单甲基肼还原Np(Ⅴ)的反应动力学

Kinetics of Reaction Between Methylhydrazine and Neptunium(Ⅴ)

摘要: 用分光光度法研究了HNO₃介质中单甲基肼(MMH)还原Np(Ⅴ)的动力学行为。通过考察还原剂浓度和酸度等条件对Np(Ⅴ)动力学过程的影响，确定了反应的动力学速率方程为-dc(Np(Ⅴ))/dt=kc(Np(Ⅴ))c^0.36(MMH)c(H⁺)，在温度θ＝35℃、离子强度为2 mol/L时，反应速率常数k＝0.004 79 (mol/L)^-1.36/min。研究了离子强度、c(U(Ⅵ))和温度对反应的影响。结果表明，离子强度和c(U(Ⅵ))对反应速率无显著影响；反应活化能为60.43 kJ/mol，随着温度的升高，反应速率加快。并在此基础上推测了可能的反应机理。

Abstract: The kinetics of redox reaction between methylhydrazine(MMH) and Np(Ⅴ) in nitric acid media was studied by spectrophotometry. Based on results about the influence of MMH concentration and acidity on the reaction, the rate equation of that redox reaction is presented as -dc(Np(Ⅴ))/dt=kc(Np(Ⅴ))c^0.36(MMH)c(H⁺). The rate constant is 0.004 79 (mol/L)^-1.36/min at 35 ℃. Effects of ionic strength, c(U(Ⅵ)), and temperature were also investigated. The results show that ionic strength and c(U(Ⅵ)) have no obvious effect on the reaction but temperature has positive effect with activation energy value of 60.43 kJ/mol. The mechanism of the redox reaction was discussed.