Synergism by β-Diketones on the Extraction of Gallium(III) with Di(2-ethylhexyl)phosphoric Acid into Heptane and Supercritical Carbon Dioxide

Abstract

The synergism caused by of six β-diketones on the extraction of gallium(III) with di(2-ethylhexyl)phosphoric acid (D2EHPA or HA) from weak acidic solution into heptane and supercritical carbon dioxide (SC-CO₂) was investigated. Thenoyltrifluoroacetone (Htta), benzoylacetone (Hbza), benzoyltrifluoroacetone (Hbfa), acetylacetone (Hacac), trifluoroacetylacetone (Htfa), and hexafluoroacetylacetone (Hhfa) were used as synergists. In the heptane extraction with 5.0 × 10⁻³ M D2EHPA and 5.0 × 10⁻⁴ M β-diketone, synergism occurred in the presence of Htta, Hbza, Hhfa, Hbfa and Htfa, but not to any extent with Hacac or Hbza. The synergistic effect increased in the following order: Htfa < Hhfa < Hbfa ≈ Htta. The synergistic extraction equilibrium of gallium(III) with D2EHPA and Htta in heptane was investigated. The results suggest that two types of complexes were extracted with D2EHPA and Htta, namely GaA₂(tta)·HA and GaA₂(tta)·2HA. This synergistic effect also occurred in SC-CO₂ extraction. However, the degree of synergism in the SC-CO₂ system is smaller than that in the heptane system.