Recovery of Pd from Spent Fuel: 1. Electrochemical Recovery of Palladium from Nitric Acid Solutions

Abstract

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...

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“…The reduction of HNO 3 is rather complicated and involves several steps in which nitrous acid is one of several intermediate N(III) species that have been identified [44]. The current for the cathodic reaction is divided between the reduction of HNO 3 and the formation of H 2 [45]. In the anodic equation m is the average number of holes that are required to dissolve one silicon atom.…”

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“…Recovery of valuable PGMs from nuclear HLLW was extensively studied [65][66][67][68][69][70] in the last two decades with particular interest in the separation of palladium. Several authors have reported the electrochemical recovery of PGMs from nitric acid medium [71][72][73][74][75]. Kirshin and Pokhitonov [73] studied the electrolytic recovery of palladium from nitric acid solutions and reported the efficiency of the process in the presence of HNO 3 , NaNO 3 , uranium, and other admixtures.…”

“…Several authors have reported the electrochemical recovery of PGMs from nitric acid medium [71][72][73][74][75]. Kirshin and Pokhitonov [73] studied the electrolytic recovery of palladium from nitric acid solutions and reported the efficiency of the process in the presence of HNO 3 , NaNO 3 , uranium, and other admixtures. Varentsov and Varentsova [74] reported the electrodeposition of rhodium on carbon fiber electrodes from nitric acid and confirmed that speciation of rhodium strongly affects the deposition behavior.…”