Thermodynamic study of phosphogypsum decomposition by sulfur

Abstract

Phosphogypsum (PG) is one of the most significant industrial solid wastes from the phosphorus chemical industry. In order to utilize PG more effectively, a new decomposition process of PG by sulfur as a reducer is proposed in this work. Thermodynamic study of the sulfur reduction process including two-step reactions was carried out by both thermodynamic simulation and experimental research. The simulation results indicate that sulfur changes its form in a complex way with rising temperature. The final decomposition temperature of PG by simulation is 993K in the first-step reaction, and this is in good agreement with that obtained by the experiments. For the second-step reaction, however, the final PG decomposition temperature from the experiments is 250K lower than the simulation results predict. The reaction heat of the sulfur reduction process is 27.95% less than that of the traditional coke reduction process at T=1473K based on enthalpy change calculations. This new process can reduce the emission of CO2 effectively and is more suitable for resource utilization of PG than the coke reduction process, so it may be a promising method for sulfuric acid production from PG.