Recovery and mutual separation of noble metals from the simulated insoluble residue of spent fuel

Abstract

The recovery of noble metals from the quaternary Mo-Ru-Rh-Pd alloy in the simulated insoluble residue was studied by means of Pb extraction and the recovery yield was found to be more than 90% for Ru, Rh and Pd. The recovery yield of Mo was very small due to the oxidative vaporization in air. The decontamination factor for Ce as a stand-in of Pu was determined to be around 200 for one stage. These results on the recovery yields of noble metals from the quaternary alloy and the decontamination factor for Ce are in good agreement with those for the ternary Mo-Ru-Pd alloy previously reported by the present authors. The mutual separation of noble metal elements recovered in Pb button was examined by means of re-extraction with molten Zn and the dissolution in boiling 3M or 6M nitric acid solution. The dissolution fractions of Pd and Rh recovered in the Pb button in boiling 3M or 6M nitric acid solution for 12 h were about 90 and 30%, respectively, and that of Ru was extremely low (~ 0.02%), which is also in good agreement with the previous results of the ternary alloy. The effects of the addition of Ag, Bi and Pd to Pb extraction on the recovery yield of noble metals in Pb button were examined and the dissolution of the Pb button, thus obtained, in nitric acid solution was also examined. By the addition of Ag, both the recovery yield in Pb button and the dissolution fraction in nitric acid solution of all noble metals Ru, Rh and Pd remained almost unchanged. By the addition of Bi and Pd, the recovery of all those noble metals in Pb button and the dissolution fractions of Pd and Ru remained unchanged, but the dissolution fraction of Rh increased significantly up to 90%.