 2%.