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

All types of gypsum binders are obtained mainly from the natural gypsum and man-made 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.