Low temperature carbonation and CO₂ mineral trapping in altered hydrotalcite-rich ultrmafic rocks

Mitigating global warming necessitates the immediate reduction of carbon dioxide (CO₂) emissions and its effective sequestration and storage. One promising strategy is geologic carbon sequestration (GCS), which relies on the mineralization of CO₂ through its reaction with mafic and ultramafic host phases to form stable carbonate minerals. While many experimental studies have focused on CO₂-basalt interactions, the carbonation processes in more reactive ultramafic rocks remain less explored. In this study, the interaction of aqueous CO₂ with pulverized serpentinized harzburgite from the Kempirsay Massif in Western Kazakhstan was studied under controlled low temperature of 40 °C and a pressure of 60 bars over a period of 14 days. The initial sample consists predominantly of serpentine, olivine, and layered double hydroxides (LDH, specifically hydrotalcite), which comprise 95% of the rock. After the end of the experiment, solid-phase transformations were observed, including the formation of approximately 70% nesquehonite, complete carbonation of hydrotalcite, and a 75% reduction in the contents of serpentine and olivine. Additionally, a two-fold increase in loss on ignition (LOI) and a reduction in SiO₂ content indicate significant silicate dissolution and effective incorporation of CO₂ into the newly formed carbonate phases. Overall, the results confirm that ultramafic rocks can be efficiently carbonated at low temperatures and pressures. Moreover, the findings highlight the critical role of LDH as reactive phases for CO₂ mineral trapping, pointing out their potential importance in GCS strategies. This research offers new insights into engineered CO₂ mineral trapping in subsurface ultramafic formations, particularly under low temperature conditions below 50 °C. However, further experiments on various ultramafic lithologies containing a broad range of LDH are still required to fully understand their potential for CO₂ mineral trapping.