Selective Uptake of Cesium by Ammonium Molybdophosphate (AMP)-Calcium Alginate Composites

The uptake properties of Cs+ for ammonium molybdophosphate (AMP, (NH4)3PMo12O40·3H2O) and its composite with alginate gel polymer have been studied by the batch and column methods. The free energy for the ion exchange ([NH4+]ad+Cs+\\rightleftharpoonsNH4++[Cs+]ad) was found to have a relatively low value of -9.7 kJ/mol compared to other inorganic ion exchangers, indicating high selectivity of AMP for Cs+ ions. The fine crystals of AMP exchanger were granulated with calcium alginate (CaALG) gel polymer as an immobilization matrices. The uptake rate of Cs+ for AMP-CaALG composite was fairly fast and the uptake attained equilibrium within 3 h; the uptake was above 96% even in the presence of 5 M (=mol/dm3) NaNO3. The distribution coefficient of Cs+, Kd,Cs, decreased in the order of coexisting ions, H+>Na+>K+>NH4+. In a wide HNO3 concentration region of 10-2-5 M, the Kd,Cs value for the composite was around 104 cm3/g, while those for other elements, Na+, Sr2+, Co2+, Eu3+ and Am3+, were less than 102 cm3/g. The uptake of Cs+ followed a Langmuir adsorption isotherm, and the uptake capacity of Cs+ increased with the content of AMP immobilized in the composite. The trace amounts of Cs+ in the presence of HNO3 were selectively adsorbed on the composite column.