Published data on the speciation and behavior of Pd in different stages of reprocessing of irradiated fuel from NPPs were analyzed. Various methods for recovering Pd from solutions and solids of different compositions, arising in reprocessing, were described. The Pd sales volumes in the recent decades were reported, and possible industrial and technical applications of Pd were discussed. An opinion is expressed that it is of interest to recover [reactor-grade] Pd to be used in reprocessing of the waste from radiochemical enterprises (e.g., immobilization of 129 I and/or TPEs), i.e., in processes where the presence of radioactive nuclide 107 Pd does not matter and exhaustive removal of other fission products is not required.The history of science and technology abounds in cases where ideas, set aside many years ago, are revived. This is true of the attempted recovery of platinum group metals (PGMs) from irradiated fuel of NPPs. The first relevant publications [133] appeared about 50 years ago, and their authors considered it very attractive to find the possibilities of recovering Pd and Rh whose yield in uranium fission products is fairly high, namely, kilograms per ton of fuel. But as yet, no country has succeeded in developing an acceptable method for commercial recovery of platinum metals from real radioactive solutions. This is due to a number of reasons.The main purpose of irradiated nuclear fuel reprocessing is to recover U and Pu and to localize fission products, rather than to recover individual radionuclides intended for commercial purposes. On the other hand, the use of any radionuclides, even minimally active, is extremely negatively received by the public. Probably, this is the most significant negative factor that questions the appearance of a demand for [reactor-grade] Pd or Rh in their traditional application spheres, even if they will be cheaper than Pd and Rh extracted from ores.At the same time, depletion of mineral resources of platinum metals will sooner or later cause their prices to rise to the level when irradiated fuel could become a real substitute to their commercial production sources. Since recently, technologies for high-level waste (HLW) partitioning have been developed, which would yield solutions that are less active and simpler in composition than the first extraction cycle raffinates containing all the fission products and, thus, will be suitable for recovery of Pd and Rh.In this work, we analyzed publications on recovery of Pd from irradiated fuel. Since the prospects for commercial recovery of Pd are directly related to technical demands and natural reserves, we considered it necessary to supplement this review with a section devoted to possible applications of Pd and its compounds.
Recovery of Pd from nitric acid solutions on various anion-exchange resins is studied. The effects of the HNO 3 concentration, temperature, and aminoacetic acid on the desorption of Pd are examined. Results of the experiments on Pd recovery from actual solutions from spent fuel reprocessing are reported.The high yield of the Pt group metals in U fission allows NPP spent fuel to be considered as a promising source of Pd and Rh, which can be widely used in various areas of engineering [1,2].After nitric acid dissolution of spent fuel, the major fraction of Pd passes into the U solution and goes to the first extraction cycle. Since Pd is poorly extracted with tributyl phosphate, after recovery of U and Pu it remains in the raffinate along with other fission products and transuranium elements.It is known that the platinum metals can be completely recovered from dilute nitric acid solutions on cation exchangers like Dowex-50 [3]. The majority of researchers believe that Pd in nitric acid solutions exists as Pd(II) in the form of [Pd(NO 3 Also Pd can be recovered from nitric acid solutions using anion exchangers bearing quaternary ammonium and tertiary amine groups, e.g., SBW, SBK, and SBU resins produced outside of Russia [5,6], and AN-31 and AV-17 resins produced in Russia [7]. Evidently, Pd is sorbed from nitric acid solutions on anion exchangers in the form of [Pd(NO 3 ) 4 ] 23 . It was demonstrated previously that, in extraction from nitric acid solutions with quaternary or tertiary ammonium nitrates, Pd is extracted as (R 4 N + ) 2 [Pd(NO 3 ) 4 ] 23 or (R 3 NH + ) 2 [Pd(NO 3 ) 4 ] 23 , respectively [8,9].In this study we determined the capacity of various anion exchangers for Pd, to elucidate their applicability to Pd recovery from NPP spent fuel. Other tasks of the study were to optimize the desorption conditions and to test the sorption process for Pd recovery with actual spent fuel solutions on a laboratory unit in a hot cell. EXPERIMENTALIn the study we used Amberlite IRA-900, Dowex 21K, and VP1-AP resins. Palladium in solutions was determined spectrophotometrically with thiourea or a-nitroso-b-naphthol.From the elution curves we estimated the distribution coefficients K d , number of column volumes to breakthrough, and dynamic exchange capacity. The breakthrough criterion was the Pd concentration in the eluate corresponding to 5% of the initial concentration. The distribution coefficient was estimated by Eqs. (1) and (2).where V b is the volume of eluate passed until reaching the concentration corresponding to 50% of the initial (cm 3 ); V f , free volume (cm 3 ); V s , volume of the sorbent bed or column volume (cm 3 ); and m, weight of air-dry sorbent (g) (K d was estimated either as a dimensionless quantity or was expressed in cm 3 per gram of sorbent). The dynamic exchange capacity (DEC) is expressed in mg Pd cm 33 of swollen sorbent or mg Pd g 33 of air-dry sorbent. This parameter was estimated as the product of K d by the initial Pd concentration. Based on the experimental dependences of K d on the so...
