Phosphogypsum Decomposition by Char under a CO2 Atmosphere

Reductivedecomposition of phosphogypsum for CaO productionisproposed to proceed under a CO2 atmosphere to avoid thepresence of CaS in the product. In combination with thermodynamicanalysis, thermogravimetric tests are conducted with the monitoringof gas composition to explore the reaction mechanism between C/CaSO4 and CO2. Three reaction stages are identified,i.e., CaSO4 reduction, reaction of CaS with CaSO4, and CaS oxidation by CO2. The reaction path dependson the C/CaSO4 molar ratio and temperature. Further, phosphogypsumdecomposition in CO2 is further conducted in a fluidizedbed reactor, and data show that over 96.2% of CaSO4 inphosphogypsum is decomposed into CaO at 1000 & DEG;C and a C/CaSO4 molar ratio of 1.0 within 83.7 min. Phosphogypsum decompositionin air or nitrogen has lower CaO production. Further, kinetic analysesof CaS oxidation with CO2 in the presence of CaSO4 were performed to illustrate the effect of the CaS-CaSO4 reaction on the CaS-CO2 reaction.