Reactions of solid CaSO 4 and Na 2CO 3 and formation of sodium carbonate sulfate double salts

Abstract

High-temperature chemical reactions in mixtures of solid CaSO 4 and Na 2CO 3 were investigated in order to explore the mechanisms of enhanced sulfur capture by limestones doped with Na 2CO 3 in fluidized bed combustion. Drastic weight loss of the mixtures was observed in a thermogravimetric analyzer near the melting temperature of Na 2CO 3, indicating chemical reaction. X-ray diffraction analysis for a mixture of the solids following a heat treatment at 850 °C revealed the existence of two sodium carbonate sulfate double salts that have not been reported before for the present system. The formation of Na 2SO 4 in the melt of Na 2CO 3 appears to precede the formation of the double salts. The two double salts are believed to have high porosity and specific surface area similar to those of a better-known double salt, burkeite. The implications of these findings for the enhancement of limestone sulfation by Na 2CO 3 are also discussed.