Sorption behavior of U and Np on zeolite

At the Fukushima Daiichi nuclear power station, spent zeolite used to remove radionuclides from contaminated water will be disposed of as the secondary wastes of water treatment. To estimate radionuclides inventory in the spent zeolite, sorption ability of radionuclides needs to be investigated. In this study, distribution coefficients (Kd) of U and Np on chabazite, which is the zeolite used in the second cesium adsorption apparatus (SARRY), were obtained by batch sorption experiments. The obtained Kd of U was 0.0021 m/kg in simulated seawater, while the Kd was 0.68 m/kg in simulated seawater diluted ten times by deionized water. On the other hand, the Kd of Np was 0.0085-0.0087 m/kg and independent of seawater concentration. From the experiments as functions of Na, carbonate concentrations and pH, the Kd of U was found to be strongly affected by carbonate concentration in the pH range 8-9, while both Na and carbonate concentrations had little effect on the Kd of Np.