Study on the Coordination of Amidoxime Small Molecule Ligands with Uranyl Ions Under Seawater Conditions

摘要

Uranium concentration in seawater is consistent at 3parts per billion (ppb) in various locations around theworld, even at depths up to 5000 feet. With the constanturanium concentration of 3 ppb in a total of 1.3 × 10~(22)liters of seawater, the amount of uranium is estimatedabout 4 billion tons in the ocean, and most of the uraniumexists mainly in U(Ⅵ) oxidation state as uranyl tricarbonate,about 98%. The extremely low concentrationof 3ppb and the very stable complex species of uranyl tricarbonatein seawater makes the recovery of uraniumvery difficult and energy unfavorable if some energy isneeded for pumping seawater uphill. In last severaldecades, scientists around the world developed apromising method using adsorbent made of nonwovenfabric or fiber functionalized with amidoxime groups forextracting uranium from sweater. These materials are allpolymers and have complicated structures. The structuresof the amidoxime functional groups and theircoordination modes with uranyl ions are also not clear.This study is focusing on the complexation of uranylions with two amidoxime-based small molecule ligands.By using potentiometry, the protonation constants of thetwo small ligands and the complexation stabilityconstants of uranyl complexes were determined. Theexperimental results indicate the complex species of theligands with uranyl ion were quite different from thosespecies of similar ligands previously investigated. Byanalyzing the effect of changes in the structure ofamidoxime ligands on their coordination ability, thisstudy provides insights for the coordination of amidoximeligands with uranyl and other metal ions.