Solubility of calcium sulfate salts in acidic manganese sulfate solutions from 30 to 105 °C

Solubility determinations of gypsum were conducted on simulated process liquors containing 0–72 g/kg solution Mn2+ (as sulfate) and 0–72 g/kg solution H2SO4 from 30 °C to 105 °C. At temperatures ≤ 80 °C gypsum solubility was shown to increase with increasing H2SO4 concentration and temperature in accord with the dissociation equilibrium of the bisulfate ion, while the addition of Mn2+, as sulfate, decreased the solubility. Above 80 °C the conversion of gypsum to anhydrite was shown to be dependent on Mn2+ and H2SO4 concentrations. In water alone hemihydrate was produced at 105 °C. Several empirical models were developed from solubility data at temperatures ≤ 80 °C and correctly predicted gypsum solubility in the experimental acidic manganese solutions.