NEW 8-HYDROXYQUINOLINE DERIVATIVE EXTRACTANTS FOR PLATINUM-GROUP METALS SEPARATION .3. PT(IV) EXTRACTION EQUILIBRIA AND STRIPPING

Studies of the extraction equilibria of platinum by chloroform solutions of 7-substituted-8-hydroxyquinoline derivatives from aqueous chloride media demonstrated that Pt(IV) is extracted as the ion-pair PtCl62-(H2Q+)2. The extraction equilibrium constants, log K(ex), were determined to be log K(ex) = 3.48 and 3.62 for TN 1911 (an unsaturated and sterically-hindered derivative) and TN 2336 (a saturated and sterically-free derivative) respectively. It was found that PtCl62-(H2Q+)2 exhibits an absorption band at 254.0 nm in chloroform solution. It was shown that platinum extraction is influenced by both the extractant concentration and reagent structure. The individual roles of platinum, proton and chloride ion concentration were quantified. It was found that platinum extraction is exothermic since metal extraction decreases with temperature and an enthalpy change of -39.8 kJ/mole was determined. The influence of pH on Pt(IV) stripping is also discussed. Finally, the respective extraction and stripping isotherms were established.