Enhanced Nesquehonite Formation and Stability in the Presence of Dissolved Silica

One possible carbon dioxide sequestration strategy is via the carbonation of dissolved Mg²⁺ obtained through olivine ((Mg,Fe)₂SiO₄) dissolution. However, silica is also produced during the breakdown of olivine. This component may have a detrimental effect on the yield of Mg-carbonate as Mg²⁺ incorporation into complex Mg silicate phases would limit CO₂ uptake by this system. Yet this potential competition is currently not considered. Here, we use crystal growth experiments at temperatures applicable for potential coastal applications to test the effect of silica on the formation of the hydrated Mg-carbonate phase nesquehonite (MgCO₃·3H₂O). Solution chemistry analysis coupled with phase identification demonstrates that the presence of silica in the solution can actually assist the formation of nesquehonite and increase its yield by as much as 60 times. Our findings suggest that the presence of silica changes interfacial stabilities, lowering the energetic barrier for nesquehonite nucleation. In addition, in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) transformation experiments demonstrated that nesquehonite precipitating in a solution containing a high concentration of dissolved silica exhibits enhanced stability against its transformation into hydromagnesite. These findings will help to better constrain what we expect for applications of olivine during carbon remediation strategies as well as assist yields for industrial applications that use Mg-based cement as building materials to facilitate a CO₂-neutral or negative footprint.