The gypsum reduction process and its validation using the Mintek Pyrosim model

Abstract

ABSTRACTWaste gypsum is produced as a by-product from the fertilizer, mining industries, and acid mine water neutralization using calcium carbonate and/or lime and desalination processes using reverse osmosis and ion-exchange processes, resulting in environmental and storage problems. The purpose of the study was to establish optimum operating conditions for the recovery of valuable products, e.g., sulfur and precipitated calcium carbonate, from waste gypsum, hence, offer an attractive solution to the gypsum waste problem. The paper presents results on thermal studies of waste gypsum in a tube furnace and its validation using the Mintek Pyrosim model. Gypsum was homogeneously mixed with coal and the reduction experiments conducted. The following findings were made: (i) reduction of waste gypsum is an endothermic reaction since, ΔH values were greater than 0 (ΔH > 0) when the reduction temperature was increased from 25 to 1200°C, (ii) energy requirement is dependent on temperature and gypsum to coal ratio. Gypsum to calcium sulfide conversion of 83.5 and 83.8% was obtained at the optimum temperature range of 1100–1200°C and gypsum to calcium sulfide conversion of 85.4% was obtained at the optimum coal to gypsum mole ratio of 2.1:1, (iii) excess coal gave a lower conversion, and (iv) the predicted data using Mintek Pyrosim were found to be similar to the experimental data.