Preparation of Ferrocyanide Molybdate and Their Selective Uptake Properties for Palladium and Cesium Ions

摘要

The selective separation of heat-generating nuclide (Cs) and platinum group metal (Pd) containing in high-level liquid wastes (HLLW) is an important subject for the advancement of nuclear fuel cycle. Selective uptake of these nuclides was accomplished by using insoluble ferrocyanide molybdates (FeMo-1approx4). The uptake properties of Pd~(2+) and Cs~(+) for MoFe 1approx4 in the presence of 1 M HNO_(3) were examined by batch method. Relatively high uptake percentages of Pd~(2+) and Cs~(+) above 90percent were obtained within 30 min. The uptake percentage above 90percent was kept in the presence of 0.1-3 M HNO_(3). The uptake selectivity of Pd~(2+) was higher than that of Cs~(+); the separation factor of Pd~(2+) to Cs~(+) increased with coexisting HNO_(3) concentration and was estimated to be 15 at 3 M HNO_(3). The uptake of Pd~(2+) and Cs~(+) on FeMo-1approx4 followed a Langmuir-type adsorption equation, and the uptake capacities of Pd~(2+) and Cs~(+) were estimated to be 0.17approx0.28 and 1.68approx2.24 mmol/g, respectively. The uptake is mainly governed by the ion-exchange reaction between exchangeable cations (Na~(+) and K~(+)) and target cations (Pd~(2+) and Cs~(+)). Further, the selective uptake of Pd~(2+) and Cs~(+) was confirmed by using simulated HLLW (28 components, SW-11, JAEA); the uptake equilibrium attained within 30 min and the uptake percentages of Pd~(2+) and Cs~(+) were 99 and 85 percent, respectively. In order to granulate the fine powders of FeMo exchangers, the alginate gel polymer was used as an immobilizing matrix for the microencapsulation. The uptake percentages of Pd~(2+) and Cs~(+) for FeMo-3 microcapsule were above 80percent even in the presence of 3 M HNO_(3). Thus the molybdate can be converted to the ion-exchanger having high selectivity towards Pd~(2+) and Cs~(+) in HLLW. This conversion method leads to the volume reduction of wastes and the utilization of useful nuclides.