Gypsum, disodium pentacalcium sulfate, and anhydrite solubilities in concentrated sodium chloride solutions

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Abstract
The solubility of gypsum and anhydrite have been determined at 65 °C in aqueous 3.0 to 6.1 m NaCl solutions. Gypsum solubility at 30 °C has been determined in 5.9 m NaCl and in saturated sodium chloride. At 65 °C gypsum reacts with sodium chloride solutions more concentrated than 3.7 m NaCl to form disodium pentacalcium sulfate, Na2Ca5(SCO4)6•3H2O, which is isomorphous with calcium sulfate hemihydrate. The solubility of this double salt has been determined at 65 °C in aqueous 4.0 to 6.3 m NaCl solutions.