Preparation of ferrocyanide molybdate and their selective uptake properties for palladium and cesium ions

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-[1-4]). The uptake properties of Pd2+ and Cs+ for MoFe-[1-4] in the presence of 1 M HNO3 were examined by batch method. Relatively high uptake percentages of Pd2+ and Cs+ above 90% were obtained within 30 min. The uptake percentage above 90% was kept in the presence of 0.1-3 M HNO3. The uptake selectivity of Pd2+ was higher than that of Cs+; the separation factor of Pd2+ to Cs+ increased with coexisting HNO3 concentration and was estimated to be 15 at 3 M HNO3. The uptake of Pd2+ and Cs+ on FeMo-[1-4] followed a Langmuir-type adsorption equation, and the uptake capacities of Pd2+ and Cs+ were estimated to be [0.17-0.28] and [1.68-2.24] mmol/g, respectively. The uptake is mainly governed by the ion-exchange reaction between exchangeable cations (Na+ and K+) and target cations (Pd2+ and Cs+). Further, the selective uptake of Pd2+ 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 Pd2+ and Cs+ were 99 and 85 %, respectively. In order to granulate the fine powders of FeMo exchangers, the alginate gel polymer was used as an immobilizing matrix for the micro-encapsulation. The uptake percentages of Pd2+ and Cs+ for FeMo-3 micro-capsule were above 80% even in the presence of 3 M HNO3. Thus the molybdate can be converted to the ion-exchanger having high selectivity towards Pd2+ and Cs+ in HLLW. This conversion method leads to the volume reduction of wastes and the utilization of useful nuclides. (authors)