Solvent extraction of zinc from ammoniacal/ammonium chloride solutions by a sterically hindered β-diketone and its mixture with tri-n-octylphosphine oxide

The extraction of zinc from ammoniacal/ammonium chloride solutions using a sterically hindered β-diketone, 4-ethyl-1-phenyl-1,3-octadione (XI-55, HA) as the extractant has been investigated in the presence or absence of tri-n-octylphosphine oxide (TOPO, B). The results indicate that the mixture of XI-55 and TOPO shows evident synergistic effects on zinc extraction. Zinc is extracted as ZnA2B by the mixture and the stability constant of ZnA2B is 2.08. Thermodynamic parameters ΔH, ΔS and ΔG are determined, which shows that the extractions of zinc by both XI-55 extraction system and the XI-55–TOPO synergistic extraction system are exothermic driven. The concentration of total ammonia has great influence on the extraction constants and distribution ratio for both extraction systems. FT-IR studies on zinc loaded organic phases confirm the non-extractability of zinc ammine complexes.