Sodium Bis 2-ethylhexyl Phosphate Research Articles

Influence of marangoni effect on liquid-liquid extraction of copper(II) by sodium bis(2-ethyl hexyl) phosphate

The influence of spontaneous convection movements on the liquid-liquid extraction of copper(II) by sodium bis(2-ethylhexyl)phosphate (SEHP) is investigated by a kinetic study. Tire origin of the movements is related to a Marangoni effect which is caused by the surfactant properties of SEHP used as an extractant : a concentration gradient of SEHP occurs spontaneously at the interface when the two phases are put into contact and creates an interfacial tension gradient which promotes an interfacial movement. By a viscous dragging effect, this convection causes a stirring of the two phases of which efficiency is equivalent to that of two external stirrers running in opposite directions at 60 rpm. In these conditions adsorption of SEHP ion and the formation of an intermediate 1:1 complex at the interface are the rate controlling steps. However, a model taking into account a mixed regime seems to be more realistic for explaining the experimental observations than a pure kinetic model.