MASS-TRANSFER MODEL OF MERCURY REMOVAL FROM WATER VIA MICROEMULSION LIQUID MEMBRANES

A diffusion/reaction model is developed for mercury extraction using a microemulsion liquid membrane. The model incorporates the uniqueness of the mercury-oleic acid chemistry by including the role of oxygen in the surfactant on equilibrium extraction and stripping. Features which distinguish microemulsions from coarse emulsions are also taken into account. The difference is manifested primarily in the emulsion macrodrop size. The Sauter mean diameter determined from photographs ranges from 0.014 to 0.017 mm compared to 0.5-1 mm for coarse emulsion systems. Experimentally determined equilibrium constants and mass-transfer coefficient for the mercury-oleic acid system are used in the model equations. Model simulations show the expected effects of pH and equilibrium constants on extraction kinetics and interior concentration profiles. The model accurately predicts both the initial extraction kinetics and final mercury extraction equilibrium. The good agreement between theory and experiment suggests that the mechanism of extraction using microemulsions is very similar to that of coarse emulsions once the appropriate physical parameters which distinguish microemulsions from coarse emulsions have been incorporated. This is the first model to describe a carrier-mediated microemulsion extraction.