Zinc extraction from chloride solutions with mixtures of solvating and chelating reagents

An equimolar mixture of weakly basic and chelating reagent was used for extracting zinc(II) from acid chloride solutions at various concentrations of chloride and hydrogen ions. N,N-dihexylpyridine-3-carboxamide was used as a weak base and 1-phenyldecane-1,3-dione (β-diketone) as a chelating extractant. In a three-step extraction-scrubbing-stripping process, zinc ions were transferred from the chloride into the sulfate solutions. In the first step, Zn(II) was extracted by N,N-dihexylpyridine-3-carboxamide. The composition of the extracted complexes (solvate or ion pairs) depends on HCl concentration. After zinc(II) extraction from acid chloride solutions, Cl− ions were scrubbed out from the organic phases with ammonia solutions. In this step, the extractants transfer zinc ions according to one of two possible mechanisms: from the solvate into the chelate, or from the ion pair into the chelate. The stripping of zinc ions from the chelate complex with β-diketone was carried out with sulfuric acid solutions. For both systems under investigation (weakly and strongly acidic solutions), the use of the reagent mixture enables the effective extraction of zinc(II) and removal of chloride ions from the organic phase. Owing to the possibility of using the extractant mixture for the recovery of Zn(II) from the chloride solutions of varied acidity, a partial protonation of the weakly basic extractant in the stripping step has no significant effect on the efficiency of a subsequent extraction-scrubbing-stripping process.