Uranium exists uniformly as uranyl carbonates (primarily as [UO2(CO3)3]4-) at a low concentration, ~3.3 ppb, in seawater. However, due to the vast volume of the oceans, the total amount of uranium in seawater is approximately 1000 times larger than the terrestrial resources. Among solid adsorbents for uranium, polyacrylamidoxime (PAO) copolymers, prepared by the amidoximation of polyacrylonitrile (PAN), have been shown to have high uranium adsorption capacities. PAO in the fiber or braid form is also found to be more deployable in seawater than in the sheet or powder form. In order to meet the deployability requirement, as well as to increase the mechanical strength of PAO adsorbents, traditional radiation-induced graft polymerization (RIGP) has been used for grafting from chemically and mechanically stable trunk polymers. In contrast to the conventional RIGP method, surface-initiated atom transfer radical polymerization (SI-ATRP) was used in this study, offering better control of grafted chain functionality and architecture, as well as minimizing homopolymerization. Though various trunk polymer fibers were used in SI-ATRP of PAN−copolymers with high degrees of grafting (up to 3400%), this presentation will focus on one type of trunk fiber. SI-ATRP allows for the grafting of PAN and other copolymers (e.g., anionic acrylate groups, cationic quaternary ammonium ions) at varying concentrations with tailorable architecture. The uranium adsorption capacity of the best-performing adsorbent (≥ 3.6 to 3.7 mg U/g at 56 days) was higher than that of RIGP-grafted non-woven polyethylene fabric (JAEA) (2.2 to 2.5 mg U/g at 56 days) in continuous-flow experiments in seawater. Structural characterization of fibrous adsorbents by IR, NMR, and elemental analysis, in correlation with their performance in uranium adsorption will be discussed.

Fibrous adsorbents prepared by SI-ATRP for the recovery of uranium from seawater

249th National Meeting (2015)

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