Wollastonite carbonation in water-bearing supercritical CO₂: Effects of water saturation conditions, temperature, and pressure

The carbonation of silicates in water-bearing supercritical CO₂ (scCO₂) can affect the performance of CO₂-enhanced subsurface operation. This study investigated the effects of water, temperature, and pressure on the carbonation of wollastonite (CaSiO₃) in water-bearing scCO₂ at 35–93 °C, 25–125 bar, and from dry conditions to 140 times more water than needed for saturation (140 × S_w). The extent of reaction increased with more water, higher pressure, and interestingly, lower temperature. In addition, for the first time, we report on water-bearing scCO₂–silicate reactions for samples with varying prior histories of water saturation conditions, temperature, and pressure. For a sample initially reacted at 100% water saturation (1 × S_w) and then with 45 × S_w, the final reaction extent was smaller than the sample reacted only with 45 × S_w. Similarly, for a sample initially reacted at 60 °C and then at 35 °C, the reaction extent was smaller than for a sample reacted only at 35 °C. In contrast, for a sample initially reacted at 50 bar and then at 100 bar, the reaction extent was the same as for a sample reacted only at 100 bar. The amorphous silica layers formed on the particle surfaces are more permeable with more water and lower temperature, and are not affected by pressure. These findings provide new insights into the extent to which water-bearing scCO₂–silicates reactions depend on environmental conditions and the reactions' impacts on subsurface CO₂ injection.