Distribution Patterns and Spatial Scale of Carbonate Coatings on Basalt during CO ₂ Mineralization

Basalt is a promising reservoir for CO 2 mineralization due to its favorable mineral composition. Understanding the distribution patterns and spatial development of carbonate minerals within basalt during supercritical CO 2 (scCO 2 ) reaction is critical for evaluating its storage potential. In this study, a novel in situ dynamic core-flooding setup, integrated with scanning electron microscopy (SEM), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), and a suite of complementary characterization analyses, was employed to investigate mineral dissolution, cation release, and carbonate precipitation, with particular focus on the distribution patterns and spatial scale of carbonate coatings. After CO 2 injection, the solution pH rapidly drops and stabilizes between 6.32 and 6.75, facilitating the release of Ca 2+ and Mg 2+ from mineral dissolution. Secondary carbonate formation initiates after 3 days, confirmed by intensified carbonate-related infrared bands and C 1s binding energy. These carbonates predominantly form on pyroxene surfaces and expand progressively with reaction time, while plagioclase shows only subtle dissolution and precipitation. The combination of dissolution and precipitation increases surface roughness on pyroxene, whereas plagioclase surfaces become smoother due to limited reactivity. Pyroxene is identified as the primary host mineral for mineralization, frequently developing well-crystallized calcite coatings. Quantitative analysis reveals that after 7 days of reaction, the carbonate coatings on pyroxene reach a spatial volume of 1499.21 × 10 9 nm 3 . This research highlights the crucial role of reaction duration and mineralogical factors in controlling carbonate mineralization within basalt and provides valuable insights into the mechanisms and potential of basalt CO 2 mineralization.