SEPARATION OF VANADIUM(V) AND VANADIUM(IV) BY SORPTION ON AN IMINODIACETIC CHELATING RESIN

The distribution of vanadium(IV) and vanadium(V) between an aqueous so lution and the chelating resin Chelex 100 was investigated on the basi s of the Gibbs-Donnan model. As expected from this model the thermodyn amic equilibrium constant in aqueous solution and in the resin phase w ere found to be equal. The following values for the complexation const ant and for the exchange coefficients in NaNO3 0.1 M were found: log K = -1.93 and log beta(10ex) = -1.89 for vanadium(IV) and log K = 0.81 and log beta(11ex) = 0.70 for vanadium(V). A complex VO(2)L (log beta( 10ex) = -1.48) was found to be formed inside Chelex 100 at pH higher t han 3.5. The competition by the hydrolysis reactions in aqueous soluti on was quantitatively considered to explain the sorption curves of van adium(V) in the acidity range up to pH 9. As vanadium(IV) is not desor bed at pH higher than 8 a separation method was proposed, based on a b atch technique. It consists of sorbing both vanadium(V) and vanadium(I V) at a pH of about 4.5, and separating them by stripping vanadium(V) at a pH of about 10 and then vanadium(IV) at pH about 0.8. A preconcen tration factor of 40 could be obtained in this way. The model was also used to predict conditions for separation by a column method, The int erference of fulvic acid on the oxidation state of vanadium and on its sorption on Chelex 100 was examined.