Effect of NaCl, MgCl2, FeCl2, FeCl3, and AlCl3 on Solubility of CaSO4 Phases in Aqueous HCl or HCl + CaCl2 Solutions at 298 to 353 K

The effect of various chloride salts (NaCl, MgCl2, FeCl2, FeCl3, and AlCl3) on the solubility of three CaSO4 modifications, namely, calcium sulfate dihydrate, hemihydrate, and anhydrite in aqueous HCl or HCl + CaCl2 solutions up to 353 K was investigated. The concentration ranges (at ambient temperature) studied are up to 6 mol·dm-3 for HCl; 1.5 mol·dm-3 for CaCl2; 3 mol·dm-3 for NaCl, MgCl2, and FeCl2; and 2 mol·dm-3 for AlCl3 and FeCl3. The solubility of CaSO4 phases in all cases investigated was found to increase with temperature. In 0.5 mol·dm-3 HCl, the effect of metal chlorides on the solubility of dihydrate was a complex one with solubility increasing up to a certain metal chloride concentration and then decreasing in higher range of metal chloride concentration. On the other hand at higher HCl concentration (3 mol·dm-3), the solubility of dihydrate and anhydrite was found to consistently decrease with increasing metal chloride concentration. The only exception was NaCl, which was found not to infl...