Synthesis of high efficiency amidoxime polymer adsorbents for uranium extraction from seawater by radiation-induced polymerization

Abstract

This study synthesized amidoxime polymer gel for uranium extraction from seawater through a polymerization process with gamma ray or UV-C radiation. The synthesis started with a mixture of acrylonitrile (AN) and methacrylic acid (MAA) monomers together with methylene bisacrylamide as a crosslinker and hydrogen peroxide in the case of UV radiation. The mixture was irradiated with gamma ray at various doses or UV-C for various durations. The resulting polymer gel was ground into fine particles and immersed in a hydroxylamine hydrochloride solution for 90 minutes in order to convert the chemical functional group from the cyano group into the amidoxime group. Results of laboratory-scale uranium extraction showed that for the case of amidoxime polymer gel prepared by gamma radiation, the ratio of monomer AN:MAA of 80:20, the amount of the crosslinker of 0.8 g/100 mL monomer, and 40 kGy gamma ray dose exhibited the highest uranium adsorption capacity. For the amidoxime polymer gel polymerized by UV-C radiation, the ratio of monomer AN:MAA of 80:20, the amount of the crosslinker of 1 g/100 mL monomer, hydrogen peroxide of 60 mL/100 mL monomer, and irradiation time of 8 hours exhibited the highest uranium adsorption capacity. The usage repeatability test indicated that after 8 cycles of repeated use, the polymer gel prepared from gamma ray did not show a decrease in the adsorption efficiency while the polymer gel prepared from UV-C showed a decrease in the adsorption efficiency of 50%. The field test results in natural seawater in front of Phuket Marine Biological Center (PMBC), Phuket province, Thailand for 8 weeks revealed that the polymer gel prepared from gamma ray exhibited the uranium adsorption of 0.05 mg/g while the polymer gel prepared from UV-C exhibited the uranium adsorption of 0.035 mg/g.