Title:
Mechanism of Chlorellestadite Carbonation in WTE Ashes
Author(s):
Garg
Publication:
Web Session
Volume:
ws_S25_Garg.pdf
Issue:
Appears on pages(s):
Keywords:
DOI:
Date:
3/30/2025
Abstract:
Chlorellestadite (Ca10 (SiO4)3(SO4)3Cl2) is a commonly occurring phase in thermally treated waste-to energy ashes and eco-cements. CO2 exposure is known to enhance the strength of chlorellestadite-enriched cementitious systems. However, the mechanism through which chlorellestadite develops strength upon CO2 exposure is not well understood. Here, we address this gap by investigating the carbonation behavior of high-purity, synthetic chlorellestadite. Our findings suggest that chlorellestadite carbonation involves three parallel reactions (R1-R3). The first reaction (R1) includes the carbonation of chlorellestadite to form CaCO 3 polymorphs, gypsum, amorphous SiO2 , and calcium chlorosilicate. In R2, the calcium chlorosilicate formed in R1 reacts with CO2 and forms CaCO3 polymorphs, sinjarite, and amorphous SiO2. Finally, in R3, the sinjarite formed in R2 also reacts with CO2 to form CaCO3 polymorphs. Stoichiometric calculations based on reactions R1-R3 indicate that chlorellestadite can theoretically sequester 29.7% of CO2. The observed CO2 reactivity of chlorellestadite can be harnessed to develop chlorellestadite containing cementitious composites where strength development comes from CO2 exposure. These findings indicate that CO2 exposure can facilitate upcycling chloride-rich industrial waste by-products, such as thermally treated waste-to-energy ashes, in cementitious systems.