Solvent extraction of cobalt(II) ions; cooperation of oximes and neutral donors

2-Hydroxy-1-naphthaldoxime (HL1) and 1-hydroxy-2-naphthaldoxime (HL2) have been synthesized and their extractive properties towards cobalt(II) ions from sodium chloride aqueous phase into dichloromethane were studied. The presence of neutral donors tri-n-octylphosphine oxide (TOPO), tributylphosphate (TBP), tris(2-ethylhexyl)phosphate (T2EHP), tributylamine (TBA), trioctylamine (TOA) and dimethylsulfoxide (DMSO) shifts the extraction percentage curves towards lower pH region, indicating a synergistic effect of these donors on the extraction of cobalt ions by the studied oximes. The examined amines present significantly higher synergistic effect in comparison with TOPO, TBP, T2EHP and DMSO donors. It is shown that the stoichiometry of adducts formed in the organic phase by both HL1 and HL2 in the presence of TOPO depends on the oxime concentration. This stoichiometry was found to be [Co(L1(2))(TOPO)Cl] and [Co(L1(2))2(TOPO)] at low and high concentration of the oximes, respectively.

Research highlights▶ 2-Hydroxy-1-naphthldoxime and 1-hydroxy-2-naphthaldoxime are able to extract Co(II) ions. ▶ Mixtures of the oximes with neutral donors show synergistic effect for the extraction of cobalt. ▶ The synergistic effect of amines are more pronounced with respect to phosphoryl neutral ligands. ▶ The stoichiometry of extracted species depends on the oxime's concentration.