Relation between the reactivity and surface area of gypsum

The specific surface area of 9 industrial flue gas desulphurization (FGD) gypsum samples was measured by the adsorption of nitrogen (BET isotherm), mercury intrusion porosimetry and the adsorption of methylene blue from aqueous solution. The results were compared with the reactivity of the studied gypsum samples during their reaction with an aqueous solution of (NH4)(2)CO3, as the reaction constant involves the specific surface area of the starting gypsum sample. It follows that the specific surface area determined by the BET isotherm for N-2 adsorption and/or the mercury porosimetry is not suitable for describing the reactivity of gypsum in aqueous solution. On the other hand, when the values of the specific surface area determined by the adsorption of methylene blue were used, the reactivity of gypsum could be described very well. The latter fact can be prescribed to comparable accessibility to the surface of the gypsum of MB and solvated NH4+ and CO32- ions released by (NH4)(2)CO3. (C) 2019 Elsevier B.V. All rights reserved.