The rate of cathodic deposition of palladium from nitrate solutions at a platinum electrode and the current efficiency of the process were studied as influenced by the concentrations of nitric acid, NaNO 3 , U, and other admixtures. In the range of potential E from +0.5 to +0.25 V, the rate of Pd deposition from 1 M HNO 3 solution was 0.73 0.9 mg cm !2 at current efficiency of about 70%. The degree of palladium recovery by cathodic deposition is more than 99% with the coefficient of separation from a-and b-emitting nuclides of 10 2 310 3 .Palladium, as a rule, almost completely passes into solution at dissolution of spent nuclear fuel in nitric acid [1] and, at further treatment, occurs in the raffinates of the first extraction cycle owing to the low distribution coefficient in TBP [23 4].Various sorbents can be used to recover Pd from nitric acid solutions [537]. The experimental data on the extraction recovery of palladium from nitric acid solutions are given in [8311].Along with the above procedures, electrochemical recovery of palladium from multicomponent nitric acid solutions is also of interest, especially owing to the absence of additional reagents, whose negative effect can appear at further treatment of the wastes.In this work we studied electrochemical deposition of palladium from nitric acid solutions as influenced by various factors.Our experimental data on the electrochemical treatment using a platinum cathode and model solutions allowed evaluation of the degree of palladium recovery and its purity. EXPERIMENTALThe experimental setup consisted of electrochemical cell equipped with a potentiometer and a programmer. The information was recorded with a GrafIt-2 interface block.The cell was a 100-ml glass vessel with a temperature-controlled water jacket; an auxiliary electrode was separated from the remaining cell volume with a porous glass membrane. This electrochemical cell made possible potentiometric and galvanostatic measurements under various experimental conditions (temperature up to 100oC, potential of the working electrode +2 V, and working current up to 0.5 A).The behavior of Pd in nitric acid solutions was studied by the procedure based on recording of the polarization curves. The working electrodes were platinum foils (70 0 10 0 0.1 mm); the measurements were performed with a saturated silver chloride reference electrode and platinum wire as an auxiliary electrode. At recording of the polarization curves, the rate of potential scanning was 10 mV s !1 . To determine the dependence of the current efficiency on the electrode potential, the cell was filled with a solution (100 cm 3 ) and, after the required temperature was attained, the polarization curves were recorded. The working electrode potential was maintained with an accuracy of + 0.005 V. In the course of the experiment, the average current and electrolysis time were recorded. After the experiment, the working electrode was removed from the cell and weighed to determine the amount of recovered palladium.The content of palladium in solu...
The principal purpose of spent fuel reprocessing consists in the recovery of the uranium and plutonium and the separation of fission products so as to allow re-use of fissile and fertile isotopes and facilitate disposal of waste elements. Amongst the fission products present in spent nuclear fuel of Nuclear Power Plants (NPPs,) there are considerable quantities of platinum group metals (PGMs): ruthenium, rhodium and palladium. Given current predictions for nuclear power generation, it is predicted that the quantities of palladium to be accumulated by the middle of this century will be comparable with those of the natural sources, and the quantities of rhodium in spent nuclear fuel may even exceed those in natural sources. These facts allow one to consider spent nuclear fuel generated by NPPs as a potential source for creation of a strategic stock of platinum group metals. Despite of a rather strong prediction of growth of palladium consumption, demand for “reactor” palladium in industry should not be expected because it contains a long-lived radioactive isotope 107Pd (half-life 6,5·105 years) and will thus be radioactive for a very considerable period, which, naturally, restricts its possible applications. It is presently difficult to predict all the areas for potential use of “reactor” palladium in the future, but one can envisage that the use of palladium in radwaste reprocessing technology (e.g. immobilization of iodine-129 and trans-plutonium elements) and in the hydrogen energy cycle may play a decisive role in developing the demand for this metal. Realization of platinum metals recovery operation before HLW vitrification will also have one further benefit, namely to simplify the vitrification process, because platinum group metals may in certain circumstances have adverse effects on the vitrification process. The paper will report data on platinum metals (PGM) distribution in spent fuel reprocessing products and the different alternatives of palladium separation flowsheets from HLW are presented. It is shown, that spent fuel dissolution conditions can affect the palladium distribution between solution and insoluble precipitates. The most important factors, which determine the composition and the yield of residues resulting from fuel dissolution, are the temperature and acid concentration. Apparently, a careful selection of fuel dissolution process parameters would make it possible to direct the main part of palladium to the 1st cycle raffinate together with the other fission products. In the authors’ opinion, the development of an efficient technology for palladium recovery requires the conception of a suitable flow-sheet and the choice of optimal regimes of “reactor” palladium recovery concurrently with the resolution of the problem of HLW partitioning when using the same facilities.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.