Abstract
This study is devoted to studying the sorption of 137Cs on mineral sorbents at a wide pH range, from 2 to 10, as well as to studying sorption mechanisms. In order to obtain the most reliable sorption characteristics, samples of high purity were examined as sorbents: bentonite, glauconite, zeolite, and diatomite. A detailed description of their mineral composition, cation exchange capacity and specific surface of sorbents is given. XRD, XRF, FTIR, SEM, and BET adsorption methods were used for assaying. The sorption and desorption values were identified for each sorbent. As a result of the conducted research, it can be concluded that 137Cs sorption mainly occurs through the exchange reaction on zeolite, glauconite and bentonite. The highest cesium Kd was observed on zeolite due to its high CEC and amounted to 4.05 mg/L at pH 7. The higher sorption capacity of glauconite in comparison with bentonite is primarily due to the high layer charge which is mainly localized in tetrahedral sheets, and to the existence of highly selective sorption sites (frayed edge sites) on the glauconite surface. Diatomite showed the lowest sorption capacity provided by the presence of a small quantity of smectite and kaolinite in its composition. The values of desorption increase in the following order: zeolite < bentonite ~ diatomite < glauconite.
Highlights
The term “natural sorbent” is valid for rocks from a wide range of mineral deposits
The most difficult challenge in analyzing the physicochemical properties of different sorbents is the lack of reliable information on their mineral composition or a relatively high content of impurities, especially those of clay minerals, which can significantly alter the properties of the sorbents
Due to the high sorption capacity of these components, a significant portion of a radionuclide can be sorbed by these impurities resulting in an incorrect interpretation of the results
Summary
The term “natural sorbent” is valid for rocks from a wide range of mineral deposits. They differ in sorption capacity and mechanism, as well as in selectivity to pollutants [1].Minerals 2019, 9, 625; doi:10.3390/min9100625 www.mdpi.com/journal/mineralsThere are two main groups of sorbents according to the filtration properties of the materials based on them: permeable and non-permeable sorbents. The term “natural sorbent” is valid for rocks from a wide range of mineral deposits. They differ in sorption capacity and mechanism, as well as in selectivity to pollutants [1]. The non-permeable sorbents include bentonites, which were proposed as barrier materials for use in underground repositories for the disposal of high-level radioactive wastes. Their features are low hydraulic conductivity after swelling in a confined space, high cation exchange, and adsorption capacity [2,3]. In addition to the safety assurance of high-level wastes to be buried in underground repositories, the safety of other nuclear legacy waste objects is required, including: the isolation of intermediate and low-level wastes in near surface disposal facilities, the decommissioning of liquid radioactive waste storage facilities and complex structural objects, and the remediation of contaminated areas
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