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Abstract
Considerable effort has been directed toward describing, through analysis of mass-transfer resistances for solute diffusion and reaction in an emulsion drop, the permeation mechanism in liquid membrane systems based on the advancing reaction front model. However, very little attention has been paid to the loss of extraction efficiency often encountered in these systems due to rupture of the emulsion globules. In the present study, an unsteady-state mathematical model for batch extraction of monovalent HCrO4 − and divalent CrO4 2− from aqueous solution, through the use of Aliquat 336 as extractant and sodium hydroxide as stripping reagent, is reported. The rate of change of internal-phase volume due to membrane breakage was assumed to be independent of time, and an instantaneous and irreversible reaction between the solute and the internal reagent at the membrane–internal droplet interface was presumed to create a reaction front within the emulsion globule. The leakage coefficient was determined experimentally and was found to be dependent on internal-phase volume fraction. Batch experiments were performed for separation of Cr(VI) from aqueous potassium dichromate solution and the validity of the model was tested through the comparisons of model predictions with experimental data for different internal-phase volume fractions. The effect of external-phase pH on overall extraction in presence of leakage was also studied with semiempirical equations of the solute distribution coefficient that were obtained through experiments.