Electrolytic Oxidation Destruction Of Oxalic Acid In Oxalate Plutonium (iv) Precipitation Mother Liquor

Electrochemical reduction and oxidation processes are easy to operate and controlremotely. In most cases these processes do not give rise to waste salts, such as result fromthe use of redox chemicals. All of these properties are especially attractive features forradiochemical processes. Accordingly, electrochemical reactions were introduced quiteextensively as intermediate steps in reprocessing, such as adjusting the valency ofplutonium, uranium or neptunium with the object of producing these metals with a highdegree of purity, dissolving nuclear fuels or destroying chemicals generated fromreprocessing.The electrolysis method for decomposing the oxalic acid in mother liquor fromplutonium oxalate precipitation without addition of any salt substance is one of thepotential techniques in the spent nuclear fuel reprocessing.In this paper, the electrolysis method is applied to the decomposition of oxalic acid inplutonium oxalate supernatant where oxalic acid is decomposed to CO₂ and H₂O due to theredox reaction on electrodes. The main results are summarized as follows:(1) The process and principle of the electrooxidation of oxalic acid in nitric acidmedium on Pt anode were studied employing linear sweep voltammetry (LSV) and cyclicvoltammetry (CV) techniques. The experimental results show that the oxidation of oxalicacid on Pt anode is irreversible reaction, the apparent reaction order, the exchangecoefficient of the reactionβand the diffusion coefficient of oxalic acid are determined tobe 0.9, 0.37 and 0.208×10^-5 cm² / s, respectively; the characteristics of electrochemicalbehavior of oxalic acid on different material electrode or under different temperature orconcentration of nitric acid are diverse.(2) The effects of varying some factors, such as current density, concentration ofoxalic acid or nitric acid, temperature, addition of metal ions and so on, on reaction ratewere measured during the electrolyzing process. The kinetic equation of theelectrooxidation of oxalic acid in nitric acid medium was given. Under the optimumconditions: platinized titanic anode, titanic cathode, 25～37mA/cm² current density, 2～3mol/L concentration of nitric acid, 30～40℃temperature, the decomposition ratio ofoxalic acid could reach to above 98%. The kind of acidic media is an important factorwhen optimizing such processes, the decomposition rate of oxalic acid in nitric acid is higher than that in the same concentration of perchtoric or sulfuric acid; the electrolysis ofoxalic acid is catalyzed by the addition of metal ions, such as Fe³⁺,MnO₄^-,Ag⁺.(3) The characteristics of electrochemical behavior of oxalic acid (OA) and plutoniumat platinum anode in simulative mother liquor generated from plutonium (Ⅳ) oxalatePrecipitation process were investigated. The cyclic voltammograms show that theoxidation of oxalic acid on Pt anode is irreversible reaction, while the redox of Pu(Ⅳ)/Pu(Ⅲ) is quasi-reversible reaction. Both of the reactions are diffusion-controlled.(4) Under the optimum condition, the experiments of decomposition of oxalic acid insimulated mother liquor generated from plutonium (Ⅳ) oxalate precipitation process wereconducted. The addition of plutonium has no obvious effect on the velocity of thedecomposition of oxalic acid; the decomposition ratio of oxalic acid also could reach toabove 98%.(5) Compared with the traditional potassium permanganate boiling oxidation method,electrochemical oxidation method is more effective. The decomposition rate of oxalic acidusing electrochemical method is twice as high as that using potassium permanganateboiling oxidation method.Therefore, it is potential that electrochemical oxidation method could be used for thedecomposition of oxalic acid in mother liquor generated from plutonium (Ⅳ) oxalateprecipitation process.