Enhanced Basalt Dissolution by Formate Ligands for In Situ CO ₂ Mineralization

This work presents the enhanced mineral dissolution of basalt by formate ligands for in situ CO 2 mineralization. Flow-through experiments were conducted under convection-dominated conditions at 138.9 bara and 75 °C. Deionized (DI) water (Case 1) and sodium formate solutions (Case 2) were compared, both of which were saturated with CO 2 as the injection fluid for in situ basalt dissolution. Case 2 confirmed a greater level of mineral dissolution, likely dominated by anorthite and diopside, than Case 1. The basalt dissolution rate was approximately 10 times greater in Case 2 than in Case 1. Transmission electron microscopy revealed a transition region containing both amorphous and crystalline phases after dissolution. Notably, the dissolution-reaction layer formed in Case 2 was approximately twice as thick as that in Case 1. This was attributed to the more rapid transport of formate ions than protons into the basalt matrix, as the basalt’s intrinsic alkalinity tends to hinder proton transport. Batch experiments validated the enhanced mineral dissolution induced by formate ligands under alkaline conditions, as indicated by X-ray photoelectron spectroscopy, which revealed lower silicate concentrations and increased surface oxyhydroxide levels.