Unveiling the Mechanism of CO2 Nanobubble-Enhanced Mineralization Sequestration and Hydrogen Production in Basalt

Summary Carbon dioxide (CO2) mineralization sequestration is one of the stable methods used to safely store CO2 in underground rock formations. However, the formation of a dense carbonate product layer during the mineralization process will seriously hinder the mass transfer efficiency at the reaction interface, resulting in mineralization kinetic hysteresis, and decreased sequestration efficiency. For this study, we prepared CO2 nanobubbles using the hydrodynamic cavitation method and conducted mineralization and hydrogen production experiments of basalt in a system containing nanobubbles and carbonated water, revealing the mechanism of action of CO2 nanobubbles. The results reveal that the CO2 content in the nanobubble water reaches 1.65 ± 0.006 mg/L, approximately 1.2-fold that of the carbonated water system, which provides a richer carbon source for the mineralization reaction. The CO2 nanobubbles prepared with 0.1 wt% nonylphenol ethoxylate (NPE) as solvent have an average diameter of 187.5 nm, a zeta potential of −40.54 mV, and a concentration of 6.3×108 nanobubbles/mL. Compared with the carbonated water system, the CO2 nanobubble system promotes basalt dissolution and enhances the release of calcium ion (Ca2+), magnesium ion (Mg2+), and total iron (TFe). The proportion of macropores (>50 nm) increases by 19%, which improves the diffusion coefficient of the product layer by one to two orders of magnitude. After 25 days of reaction, the degree of mineralization and hydrogen production reaches 0.15 mmol/kgBS and 1.82 mmol/kgBS, respectively, representing increases of 1.67-fold and 1.26-fold compared with the carbonated water system. This study proposes a novel approach for improving mineralization and hydrogen production efficiency using CO2 nanobubbles, which provides technical guidance for CO2 geological sequestration.