CaS, generated from H2S removal process using calcium-based sorbents during coal gasification, is a hazardous chemical. The unstable CaS can be converted to stable CaSO4 via oxidation. Using Fourier Transform Infrared Spectroscopy (FTIR) technique, the experiments of CaS oxidation were performed in a thermogravimetric analyzer (TGA) qualitatively and quantitatively. FTIR coupled with TGA, which can provide insitu data in real time, was applied to illuminate the SO, evolution in the product gases during CaS oxidation. There is a maximum concentration of SO, about 4 min after the CaS reaction starts. The FTIR analyses for the solid products obtained at ambient pressure show that the molar contents of CaSO4 and CaO both increase with temperature, and the content of CaS diminishes accordingly. However, an exception is that at 950 OC the conversion of CaS to CaSO4 by FTIR analyses is lower than that at 900 degrees C due to the sintering of the product CaSO4 and the change of the mechanism at higher temperatures. The higher the pressure (1.0 MPa), the more molar contents of CaSO4 and CaO in the products can be attained, which is more pronounced at lower temperatures. The experimental results indicate that the FTIR technique can be applied to the oxidation of CaS experiments effectively to obtain the contents of the solid products. (C) 2007 Elsevier B.V All rights reserved.