Limestone type determines how quickly industrial quicklime degrades in production

<p>Carbonation of quicklimes degrades their quality and can occur when process temperatures become sufficiently low. This risk can be heightened in process atmospheres containing high CO2 and steam. To assess this, carbonation experiments involving atmospheres with different CO2 concentrations and steam were performed at 700 °C on 2.5–5 mm quicklime granules derived from sedimentary and metamorphic limestones. The carbonation extents of the quicklimes derived from metamorphic limestones during the fast stage were higher, corresponding with their larger specific surface areas. However, SEM analysis revealed that these quicklimes had fine structures with relatively small pores that likely became blocked during carbonation, causing plateauing of carbonation that appeared to be mainly limited to particle surfaces. The presence of steam caused only mild enhancements in carbonation of these quicklimes. Contrastingly, the quicklimes derived from sedimentary limestones had lower specific surface areas that concurred with their thicker structures and larger pores. The carbonation extent during the initial fast stage was correspondingly lower, but carbonation progressed at a sustained rate thereafter. The resulting high carbonation extents appeared to be facilitated by the larger pore volumes available for carbonate growth, including locations inside particles. The presence of steam greatly enhanced the carbonation of these quicklimes. Overall, every quicklime exhibited high carbonation extents despite being granular-sized. Moreover, their distinctive carbonation behaviors and microstructures could be delineated by their parent limestone type. These findings should be considered when carbonation in high CO2 atmospheres may occur, e.g., during cooling in electrical lime kilns.</p>