Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by Acetaldoxime
The separation of neptunium (Np) from spent nuclear fuel was accomplished by availably changing the oxidation state of Np from +Ⅵ to +Ⅴ during the plutonium uranium reduction extraction (Purex) process. Therefore, a lot of salt-free reductants were explored experimentally, including hydroxylamine, h...
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Editorial Board of Atomic Energy Science and Technology
2025-01-01
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| author | LI Xiaobo1, 2, ZHANG Meng1, , WU Qunyan2, , SHI Weiqun2, |
| author_facet | LI Xiaobo1, 2, ZHANG Meng1, , WU Qunyan2, , SHI Weiqun2, |
| author_sort | LI Xiaobo1, 2, ZHANG Meng1, , WU Qunyan2, , SHI Weiqun2, |
| collection | DOAJ |
| description | The separation of neptunium (Np) from spent nuclear fuel was accomplished by availably changing the oxidation state of Np from +Ⅵ to +Ⅴ during 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 (CH3CHNOH) effectively achieves the reduction from Np(Ⅵ) to Np(Ⅴ), but the reduction mechanism is not clear. Cis (Z) and trans (E) isomers of CH3CHNOH exist in solution, which may have different reduction abilities and reaction processes for Np(Ⅵ). In this study, scalar relativistic density functional theory was used to investigate the reduction mechanism of Np(Ⅵ) by Z/E-CH3CHNOH. One Z/E-CH3CHNOH molecule can reduce two Np(Ⅵ) ions. The H atom of the hydroxyl group on the Z-CH3CHNOH contacts with the neptunyl oxygen atom, which results in the first Np(Ⅵ) reduction and forms the Np(Ⅴ) and free radical Z-[CH3CHNO]•. Subsequently, the C atom of free radical Z-[CH3CHNO]• 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 (CH3CH(OH)NO). Finally, CH3CH(OH)NO dissociates into nitroxyl (HNO) and acetaldehyde (CH3CHO) by intermolecular hydrogen transfer. E-CH3CHNOH also achieves the reduction of two Np(Ⅵ) ions by similar processes of Z-CH3CHNOH, but the complexation structures and energy barriers of Np(Ⅵ) with two isomers are different. The reduction process of Np(Ⅵ) by Z-CH3CHNOH is thermodynamically more favorable than that of E-CH3CHNOH 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-CH3CHNOH needs to overcome the 22.36 and 19.19 kcal/mol energy barrier, respectively, which suggests that the first Np(Ⅵ) reduction is the rate-determining step. E-CH3CHNOH overcomes the energy barriers of 21.17 and 23.03 kcal/mol for the first and second Np(Ⅵ) reductions respectively, indicating that the second Np(Ⅵ) reduction is the rate-determining step. These results clarify that Z-CH3CHNOH and E-CH3CHNOH have nearly identical reduction abilities to Np(Ⅵ). The results of bond distance and localized molecular orbitals indicate that the reduction process of both Np(Ⅵ) by Z/E-CH3CHNOH is accompanied by the breakage and formation of related bonds. The reduction nature of the first and second Np(Ⅵ) reduction belongs to hydrogen atom transfer and water-participated single electron transfer respectively, which is also confirmed by the values of spin density and Np-Oyl bond distance. This work elucidates the reduction nature of Np(Ⅵ) by Z/E-CH3CHNOH, which provides a theoretical basis for the Np separation in spent nuclear fuel. |
| format | Article |
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| institution | Kabale University |
| issn | 1000-6931 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | Editorial Board of Atomic Energy Science and Technology |
| record_format | Article |
| series | Yuanzineng kexue jishu |
