Cobalt extraction by hdnns in the presence of an alpha-hydroxyoxime

The method of slope analysis has been used to analyze cobalt extraction by dinonylnapthalene sulfonic acid (HDNNS) in hexane/aqueous nitrate systems in the absence and presence of 0.01 mol. dm^-3 5, 8-diethy1-7-hydroxy-6-dodecanone oxime (H₂Ox; the active extractant in the commercial reagent, LIX63, a product of Henkel Corp.). In the absence of H2OX, cobalt is extracted by HDNNS micelles and the log D versus log [HDNNS] plot gives a slope of unity. In the presence of 0.01 mol-dm^-3 H₂Ox, the corresponding plot shows a maximum at 5.6x10^-2 mol.dm^-3 HDNNS and a minimum at 3x1010^-2 mol.dm^-3 HDNNS. At low HDNNS concentrations ≤ 5.6x10^-3 mol.dm^-3), the log D versus log [HDNNS] plot has a slope of 1.0 while at high HDNNS concentrations (≥ 3x10^-2 mol-dm^-3) cobalt distribution approaches that of the HDNNS-alone system. The HDNNS behavior in the presence of H₂Ox is explained in terms of the presence of a mixed oxime-sulfonate micelle whose concentration goes through a maximum as HDNNS concentration is increased. The pH dependence of log D expected from the slope analysis (i.e. a slope of 2.0 for a log D vs pH plot) is masked by the presence of an H⁺/K⁺ cation exchange between HDNNS and the aqueous KNO supporting electrolyte.