Phosphonate-based resins for the selective enrichment of uranium(VI)

Phosphonate-derivatized polystyrene-divinylbenzene-based (PS-DVB) resins ha ve been prepared from chloromethylpolystyrene-divinylbenzene (Cl-CH2-PS-DVB ) by the Arbuzov-reaction using lithium or sodium alkyl chlorophosphites. B ase-promoted hydrolysis of the diethyl phosphite-derivatized resin in reflu xing 1,4-dioxane resulted in phosphonic acid-derivatized PS-DVB resins with an average capacity of 0.8-2.2 mmol phosphonate, depending on the alkyl ch lorophosphate used. Both the free phosphonic acid as well as the diethyl, d ibutyl- and bis(2-ethylhexyl)-phosphonate-derivatized sorbents were investi gated in terms of their extraction characteristics for U(VI), Th(VI) as wel l as for other transition metal ions such as Fe(III), Zn(II), Co(II), Cd(II ), Ni(II) and Cu(II) from acidic aqueous solutions. In contrast to phosphon ate resins, the phosphonic acid-derivatized resins exhibited a high sorptio n capacity and selectivity for U(VI). Breakthrough experiments were conduct ed for both U(VI) and Th(IV) within a pH-range of 0-4. U(VI)-uptake was mea sured as a function of the concentration of nitric and hydrochloric acids, respectively. The sorbent was found to possess a high selectivity for U(VI) with an optimum extraction pH of 4. Recoveries for U(VI) determined prior to breakthrough were found to be quantitative (97-99%) on the free phosphon ic acid resin within the investigated pH-range. Finally, masking and synerg etic effects on the extraction efficiency of the phosphonic acid-derivatize d resin for U(VI) have been investigated using 5-sulfosalicylic acid as a m asking reagent and dipyridyl amine as an auxiliary ligand. (C)1999 Elsevier Science B.V. All rights reserved.