An investigation of a thermochemical process for conversion of gypsum and pyrite wastes into useful products

摘要

Pre-combustion coal cleaning and post-combustion flue gas desulfurization (FGD) using lien or limestone are the primary methods employed to reduce sulfur dioxide (SO_2) emission form high-sulfur coal combustion. These processes generate voluminous pyrite and gypsum solid wastes that are usually landfilled, occupying thousands of acres of land and creating serious land and water pollution problems due to the release of acids and toxic substances. An integrated thermochemical process has been developed for the combined utilization of gypsum and pyrite wastes by converting them into useful products including lime, sulfur, and direct reduced iron (DRI). The process includes four major steps. The first step is to concentrate pyrite from coal tailings using flotation or gravity separation. The second is the thermal decomposition of pyrite to pyrrhotite and sulfur. This is followed by the reduction of pyrrhotite with carbon in the presence of lime to produce iron and calcium sulfide. The fourth step involves the reaction of calcium sulfide with gypsum to regenerate lime. The chemical reactions involved in the process were studied using thermogravimetric analysis (TGA) and X-ray diffraction (XRD) techniques. Process variables studied included reaction temperature, time, reactant composition, and the purity of reactants.