Study On Electrochemical Properties Of Palladium In High Acid Media

Palladium is a noble metal. Owing to its irreplaceable physical andchemical properties, such as high ductility, strong hydrogen adsorptioncapability and excellent catalytic properties, there is a huge demand forpalladium and its compounds in various industrial fields.At a burn up of33GWd/t （gigawatt days per metric ton）, one metricton of spent fuel contained more than1kg palladium. It’s estimated that by2030spent nuclear fuel could provide as much as1000t palladium. Fissionpalladium is comprised of isotopes104（17wt.%）,105（29wt.%）,10⁶（21wt.%）,107（17wt.%）,108（12wt.%）, and110（4wt.%）. Among them,Pd-107is the only one radioactive isotope with a half-life of6.5×10⁶years.Since the maximum energy of β-ray emitted by Pd-107is35KeV and theradiation intensity at the surface of fission palladium is only merely520Bq cm-2. Thus, if recovered, its week radioactivity can be tolerated formany industrial applications.In this study, the electrochemical behavior of Pd（II） in nitric acidmedia has been investigated using various electrochemical techniques. Byanalyzing the cyclic voltammogram of Pd（II） recorded at Pt electrode, aseries of electrochemical reactions associated with Palladium wererecognized, indicating that Pd（II） undergoes a single step two-electronsirreversible process. Electroreduction reaction of Pd（II） and auto-catalyticreactions of nitrous acid are supposed to play a leading role in lowconcentration and high concentration nitric acid solutions respectively.Stirring could facilitate the reduction of Pd（II） in relatively low nitric acidconcentration （≤3M）. The value of charge transfer coefficient wasdetermined to be0.18for the measurements at298K. The diffusion coefficient of Pd（II） increases from1.89×10^-8cm²/s at288K to4.23×10^-8cm²/s at318K and the activation energy was calculated to be21.5kl/mol.In electrowinning experiments, the recovery ratios of Pd at different nitricacid concentrations are high, and the faradic efficiency of electrolysisdecreases as the nitric acid concentration increases. When stirring wasintroduced during electrolysis, the electrodeposition rate of Pd increasedsubstantially.Moreover，the electrochemical behavior of Pd in chloride acid mediaand the valance adjustment of Ru in chloride acid media were alsoinvestigated and a lot of important results were got.