Determination of Vanadium Binding Mode on Seawater-Contacted Polyamidoxime Adsorbents

Technical Report · Fri Sep 01 04:00:00 EDT 2017

DOI:https://doi.org/10.2172/1410923· OSTI ID:1410923

Zhang, Zhicheng ^[1]; Rao, Linfeng ^[1]; Abney, Carter W. ^[2]; Bryantsev, Vyacheslav ^[2]; Ivanov, Aleksandr ^[2]

---

1. Lawrence Berkeley National Laboratory (LBNL)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Adsorbents developed for the recovery of uranium from seawater display poor selectivity over other transition metals present in the ocean, with vanadium particularly problematic. To improve selectivity, an indispensable step is the positive identification of metal binding environments following actual seawater deployment. In this work we apply x-ray absorption fine structure (XAFS) spectroscopy to directly investigate the vanadium binding environment on seawater-deployed polyamidoxime adsorbents. Comparison of the x-ray absorption near edge spectra (XANES) reveal marked similarities to recently a reported non-oxido vanadium (V) structure formed upon binding with cyclic imidedioxime, a byproduct of generating amidoxime functionalities. Density functional theory (DFT) calculations provided a series of putative vanadium binding environments for both vanadium (IV) and vanadium (V) oxidation states, and with both amidoxime and cyclic imidedioxime. Fits of the extended XAFS (EXAFS) data confirmed vanadium (V) is bound exclusively by the cyclic imidedioxime moiety in a 1:2 metal:ligand fashion, though a modest structural distortion is also observed compared to crystal structure data and computationally optimized geometries which is attributed to morphology effects from the polymer graft chain and the absence of crystal packing interactions. These results demonstrate that improved selectivity for uranium over vanadium can be achieved by suppressing the formation of cyclic imidedioxime during preparation of polyamidoxime adsorbents for seawater uranium recovery.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE), Fuel Cycle Technologies (NE-5)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1410923
• Report Number(s): ORNL/TM-2017/470
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY