The device of the invention includes the following 5 new elements in each mixer-settler: a) agitators with blunt edged turbines, b) decreasing degree of agitation throughout the series of mixing compartments, c) baffle with a central window in the settler interface, located after the flow buffers, and d) baffle without a window, centered in the settler interface, located after the baffle with a window. These elements allow for an operative method which inhibits secondary dispersion, reducing the formation of micro-droplets, without affecting the mass transfer between the phases. Consequently, this obtains a phase separation process with entrainments so small that it is possible to drastically increase the quality of the product, by obtaining an ultra-pure aqueous extract, simultaneously reducing the settling surface required.