Development of selective adsorbents is very important subject for the effective multi-nuclide decontamination related to the severe accident of Fukushima Daiichi Nuclear power Station (Fukushima NPS). In this study, the adsorption properties for nine kinds of zeolites (Zeolite A, Zeolite X, Zeolite Y, Zeolite L, Modified Chabazite, Phillipsite, Erionite, Synthetic Mordenite, Natural Mordenite and Clinoptilolite) are evaluated in the presence of sodium salts, boric acid and seawater. The present study deals with (1) selective adsorption properties for single nuclide ions (Cs+, Sr2+, Eu3+, I, UO22+, Am3+ and NpO2+), and (2) multi-nuclide adsorption properties of 26 elements (typical elements in Advanced Liquid Processing System (ALPS) in Fukushima NPP-1) for the above zeolites. The distribution coefficient (Kd, ml/g) and uptake (R, %) were estimated by batch method using NaI (Tl) scintillation counter, ICP-AES and AAS.

Zeolites with different crystal structures have the diversity of the adsorption selectivity for various radioactive nuclides. Chabazite, mordenite and clinoptilolite with lantern or tunnel structure were very effective for the adsorption of monovalent Cs+ ions even in real seawater. Zeolite A and X with three-dimensional cage structures were effective for the adsorption of divalent Sr2+ and Co2+ ions under the practical condition (30% diluted seawater). Zeolite L was effective for the adsorption of Eu3+ ions under the practical condition. As for I adsorption, Ag-zeolites are found to be effective, and the uptake (%) of I (NaI in pure water) for Ag-zeolites was estimated to be above 98% in pure water. As for actinoid adsorption, the distribution profile, Kdvs pH, had a maximum depending on the hydrolysis pH. Zeolite A, Zeolite L and Zeolite X showed an excellent adsorption property for UO22+, Am3+ and NpO2+, respectively.

Selective adsorption tendencies of different zeolites were evaluated for 26 elements referred to ALPS. Comparing the uptake results for different zeolites, the following tendency of adsorbability was observed. Mordenite had adsorption selectivity for monovalent alkali metal ions of Rb+ and Cs+. Zeolite A and X exhibited relatively high adsorption selectivity for divalent ions of Sr2+ and Co2+. Zeolite L had adsorption selectivity for trivalent lanthanide ions such as Ce3+ and Eu3+. These tendencies were the same as those without boric acid.

Thus, the zeolites with diverse adsorption selectivity are effective for the multi-nuclide decontamination of radioactive contaminated water.

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