Adsorption and Elution Behavior of Cesium and Rubidium on Ammonium Tungstophosphate (AWP)-CaALG Alginate Microcapsules

Fine crystals of ammonium tungstophosphate (AWP) exchanger having high selectivity toward Cs+ were encapsulated in the bio-polymer matrices (calcium alginate, CaALG). The characterization of AWP-CaALG microcapsule was examined by scanning electron microscope (SEM), and the uptake and recovery of Cs+ and Rb+ were investigated by batch and column methods. Spherical and elastic microcapsules were obtained, and the particle size of microcapsules was about 700 μm. A relatively high uptake (%) of Cs+ and Rb+ above 70% was obtained in the presence of 2.5 M HNO3 - 1 M NaNO3 solution, and the uptake equilibrium was attained within 5 h. The distribution coefficient of Cs+ (Kd,Cs) and Rb+ (Kd,Rb) decreased in the order of coexisting ions, H+ > Na+ >> NH4+. In a wide HNO3 concentration range of 10-2 - 3 M, Kd,Cs value for the microcapsule was above 105 cm3/g, while the Kd,Rb value was around 500 cm3/g even in the presence of 3 M HNO3. The uptake of Cs+ and Rb+ followed a Langmuir-type adsorption equation, and the maximum uptake capacity was estimated to be 0.096 and 0.071 mmol/g, respectively. A linear relationship with a slop of about -1 was obtained between log Kd and log [NH4+] ([NH4+] > 0.01 M), and the retention volume (VR) values of Cs+ and Rb+ in chromatography also decreased similarly to the Kd value. The VR value can be predicted from the Kd value based on the linear relation, and the experimental VR values were closed to the calculated ones. Well-resolved chromatogram with resolution (Rs) = 1 was obtained by flowing 0.6 M NH4NO3. In this case, the total elution percentage of Cs+ and Rb+ was estimated to be 71% and 83%, respectively. The loaded Cs+ and Rb+ on column were thus successfully eluted with NH4NO3 solution, yielding a large deference in VR values. (authors)