[H-CG20] Nuclear Energy and Geoscience

[HCG20-P04] Sorption characteristics of cesium on the tourmaline and the layered double hydroxide (LDH) improved by the supercritical CO₂ treatment

*Soyoung Jeon¹, Soyoung Park¹, Wonbeom Heo², Jungtaek Kim³, Minhee Lee⁴ (1.Major of Earth and Environmental Sciences, Division of Earth Environmental System Science, Pukyong National University, Republic of Korea, 2.Division of Earth Environmental System Science, Pukyong National University, Republic of Korea, 3.Chemical Analysis Center of Korea Research of Chemical Technology, Republic of Korea, 4.Major of Environmental Geosciences, Division of Earth Environmental System Science, Pukyong National University, Republic of Korea)

Keywords:Cesium, LDH, Mineral carbonation, Sorption, Supercritical CO2, Tourmaline

The combustion of fossil fuels has significantly increased the atmospheric carbon dioxide (CO₂) emission, contributing to the global warming. Therefore, it is essential to develop effective solutions that achieve substantial and sustained reductions in the CO₂ emissions while simultaneously meeting energy demands. The utilization of the nuclear power is recognized as one of the good alternatives for reducing the CO₂ emissions and ensuring a stable energy supply. However, the nuclear power generation poses a critical challenge due to hazardous radioactive waste, and accidents can lead to the release of radionuclides, posing significant risks to ecosystems and human health. The ¹³⁷Cs is particularly concerning due to its relatively long half-life (30 years) and high solubility in water. Although numerous Cs sorbents have been developed, they often suffer from high material costs and low removal efficiency in solutions with high ionic strength such as seawater. This study aims to develop the cost-effective Cs sorbent having outstanding sorption capacity through the supercritical CO₂ treatment process, promoting mineral carbonation reactions.
Mineral carbonation is an effective approach within carbon dioxide capture and storage (CCS) technology, well known for its CO₂ emission reduction. Most previous studies have used only gaseous CO₂, which has low reactivity with solid materials. However, the supercritical CO₂ (scCO₂) has properties such as the rapid diffusion and penetration characteristics of a gas, and the high density and solvation power of a liquid, enhancing the reactivity and efficiency of the carbonation process. Tourmaline and layered double hydroxide (LDH) were selected for this study due to their unique properties. Tourmaline has a negatively charged surface, which facilitates electrostatic sorption of Cs⁺, while its structure also allows for the ion exchange with similarly sized cations, enhancing Cs⁺ removal. The LDH has a unique layered structure, the high ion exchange capacity, and strong physical characteristics such as structural flexibility, making it suitable for modification to achieve efficient Cs⁺ sorption. In this study, both materials were modified using the scCO₂ treatment. Tourmaline and LDH powders were placed in reactor vessels, with the gaseous CO₂ injected at 10 MPa. The reactors were maintained in an oven at 60°C for 24 hours, exceeding the critical point of CO₂ to form the scCO₂. The scCO₂ facilitated the structural modification of tourmaline and LDH to promote the Cs⁺ sorption capacity. The improved materials, referred to as the ‘sc-tourmaline’ and ‘sc-LDH’, were analyzed for their chemical and mineralogical characteristics using XRD, XRF, and XPS analyses. Subsequently, the Cs⁺ sorption capacity of sc-tourmaline and sc-LDH was evaluated through batch experiments under varying conditions such as Cs concentration, reaction time, pH, and ionic strength. Results in this study supported that these improvement materials by the scCO₂ treatment showed very high Cs⁺ sorption capacity. This research aims to address both CO₂ emission reduction and the Cs removal, contributing to carbon neutrality and environmental restoration.

Acknowledgements
*This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. RS-2024-00409497).
*This study was conducted with the Korea Basic Science Institute (National research Facilities and Equipment Center) grant funded by the Ministry of Education (No. 2021R1A6C101A415).