Radiocesium was deposited on the soils of Fukushima Prefecture in Japan after the meltdown of the Fukushima Daiichi Nuclear Power Plant in 2011. The radiocesium bound to 2:1 clay minerals, such as vermiculite, common in the soil of that region and became non-exchangeable due to the strong affinity of these clay minerals for the Cs+ adsorbed. The current study generated adsorption envelopes for Cs+ on three zeolite minerals: zeolite Y, ZSM-5, and ferrierite. Two of these (ZSM-5 and ferrierite) caused monovalent cations to adsorb via a strong inner-sphere mechanism. A comparison of Cs+ adsorption on these zeolites to Na+ adsorption on the same zeolites showed that Cs+ adsorbs much more strongly than Na+, which is explained by its atomic properties. Despite the inner-sphere adsorption of Cs+ on ZSM-5 and ferrierite, the affinity of vermiculite for Cs+ is even stronger. An adsorption envelope for Cs+ on vermiculite failed to show a low-pH adsorption edge even at a pH of 1.01, with adsorption remaining at ~65% of the maximum even at this low pH. The adsorption envelopes for Cs+ on ZSM-5 and ferrierite minerals did show low-pH adsorption edges centered at pH 3.5 and 3.0, respectively, where Cs+ adsorption dropped to zero. The greater affinity of vermiculite for Cs+, even when compared with that for two zeolite minerals known to have significant affinities for monovalent ions, highlights the difficulty in removing Cs+ from contaminated Fukushima soils.

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