Influence of alkyl chain length and structure on the extraction of copper(II) from aqueous acid by 5-alkyl-2-hydroxybenzaldoximes in hydrocarbon solvents: Diffusion coefficients of extractants and their complexes

Measurement of the kinetics of extraction of copper(II) by 19 different 5-a lkyl-2-hydroxybenzaldoximes (alkyl is C7H15 and C9H19) from acidic (hydroge n sulfate buffer) aqueous solution in the range pH 3.4-2.0, into 20% v/v to luene in n-hexane is reported. The lowering of the interfacial tension has been measured in some cases. The solubility of the extractants in water has been measured spectrophotometrically. A modified Taylor-Aris dispersion te chnique has been used to measure the diffusion coefficients in n-hexane and Orfom SX7 of some of the extractants and of the copper(II) complexes which they form. At low initial bulk concentrations (<10 mol m(-3)) of the extra ctants, the rate of extraction is controlled by the rate of diffusion of th e extractant from the bulk to the organic-aqueous interface. The diffusion coefficient is related to the steric bulk of the alkyl substituent. At high er initial bulk concentrations (200 mol m(-3)) of the extractants, when the interface is saturated, the rate of extraction is inversely related to the apparent steric bulk of the alkyl substituent. (C) 1999 Academic Press.