Temperature dependency of gypsumsolubility in well water

The following amounts of gypsum dissolve at the corresponding temperatures  

5 Temperature dependency of gypsum solubility in distilled water 

Compared to well water, distilled water can dissolve more gypsum (Fig. 49), since the initial concentrations of calcium and sulfate are lower. 

The optimum calcite solubility occurs at 30°C (Fig. 50), not at the maximum temperature of 40°C (Table 41). 

Different factors have an influence on the calcite solubility. First of all, like for gypsum (chapter 4.1.1.4) the formation of the CaC03° complex is endothermic (AH(CaC03°) = +3.5), while the mineral dissolution is exothermic (AH(CaC03(s)) = -2.3). Thus, the maximum solubility occurs at some medium temperature, at which the formation of the CaC03° complex is already increased and the decreasing solubility of CaC03(s) does not predominate yet. 

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