Synthesis and Carbonation Reactivity of Chlorellestadite: Ca₁₀(SiO₄)₃(SO₄)₃Cl₂

Chlorellestadite (ideal formula of Ca₁₀(SiO₄)₃(SO₄)₃Cl₂, CE) is an intermediate phase during ordinary Portland cement preparation and a potential component of the synthesized ecological clinker from solid wastes when sulfate and chlorine coexist. This study synthesized pure CE at 1100 °C with the assistance of theoretical thermodynamic calculations and revealed its carbonation reactivity. Analytical investigations were conducted to reveal the carbonation reactivity of CE and underlie the mechanism of strength development, including mineralogy and microstructural characterization. CE pastes could sequester 4.8% (by mass) of CO₂ and develop a compressive strength of 25.8 MPa after being subjected to 1 day carbonation curing with vaterite, gypsum, calcium chloride, and silica gel as carbonation products, far higher than that under normal hydraulic curing (1.5 MPa). It is concluded that CE is a carbonation-reactive and weakly hydraulic compound. The advantages of CE are not only the possibility to use sulfate- and chlorine-contained wastes as raw materials for synthesis to reduce the environmental risk of wastes but also to develop strength under carbonation curing to be a potential binder.