Research On Crystallization Of Calcium Sulfate In Zinc Hydrometallurgical Process

To reduce the harm of calcium sulfate scaling in zinc hydrometallurgical process is still a worldwide tough task. In order to understand the crystallization mechanism and develop an economic and efficient method to avoid the scale formation of calcium sulfate, we have carried out following work:The solubility isotherms of gypsum and self-made calcium removing reagent at different temperatures (25～80℃) in the simulated zinc sulfate solution (98-194g/L) were determined by an isothermal method. The results showed that the solubility of dihydrate calcium sulfate and self-made calcium removing reagent decreases with increasing zinc sulfate concentration at a certain temperature. However, in a certain zinc sulfate concentration solution, the solubility of dihydrate calcium sulfate increases with increasing temperature, in contrast, one of self-made calcium removing reagent decreases with increasing temperature. A further study on the solubility of dihydrate calcium sulfate and self-made calcium removing reagent was carried out in practical electrolyte solution after the removal of copper and cadmium. The results showed that the solubility behaviors of dihydrate calcium sulfate and self-made calcium removing reagent are the same with those in simulated zinc sulfate solutions.Also, the influences of the quantity of calcium removing reagent added and stirring time on the concentration of Ca(Ⅱ) ion in the leaching solution after the removal of copper and cadmium were studied. The experimental results indicate that the "best" conditions for removal of calcium from the solution are:temperature80℃, pH5.2, amount of calcium removing reagent seed5.0g/L, stirring time1to2hours. Under the optimal condition, the concentration of calcium ion can be reduced to350ppm. Good results in removing calcium sulfate from electrolyte solution in zinc hydrometallurgical process could be achieved.Based on the above research, a new approach has been developed to remove the scaling of calcium sulfate in the zinc hydrometallurgy.