Equilibria and kinetics of the extraction of gallium with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone.
The equilibria and kinetics of the solvent extraction of gallium(III) from aqueous monochloroacetic acid [HA] media with a benzene solution of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone [PMBP or HL] has been studied at 25 +/- 0.1 degrees and an ionic strength of 0.2. The species extracted was found to be GaL(3). The value of the acid dissociation constant of PMBP determined spectrophotometrically was 1.17 x 10(-4). The values of the partition coefficient of PMBP and the extraction constant of its gallium complex between an aqueous and a benzene phase were found to be 3.72 x 10(3) and 2.51 x 10(4), respectively. The rate of extraction was first-order with respect to the concentrations of gallium(III) in the aqueous phase and PMBP in the organic phase, inversely first- and second-order with respect to the hydrogen-ion concentration and zero- and first-order with respect to the concentration of monochloroacetate ions. Two mechanisms operate for this extraction, depending on the pH of the aqueous phase, one where the formation of the first complex, GaL(2+), between Ga(3+) and L(-) in the region of pH < 1.6 becomes the rate-determining step, and the other where the formation of the first complex between GaA(2+) and L(-) in the region of pH 2.0-2.3 is the rate-determining step. The rate constant for the first of these reactions was calculated to be 1.62 x 10(4)l.mole(-1).sec(-1), but that for the second could not be determined.
Odashima
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Chemical Research Institute of Non-Aqueous Solutions, Tohoku University, Katahira, Aoba-ku, Sendai, 980 Japan.
Endoh
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Ishii
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