THE INFLUENCE OF CARBON-MONOXIDE ON THE REACTION BETWEEN SULFUR-DIOXIDE AND CALCIUM-OXIDE

The influence of carbon monoxide on the reaction between SO2 and CaO prepared from reagent grade CaCO3 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-degrees-C with SO2-CO-N2 mixtures varying from 0.1% to 0.9% SO2 and from 1% to 9% CO, with N2 providing the balance. The reaction between SO2 and CaO in the presence of CO led initially to the formation of a mixture of CaSO4, CaSO3 and CaS. The formation of CaSO3 and CaSO4 increased with increasing SO2 concentration at a given CO concentration and temperature. The product composition changed from a mixture of CaSO3 and CaSO4 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 CaCO3 and natural limestones. The formation of CaSO3 as an intermediate, followed by direct reduction to CaS, is discussed and is assumed in a proposed reaction pathway.