Characterisation of nickel(II) extraction by 2-hydroxy-5-nonylacetophenone oxime (LIX 84) in a micellar phase

The properties of the nickel(II)/2-hydroxy-5-nonylacetophenone oxime (HNAPO), an active ingredient in LIX 84, extraction system were characterised in a micellar system. The extinction coefficient, &lambda;max of HNAPO (316 nm) and the Ni2+ complex (387 nm) in a neutral micellar system, poly dispersed octa-ethyleneglycol mono-n-dodecyl ether (G12A8) were determined as 3100 and 3500 M&minus;1 cm&minus;1, respectively. HNAPO was found to have a neutral micellar phase and bulk aqueous phase pKa of 11.5 and 12.5, respectively. The extraction equilibrium constant, Kex, was determined to be 10&minus;8.0, and the deviation from theory observed at high pH can be accounted for by consideration of the competition for nickel(II) ions by hydroxide ions and HNAPO. A micellar phase of octa-ethyleneglycol mono-n-dodecyl ether (C12E8) was determined to be an appropriate model of the free oil/water interface from the solubilised location of HNAPO. Utilising the interfacial probe, 4-heptadecyl-7-hydroxy coumarin (HHC) allowed the determination of the electrostatic surface potential of mixed micelles of G12A8 and sodium dodecyl sulphate (SDS) or dodecyl trimethyl ammonium chloride (DTAC). The electrostatic surface potential was a linear function of the number of additional surfactant monomers within the G12A8 micelle, for the concentration range studied. For G12A8/DTAC mixed micelles, the surface potential was given by +1.1 mV per DTAC molecule per micelle, and for G12A8/SDS mixed micelles the relationship was &minus;1.4 mV per SDS molecule per micelle.<br /