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Kinetics and instabilities in the extraction of Co(II) by sodium di-(2-ethylhexyl) phosphate at the water/toluene interface. I. Kinetics and mechanism

par Danes, Florin;Gentric, Emilie;Lijour, Yves;Sanfeld, Albert ;Saumagne, Pierre
Référence Journal of colloid and interface science, 129, 1, page (120-129)
Publication Publié, 1989

Article révisé par les pairs

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Résumé :

A toluenic solution of sodium di-(2-ethylhexyl) phosphate (NaD2EHP) was allowed to react with an aqueous solution of Co(II) in a nonagitated system. Two layers of NaD2EHP emulsions in water appeared: a dilute emulsion A and an opaque emulsion B located below the toluenic phase. Furthermore, spontaneous convective motions were observed. The kinetics of complexation was investigated by spectrophotometry. The influence of four factors was studied: the Co2+ concentration Cm, the NaD2EHP concentration Cd, the inert anti-emulsifier (KBr) concentration Ce, and the hydration degree Ih of the surfactant. When Cm was increased, the reaction rate w exhibited a maximum at Cm = 15 moles m-3 and then a minimum at Cm = 30 moles m-3. The whole dependence w(Cm, Cd, Ce, Ih) is explained by a double location of a superficial reaction with proper reaction orders of 1 relative to Co2+ and 0 relative to NaD2EHP. The results show that, in the absence of forced convection, the rate w of the Co(II) extraction is the sum w1 + w2 where w1 is the reaction rate at the surface of the droplets in layer B and w2 represents the reaction rate at the macroscopic W/O interface. An increase in Cm resulted in a strong reduction of the intensity E of the emulsification. Conversely, an increase in E led to an increase in the droplet area and therefore an increase in w1, while w2 was reduced via an increase in the resistance to the diffusion of Co2+ through the aqueous interstices of emulsion B. © 1989.