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Kinetics and instabilities in the extraction of Co(II) by sodium di-(2-ethylhexyl) phosphate at the water/toluene interface. II. Spontaneous turbulence induced by interfacial reactions

par Calves, Jean Yves;Danes, Florin;Gentric, Emilie;Lijour, Yves;Sanfeld, Albert ;Saumagne, Pierre
Référence Journal of colloid and interface science, 129, 1, page (130-138)
Publication Publié, 1989

Article révisé par les pairs

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Résumé :

Spontaneous turbulences induced by interfacial reactions in liquid/liquid systems (STIR) and their accelerating effects on the total reaction rate are examined. A model of the mechanism of STIR and of its kinetic effects on the nonagitated system H2O/CoBr2/NaD2EHP/toluene (where NaD2EHP is sodium di-(2-ethylhexyl) phosphate) is proposed. STIR arise from inhomogeneous accumulation of the Co(D2EHP)2 complex in a layer B which appears between the aqueous and the organic bulk phases. This surfactant-rich layer offers strong resistance to the diffusion of Co2+ ions from the aqueous phase toward the interfacial reaction site. The STIR intensity I is equal to the product v2 × E between the superficial reaction rate v2 and the intensity E of the emulsification (represented by the ratio se/Smi between the overall droplet area se in layer B and the surface smi of the macroscopic water/toluene interface). The v2 reaction rate is also influenced by STIR according to v2 = Cm/[1/kc + E/(k′ + k″ I)], where kc is a chemical rate constant, and k′ and k″ are actual rate constants. The ratio E/(k′ + k″ I) represents the mass transfer resistance and Cm the metal-ion concentration in the aqueous phase. The model is in good agreement with the experimental dependence I(Cm) and v(Cm). © 1989.