Study On The Mechanism Of Hydrazine Decomposition Catalyzed By Pt In Acidic Solution

Pu???in 1B tank of Purex process can be rapidly and effectively reduced to aqueous phase by using U???-hydrazine as reductant and loaded reductant.It is the most ideal separating and reducing agent for uranium and plutonium in the current uranium-plutonium co-purification and separation cycle.Hydrazine is used as a loaded reductant in the decontamination and separation cycle of uranium and plutonium to prepare U???by reducing U???.Although hydrazine can be highly reduced,N2H4 has a high energy barrier and cannot directly reduce U???in solution.It requires other methods to reduce U???by destroying hydrazine bonds to produce free radicals.In recent years,the catalytic reduction of U???to U???by hydrazine in acidic medium has been preliminarily studied at home and abroad.The results show that under certain conditions,Pt catalyzes the reduction of U???by hydrazine,but the reaction mechanism of hydrazine bond cleavage catalytic reduction of U???with U???is still unclear.The key problem in studying the reaction mechanism is to elucidate the types of free radicals produced by hydrazine on the surface of catalyst and their related characteristics and behaviors.In order to elucidate the decomposition mechanism of Pt-catalyzed hydrazine in acidic medium,the decomposition of Pt-catalyzed hydrazine in acidic system was studied by Electron Paramagnetic Resonance?EPR?.The main contents and conclusions of the study are as follows:1.EPR signals of free radical adducts in DMPO and solution systems were analyzed and studied under different acidity conditions using hydrazine,ammonium chloride and ethylenediamine as solutes in acidic water.The results show that the reason for the capture of amino transformation by DMPO is that the amino radicals in acidic solution exist in the form of[NH₃,H₂O]^·+,[NH₂,H₂O]^·is prone to[NH₃,H₂O]^·++DMPO=NH₄⁺+DMPO-OH.The relationship between DMPO-OH and the number of[NH₃,H₂O]^·+involved in the capture reaction was determined to be 1:1.2.By detecting EPR signals of free radical adducts in DMPO and solution system,the differences of free radicals produced by hydrazine decomposition under different acidic conditions in per chloric acid system and the mechanism of Pt catalytic hydrazine decomposition in general non-oxidation process were studied.Determine the acid solution.The results show that the N-N bond breaking coexists with the N-H bond breaking in the reaction system,and the N-H bond breaking plays a dominant role in acidic solution.Hydrazine exists in acidic solution in the form of N₂H₄,N₂H₅⁺and N₂H₆²⁺.Their amount in solution determines the breaking rate of N-N bond and the breaking rate of N-H bond.Under different acidic conditions,the change trends of N-N bond breakage and N-H bond breakage rate are different:1<pH<7,N-N bond breakage rate increases with the increase of H⁺concentration,N-H bond breakage rate decreases with the increase of H⁺concentration,N-N bond breakage rate reaches the maximum near[H⁺]=0.1mol/L,0.1mol/L<[H⁺]<1mol/L,with the increase of H⁺concentration,N-H bond breakage rate and N-N bond breakage rate decrease rapidly.But the breaking rate of N-N bond decreases rapidly.When[H⁺]>1.0mol/L,with the increase of H⁺,the fracture rates of N-H and N-N decrease slowly,and the fracture rate of N-N decreases at the same rate as that of N-H.Generally speaking,with the increase of acidity,the decomposition rate of hydrazine is positively correlated with the breaking rate of N-H bond,and the breaking of N-H bond plays a leading role.3.By detecting EPR signals of free radical adducts in DMPO and solution system,the differences of free radicals produced by hydrazine decomposition at different nitric acid concentrations were studied.The results showed that nitric acid?oxidizing acid?was gradually activated and oxidized with the increase of H⁺concentration in the reaction system.It will compete with[NH₃,H₂O]·⁺to·H or e-even oxidize hydrazine directly,thus increasing the decomposition rate of hydrazine.