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 beta-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 ZnA2(B) by the mixture and the stability constant of ZnA(2)B is 2.08. Thermodynamic parameters Delta H, Delta S and Delta G 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. (C) 2009 Elsevier B.V. All rights reserved.