A two-step approach to phosphogypsum decomposition: oxidation of CaS with CO₂

CO2 is proposed as an oxidant in a two-step phosphogypsum decomposition process, to oxidize the intermediate product of CaS into CaO. Isothermal and non-isothermal tests are conducted at a thermogravimetric analyzer combined with a Fourier transform infrared spectroscopy to reveal the reaction mechanism of CaS oxidation with CO2.

During the course of non-isothermal process, several side reactions have been observed at low temperatures with CaCO3 and CaSO4 formations. CaS cannot be fully converted into CaO owing to the liquid melt formed by the mixture of CaSO4 and CaS. Full conversion into CaO is observed in the isothermal tests.

The reaction order model fits the description of CaS oxidation into CaO with CO2, which is validated by both isothermal and non-isothermal data. In comparison with pure CaS, the CaS prepared from PG has a relatively lower reaction temperature with CO2, indicating the presence of impurities may have a catalytic effect.