An X-ray Absorption Spectroscopy Study of Neptunium(V) Reactions with Mackinawite (FeS)

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• 作者：Lesley N. Moyes ; Mark J. Jones ; Wendy A. Reed ; Francis R. Livens ; John M. Charnock ; J. Frederick W. Mosselmans ; Christoph Hennig ; David J. Vaughan ; and Richard A. D. Pattrick
• 刊名：Environmental Science & Technology
• 出版年：2002
• 出版时间：January 15, 2002
• 年：2002
• 卷：36
• 期：2
• 页码：179 - 183
• 全文大小：81K
• 年卷期：v.36,no.2(January 15, 2002)
• ISSN：1520-5851

文摘

Neptunium is a transuranium element, produced in tonnequantities in nuclear reactors. Because it has access to arange of oxidation states, neptunium may undergo redoxtransformations in the environment and these can have far-reaching effects on its environmental mobility. Here, thereaction of NpO₂⁺ (the soluble and thermodynamically stableneptunium species in oxic systems) with microcrystallinemackinawite is studied. Uptake of neptunium from solutionis relatively low (~10% of the total initially present insolution) and independent of initial solution concentrationover the range 0.27-2.74 mM and of equilibration time.X-ray absorption spectroscopy (XAS) of the solid sulfidesamples indicates nearest neighbor oxygen atoms at distancesaround 2.25-2.26 Å, sulfur atoms at around 2.61-2.64 Å,and two more distant shells fitted with iron, at 3.91-3.95 Åand 4.15-4.16 Å. These observations suggest that oninteraction with the sulfide surface reduction of Np(V) toNp(IV) occurs, accompanied by loss of axial oxygen atoms.Neptunium coordinates directly to surface sulfide atoms,in contrast to the behavior previously observed for uraniumunder similar conditions. These results demonstrate theimportance and variability of the speciation of redox sensitiveactinides under anoxic conditions.