(138c) Direct Carbonation of Ca(OH)2 Using Liquid and Supercritical CO2

Daniel Klingenberg, Ali Zolhadr and Joseph J. Biernacki

Abstract:

The production of portland cement is responsible for about 7% of the global carbon dioxide (CO2) emissions. Roughly one ton of CO2 is produced for every ton of cement. The direct carbonation of calcium hydroxide (Ca(OH)2) has recently been suggested as a possible CO2-neutral replacement for portland cement in some applications, e.g. prefabricated cement-based construction components. The art of burning limestone (CaCO₃), the formation of slaked lime (calcium hydroxide) and subsequent carbonation has been practiced since at least Roman times as a form of cement. The process, however, is generally too slow to be practical for most modern applications. This study examines the use of liquid and supercritical carbon dioxide to accelerate carbonation. Discs of Ca(OH)2 were compacted at various pressures and thicknesses (different mass) to produce samples of different density and size. The primary goal of this study was to determine the practical limits of carbonation Ca(OH)2 and to glean relevant kinetic and morphological (microstructural) information. X-ray diffraction and electron microscopy was used to characterize carbonated samples.