Dissolution Modeling and Experimental Measurement of CaS-H2O Binary System

CaS formed during the retorting process of oil shale has a hazardous influence on surface water quality. Interaction of retorted oil shale with water generates highly alkaline leachate with a high content of sulfur due to the CaS component. A theoretical model describing the behavior of solid calcium sulfide in contact with water was developed. The model was consistent with the measurements showing change in dissolution behavior when solid CaS remained in the solution. Experimental measurements of pH and concentrations of ions were carried out in oxygen‐free water at 25°C using CaS concentrations from 24.2–131.5 mg·L−1 (0.335–1.823 mmol/L). Analysis of pH and concentrations of ions in the solution and calculations by the developed model showed that the solubility of CaS was estimated as 125.0 mg·L−1 (1.733 mmol/L), and therefore the solubility product of CaS is 3.41×10−10 (mo·L−1)2 at a temperature of 25°C. The scheme of the system of solid CaS in equilibrium with water.