Dehydration Pathways of Gypsum and the Rehydration Mechanism of Soluble Anhydrite γ-CaSO₄

Abstract

The dehydration products of gypsum under different temperature and water vapor pressure were investigated by thermodynamic theory. Additionally, the rehydration mechanism of soluble anhydrite was also studied by Monte Carlo (MC) simulations. The thermodynamic calculation results reveal that the dehydration mechanism of gypsum significantly depended on ambient temperature and water vapor pressure. In the high-temperature and low water vapor pressure region, gypsum dehydrates to form γ-CaSO 4 in a single-step process (CaSO 4 ·2H 2 O → γ-CaSO 4 ); with increasing water vapor pressure, gypsum undergoes the CaSO 4 ·2H 2 O → γ-CaSO 4 → β-CaSO 4 ·0.5H 2 O reaction path and as water vapor pressure increases further, the occurrence of a two-step conversion path CaSO 4 ·2H 2 O → β-CaSO 4 ·0.5H 2 O → γ-CaSO 4 was observed. It was also found that gypsum is stable in the low-temperature and high water vapor pressure region and does not dehydrate to form any calcium sulfate hemihydrate. Finally, the rehydration mechanism of soluble anhydrite was studied by MC simulations. The simulation results are in agreement with the experimental data and support the finding that γ-CaSO 4 rehydration forms CaSO 4 ·0.67H 2 O in high relative humidity. Another important result revealed by the MC simulation is that γ-CaSO 4 has an extraordinary ability to capture water molecules from an extremely dry atmosphere, which is very useful in some fields, such as in drying processes and even for extracting liquid water from extremely dry atmosphere.

Mechanism of water extraction from gypsum rock by desert colonizing microorganisms

“…where n is the hydration number (19,36,37). Thus, the phase transformation is determined by the solubility of the different phases in this specific environment, and anhydrite has been proved to be a more stable phase and has lower solubility (19,20).…”

Reactivity of Gypsum-Based Materials Subjected to Thermal Load: Investigation of Reaction Mechanisms

“…Thus, Stark and Wicht [2] in their compilation of the history of gypsum emphasized the importance of gypsum-based materials in fire protection in the Middle Ages in Europe. Although the thermal behavior of gypsum-based systems has been important for numerous technologies for thousands of years and has always been the subject of scientific activities, the mechanisms of the processes that take place during the exposure of gypsum to elevated temperatures are still controversial, as stated and reviewed, e.g., in [3].…”

Rapid Micelle-Mediated Size-Controlled Fabrication of Calcium Sulfate Nanorods Using Silver Nanoparticles

“…Previously, Tang reported that the dehydration of the gypsum (atmospheric pressure) required a temperature of 400 K or greater. 37 The outcomes of the miniaturization using Ag-NPs are illustrated in Figure 5A. The two face areas in the CS-NRs, i.e., the long side face (length × short side [nm 2 ]) and the crosssection face (short side × short side [nm 2 ]) were calculated.…”

“…However, based upon the fact that the CS-NRs were fabricated in an aqueous medium, it is likely that they correspond to CaSO 4 ·2H 2 O (gypsum). Previously, Tang reported that the dehydration of the gypsum (atmospheric pressure) required a temperature of 400 K or greater …”