No abstract

Fibrous amidoxime adsorbents were prepared by radiation-induced co-grafting of acrylonitrile (AN) and methacrylic acid (MAA) and subsequent amidoximation. Adsorption of uranium in seawater was evaluated by pumping seawater into the adsorbent column. The best monomer ratio of AN and MAA was 7 : 3 for continual usage of uranium adsorption. Though hydrochloric acid is an effective eluting agent for the metals adsorbed on the adsorbent, amidoxime groups were simultaneously damaged after five cycles of adsorption -desorption. This deterioration was reduced by an alkaline treatment of the adsorbents after each elution. Furthermore, various organic acids were examined as elution agents. It was found that the 80% of adsorption activity was still maintained after five cycles of adsorption -desorption when tartaric acid was used for eluting agent.

Uranium is one of the most valuable metals in seawater. Various inorganic and organic adsorbents for the recovery of uranium in seawater have so far been synthesized and evaluated. [1][2][3][4] Among the adsorbents reported, amidoxime polymers are noted as being the most promising. 1,3,4 Hirotsu et al. 5,6 have already investigated a separative elution of uranium from an amidoxime polymer which had been immersed in seawater, and proposed the selective elution of uranium from an amidoxime polymer with 0.5 or 1 mol dm -3 hydrochloric acid after complete elution of co-adsorbed magnesium(II), calcium(II), zinc(II), and nickel(II) with 0.1 mol dm -3 hydrochloric acid. However, the fraction of uranium also contained iron(III) and copper(II), which have had to be removed in the succeeding step, and no information about the adsorption and elution of vanadium was given in the work by Hirotsu et al. 5,6 We undertook the present work to obtain further information about the characteristics of the amidoxime polymer, and explored a method to elute iron and copper adsorbed on the amidoxime fiber from seawater prior to the release of uranium. Furthermore, we also found that vanadium adsorbed strongly on amidoxime fiber, and established a procedure to recover vanadium quantitatively from it.

No abstract

Methacrylic acid (MAA) and 2-hydroxyethyl methacrylate (HEMA) were cografted with acrylonitrile (AN) onto polyethylene fiber by radiation-induced graft polymerization. The cyano groups produced were converted to amidoxime groups (−C(NOH)NH2) by reaction with hydroxylamine (NH2OH) to recover uranium in seawater. Various weight ratios of AN/MAA or AN/HEMA in the monomer mixture for cografting generated MAA- and HEMA-cografted amidoxime (AO) fibers with various hydrophilicities. The amidoxime group density and water content were balanced to enhance the uranium adsorption from seawater. MAA-cografted AO fibers exhibited a higher adsorption rate than HEMA-cografted AO fibers. The optimum value of the weight ratio of AN/MAA = 60/40 in the monomer mixture was observed both in a submerged mode at an ocean site and in a flow-through mode in the laboratory. The amount of uranium adsorbed was 0.90 g/kg of the MAA-cografted AO fiber at 293−298 K after 20 days of contact at the ocean site.