NEW 8-HYDROXYQUINOLINE DERIVATIVE EXTRACTANTS FOR PLATINUM-GROUP METALS SEPARATION .2. PD(II) EXTRACTION EQUILIBRIA AND STRIPPING

Equilibrium measurements of palladium extraction by chloroform solutions of 7-substituted-8-hydroxyquinoline derivatives from aqueous chloride media demonstrated that palladium is extracted as the chelate PdQ2. The formation of the chelate PdQ2 was also confirmed with direct spectroscopic analysis. The extraction equilibrium constants, K(ex), were determined to be log K(ex)=5.59 and 5.84 for TN 1911 (an unsaturated and sterically-hindered derivative) and TN 2336 (a saturated and sterically-free derivative) respectively. It was found that PdQ2 exhibits an absorption band at 460 nm in chloroform. It was shown that palladium extraction is influenced by both the extractant concentration and reagent structure. The importance of steric over electronic effects with respect to metal extraction was discussed. The individual roles of palladium, proton and chloride ion concentration were demonstrated. It was found that palladium extraction is exothermic with an enthalpy change of -29.6 kJ/mole. The influence of stripping agent composition with respect to metal stripping was investigated. The addition of MgCl2 in the HCl strip solution was found to enhance stripping performance.