NEW 8-HYDROXYQUINOLINE DERIVATIVE EXTRACT ANTS FOR PLATINUM GROUP METALS SEPARATION PART 3: Pt(IV) EXTRACTION EQUILIBRIA AND STRIPPING

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Abstract
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 PtCl6 2−(H2Q+)2. The extraction equilibrium constants, log Kex, were determined to be log kex=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 PtCl6 2−(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.