REMOVAL OF URANIUM FROM ACIDIC SULFATE-SOLUTION BY ION-EXCHANGE ON POLY(4-VINYLPYRIDINE) AND POLYBENZIMIDAZOLE IN PROTONATED SULFATE FORM

Microporous polybenzimidazole (PBI) of 0.25-0.50 mm spherical bead size from Celanese and spherical crosslinked poly(4-vinyl-pyridine), Reillex 425 PVP, of diameter 0.5-1.5 mm from Reilly Industries Inc. were used in the protonated sulfate form for the sorption of uranium from acidic sulfate solution and compared with conventional strong-acid and strong-base ion-exchange resins Dowex-50(H+) and Dowex-1 (SO42-) for the same application. Both PBI(H2SO4) and PVP(H2SO4) exhibit significantly greater acid tolerance than both Dowex-50(H+) and Dowex-1 (SO42-), on which the uranium uptake drops drastically at low pH with the result that at pH values below 1.0, PVP(H2SO4) has considerably greater uranium sorption than both Dowex-50(H+) and Dowex-1 (SO42-). The uranium capacity of PBI(H2SO4) is, however, less than half that of PVP(H2SO4). The protonated PVP also has considerably greater salt tolerance than the Dowex resins and exhibits high uranium selectivity in the presence of large excesses of NaCl and Na2SO4, while in comparison the uranium selectivity on Dowex-1(SO42-) is sharply reduced by NaCl and that on Dowex-50(H+) by both NaCl and Na2SO4. Thus, for uranium sorption against high salt background, PVP(H2SO4) exhibits higher capacity than the Dowex resins. Of the three resins, however, PVP(H2SO4) has the slowest sorption kinetics, the approximate half times for exchange being 4, 21 and 65 min for Dowex-50(H+), Dowex-1 (SO42-) and PVP(H2SO4), respectively. The sorbed uranium species can be stripped with HCI, H2 SO4, NaCl or Na2SO4 which give different stripping rates. The fastest stripping for all the sorbents is obtained with HCl.