Mass transfer coefficients in mixer-settler extraction column

The volumetric over-all mass transfer coefficient K(c)a and the volumetric dispersed phase mass transfer coefficient k(d)a in a mixer-settler extraction column were measured. In the measurement of K(c)a, iodine was extracted from I(2)-KI aqueous solution into heptane, while iodine was back-extracted from a heptane solution of iodine into sodium thiosulfate aqueous solution to obtain k(d)a. By using specific interfacial area determined from the estimated Sauter mean diameter of the dispersed drops and the estimated holdup of the dispersed phase, the mass transfer coefficients for the dispersed and the continuous phases were determined from the volumetric coefficients K(c)a and k(d)a. The coefficient k(d) for the dispersed phase coincided with the theoretical value based on diffusion within a rigid sphere using the residence time distribution of dispersed drops. On the other hand, the coefficient k(c) for the continuous phase agreed well with the correlation of mass transfer around a rigid sphere by assuming that the relative velocity of the dispersed drop to the continuous phase was given by the terminal settling velocity of a rigid sphere having the same diameter and density as the drop.