Dehydration of gypsum under dry CO2 injection

Experiments in microcapillary tubes have been developed to mimic the effect of dry CO2 onto hydrated minerals such as gypsum. It is concluded that gypsum-bassanite-anhydrite transformations are controlled by the state of the fluid phase. For samples of gypsum heated in vacuum, gypsum-bassanite transition occurs by pseudomorph substitution at 120 degrees C. For samples of gypsum in aqueous medium, the gypsum-bassanite transition starts at 135 degrees C and then the bassanite-anhydrite transition occurs by dissolution / recrystallization at 220 degrees C. There is a strong CO2 effect that facilitates the dehydration of gypsum. In the presence of dry CO2, gypsum-bassanite transition is instantaneous at 31 degrees C. In aqueous media saturated with CO2, gypsum - anhydrite transition appears at 125 degrees C. These experimental results are in full agreement with the conclusions of thermodynamic simulations. (C) 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.