Synergic extraction of nickel and cobalt by LIX63-dinonylnaphthalene sulfonic acid mixtures

The extraction of nickel and cobalt by mixtures of 5,8-diethyl-7-hydroxy-6-dodecanone oxime (H₂Ox, active extractant in LIX63, a product of Henkel Corp.) and dinonylnaphthalene sulfonic acid (HDNNS or HD) has been studied by using the methods of slope analysis and continuous variation. On the basis of distribution and spectrophotometric data, the observed synergic extraction of nickel and cobalt by H₂Ox-HDNNS mixtures is attributed to the formation of a mixed ligand complex with the stoichiometry: Me/H₂Ox/HDNNS = 1/3/2. In the absence of H₂Ox, log D versus log [HDNNS] plots give straight lines with slopes of unity for both nickel and cobalt extraction, thus indicating that the active extractant is the HDNNS micelle. In the presence of H₂Ox the log D versus log [HDNNS] plots go through a maximum and a minimum. It is proposed that the active extractant under these conditions is a mixed HDNNS-H₂Ox micelle of the form (HD)_p·3H₂Ox, and that the shape of the metal distribution curve, as a function of HDNNS concentration, follows the organic-phase concentration of this mixed micelle.