Unique environmental conditions required for dawsonite formation: Implications from dawsonite synthesis experiments under alkaline conditions

Although many numerical simulation studies suggest the formation of dawsonite in CO ₂ reservoirs and its resulting contribution to secure geological carbon storage, dawsonite formation is not observed in experimental studies. In addition, the natural occurrence of dawsonite is scarce. The lack of certainty in "whether dawsonite forms in CO ₂ reservoirs" is a major concern for evaluating the security of geological carbon storage and has been discussed for decades. This study performed dawsonite synthesis experiments with co-existing elements (K, Ca, and Mg) and investigated the unique formation conditions of dawsonite. Our experiments clearly show that co-existing magnesium (MgCl ₂ ) inhibits dawsonite formation to form hydrotalcite and/or manasseite instead of dawsonite under alkaline conditions. Because magnesium is widespread in the Earth's crust, dawsonite could be formed only under extremely restricted conditions (Mg-poor conditions) and is unlikely to form in CO ₂ reservoirs during the post-injection period. We also indicate that the discrepancy between numerical simulations and experiments arises from the incompleteness of thermodynamic databases. Our results significantly contribute to resolving the long-running controversy regarding the formation of dawsonite in CO ₂ reservoirs.