Date of Award
Master of Science (MS)
Hubert L. Youmans
This work concerns studies of two possible methods of separating rhodium from iridium. The first method was to complex the rhodium(III) and iridium(IV) with ethylenediaminetetraacetic acid and remove the anionic rhodium(III) -EDTA complex by its adsorption on an exchange resin. The neutral iridium(IV) EDTA complex was expected to pass through the resin column unaffected. The second separation study involved the hydrolytic precipitation of rhodium hydroxide in the presence of a soluble and stable iridium-EDTA complex. Hence, the rhodium precipitate could be filtered from the dissolved iridium complex. In the ion exchange separation, experiments were conducted to determine if the iridium(IV)-EDTA complexes were neutral and could be quantitatively passed through an anionic exchange column at pH 11.4 to 12.6. The effects of pH on complexation of EDTA with the iridium(IV) ion was studied by varying the pH from 2 to 12. It was found that it was not possible to make a separation on the anionic exchange column based upon the charge differences of the ions. Only 40 per cent of the iridium complex passed through the exchange column, while 60 per cent was adsorbed on the resin. Work was performed to determine the optimum condition of the hydrolytic separation. It was found that the rhodium (III) could be almost quantitatively precipitated in a 2:1 ratio of EDTA at pH 10. A heating period of 30 minutes at 80-90 degrees C. and treatment with ethyl alcohol was necessary to help eliminate the colloid effects. Under these same conditions, the iridium(III) or (IV) ion was present as a soluble EDTA complex. These individual conditions held as long as only rhodium or iridium was present in the solution. In a mixture of the two, adsorption of the iridium EDTA complex on the surface of the rhodium hydroxide prevented a quantitative separation. It was possible to separate approximately 92 to 93 per cent of rhodium from iridium, although each was slightly contaminated with the other. Dialysis of the dissolved rhodium hydroxide showed that approximately seven per cent of the precipitate was in a polymer form. The polymer could be broken by treatment with NaBrO3 and HCL. A procedure for the spectrophotometric determination of iridium (III) in the presence of a 2:1 ratio of EDTA and a pH of 11.4 to 12.6 was formulated. All of the iridium samples were quantitatively analyzed using spectrophotometric methods involving the complexation of iridium (III) or (IV) with EDTA. The tin (II) chloride determination was used for all rhodium analyses.
Schmidt, Gene W., "The Hydrolytic Separation of Rhodium from Iridium" (1962). Master's Theses. 758.
Copyright 1962 Gene W. Schmidt