Process Conditions And Kinetics Of Oxalic Acid Oxidation By Nitric Acid Catalyzed By Mn²⁺

In spent fuel reprocessing plants,oxalic acid is often used as a precipitator in the tail-end process of plutonium to obtain plutonium products.A small amount of plutonium and oxalic acid are still contained in the mother liquor of oxalate precipitation after oxalate precipitation.In order to further recover plutonium,after destroying the oxalic acid in the mother liquor of plutonium oxalic acid,our country returns directly to the purification cycle of plutonium,which seriously dilutes AF material solution.The reprocessing plants in advanced nuclear energy countries use evaporative enrichment technology to treat the mother liquor of plutonium oxalate precipitation and then return to the purification cycle of plutonium,which reduces the effect of the mother liquor of plutonium oxalate precipitation on the recovery of plutonium in the purification cycle of plutonium.In the process of concentration of plutonium precipitation mother liquor,the concentration of plutonium increases.If oxalic acid is not destroyed in time,it may precipitate in the inner wall of evaporator,and there is a nuclear critical risk.Therefore,the failure of oxalic acid is an important factor affecting the evaporation and concentration of oxalic acid mother liquor.Therefore,this paper mainly uses Mn²⁺catalytic nitric acid oxidation oxalic acid method to study the destruction behavior of oxalic acid in the evaporation and concentration of plutonium oxalate precipitation mother liquor,which provides a theoretical basis for the evaporation and concentration process of plutonium oxalate precipitation mother liquor.Through experimental research,the main conclusions are as follows:（1）To investigate the chemical behavior of oxalic acid destruction under different technological conditions,the effects of nitric acid concentration,oxalic acid concentration,Mn²⁺,Fe³⁺ concentration and temperature on the destruction rate of Mn²⁺ catalytic oxidation of oxalic acid by nitric acid were studied,The optimum conditions were as follows:4.0mol/L～7.0mol/L,0.1mol/L,Mn²⁺0.01mol/L and 363K.respectively.As a result,the increase of nitrite concentration can significantly shorten the induction period,promote the initial decomposition rate of oxalic acid,Fe³⁺inhibit the destruction of oxalic acid.The effects of evaporation rate,oxalic acid and formic acid concentration on the destruction rate of oxalic acid were studied,the results showed that denitration evaporation concentration could significantly reduce the acidity of the solution in the evaporator,but the addition of formic acid significantly inhibited the oxidative destruction of oxalic acid.（2）Investigating the influence of oxalic acid,nitric acid,and Mn²⁺concentration on the reaction rate of Mn²⁺ catalyzing the oxidation of oxalic acid by nitric acid,the initial kinetic rate equation of the reaction was determined as:-dc（H₂C₂O₄）/dt=kc^0.7840（H₂C₂O₄）c^0.3192（HNO₃）At 363K,the reaction rate constant is 3.0×10^-3（mol/L）^-0.1032/m:n When the concentration of Mn²⁺ is in the range of 0.008～0.020mol/L,the reaction order of Mn²⁺ is positive,which has a positive catalytic effect on the reaction.