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 ([NH⁺ ₄]_ad+Cs⁺NH⁺ ₄+[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 5M (=mol/dm³) NaNO₃. The distribution coefficient of Cs+, Kd-Cs, decreased in the order of coexisting ions, H⁺>Na⁺>K+>NH⁺. In a wide HNO₃ concentration region of 10^-2-5M, the K_d,cs value for the composite was around 10⁴cm³/g, while those for other elements, Na⁺, Sr²⁺, Co²⁺, Eu³⁺ and Am³⁺, were less than 10²cm³/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.