Resource recovery of CaO and SO2 from phosphogypsum: Autothermal potential evaluation of oxygen-enriched atmosphere and conventional air calcination processes.

The environmental degradation and resource wastage caused by phosphogypsum (PG) hazardous waste are restricting the sustainable development of the phosphating industry. An autothermal full-flow pilot system model for processing 10,000 tons of PG pellets per year is established to achieve large-scale recovery of CaO and SO2 in PG. The thermodynamic performance of air and oxygen-enriched (CO2+O2) calcined PG are compared and analyzed. The results indicate that the total gas supply is the key parameter that determines the operational potential of the autothermal system. When the total gas supply of the two processes is different, since the oxygen partial pressure in the oxygen-enriched atmosphere can be adjusted, the coal-oxygen consumption of the autothermal system is lower, and the SO2 molar concentration is higher (16.00%-16.65%). Conversely, although the gas-solid product distributions between the two is close, the endothermic reaction between CO2 and C/CaS will increase the coal-oxygen demand for the oxygen-enriched system autothermal, thereby reducing the thermal and exergy efficiency of the system. Additionally, the irreversible exergy loss mainly comes from thermal decomposition reactions, gas-solid phase separation and cold-heat flow heat exchange, which is the focus of future pilot system design and optimization.