In this study, using high-sulfur-concentration coal as a reducer, we have carried out the thermal decomposition of phosphogypsum to produce SO2 in a nitrogen atmosphere at different conditions. Scanning electron microscopy and XRD-ray diffraction were used to analyze the solid products and the output gas consisting of mainly SO2 was analyzed with gas analyzers. Both experiment results and theoretical analysis indicated that the optimum conditions to produce SO2 were a mole ratio C:CaSO4,= 1.2:1 and a decomposition temperature about 1000 degrees C. Under optimum conditions, the maximum SO2 concentration was 7.6 vol.%, which can be used to produce sulfuric acid. The CaO concentration of the product was 57.13%, which can be recycled to be an alternative CaO sorbent or a raw material of cement. The conversion of phosphogypsum to sulfur dioxide was 92.2%, and the desulfurization rate of phosphogypsum was 95.16%. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.