Abstract Simultaneous DSC-TGA (SDT) and Fourier transform infrared spectrometer (FTIR) and diffuse reflectance in situ Fourier transform spectroscopy (DRIFTs) were used to study the thermogravimetric behavior and the reaction path of hemihydrate calcium sulfite in nitrogen atmosphere. The gas phase products and solid phase products were detected by FTIR. The main conclusions are as follows: in the thermal decomposition process, disproportionation reaction starts at 853 K: 4CaSO3 → CaS + 3CaSO4, and decomposition reaction and desulfurization reaction start simultaneously at 963 K: CaSO3 → CaO + SO2, CaS + 2SO2 → CaSO4 + S2(g), and disproportionation reverse reaction starts at about 1053 K: CaS + 3CaSO4 → 4CaO + 4SO2, calcium sulfate decomposition reaction begins at 1393 K: CaSO4 → CaO + SO2 + 1/2O2. The oxidation temperature and reaction products were obtained through oxidation experiments, which proved that the calcium sulfite has sufficient thermal stability at ambient temperature.
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