Separation and recovery of ruthenium: a review

• Published in: Journal of radioanalytical and nuclear chemistry 2013-11, Vol.298 (2), p.781-796
• Main Authors: Swain, Pravati, Mallika, C., Srinivasan, R., Mudali, U. Kamachi, Natarajan, R.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Diagnostic Radiology; Hadrons; Heavy Ions; Inorganic Chemistry; Nuclear Chemistry; Nuclear energy; Nuclear Physics; Nuclear radiation; Physical Chemistry; Ruthenium; Spent reactor fuels
• ISSN: 0236-5731; 1588-2780
• DOI: 10.1007/s10967-013-2536-5

The chemistry of the noble metal fission product, ruthenium is very complex due to the existence of many oxidation states in addition to forming a large number of co-ordination complexes. In the PUREX process for the separation of U and Pu from the spent nuclear fuels from fast breeder reactors, owing to the high volatile nature of RuO 4 problems arise not only during the extraction stages but also in the treatment of high active liquid waste and subsequent vitrification. As this volatile RuO 4 can deposit in cooler parts, there is an increase in the radiation field due to the presence of 106 Ru. The problem is very acute in the reprocessing of fast reactor fuels due to the increased concentration of ruthenium in the spent fuel. In nitric acid medium Ru can exist in various nitroso nitrate complexes and nitroso complexes are more stable than nitrates. The nitrates are non-extractable by the solvent TBP; however, they are extractable to a higher degree by DBP (the primary degradation product of TBP). The extractability of Ru nitrates into the solvent is inhibited by high acid content, temperature and prolonged hold-up time. Nevertheless, these factors promote the volatilization of Ru as RuO 4 . The volatilization is enhanced by the addition of phosphate ions, but is suppressed by phosphite or hypophosphite ions. Thus, it would be advantageous if ruthenium is removed so that not only the purity of the product (Pu) is improved, but also the problem related to volatilisation can be resolved. High molecular weight amines (tertiary amines) capable of forming co-ordinate bonds are reported to be ideal extractants for Ru. Gas phase separation is an effective method for the recovery of Ru from catalysts, lead button and from other platinum group metals. Separation and pre-concentration of noble metals can be accomplished from non-metals by simple sorbents like coconut shell activated carbon to complicated chelating resins, aromatic polymers and zeolites. In the electro-oxidation of active Ru from nitroso salts, Pd was found to interfere and removal of Pd prior to oxidation of Ru is recommended. Redox catalysts such as Ag 2+ and Ce 4+ are found to play a prominent role in the electro-oxidation of Ru. Though, various methods and extractants are reported in the literature for the separation of Ru, R&D is being pursued for the removal of Ru during aqueous reprocessing of spent fuels using extractants and methods which are conducive to plant conditions. Hence, an exhaus