Equilibrium studies of nickel(II), copper(II), and cobalt(II) extraction with aloxime 800, D2EHPA, and Cyanex reagents

A study has been made of the extraction equilibrium of nickel(II), cobalt( II) and copper( II) from chloride solutions with 5-dodecylsalicylaldoxime (Aloxime 800), di(2-ethylhexyl) phosphoric acid (D(2)EHPA), bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) and its sulphur substituted analogs, called respectively Cyanex 302 and Cyanex 301, dissolved in hexane. The configuration of the metal complexes has been determined by the method of continuous variation. With D2EHPA, Cyanex 272 and Aloxime 800, NiL2, and CuL2 complexes were found. To obtain the octahedral coordination in the case of nickel( II), water molecules are required to occupy the axial positions. Similar results were found for cobalt, although in the case of Aloxime 800, the oxidation of cobalt( II) towards cobalt(III) was suggested. In the presence of Cyanex 301 and 302, NiL2(HL)(2) species were formed, whereas for cobalt, the coordination of neutral extractant molecules was only observed with Cyanex 302. The coordination of copper( II) with Cyanex 301 and Cyanex 302 was less pronounced based on Job's method. Furthermore, equilibrium constants and distribution coefficients were calculated for the different metal ions principally assuming that only monomeric ligands are involved.