Structurally controlled synthesis of calcium sulphate dihydrate from industrial wastes of spent sulphuric acid and limestone

Abstract

All types of gypsum binders are obtained mainly from the natural gypsum and manmade products. As a sustainable analogue of these materials, synthetic gypsum as a product of spent dilute sulphuric acid and calcium carbonate was proposed. We investigated the effect of various technological parameters on the production of calcium sulphate dihydrate particles with a given morphology. The sizes of calcium sulphate dihydrate crystals with optimal values of technological parameters and exposure time up to 4.5 h increased from 18 to 28 μm and combined into agglomerates with sizes that mostly lie in the range from 200 to 600 μm. Synthesized calcium sulphate crystals acquiring a prismatic shape instead of a needle shape which simplified and accelerated the industrial filtration process. Our study shows that a promising sustainable and cheap source of gypsum-containing raw materials is synthetic gypsum, obtained by reacting a suspension of calcium carbonate and spent sulphuric acid.