Advanced Polymer Sorbents: Performance for Lower V/U Adsorption in Natural Seawater

Our previous studies indicated that the uranium adsorption from seawater can be significantly enhanced by dropping the V/U ratio. Four different kinds of amidoxime-based adsorbents were prepared by grafting acrylonitrile along with 2-hydroxyethyl acrylate (HEA) or itaconic acid (AF8) onto polyethylene (PE) matrix through radiation-induced graft polymerization (RIGP) approach. Conversion reaction parameters of the attached nitrile functional groups (-CN) into amidoxime moieties were optimized by variation of reaction time, temperature, and solution type. FTIR and 13 C CP/MAS NMR spectra confirmed the generation of open chain amidoxime and cyclic imide dioxime by conversion of -CN. These studies also indicated significant hydrolysis of grafted HEA upon amidoximation. The braided AF8 adsorbents that were amidoximated in Water-Methanol (50:50 w/w) at 80 oC for 3 days had an average uranium adsorption capacity of 4.44 ± 0.28 g-U/Kg-ads. after 56 days of exposure in natural seawater, with a V/U (g/g) ratio of only 1.24 ± 0.01. The new HEAEC/F18/80/12/PB adsorbent, evaluated for uranium adsorption capacity and adsorption kinetics in seawater, emerged as very promising for a lower V/U ratio. Seawater exposure for 55 days of the HEAEC/F18/80/12/PB adsorbent resulted in a uranium uptake of 3.40 ± 0.63 g-U/Kg-ads. and V/U (g/g) ratio less than one.