One of the major by-products of the nuclear fission process used for power generation is 137Cs (an isotope of cesium), a radioactive element that has a half-life of 30 years and is often removed from nuclear powerplant 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.
A team of researchers led by Prof. Kuk Cho from Pusan National University, Korea, published recently in the Journal of Hazardous Materials a way to turn this adversity into an advantage. They presented a new layered calcium (Ca2+)-doped chalcogenide ion exchanger with potassium calcium thiostannate (KCaSnS), which utilizes the typically problematic H+ ions in acidic wastewater to enhance the cesium ion (Cs+) adsorption process. Essentially, the Ca2+ ions from KCaSnS are leached out by H+ and Cs+, making way for Cs+.
So, the troublesome proton is converted into a functional agent by incorporating Ca2+ into the Sn–S matrix, resulting in a metastable structure. Moreover, Ca2+ is a harder Lewis acid than Cs+ and can thus leave the lattice easily because of its weaker affinity to the Lewis soft base S2- under acidic conditions. This provides a large enough space for Cs+ to reside after its release from the lattice structure. In the study, the research 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.
These results establish KCaSnS as a promising candidate for the removal of radioactive ions from Nuclear Power Plant wastewater.
Chenyang Yang et al, Leaching of structural Ca2+ ions from a chalcogenide adsorbent by H+ lifts Cs(I) uptake, Journal of Hazardous Materials (2023). DOI: 10.1016/j.jhazmat.2023.131648