Recovery of chemical values from waste gypsum. Final report, December 1989-August 1992

A two-stage, two reactor process is being developed to recover sulfur or sulfuric acid and lime from waste gypsum. Waste gypsum is produced by a variety of industries including chemical, fertilizer and electric utilities. Current environmental regulations are increasing the landfill disposal cost to $30/ton or more depending on specific local conditions. These costs are expected to increase and the quantity of waste gypsum is also expected to increase. The two-stage gypsum recovery process uses two separate fluidized bed reactors to (1) reduce the gypsum to calcium sulfide (CaS) and then (2) roast the sulfide with air producing a SO2-rich gas and regenerated CaO. Fluidization and elutriation problems in the first stage were overcome to achieve up to 85 percent conversion of gypsum to CaS. Reducing gas composition, temperature, and solids residence time were shown to be the primary parameters affecting the reactions. Additional work is needed to achieve even greater conversion and to demonstrate the integrated 2-stage operation. A preliminary economic evaluation indicated a 3-year payback could be achieved for a 1000 ton/day plant. The capital cost was estimated to be $8.5 million. Operating cost savings were based on reduced disposal cost, use/sale of sulfuric acid and use/sale ofmore » lime.« less