CO2 Nanobubbles Break Through the Product Layer Barrier: Synergistic Acceleration of Basalt Mineralization and Green Hydrogen Generation

Abstract CO2 mineral sequestration is one of the stable methods to store CO2 in underground rock formations for a long time and safely. However, the formation of a dense carbonate product layer in the traditional carbonation process will seriously hinder the mass transfer efficiency at the reaction interface, resulting in carbonization kinetic hysteresis and decreased sequestration efficiency. In this work, CO2 nanobubbles were prepared by hydraulic cavitation, a comparative experiment of basalt (BS) mineralization of nanobubbles and carbonated water systems was carried out. Results reveal that under 0.1% NPE conditions, the prepared CO2 nanobubbles have a particle size of 187.5 nm, a zeta potential of −40.54 mV, and a concentration of 6.3×108 Particles/mL. The CO2 content in nanobubble water reached 1.65 mg/L, an increase of 1.2 times. During the BS mineralization reaction, silicate minerals will dissolve and induce the formation of secondary carbonate minerals. In addition, the generation of H2 comes from the breaking of hydrogen bonds of water molecules on the BS surface and the oxidation of Fe2+. It is worth noting that CO2 nanobubbles can increase the diffusion coefficient of the product layer (increase by 1–2 orders of magnitude) and break through the product layer barrier, thereby improving the efficiency of mineralization and hydrogen generation. Compared with the carbonated water system, the mineralization degree and hydrogen generation of the CO2 nanobubble system are 0.15 and 1.82 mmol/kgBS, respectively, which are increased by 1.67 times and 1.26 times, respectively. This study proposes a new method for CO2 nanobubbles to improve the mineralization and hydrogen generation efficiency, and promoted the transformation of carbon sequestration technology from energy-consuming to high-efficiency.