An Experimental Method for Diffusion and Extraction Studies across the Liquid-Liquid Interface

Journal/Book: Reprinted from Nature Vol. 183 pp. 312-313 Jan. 31 1959. 1959;

Abstract: Department of Chemistry Vanderbilt University Box 1506 Nashville 6 Tennessee. Oct. 16. THE prototype apparatus shown schematically in Fig. 1 offers a promising experimental approach for diffusion and extraction studies across the Interface between certain aqueous-organic systems uncomplicated by diffusion control in the adjacent bulk phases. It may also prove an effective probe of factors which influence the behaviour and 'structure' of the interface. The apparatus is operated in the following way. The substance being extracted (with tracer) is dissolved in 1 cm.3 of static aqueous phase placed so the aqueous surface formed at the bottom of the 'Teflon' slit (0·25 in. x 0·001 in.) is oriented lengthwise across the width of the rim and about 0·006 in. above the wheel. Individual organic drops at 1-5 drops/sec. are dropped an the ´Teflon' rim spinning at 10-200 r.p.m. Each drop is squeezed past the slit where it makes brief 'contact' with the aqueous phase before being almost entirely dragged away from the slit wiped off and collected at the bottom of the wheel. The activity/cm.3 of substance in the extract multiplied by the rate of production of drops is a measure of the 'apparent extraction rate' a parameter sensitive to the concentration of constituents involved in the extraction process. In a study at 100 r.p.m. of the simultaneous extraction of radioactive iron(III) and cæsium(I) from a 1 M nitric acid/water solution with pure tributyl phosphate the ratio of the activity of caesium to that of iron in the extract was 0·80 ± 0·02 compared to the original value in water of 1·1 8 ± 0·03. The activity/cm.3 in this extract was about 10-3 times that of the aqueous phase but it was about ten times more than is picked up by tributyl phosphate in a single equilibrium extraction with the same volume. These results indicate that a 'stable' interface with diffusive flow across it was achieved and that a differential rate of extraction in favour of iron(III) over cæsium(I) was obtained. Furthermore the ratio of caesium to iron in the extract differed markedly from the equilibrium value of 2·0 for this phase which is good evidente that the extraction depends an irreversible processes. ... ___MH

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