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Effects of Titanium Doping in Titanomagnetite on Neptunium Sorption and Speciation.

Authors :
Wylie EM
Olive DT
Powell BA
Source :
Environmental science & technology [Environ Sci Technol] 2016 Feb 16; Vol. 50 (4), pp. 1853-8. Date of Electronic Publication: 2016 Feb 01.
Publication Year :
2016

Abstract

Neptunium-237 is a radionuclide of great interest owing to its long half-life (2.14 × 10(6) 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 (Fe(2+)Fe(3+)2O4). Natural magnetites often contain titanium impurities which have been shown to enhance radionuclide sorption via titanium's influence on the Fe(2+)/Fe(3+) 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.

Details

Language :
English
ISSN :
1520-5851
Volume :
50
Issue :
4
Database :
MEDLINE
Journal :
Environmental science & technology
Publication Type :
Academic Journal
Accession number :
26756748
Full Text :
https://doi.org/10.1021/acs.est.5b05339