Calcium Silicate Crystal Structure Impacts Reactivity with CO2 and Precipitate Chemistry

Abstract

The reaction of CO2(aq) with calcium silicates creates precipitates that can impact fluid flow in subsurface applications such as geologic CO2 storage and geothermal energy. These reactions nominally produce calcium carbonate (CaCO3) and amorphous silica (SiOx). Here we report evidence that the crystal structure of the parent silicate determines the way in which it reacts with CO2 and the resulting structures of the reaction products. Batch experiments were performed using two polymorphs of a model calcium silicate (CaSiO3), wollastonite (chain-structured) and pseudowollastonite (ring-structured), at elevated temperatures (150 °C) and partial pressures of CO2 (0–11 MPa). Reaction of CO2(aq) with wollastonite produced CaCO3 and SiOx, whereas reaction of CO2(aq) with pseudowollastonite produced platelike crystalline calcium silicate phases, along with CaCO3 and SiOx. A reaction mechanism that explains the observations in relation to dissolution of the parent silicate, the pH of the solution, and the presenc...