Abstract
Formation of solid solution of calcium sulfate dihydrate and calcium sulfite hemihydrate is a problem of importance in science basically and also in technology, particularly in connection with the production of flue gas gypsum. In the previous paper2) , the solid solution of calcium sulfite hemihydrate incorporated with sulfate ions was investigated. In the present paper, the reverse solid solution are investigated.
In the products prepared by coprecipitation from aqueous solution of mixture of Na2SO4 and Na2SO3 (Na2SO4 is predominant) and aqueous solution of CaCl2, presence of sulfite ions which can not be removed by dissolving with dilute acid and is assumed to be incorporated into CaSO4 2H20 crystal lattice was confirmed. The products were verified to be solid solution of CaSO4 2H20 incorporated with sulfite ions by means of TG-DTA, IR spectroscopy and X-ray diffraction analysis. Solid solubility of calcium sulfite in CaSO4.2H2O was the maximum amount of 5 mol% at the reaction temperature of 15-25°C, decreasing directly with temperature to about 0.8 mol%at 92°C.
