Investigation of the ion exchange behaviour of chromium (III) in oxalic acid solutions.

The distribution coefficients of aluminium (III) and ion (III) in oxalic acid hydrochloric acid media were determined for strongly basic and strongly acidic ion exchange resins. In hydrochloric acid media alone and in the concentration range of 0 to 0.4 M HCL the distribution coefficients of AL (III) and Fe (III) are of the same order of magnitude. Under those conditions therefore selective separation of those metal ions is not possible. In hydrochloric acid oxalic acid solutions the situations is different. By careful choice of hydrochloric acid oxialic acid proportion it is possible to obtain sufficiently large difference in the values of the distribution coefficients of the respective metals. Results have shows that good separations are obtained by eluting those metals from anion exchange resins with a 0.3M hydrochloric acid solution containing 0.019M oxalic acid. Elution characteristics at this optimal concentration of the eluting reagents are presented. Aluminium appears first in the eluate due to a lesser degree in the retention of its oxalate complexes on the rasin this is accounted for by the relatively lower stability of the Al-oxalate complexes. The Fe (III) oxalate complexes have a higher relative stability and hence due to stronger retention; Fe(III) is selectively desorbed after the AL fraction. As a consequence of the kinetic inertness that is characteristics of Cr (III), results obtained for the substitution reaction of hexaquochromium (III) indicate a poor rate in the formation of sorbable anionic chromium oxalate complexes. This difference in properties offers a unique possibility for selective anion exchange separation of chromium (III) from the multi-component system Cr (III) - Fe (III) AL (III). By use of low temperature, moderate concentrations of oxalic acid and minimal times of interactions between (Cr (III) and oxalic acid the unreacted hexaquochromium (III) posses uretained through the column and almost 100 percent recoveries are possible by washing with cold oxalic acid at high flow rate. The retained AL (III) and Fe (III) are selectively eluted with HCL oxalic acid solution. Selective cation exchange separation of two component mixture Cr (III) AL (III) or Cr(III) Fe (III) is also discussed. By a similar manipulation of conditions, the unreacted chromium (II) is retained on the cation exchange resin while AL (III) or Fe (III) is eluted by washing with oxalic acid. The disruption of Cr (IIII) from the resin in this case is best affected by peroxide oxidation to Cr (IV).