[H-SC06] CCUS (Carbon Dioxide Capture, Utilization, and Storage) for Climate Mitigation

[HSC06-P03] Study on CO₂ Mineralization Sequestration of Penghu Alkaline Basalt Using Different Saline

*Tzu Wen Huang¹ (1.Department of Environmental Engineering, National Ilan University, Taiwan)

Keywords:mineralization, basalt, saline, Carbon dioxide, CCUS

According to the report by the World Meteorological Organization (WMO), global carbon emissions in 2024 have reached 37.4 billion tons and are gradually increasing each year. To address the issue, Taiwan’s National Development Council (NDC) released a 2050 net-zero emissions strategy in 2022, which includes the development of carbon-negative technology—Carbon Capture, Utilization, and Storage (CCUS). This technology focuses on capturing and storing CO₂ to mitigate emissions. Among these technologies, geological storage has emerged as a viable method for the long-term storage of CO₂. Globally, over 200 million tons of CO₂ have been successfully injected in geological formations (Ameh Peter, 2022). Geological storage mechanisms include structural trapping,residual trapping, solubility trapping, and mineral trapping. Among them, mineral trapping is the most permanent and safest mechanism, as it ensures long-term stability without leakage risks. Additionally, the carbonate materials formed after the reaction can be reused, making it a highly potential sequestration method.
Simulations by the IPCC show complete mineralization of CO₂ in sedimentary rocks takes thousands of years (IPCC, 2005).Additionally,Gaseous and supercritical CO₂ have lower densities than formation water, which increases leakage risk. Pre-dissolving CO₂ in an aqueous solution eliminates this risk, improving rock contact, enhancing mineral trapping, and potentially achieving mineralization in a few years (Gislason, Matter 2013).
The mineralization process occurs in two stages. The first stage is the dissolution reaction, in which CO₂ dissolves in water to form carbonate, which reacts with rock minerals, releasing cations and carbonate ions. The second stage is the mineralization reaction, where the released cations react with carbonate ions to form stable carbonate minerals. Regarding the choice of aqueous solutions for the first stage, most geological CO₂ sequestration sites are saline aquifers. Moreover, CO₂ has lower solubility in saline , promoting the formation of supercritical CO₂, which enhances stable physical sequestration. In saline environments, CO₂ also reacts more readily with cations in rocks, forming stable carbonate minerals. Since saline is typically rich in cations, it facilitates carbonate crystallization. However, different types of saline can impact CO₂ sequestration capacity and efficiency.
The rock used is basalt, which contains 25% by weight of divalent metal cations such as calcium, magnesium, and iron. These abundant cations react with carbonate ions to form carbonate mineral precipitates. Additionally, basalt exhibits high reactivity with water, allowing carbonate minerals crystallizes more shorter than other rocks, achieving effective mineralization storage. Taiwan has abundant basalt formations, but the only suitable CO₂ sequestration experimental site is in the offshore Penghu region.
Therefore, this study investigates the mineralization reaction of Penghu basalt using different saline sources, including brine from Penghu , saline groundwater from Yunlin , seawater from Keelung , and ultrapure water. It is known that the ratio of aqueous solution to rock powder affects pH changes and the release concentration of cations in the solution. The elements dissolved in different pH environments vary, and pH changes are influenced by the concentration of injected CO₂ and the properties of basalt.
To ensure controlled conditions, this experiment maintains constant CO₂ flow rate, pressure, temperature, and water-to-rock ratio. Each water sample undergoes triplicate testing, resulting in twelve experimental groups and four control groups for mineralization reaction studies. Samples are collected periodically, and the ion in the aqueous solution is analyzed using IC. Additionally, XRD, BET, and XRF are employed to analyze and compare the changes in basalt before and after the reaction.