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

The synergism caused by of six beta-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 x 10(-3) M D2EHPA and 5.0 x 10(-4) M beta-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 GaA(2)(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.