Kinetics and Mechanism of Catalytic Reduction of U(Ⅵ)with Hydrazine on Platinum Catalysts in Nitric Acid Media  

硝酸体系中Pt催化N_(2)H_(4)还原U(Ⅵ)制备U(Ⅳ)的反应动力学及反应历程

作　　者：Xiao-teng Zhang Shuai Hao Fei-fei Tang Bin Li Xian-ming Zhou Li-sheng Liu Liang-shu Xia 张晓腾;郝帅;唐菲菲;李斌;周贤明;刘利生;夏良树(南华大学核科学技术学院,衡阳421001;中国原子能科学研究院放射化学研究所,北京102413)

机构地区：[1]School of Nuclear Science and Technology,University of South China,Hengyang 421001,China [2]Institute of Radiation Chemistry,China Institute of Atomic Energy,Beijing 102413,China

出　　处：《Chinese Journal of Chemical Physics》2022年第5期813-822,I0012,共11页化学物理学报（英文）

基　　金：supported by the National Natural Science Foundation of China(No.11575078);Hunan Provincial Innovation Foundation for Postgraduates(CX20190713)。

摘　　要：The kinetics of U(IV)produced by hydrazine reduction of U(VI)with platinum as a catalyst in nitric acid media was studied to reveal the reaction mechanism and optimize the reaction process.Electron spin resonance(ESR)was used to determine the influence of nitric acid oxidation.The effects of nitric acid,hydrazine,U(VI)concentration,catalyst dosage and temperature on the reaction rate were also studied.In addition,the simulation of the reaction process was performed using density functional theory.The results show that the influence of oxidation on the main reaction is limited when the concentration of nitric acid is below 0.5 mol/L.The reaction kinetics equation below the concentration of 0.5 mol/L is found as:−dc(UO_(2)^(2+))/dt=kc^(0.5323)(UO_(2)^(2+))c^(0.2074)(N_(2)H_(5)^(+))c^(−0.2009)(H^(+)).When the temperature is 50℃,and the solid/liquid ratio r is 0.0667 g/mL,the reaction kinetics constant is k=0.00199(mol/L)^(0.4712)/min.Between 20℃ and 80℃,the reaction rate gradually increases with the increase of temperature,and changes from chemically controlled to diffusion-controlled.The simulations of density functional theory give further insight into the influence of various factors on the reaction process,with which the reaction mechanisms are determined according to the reaction kinetics and the simulation results.

关 键 词：URANIUM Reaction kinetics Electron spin resonance HYDRAZINE Density functional theory 

分 类 号：TQ426[化学工程] X771[环境科学与工程—环境工程]