Basalt Petrology, Water Chemistry, and Their Impact on the CO_(2) Mineralization Simulation at Leizhou Peninsula Sites, Southern China

雷州半岛玄武岩岩石学、水化学及其对CO_(2)矿化模拟的影响

Mineral carbonation, which precipitates dissolved carbon dioxide(CO_(2)) as carbonate minerals in basaltic groundwater environments, is a potential technique for negative emissions. The Leizhou Peninsula in southwest Guangdong province has extensive basalt, indicating a promising potential for CO_(2) storage through rapid mineralization. However, understanding of the basic geological setting, potential, and mechanisms of CO_(2) mineralization in the basalts of the Leizhou Peninsula is still limited. The mineralization processes associated with CO_(2)storage at two candidate sites in the area are investigated in this paper: Yongshi Farm and Tianyang Basin(of the dried maar lake). Petrography,rock geochemistry, basalt petrophysical properties, and groundwater hydrochemistry analyses are included in the study. Numerical simulation is used to examine the reaction process and its effects. The results show that basalts in the study areas mainly comprise plagioclase, pyroxene, and Fe–Ti oxides, revealing a total volume fraction exceeding 85%. Additionally, small amounts of quartz and fayalite are available, with volume fractions of 5.1% and 1.0%, respectively. The basalts are rich in divalent metal cations, which can form carbonate minerals, with an average of approximately 6.2 moles of metal cations per 1 kg of rock. The groundwater samples have a pH of 7.5–8.2 and are dominated by the Mg–Ca–HCO3 type. The basalts demonstrate a porosity range of 10.9% to 28.8%, with over 70% of interconnected pores. A 20-year geochemical simulation revealed that CO_(2) injection dissolves primary minerals, including anorthite, albite, and diopside, while CO_(2)mineralization dissolves precipitation secondary minerals, such as calcite, siderite, and dolomite. Furthermore, a substantial rise in pH from 7.6to 10.6 is observed in the vicinity of the injected well, accompanied by a slight reduction in porosity from 20% to 19.8%. Additionally, 36.8% of the injected CO_(2) underwent complete mineralization within five years, revealing an increasing percentage of 66.1% if the experimental period is extended to 20 years. The presence of abundant divalent metal cations in basalts and water-bearing permeable rocks in the Leizhou Peninsula supports the potential for mineral carbonation in basalts, as indicated by the geochemical simulation results. Additional research is necessary to identify the factors that influence the CO_(2) mineralization, storage, and sensitivity analysis of basalt in the Leizhou Peninsula.