Accelerated Carbonation of High-Calcite Wollastonite Tailings

Wollastonite (CaSiO3) is the most researched and well-defined mineral in the field of CO2 mineralization, but it is also a sought-after process mineral and thus, not easily justified for large scale ex situ carbon sequestration, which requires an energy-intensive step of comminution to increase reactivity. Wollastonite-rich mine tailings are a side stream with an already fine particle size resulting from the extractive process, but their effective utilization is problematic due to legislation, logistics, a high number of impurities, and chemical inconsistency. In this study, the accelerated weathering (aqueous carbonation) of high-calcite (CaCO3) wollastonite tailings was studied under elevated temperatures and high partial pressures of CO2 to determine the carbon sequestration potential of those tailings compared to those of pure reference wollastonite originating from the same quarry. The main process variables were pressure (20–100 bar), temperature (40 °C–60 °C), and time (10 min–24 h). Despite consisting largely of non-reactive silicates and primary calcite, very fine tailings showed promise in closed-chamber batch-type aqueous carbonation, achieving a conversion extent of over 28% in one hour at 100 bar and 60 °C.