ROLE OF THE INTERFACE IN THE KINETICS AND MECHANISM OF SOLVENT EXTRACTION SYSTEMS (DITHIZONE, OXINE, INTERFACIAL AREA, DISPERSION).
AuthorAPRAHAMIAN, EDWARD, JR.
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PublisherThe University of Arizona.
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AbstractA high speed stirring apparatus was constructed for following the kinetics of metal ion extraction by chelating agents. The semi-automated system is capable of measuring reactions with half lives of 20 seconds or more with data being collected every second. Experimental data obtained with the device are superior to those collected by batch shakers, fixed interface cells, falling drop, or other stirring devices. The use of a microporous Teflon membrane phase separator along with the thermodynamic relation, the Gibbs Equation, enabled the measurement of drop sizes in a two phase liquid-liquid dispersion. This allowed the determination of the quantity of interfacial area as a function of stir rate. The effect of interfacial area on the rate of extraction of five different chelating agents with various divalent metal ions was determined in this study. The role of the interfacial area in extraction kinetics was found in a system where diffusional effects are negligible. This information provides an answer to the question of whether the rate determining step of extraction occurs in either the bulk aqueous phase or in the interfacial region. The proportionality between rate and specific interfacial area was employed to find the magnitude of the contributions of the bulk and interfacial components and also allowed the calculation of the individual rate constants. Evaluation of the bulk and interfacial rate constants yields important fundamental information as to the chemical nature and differences between the chloroform/water interface and the bulk aqueous phase. The results appear to illustrate that the interface is a more conducive medium for reaction between metal and ligand than the aqueous phase. The role of foreign species, namely nonionic surfactants, on the rate of extraction was investigated to explore their applicability in solvent extraction. Nonionic surfactants were found to enhance the rates of extraction to different extents in different metal systems.