Solvent extraction of zinc from chloride solutions using dialkyl derivatives of 2,2′-bibenzimidazole as extractants

Abstract Four new 1,1′-dialkyl-2,2′-bibenzimidazoles were used to extract zinc(II) from acid chloride solutions at various concentrations of chloride and hydrogen ions. In low acidity media (pH > 2), the maximum zinc(II) extraction with the compounds is observed at chloride concentrations in the range 0.7–1.8 M. Zinc(II) ions are extracted as neutral (ZnCl 2 ) m L n complexes (L = extractant) in which the m:n ratio varies from 1:2 to 3:3, depending on the metal-to-extractant molar ratio in the extraction media. In strongly acidic systems, anionic zinc(II) chloro-complexes may be extracted from aqueous solutions by protonated bibenzimidazoles as (LH + ) 2 (ZnCl 4 2− ) or/and (LH + )(ZnCl 3 − ) ion pairs. In weakly acidic media, at [Cl − ]