The Transition Temperature of Gypsum to Anhydrite

A thermodynamic model for the prediction of phase equilibria and speciation in the H2O–CO2–NaCl–CaCO3–CaSO4 system from 0 to 250°C, 1 to 1000 bar with NaCl concentrations up to halite saturation

“…All these minerals are frequently encountered in sediments or sedimentary rocks. There have been many experimental work on the solubility of gypsum and anhydrite in aqueous solutions and their phase transitions under different temperatures and pressures (Hulett and Allen, 1902;Partridge and White, 1929;Hill, 1937;Booth and Bidwell, 1950;Madgin and Swales, 1956;Dickson et al, 1963;Power and Fabuss, 1964;Blount and Dickson, 1969;Blount and Dickson, 1973), but there is no systematic model to calculate them as a function of temperature, pressure, CO 2 concentration and salinity. As we know, CO 2 sequestration is considered to be a viable way to reduce the CO 2 emission to the air.…”

Improvement of Thermodynamic Modeling of Calcium Carbonate and Calcium Sulfates at High Temperature and High Pressure in Mixed Electrolytes

“…either from experiments or from thermodynamic derivation ( Van't Hoff et al 1903;Hill 1937;Posnjak 1938;Dickson et al 1963;Hardie 1967;Blount and Dickson 1973). It is well accepted that the transition temperature between gypsum and anhydrite at 1 atm in pure water is between 40 to 42 o C with confidence from experimental data.…”

“…It is well accepted that the transition temperature between gypsum and anhydrite at 1 atm in pure water is between 40 to 42 o C with confidence from experimental data. It is also believed that under 40 o C gypsum will be the dominant phase and over 100 o C anhydrite will be dominant and stable (Partridge and White 1929;Hill 1937;Posnjak 1938;Rolnick 1954). Since water molecules are also incorporated in the mineral lattice of calcium sulfates to different extent, water activity changes will also impact the stabilities of different phases.…”

Desert Crusts and Rock Coatings

“…The solubility of gypsum in pure water is about 2.0 g CaSO 4 /Land varies very little with temperature (Hill, 1937). However, in the presence of sodium chloride, gypsum solubility is raised to 8.0 g CaSO 4 /L at 35 • C when the solvent contains 100 g NaCl/L (Zen, 1965).…”