Reaction of carbon dioxide (CO₂) with minerals to generate stable carbonates, also known as CO₂ mineralization, has been regarded as one of the most promising methods for safe and permanent carbon storage. As a promising feedstock, basaltic rock has gained special interest, and elevating basalt carbonation efficiency with the reduction of negative environmental impact is the main challenge for CO₂ mineralization system development. Considering multiple potential positive effects of the CO₂ carrier, NaHCO₃, we conducted this study to experimentally evaluate the CO₂ storage efficiency during water-basalt-NaHCO₃ interactions under hydrothermal conditions at 200–300°C. The inclusion of NaHCO₃ was confirmed to drastically promote the alteration of basalt, especially at higher temperatures. As revealed by experiments conducted at the saturated vapor pressure of water, the carbon storage efficiency at 300°C reached 75 g/kg of basalt in 5 days, which was 12 times higher than that at 200°C. In such hydrothermal systems, basalt was carbonated to generate calcite (CaCO₃), where the Ca was mainly from plagioclase; Mg and Fe were incorporated into smectite, and Na in the saline system participated in the formation of Na silicates (i.e., analcime in the case of basalt). Due to the presence of additional Na in solution, all the released elements were consumed quickly with generation of secondary minerals in turn promoted basalt dissolution to release more Ca for CO₂ storage. This study illuminated the role of NaHCO₃ in basalt carbonation and provided technical backup to the design of advanced CO₂ mineralization systems.

Hydrothermally altered basaltic rocks are widely distributed and more accessible than fresh basaltic rocks, making them attractive feedstocks for permanent CO₂ storage through mineralization. This study investigates the reactivity and dissolution behaviors of altered basalt during the reaction with CO₂-rich fluids and compares it with unaltered basalt through batch hydrothermal experiments using a brine that simulates reservoir conditions with 5 MPa CO₂ gas at 100 °C. When using basalt powders to evaluate reactivity, results show that although the leaching rates of elements (Mg, Al, Si, K, and Fe) from altered basalt were generally an order of magnitude lower than those from unaltered basalt in a CO₂-saturated acidic environment, similar elemental leaching behavior was observed for the two basalt samples, with Ca and Mg having the highest leaching rates. However, in a more realistic environment simulated by block experiments, different leaching behaviors were observed. When the CO₂-rich fluid reacts with altered basalt, rapid and preferential dissolution of smectite occurs, providing a significant amount of Mg to the solution, while Ca dissolution lags. This implies that when altered basalt is utilized for CO₂ mineralization, the carbonation step may differ from that of fresh basalt, with predominant Mg carbonation followed by Ca carbonation. This rapid dissolution of Mg suggests that altered basalt is a promising feedstock for CO₂ mineralization. This study provides theoretical support for developing technologies to utilize altered basalt for carbon storage.

Among the CaCO₃ polymorphs, aragonite demonstrates a better performance as a filler material in the paper and plastic industries. Despite being ideal from the environmental protection perspective, the production of aragonite particles via CO₂ mineralization of rocks is hindered by the difficulty in achieving high production efficiencies and purities, which, however, can be mitigated by exploiting the potential ability of chelating agents on metal ions extraction and carbonation controlling. Herein, chelating agent N,N-dicarboxymethyl glutamic acid (GLDA) was used to enhance the extraction of Ca from calcium silicate and facilitate the production of aragonite particles during the subsequent Ca carbonation. CO₂ mineralization was promoted in the presence of 0.01–0.1 M GLDA at ≤ 80 °C, with the maximal CaCO₃ production efficiency reached 308 g/kg of calcium silicate in 60 min using 0.03 M GLDA, which is 15.5 times higher than that without GLDA. In addition, GLDA showed excellent effects on promoting aragonite precipitation, e.g., the content of aragonite was only 5.1% in the absence of GLDA at 50 °C, whereas highly pure (> 90%, increased by a factor of 18) and morphologically uniform aragonite was obtained using ≥ 0.05 M GLDA under identical conditions. Aragonite particle morphologies could also be controlled by varying the GLDA concentration and carbonation temperature. This study proposed a carbon-negative aragonite production method, demonstrated the possibility of enhanced and controlled aragonite particle production during the CO₂ mineralization of calcium silicates in the presence of chelating agents.