Enhancing aqueous carbonation via co-milled serpentine and wollastonite: Effects of mechanochemical activation

Carbon dioxide (CO₂) storage through aqueous mineral carbonation is recognized as a promising technology for geochemical carbon removal. Previous studies predominantly focused on individual alkaline earth silicates, such as wollastonite or serpentine, overlooking their interactive effects on carbonation processes. To address this knowledge gap, we conducted aqueous carbonation tests using individually ball-milled serpentine (m-serpentine), wollastonite (m-wollastonite), mixtures of ball-milled serpentine and wollastonite (m-serpentine + m-wollastonite), and the co-milled serpentine and wollastonite (m-(serpentine + wollastonite)). The carbonation of (m-serpentine + m-wollastonite) involved the formation of a combination of calcite (CaCO₃) and magnesite (MgCO₃), suggesting that no significantly interactive effect between the serpentine and wollastonite. In contrast, carbonating m-(serpentine + wollastonite) results in the precipitation of Mg-bearing calcite ((Mg, Ca)CO₃). Upon quantification, the carbonation degrees of m-(serpentine + wollastonite) is relatively higher than that of (m-serpentine + m-wollastonite). During the carbonation of m-(serpentine + wollastonite), the combination of serpentine and wollastonite facilitates mutual dissolution, leading to the release of more cations. However, these released ions do not diffuse into the bulk carbonating solution; instead, carbonation occurs exclusively at the mineral-water interface. Consequently, the co-milling process, merging Ca-rich wollastonite into Mg-rich serpentine, induces the formation of (Mg, Ca)SiO₃. These novel insights into aqueous carbonation using a combination of Mg-containing and Ca-containing minerals underscore the significant role of mineral-mineral reactions in CO₂ mineralization.