Green approach for low-energy direct synthesis of anhydrite from industrial wastes of lime mud and spent sulfuric acid

Abstract

Millions of tons of hazardous spent sulfuric acid and lime mud from water treatment facilities are produced per year. A green approach for the synthetic gypsum and anhydrite derived from such industrial wastes was proposed. It was found that direct structural controlled synthesis of anhydrite can be performed at usual conditions for synthesis of gypsum: 55 °C and atmospheric pressure. High-quality gypsum can be obtained at room temperature. The results obtained were confirmed by XRD, SEM, TEM, DTA, thermochemical and thermodynamics calculations. It was shown by a number of indicators that such approach is advantageous from technological, environmental and economic point of view. The filtrate formed during the synthesis contains sulfur, calcium, magnesium, sodium and potassium and can be used as a complex fertilizer. The results of bioindication when growing oil radish showed a double increase in the length of the main root when using a neutralized filtrate.