Electrochemical and complexation behavior of neptunium in aqueous perchlorate and nitrate solutions

Ikeda, Atsushi ; Hennig, C.*; Rossberg, A.*; Funke, H.*; Scheinost, A. C.*; Bernhard, G.*; Yaita, Tsuyoshi

Electrochemical and complexation properties of neptunium (Np) are investigated in aqueous perchlorate and nitrate solutions by means of cyclic voltammetry, bulk electrolysis, UV-visible absorption and Np L $_{rm III}$ -edge X-ray absorption spectroscopies. The redox reactions of Np(III)/Np(IV) and Np(V)/Np(VI) couples are reversible or quasi-reversible, while the electrochemical reaction between Np(III/IV) and Np(V/VI) is irreversible because they undergo the structural rearrangement from spherical coordinating ions (Np $^{3+}$ and Np $^{4+}$ ) to transdioxo neptunyl ions (NpO $_{2}$ $^{n+}$ , n = 1 for Np(V) and 2 for Np(VI)). A detailed analysis on extended X-ray absorption fine structure (EXAFS) spectra suggests that Np(IV) forms a decaaquo complex of [Np(H $_{2}$ O) $_{10}$ ] $^{4+}$ in 1.0 M HClO $_{4}$ , while Np(V) and -(VI) exist dominantly as pentaaquo neptunyl complexes, [NpO $_{2}$ (H $_{2}$ O) $_{5}$ ] $^{n+}$ (n = 1 for Np(V) and 2 for Np(VI)).

Language	:	English
Journal	:	Inorganic Chemistry
Volume	:	47
Number	:	18
Pages	:	p.8294 - 8305
Publication Year/Month	:	2008/09
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Paper URL	:	https://doi.org/10.1021/ic8009095
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Keywords	:	no keyword
Research Facility	:	SPring-8(大型放射光施設)
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Article of JAEA R&D Review	:
Cooperating Institute	:	Forschungszentrum Dresden-Rossendorf

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Registration No. : AA20080505
JAEA Abstracts No. : 36001409
Paper Submission No. : 4694

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