Solubilization and metal complexation in a reversed micellar hydroxyoxime-sulfonic acid liquid-liquid extraction system

The solubilization of 5,8-diethyl-7-hydroxy-6-dodecanone oxime (HL, the active reagent in the commercial metal extractant LIX63) by reversed micelles of dinonylnaphthalene sulfonic acid (HDNNS) in hexane has been investigated with the vapor pressure osmometry (VPO) technique. The effect of HDNNS concentration on the solubilization of HL is compared with the corresponding effect on the distribution of nickel between an HDNNS-HL-hexane organic phase and an aqueous phase containing 1.0 mol dm^-3 KNO₃ at pH 1.0. For a given total concentration of hydroxyoxime, s, the number of HL molecules solubilized per HDNNS reversed micelle (i.e., (HDNNS)₇) decreases with increase in total HDNNS concentration. The HDNNS concentration that gives s = 3 coincides approximately with the corresponding concentration that gives a maximum in nickel distribution. It is concluded that the formation of a tris metal-hydroxyoxime complex depends on the availability of HDNNS reversed micelles that contain at least three molecules of solubilized HL per reversed micelle.