Phosphogypsum pyrolysis with mineralization agent under weak reducing atmosphere

Abstract

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.

Process Optimization and Mechanism Study for Sulfur Recovery from High-Silica Phosphogypsum via Carbothermal Reduction Smelting

“…In summary, it can be concluded that the amount of reducing agent and smelting temperature are the key factors affecting the desulfurization effect and slag phase structure in the new process of acid-making and slag wool production based on phosphogypsum. It was appropriate to add the reductant with a C/S molar ratio of 0.5–0.8, which was consistent with the previous research results . The desulfurization effect of phosphogypsum can be greatly improved in the molten state due to the enhanced mass and energy transfer.…”

“…It was appropriate to add the reductant with a C/S molar ratio of 0.5–0.8, which was consistent with the previous research results. 53 The desulfurization effect of phosphogypsum can be greatly improved in the molten state due to the enhanced mass and energy transfer. The XRD patterns of the slags obtained above 1300 °C were all amorphous structures, which were the same as those at 1300 °C in Figure 6 d and were no longer listed.…”