Solvent extraction of copper(II) from chloride solutions using 1,1′-dialkyl-2,2′ bibenzimidazoles as extractants

The solvent extraction ability of 1,1′-dialkyl-2,2′-bibenzimidazoles (L) for the recovery of copper(II) ions from aqueous chloride solutions has been investigated. It was found that 1,1′-didecyl- 2,2′-bibenzimidazole is a useful extractant for the separation of copper(II) ions from both weakly and strongly acidic solutions. Copper(II) can be effectively stripped of organic solutions by a water or ammonia solution in a one-stage process. In low acidity media (pH _feed > 1), the extraction percentage of Cu(II) increases with an increase in metal ions and chloride concentrations. Copper(II) ions are extracted as binuclear complexes (CuCl₂) ₂L₂ (L = extractant). The constructed McCabe−Thiele diagram shows that the reduction of copper(II) ions concentration from 25 to approximately 5 g/dm³ in an aqueous feed is possible in two extraction stages. When [HCl] _feed ≥ 1 M, (LH⁺)₂(CuCl ₄ ²)L complex is formed. From the strongly acidic solutions ([HCl] = [LiCl] = 4 M), almost 100% of copper(II) ions can be removed by 1,1′-didecyl-2,2′-bibenzimidazole. Benzyl alcohol, used as an organic phase modifier, enables the selective extraction of copper(II) over zinc(II) ions from a weakly acidic chloride solution.