Speaker
Description
Migration of radioactive substances into aquatic environments remains a major concern for nuclear accident preparation and environmental protection. In particular, the role of caesium isotopes can be emphasised, as they are characterized by high migration efficiency. One of the areas of research in this field is the search for effective sorbents to be used as barriers or for environmental decontamination.
Due to the negative surface charge and high specific surface area clay minerals are widely studied as potential Cs sorbents. Because of significant variations in properties, including layer charge and interlayer swelling behaviour, clay minerals have fundamentally different caesium absorption mechanisms and selectiveness, which justifies studies of different mineral compositions for cesium removal. This study provides new insights, into adsorbtion properties of Fe-beidellite from Bełachatów, Poland, and its potential for the removal of radiocesium from waters of different ionic compositions (including seawater).
The material used in the current study was a natural beidellite-bearing clay (bentonite) exploited selectively at the Belchatów mine (Poland) from the overburden of brown coal. The material was collected in 2018 from a stockpile at the Chabielice unit belonging to the Bełchatów Coal Mine. Quantitative XRD analysis of the sample, performed using the Rietveld method, revealed a composition of 62% wt smectite, 26% wt. quartz, 6% wt. kaolinite, 4% wt. dioctahedral mica,~1% wt., amorphous material and <1% anatase.
Adsorbtion experiments were performed using 134Cs as a radiotracer in deionised water, tap water, and synthetic seawater that simulates the salinity of the Baltic Sea. Two experimental configurations were applied. One in which a portion of clay was placed inside dialysis tubing and immersed in the radioactive solution, and another experiment of a direct contact batch system without membrane separation. The experiments also varied with respect to the level of caesium isotope contamination, with initial radioactive concentrations of approximately 30 kBq/l and 90 kBq/l, respectively. Changes in 134Cs radioactivity concentration were monitored in solution over time by liquid scintillation counting.
The results demonstrate the uptake kinetics, equilibrium conditions, and middle-term sorption stability. The effectiveness of sorption was influenced by the ionic composition of the water matrix, particularly for salt water. However, in the case of this most demanding matrix, the removal efficiency was approximately 80%, while under reference conditions (deionised water) the equilibrium point was 90%. On the basis of the moderate decrease in the efficiency of caesium isotope removal, it is possible to conclude that the material has good selectivity and great potential for use in environmental decontamination.
The work was created as a result of research project no. 2021/43/B/ST10/00632 financed by the National Science Centre.