On the solubility of radium and other alkaline earth sulfate and carbonate phases at elevated temperature

Artikel i vetenskaplig tidskrift, 2019

Solubility constant data for alkaline earth sulfate and carbonate phases were collated. Thermodynamic data for these phases were determined by assuming that the solubility (log K-s) of each phase is a function of the inverse of absolute temperature with a constant, but non-zero, heat capacity change. The solubility for all phases, both sulfate and carbonate, exhibits a maximum at a particular temperature, with the temperature at which the maximum solubility occurs increasing as the alkaline earth metals become heavier (for both sulfate and carbonate phases). The heat capacity change was found to be a quadratic function of the square root of the ionic radius. The enthalpy of reaction, at 25 degrees C, is related to the temperature at which the maximum solubility occurs. Combination of these behaviours allows the solubility of the alkaline earth sulfate and carbonate phases to be determined across a temperature range of 0 to 300 degrees C. These relationships allow solubility data to be determined for the same temperature range for radium sulfate and carbonate for which very few literature data are available, particularly for radium carbonate.