The influence of carbon monoxide on the reaction between sulphur dioxide and calcium oxide

Abstract The influence of carbon monoxide on the reaction between SO 2 and CaO prepared from reagent grade CaCO 3 and two different naturally occurring limestones was investigated using thermogravimetric analysis, mass spectrometry, X-ray diffraction and infrared spectroscopy. The experiments covered the temperature range 600–950°C with SO 2 -CO-N 2 mixtures varying from 0.1% to 0.9% SO 2 and from 1% to 9% CO, with N 2 providing the balance. The reaction between SO 2 and CaO in the presence of CO led initially to the formation of a mixture of CaSO 4 , CaSO 3 and CaS. The formation of CaSO 3 and CaSO 4 increased with increasing SO 2 concentration at a given CO concentration and temperature. The product composition changed from a mixture of CaSO 3 and CaSO 4 to CaS as sole product, by increasing temperature and/or increasing CO concentration. The rate at which a complete conversion of CaO to CaS occurred was relatively fast. The results also suggested that the extent of the overall conversion of CaO to the product compounds, particularly CaS, differed between reagent grade CaCO 3 and natural limestones. The formation of CaSO 3 as an intermediate, followed by direct reduction to CaS, is discussed and is assumed in a proposed reaction pathway.