Thermal decomposition mechanism and characterization of phosphogypsum in suspension under multifactor coupling effect

Phosphogypsum (PG) is solid waste generated by the phosphate fertilizer industry. However, by high-temperature thermal treatment, it can be effectively decomposed into byproducts like SO2 and CaO, which are valuable raw materials for the production of sulfuric acid and construction materials, respectively. In this study, we investigated the thermal decomposition properties of suspended PG, as well as the factors governing the PG decomposition procedure. The results show that the PG decomposition rate was influenced by several parameters, with temperature being the most significant, followed by time, atmosphere, and charcoal powder dosing. Similarly, the desulfurization rate was primarily influenced by time, followed by temperature, atmosphere, and charcoal powder dosing. The PG exhibited maximum decomposition and desulfurization rates of 97.73% and 97.2%, respectively, at a calcination temperature of 1180 °C, a calcination period of 15 min, a carbon powder dosage of 4%, and a CO concentration of 6%. Kinetic studies revealed that the activation energy of the PG decomposition reaction decreased from 303.45 to 254.28 kJ/mol as the CO concentration increased from 4% to 6% upon addition of charcoal powder as a reducing agent. Furthermore, higher CO concentrations had a more pronounced effect on lowering the activation energy of PG pyrolysis. When the contents of SiO2 and Al2O3 impurities in the PG content were higher, they reacted with CaO in the decomposition products to produce silicate and aluminate minerals, respectively, decreasing both the CaO content in the product and the PG decomposition rate.