乙醛肟还原Np(Ⅵ)的机理研究  

Unraveling Reduction Mechanisms from Np(Ⅵ)to Np(Ⅴ)by Acetaldoxime

作　　者：李小波 张萌[1] 吴群燕 石伟群[2] LI Xiaobo;ZHANG Meng;WU Qunyan;SHI Weiqun(School of Nuclear Science and Technology,Harbin Engineering University,Harbin 150001,China;Laboratory of Nuclear Energy Chemistry,Institute of High Energy Physics,Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]哈尔滨工程大学核科学与技术学院,黑龙江哈尔滨150001 [2]中国科学院高能物理研究所核能放射化学实验室,北京100049

出　　处：《原子能科学技术》2025年第1期35-45,共11页Atomic Energy Science and Technology

基　　金：国家自然科学基金(22376197,21925603)。

摘　　要：在Purex流程中,调控Np的价态能实现乏燃料中镎的分离。乙醛肟(CH_(3)CHNOH)作为无盐还原剂可有效将Np(Ⅵ)还原为Np(Ⅴ),但微观还原机理尚不清楚。CH_(3)CHNOH存在顺式(Z)和反式(E)异构体,这两种异构体对Np(Ⅵ)可能具有不同的还原能力和反应过程。本研究利用标量相对论密度泛函理论分别探讨了Z/E-CH_(3)CHNOH还原Np(Ⅵ)的反应机理。反应的热力学结果表明,Z-CH_(3)CHNOH还原Np(Ⅵ)的过程比E-CH_(3)CHNOH更有利,这可能归因于前者形成更多的氢键和反应过程中结构变化较小。动力学结果表明,两种同分异构体还原Np(Ⅵ)的决速步能垒非常相近,分别为22.36、23.03 kcal/mol,表明两者的还原能力基本一致。键长分析结果表明,Z/E-CH_(3)CHNOH还原2个Np(Ⅵ)的过程都伴随着相关键的断裂与形成。第1个Np(Ⅵ)还原属于氢原子转移,第2个Np(Ⅵ)还原是水参与的单电子转移。自旋密度和Np-O_(yl)键长的结果也证实了乙醛肟还原Np(Ⅵ)的本质。本研究解释了Z/E-CH_(3)CHNOH还原Np(Ⅵ)的微小差异,并揭示了其还原本质,为乏燃料中镎的分离提供了理论依据和支持。The separation of neptunium(Np)from spent nuclear fuel was accomplished by availably changing the oxidation state of Np from+Ⅵto+Ⅴduring the plutonium uranium reduction extraction(Purex)process.Therefore,a lot of salt-free reductants were explored experimentally,including hydroxylamine,hydroxamic acid,aldehydes,hydrazine,oxime,and their derivatives.Acetaldoxime(CH_(3)CHNOH)effectively achieves the reduction from Np(Ⅵ)to Np(Ⅴ),but the reduction mechanism is not clear.Cis(Z)and trans(E)isomers of CH_(3)CHNOH exist in solution,which may have differen reduction abilities and reaction processes for Np(Ⅵ).In this study,scalar relativistic density functiona theory was used to investigate the reduction mechanism of Np(Ⅵ)by Z/E-CH_(3)CHNOH.One Z/E-CH_(3)CHNOH molecule can reduce two Np(Ⅵ)ions.The H atom of the hydroxyl group on the Z-CH_(3)CHNOH contacts with the neptunyl oxygen atom,which results in the first Np(Ⅵ)reduction and forms the Np(Ⅴ)and free radical Z-[CH_(3)CHNO]~·.Subsequently,the C atom of free radical Z-[CH_(3)CHNO]~·touches the O atom of the coordinated water molecule of the second Np(Ⅵ)species,with the formation of Np(Ⅴ)and 1,1-nitrosoethanol(CH_(3)CH(OH)NO).Finally,CH_(3)CH(OH)NO dissociates into nitroxyl(HNO)and acetaldehyde(CH_(3)CHO)by intermolecular hydrogen transfer.E-CH_(3)CHNOH also achieves the reduction of two Np(Ⅵ)ions by similar processes of Z-CH_(3)CHNOH,but the complexation structures and energy barriers of Np(Ⅵ)with two isomers are different.The reduction process of Np(Ⅵ)by Z-CH_(3)CHNOH is thermodynamically more favorable than that of E-CH_(3)CHNOH based on their potential energy profiles(PEPs),probably due to the formation of more hydrogen bonds in the former.The reduction of the first and second Np(Ⅵ)by Z-CH_(3)CHNOH needs to overcome the22.36 and 19.19 kcal/mol energy barrier,respectively,which suggests that the first Np(Ⅵ)reduction is the rate-determining step.E-CH_(3)CHNOH overcomes the energy barriers of 21.17 and 23.03 kcal/mo for the first and seco

关 键 词：镎 乙醛肟 还原反应 密度泛函理论 乏燃料 

分 类 号：TL241[核科学技术—核燃料循环与材料] O643.12[理学—物理化学]