| spelling | doaj-art-c18c0c4acab44720ad1a4a7bbbe624462025-08-20T03:35:16ZengEditorial Board of Atomic Energy Science and TechnologyYuanzineng kexue jishu1000-69312025-01-01591354510.7538/yzk.2024.youxian.0257Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by AcetaldoximeLI Xiaobo1, 2, ZHANG Meng1, , WU Qunyan2, , SHI Weiqun2, 01. School of Nuclear Science and Technology, Harbin Engineering University, Harbin 150001, China 2. Laboratory of Nuclear Energy Chemistry, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, ChinaThe separation of neptunium (Np) from spent nuclear fuel was accomplished by availably changing the oxidation state of Np from +Ⅵ to +Ⅴ during 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 (CH3CHNOH) effectively achieves the reduction from Np(Ⅵ) to Np(Ⅴ), but the reduction mechanism is not clear. Cis (Z) and trans (E) isomers of CH3CHNOH exist in solution, which may have different reduction abilities and reaction processes for Np(Ⅵ). In this study, scalar relativistic density functional theory was used to investigate the reduction mechanism of Np(Ⅵ) by Z/E-CH3CHNOH. One Z/E-CH3CHNOH molecule can reduce two Np(Ⅵ) ions. The H atom of the hydroxyl group on the Z-CH3CHNOH contacts with the neptunyl oxygen atom, which results in the first Np(Ⅵ) reduction and forms the Np(Ⅴ) and free radical Z-[CH3CHNO]•. Subsequently, the C atom of free radical Z-[CH3CHNO]• 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 (CH3CH(OH)NO). Finally, CH3CH(OH)NO dissociates into nitroxyl (HNO) and acetaldehyde (CH3CHO) by intermolecular hydrogen transfer. E-CH3CHNOH also achieves the reduction of two Np(Ⅵ) ions by similar processes of Z-CH3CHNOH, but the complexation structures and energy barriers of Np(Ⅵ) with two isomers are different. The reduction process of Np(Ⅵ) by Z-CH3CHNOH is thermodynamically more favorable than that of E-CH3CHNOH 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-CH3CHNOH needs to overcome the 22.36 and 19.19 kcal/mol energy barrier, respectively, which suggests that the first Np(Ⅵ) reduction is the rate-determining step. E-CH3CHNOH overcomes the energy barriers of 21.17 and 23.03 kcal/mol for the first and second Np(Ⅵ) reductions respectively, indicating that the second Np(Ⅵ) reduction is the rate-determining step. These results clarify that Z-CH3CHNOH and E-CH3CHNOH have nearly identical reduction abilities to Np(Ⅵ). The results of bond distance and localized molecular orbitals indicate that the reduction process of both Np(Ⅵ) by Z/E-CH3CHNOH is accompanied by the breakage and formation of related bonds. The reduction nature of the first and second Np(Ⅵ) reduction belongs to hydrogen atom transfer and water-participated single electron transfer respectively, which is also confirmed by the values of spin density and Np-Oyl bond distance. This work elucidates the reduction nature of Np(Ⅵ) by Z/E-CH3CHNOH, which provides a theoretical basis for the Np separation in spent nuclear fuel.neptuniumacetaldoximereduction reactiondensity function theoryspent nuclear fuel |
| spellingShingle | LI Xiaobo1, 2, ZHANG Meng1, , WU Qunyan2, , SHI Weiqun2, Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by Acetaldoxime Yuanzineng kexue jishu neptunium acetaldoxime reduction reaction density function theory spent nuclear fuel |
| title | Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by Acetaldoxime |
| title_full | Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by Acetaldoxime |
| title_fullStr | Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by Acetaldoxime |
| title_full_unstemmed | Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by Acetaldoxime |
| title_short | Unraveling Reduction Mechanisms from Np(Ⅵ) to Np(Ⅴ) by Acetaldoxime |
| title_sort | unraveling reduction mechanisms from np vi to np v by acetaldoxime |
| topic | neptunium acetaldoxime reduction reaction density function theory spent nuclear fuel |
| work_keys_str_mv | AT lixiaobo12zhangmeng1wuqunyan2shiweiqun2 unravelingreductionmechanismsfromnpvitonpvbyacetaldoxime |