Temperature dependency of gypsum solubility

Temperature dependency of gypsum solubility in well water... 

Measurements were undertaken of the solubility of each phase in acid solutions, of the growth rate of gypsum crystals and the dissolution rate of hemihydrate. The growth rate depends on the square of the supersaturation and on temperature with an activation energy of 64 kJ/mol. The nucleation rate appears to vary linearly with supersaturation. 

Minerals with the Diffuse Dissolution Condition To this group belong minerals with relatively simple dissolution mechanism (hydration and dissociation) and with solubihty much higher that 10" mole l". Their total max dissolution rate is usually no lower than 0.01 mole-m s" and little depend on water temperature and pH. Their solubility value reaches 7 mole-1 F Examples of such salts are sylvinite, soda, bischofite, etc. (Table 2.20) but most common among them are, without a doubt, halite and gypsum. 

Most calcium sulfate scales in oil-field work are gypsum, which has the formula CaS04.2H20. The solubility of gypsum is greatest at 43 °C. A temperature change can make either an increase or a decrease in solubility depending on its position on the curve. 

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