Effects of Titanium Doping in Titanomagnetite on Neptunium Sorption and Speciation

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• 作者：E. Miller Wylie ; Daniel T. Olive ; Brian A. Powell
• 刊名：Environmental Science & Technology
• 出版年：2016
• 出版时间：February 16, 2016
• 年：2016
• 卷：50
• 期：4
• 页码：1853-1858
• 全文大小：399K
• ISSN：1520-5851

文摘

Neptunium-237 is a radionuclide of great interest owing to its long half-life (2.14 × 10⁶ years) and relative mobility as the neptunyl ion (NpO₂⁺) under many surface and groundwater conditions. Reduction to tetravalent neptunium (Np^IV) effectively immobilizes the actinide in many instances due to its low solubility and strong interactions with natural minerals. One such mineral that may facilitate the reduction of neptunium is magnetite (Fe²⁺Fe³⁺₂O₄). Natural magnetites often contain titanium impurities which have been shown to enhance radionuclide sorption via titanium’s influence on the Fe²⁺/Fe³⁺ ratio (R) in the absence of oxidation. Here, we provide evidence that Ti-substituted magnetite reduces neptunyl species to Np^IV. Titanium-substituted magnetite nanoparticles were synthesized and reacted with NpO₂⁺ under reducing conditions. Batch sorption experiments indicate that increasing Ti concentration results in higher Np sorption/reduction values at low pH. High-resolution transmission electron microscopy of the Ti-magnetite particles provides no evidence of NpO₂ nanoparticle precipitation. Additionally, X-ray absorption spectroscopy confirms the nearly exclusive presence of Np^IV on the titanomagnetite surface and provides supporting data indicating preferential binding of Np to terminal Ti—O sites as opposed to Fe—O sites.