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 presence of nucleation sites is proposed. The mechanism is supported with inductively coupled plasma optical emission spectrometry measurements and scanning electron microscopy/transmission electron microscopy-selected-area electron diffraction characterization of solid products. These findings are important for a number of reasons, among them, the fact that the crystalline silicate precipitates are more stable than CaCO3 under low-pH conditions, which could be valuable for creating permanent seals in subsurface applications.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Water Science and Technology
- Waste Management and Disposal
- Health, Toxicology and Mutagenesis