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

Abstract

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, λ max of HNAPO (316 nm) and the Ni 2+ complex (387 nm) in a neutral micellar system, poly dispersed octa-ethyleneglycol mono- n -dodecyl ether (G 12 A 8 ) were determined as 3100 and 3500 M −1 cm −1 , respectively. HNAPO was found to have a neutral micellar phase and bulk aqueous phase p K a of 11.5 and 12.5, respectively. The extraction equilibrium constant, K ex, was determined to be 10 −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 (C 12 E 8 ) 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 G 12 A 8 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 G 12 A 8 micelle, for the concentration range studied. For G 12 A 8 /DTAC mixed micelles, the surface potential was given by +1.1 mV per DTAC molecule per micelle, and for G 12 A 8 /SDS mixed micelles the relationship was −1.4 mV per SDS molecule per micelle.