Nuclear power is typically considered a cleaner way of generating power compared to fossil fuels. It does not release air pollutants and greenhouse gases like carbon dioxide as by-products. However, it creates radiotoxic waste that needs proper treatment to prevent adverse environmental and health conditions.
One of the major by-products of the nuclear fission process used for power generation is 137 Cs (an isotope of cesium), a radioactive element that has a half-life of 30 years and is often removed from nuclear powerplant (NPP) wastewater via selective adsorption using ion exchangers. However, this process is severely hindered in acidic wastewater where excess protons (H + ) impair the adsorption ability and damage the lattice structure of the adsorbent.
Recently, a team of researchers led by Prof. Kuk Cho from Pusan National University, Korea, found a way to turn this adversity into an advantage. In their breakthrough work, made available online on 16 th May 2023 and to be published in Volume 455 of the Journal of Hazardous Materials on 5 th August 2023, they have presented potassium calcium thiostannate (KCaSnS), a new layered calcium (Ca 2+ )-doped chalcogenide ion exchanger. It utilizes the typically problematic H + ions in acidic wastewater to enhance the cesium ion (Cs + ) adsorption process. Essentially, the Ca 2+ ions from KCaSnS are leached out by H + and Cs + , making way for Cs + .
“ Through a transformative approach, the troublesome proton was converted into a functional agent by incorporating Ca 2+ into the Sn – S matrix, resulting in a metastable structure. Moreover, Ca 2+ is a harder Lewis acid than Cs + and can thus leave the lattice easily because of its weaker affinity to the Lewis soft base S 2- under acidic conditions. This provides a large enough space for Cs + to reside after its release from the lattice structure ,” explains Prof. Cho, speaking of the mechanism underlying the action of KCaSnS.
In the study, the team used the hydrothermal process to synthesize the novel KCaSnS ion-exchange material, which was then used to investigate the adsorption of a non-radioactive isotope of Cs + (to avoid radioactivity exposure) in different solutions with pH values ranging from 1 to 13.
The team found that at pH 5.5 (neutral condition), the Cs + adsorption capacity was 370 mg/g, whereas at pH 2 (strongly acidic), the capacity increased by 68% to 620 mg/g. Remarkably, this trend was completely opposite to what previous studies had established.
The researchers attributed this observation to the fact that under neutral conditions, the Ca 2+ was leached out only from the interlayers, which accounted for around 20% of the total spots available for Cs + to be adsorbed by the S 2- ions in the Sn – S matrix. In contrast, under highly acidic conditions, nearly 100% of Ca 2+ ions were leached out from both the interlayer and the backbone structure, allowing more Cs + ions inside the lattice. Additionally, in all cases, interlayer K + was involved in the ion exchange.
These results establish KCaSnS as a promising candidate for the removal of radioactive ions from NPP wastewater. The insights gained from this study could open up new avenues for the development of high-performance adsorbents for highly acidic environments. “ The impressive adsorption capacity of KCaSnS can help alleviate the challenges associated with managing radioactive waste by providing a practical solution for reducing the volume of radioactive waste produced during spent fuel reprocessing and decommissioning of nuclear power plants ,” concludes a hopeful Prof. Cho.
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Reference
DOI: https://doi.org/10.1016/j.jhazmat.2023.131648
About the Institute
Pusan National University, located in Busan, South Korea, was founded in 1946 and is now the No. 1 national university of South Korea in research and educational competency. The multi-campus university also has other smaller campuses in Yangsan, Miryang, and Ami. The university prides itself on the principles of truth, freedom, and service, and has approximately 30,000 students, 1200 professors, and 750 faculty members. The university is composed of 14 colleges (schools) and one independent division, with 103 departments in all.
Website: https://www.pusan.ac.kr/eng/Main.do
About the author
Kuk Cho is a Professor of Environmental Engineering at Pusan National University, Korea. He received his Ph.D. in Environmental Engineering from Washington University in St. Louis in 2005 and did his postdoctoral training at the University of Maryland, College Park, USA. Prof. Cho and his group focus on designing new ways of dealing with the toxicity of atmospheric particulate matter. Currently, they are developing approaches to separate metal ions including radionuclides and heavy metals from water by designing functional materials.
Lab Website: Particle.pusan.ac.kr
ORCID id: 0000-0003-4485-2216
Journal of Hazardous Materials
Experimental study
Not applicable
Leaching of structural Ca2+ ions from a chalcogenide adsorbent by H+ lifts Cs(I) uptake
5-Aug-2023
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Kuk Cho reports financial support was provided by the National Research Foundation of Korea. Yong Jae Suh reports financial support was provided by the Ministry of Science and ICT of Korea.