SELECTIVE CHROMATE RECOVERY WITH QUATERNIZED POLY(4-VINYLPYRIDINE)

A recently available macroporous resin, Reillex(TM) HPQ, which is derived from poly(4-vinylpyridine) by quaternization to the extent of about 70% and is reported to offer much higher resistance to oxidation than conventional strong-base polystyrene anion-exchange resins, has been evaluated for selective chromate recovery in low concentrations from aqueous solutions in the pH range 2-8 in comparison with the conventional strong-base resin Amberlite IRA-400. Employed in chloride form, HPQ offers marginally higher chromate sorption capacity than IRA-400 in absence of sulfate and chloride, but significantly higher selectivity (typically twice) in chromate recovery in the presence of several hundred-fold molar excesses of sulfate and chloride. HPQ also offers a higher rate of chromate sorption than IRA-400 (values of t1/2, for example, being 23 and 38 min, respectively, in 0.4 mmol/I chromate solution) and significantly higher initial stripping rate (the tl/2 values for stripping with 0.1 N NaOH, for example, being 45 s and 4.5 min, respectively). The rate data of chromate sorption on HPQ seem to support a model based on chemical reaction control instead of diffusion control.