Solubility of Radium and Strontium Sulfate across the Temperature Range of 0 to 300°C

Solubility constant data for radium and strontium (celestite) sulfate has been determined across the temperature range of 0 to 300°C based on the available literature data for these two phases as well as similar data for calcium (anhydrite) and barium (barite) sulfate for which solubility constant data is available across the same temperature range. The thermodynamic data for the phases have been determined by assuming that the solubility constants are a function of the inverse of absolute temperature with a constant, but non-zero, heat capacity change. The sol-ubility for all phases shows a peak with respect to temperature, with the temperature at which the peak occurs increasing as the alkaline earth metals become heavier. The heat capacity change is a function of the ionic radius of the alkaline earth metal ion whereas the enthalpy of reaction at 25°C is related to the peak at which the maximum solubility occurs. The entropy of reaction at 25°C is related to the solubility constant and the derived enthalpy of reaction at that temperature.