Formation of Neptunium(IV)鈥揝ilica Colloids at Near-Neutral and Slightly Alkaline pH

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• 作者：Richard Husar ; Stephan Weiss ; Christoph Hennig ; Ren茅 H眉bner ; Atsushi Ikeda-Ohno ; Harald Z盲nker
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：January 6, 2015
• 年：2015
• 卷：49
• 期：1
• 页码：665-671
• 全文大小：348K
• ISSN：1520-5851

文摘

The reducing conditions in a nuclear waste repository render neptunium tetravalent. Thus, Np is often assumed to be immobile in the subsurface. However, tetravalent actinides can also become mobile if they occur as colloids. We show that Np(IV) is able to form silica-rich colloids in solutions containing silicic acid at concentrations of both the regions above and below the 鈥渕ononuclear wall鈥?of silicic acid at 2 脳 10^鈥? M (where silicic acid is expected to start polymerization). These Np(IV)鈥搒ilica colloids have a size of only very few nanometers and can reach significantly higher concentrations than Np(IV) oxyhydroxide colloids. They can be stable in the waterborne form over longer spans of time. In the Np(IV)鈥搒ilica colloids, the actinide鈥攐xygen鈥攁ctinide bonds are increasingly replaced by actinide鈥攐xygen鈥攕ilicon bonds due to structural incorporation of Si. Possible implications of the formation of such colloids for environmental scenarios are discussed.