Analytical Sciences

Synergistic Extraction of Gallium(III) and Indium(III) with2,4-Pentanedione and 3,5-Dichlorophenol on the Basis of Outer-SphereComplexation

Hisanori IMURA,Akiko OSHIRO and KousaburoOHASHI

Department of EnvironmentalSciences, Faculty of Science, Ibaraki University, Mito 310-8512, Japan

The synergistic extraction of gallium(III) andindium(III) with 2,4-pentanedione (Hacac) in heptane and carbontetrachloride has been studied using 3,5-dichlorophenol (DCP) as thesynergist. A remarkable enhancement of the extraction of both metals(III)with 0.01 mol dm^-3 Hacac was observed upon the addition of 0.05mol dm^-3 DCP, especially in heptane. From anextraction-equilibrium study, the synergistic enhancement was ascribed tothe formation of outer-sphere complexes, M(acac)₃.n(DCP)(M=Ga or In; n=1 - 3), in the organic phase. Furthermore, using thesynthetic metal(III) chelates hydrogen-bond formation betweenM(acac)₃ and DCP was observed by IR and ¹H NMR in carbon tetrachloride. The effect of DCP on the separation efficiency ofgallium(III) and indium(III) from aluminium(III) was discussed by means ofthe equilibrium constants such as the formation constants of outer-spherecomplexes as well as the extraction constants obtained so far. It wasconcluded that the present synergism caused by outer-sphere complexationimproved not only the extraction efficiency, but also the separationefficiency of those metals(III). (Keywords: Solvent extraction, synergism, gallium, indium,acetylacetone, dichlorophenol, hydrogen bond)

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