Identification of the parameters affecting the in situ dissolution process of natural gypsum

Abstract

This study aims at quantifying the parameters involved in water-gypsum interactions to better assess of the development of dissolution cavities in areas where gypsum is present at depth.The effect of erosion and particle transport on gypsum dissolution is first determined by an original leaching set-up under constant flow including a collector of the released grains. Different types of natural gypsum facies are tested, impure alabaster, sacharoidal, clay/carbonate matrices ones. The flow of released particles is globally low and mostly composed of insoluble grains. The distribution of insoluble at the water/solid interface has a significant impact on the dissolution. The effects of the mineralogy of the impurities present in gypsum deposits and of the groundwater chemistry are then investigated by geochemical modeling. These findings are then applied to in situ conditions. The use of a simple criteria such as dissolved sulfate content or electrical conductivity is not sufficient. An effective recession rate is derived from the porosity, the insoluble contents and the groundwater saturation index obtained from its chemical analysis.