Extraction of zinc from ammoniacal solution with β-diketone: A comparative study of solvents used

The extraction behaviors of zinc by 1-(4′-dodecyl)-phenyl-3-tertiary butyl-1,3-octadione (HA) from ammoniacal solutions into ionic liquid (1-butyl-3-methyl-imidazolium hexafluorophosphate, [BMIM]PF6) and molecular organic solvent (nonane) were investigated. The effects of extractant concentration in the extracting organic phase, aqueous pH and total ammonia concentration in the aqueous phase were examined. The extraction efficiency of zinc in both extraction systems decrease with the increase of pH and total ammonia concentration. The extraction performance was evidently enhanced in the extraction system of [BMIM]PF6 with HA, especially at higher pH and total ammonia concentration. This can be attributed to the strong polarity environment of [BMIM]PF6. The extraction mechanism and the effect of zinc amine complexes on the extraction were discussed. The coordination environment of zinc ion in extracting phases were investigated by X-ray absorption spectra. The results showed that the different extraction behavior between nonane and [BMIM]PF6 is probably determinated by the hydration state of extracted zinc complex and the solvent polarity. Five extraction/stripping cycles were performed to examine the reusability of the extraction system and stripping characteristics.