Phosphogypsum pyrolysis with mineralization agent under weak reducing atmosphere

Batch experiments of phosphogypsum (PG) pyrolysis were carried out under weak reducing atmosphere, adding coke as reductant and CaF2 as mineralization agent. As 3 wt% CaF2 was added to the mixture, the optimal parameters of PG decomposition were mole ratio (C: CaSO4) 0.7, reaction temperature 950 °C, pyrolysis time 60 min, and 1.9-2.2% oxygen content of inlet gas. Under this condition, the decomposition ratio of CaSO4 was up to 90.6%, the SO2 conversion was 70.4%, and the average volume concentration of SO2 was 11.9%. With the aid of CaF2, the pyrolysis temperature of CaSO4 decreased significantly. The surface structure and morphology analysis revealed that CaF2 was beneficial to the pyrolysis efficiency of CaSO4. TG curve, XRD analysis and kinetic process have proved that the generation of intermediate substance CaS is the first stage for thermal decomposition of CaSO4, and CaO is the end product of CaSO4 pyrolysis under weak reducing atmosphere.