Solubility of CaSO₄Phases in Aqueous HCl + CaCl₂Solutions from 283 K to 353 K

Abstract

Solubilities of calcium sulfate dihydrate, hemihydrate, and anhydrite in concentrated HCl, CaCl 2, and their mixed aqueous solutions were measured by using the classic isothermal dissolution method at the temperature range from (283 to 353) K. The concentration investigated for HCl is up to 12 mol·dm -3 and for CaCl 2 is up to 3.5 mol·dm -3 at room temperature. The solubility of CaSO 4 phases in all cases investigated was found to increase with the temperature increment with the exception of anhydrite in CaCl 2 solutions. In pure HCl media, increasing the acid concentration in the range of (0.0 to 3) mol·dm -3 HCl causes the solubility of CaSO 4 ·2H 2 O or CaSO 4 to increase reaching a maximum value and then decrease gradually with further increasing HCl concentration. In the concentrated range of (8 to 12) mol·dm -3 HCl, the solubility of CaSO 4 · 1 / 2 H 2 O decreases with acid concentration. In HCl + CaCl 2 mixed media, the addition of CaCl 2 causes the solubility of all three phases to decrease due apparently to common ion effect.