Carbonation of quicklimes during cooling in moderate and high CO2 atmospheres

Abstract

Four limestones were calcined in atmospheres containing moderate ($\sim$30%) and high ($\sim$100%) CO₂ levels, and the carbonation characteristics of the quicklimes during cooling in these atmospheres were studied using thermogravimetric analysis. The carbonation rates, extents, and onset temperatures varied depending on the atmosphere and parent limestone type. Scanning electron microscopy showed that the quicklimes produced from sedimentary limestones exhibited larger pores and thicker structures, especially after calcination in the high CO₂ atmosphere. The quicklimes produced from metamorphic limestones exhibited smaller pores among finer structures, with no major observed differences due to the different calcination atmospheres. However, the carbonation extents differed more in the quicklimes produced from metamorphic limestones after calcination in the different atmospheres, and their carbonation rates were also generally higher. Pore filling was observed in all carbonated quicklimes. Practically, the results indicate significant carbonation of all the tested quicklimes when cooling is conducted in atmospheres containing moderate or high levels of CO₂. This has ramifications for processes where such conditions can occur, especially if excessive carbonation is unacceptable; e.g., in the cooling zone of electrified lime-based production kilns.