Sorption of fluoride on partially calcined dolomite

Natural dolomite was calcined at different temperatures in the range 873–1373 K and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and N2 adsorption/desorption isotherm. The calcination temperature had considerable effect on the surface chemical composition, crystallinity, and basicity of CO2 gas sorption of each component in the calcined products. The sorption isotherm of both in low and high concentrations of fluoride (F–) was investigated for selected calcination products. The sample calcined at 973 K was found to show the highest sorption density for F– at equilibrium concentrations lower than 0.5 mM, which was equivalent to the maximum concentration limit of F–. In this range, the principle of F– removal is mainly based on destructive hydration of MgO. At equilibrium concentrations of F– higher than 0.5 mM, the sorption process was controlled by precipitation of CaF2 and co-precipitation with Ca(OH)2 due to excess liberation of Ca2 ions from CaO. In this concentration region the products of calcination at higher temperatures are profitable for the immobilization of F–. Additionally, the effect of CO2 gas derived from carbonates on the reactivity of MgO to remove F– during calcination of natural dolomite was also discussed.