The solubility of calcium sulfate in brine produced by ion exchange membrane method was determined by adding CaSO₄ and its hydrates to the brine and at varied temperatures from 25 to 150°C. Results obtained were as follows:
1.The solubility of calcium sulfate decreased in line with an increase in the concentration of brine, and its decreasing rate was greater after crystallization of sodium chloride.
2. The solubility of CaSO₄·2H₂O increased with a rise of temperature, and those of CaSO₄·1/2 H₂O and CaSO₄·anhyd. declined as the temperature became higher. In higher concentration, the difference of solubility by crystal form showed smaller values.
3. A certain relation was observed between the solubility of calcium sulfate and the total. concentration of calcium and magnesium in the ion exchange membrane brine containing about. 90% sodium chloride in total salt.
4. A cmparison of the ionic product of calcium sulfate in the ion exchange membrane brine with the values in evaporated brine and sodium chloride solution, indicated that the value in brines was greater than in sodium chloride solution in the range of high concentration.
5. The solubility product of calcium sulfate calculated with the corrected activity coefficients. of calcium and sulfate ions, showed a continuous decrease until the crystallization of sodium chloride if the ionic strength and temperature of the solution became greater.