Thermogravimetric analysis of Ontario limestones and dolomites. II. Reactivity of sulfur dioxide with calcined samples

Abstract

Thermogravimetric analysis was done for representative calcined samples of Ontario limestones and dolomites in a 5% SO 2 controlled atmosphere. The SO 2 absorption vs. temperature curves showed three distinct regions. (i) A unimolecular chemisorption of SO 2 at room temperature. (ii) An intermediate temperature region between 200–450 °C where absorption of SO 2 was due to increased rate of SO 2 diffusion into the interior of CaO via grain boundaries. When the surfaces of these internal spaces were almost fully occupied the rate of SO 2 absorption decreased. Further absorption was due to diffusion of SO 2 into CaO lattice, which was a much slower process. (iii) A fast absorption region between 500–700 °C, where a disproportionation of CaSO 3 into CaSO 4 and CaS took place which effectively broke down the original CaO structure to expose fresh layers of CaO. The amount of SO 2 absorption after 1 h at 745 °C corresponded to approximately 80% conversion of CaO to mainly CaSO 4 and CaS and smaller amount CaSO 3 .Finally, the calculations showed that the reaction of SO 2 with CaO was more exothermic than the reaction of SO 2 with MgO, which accounted for the faster rate of the former.