Studies in Solvent Extraction Using Polyaphrons II. Semibatch and Continuous Countercurrent Extraction Flotation of a Hydrophobic Organic Dye from Water
Transport mechanisms and a mathematical model for a continuous countercurrent predispersed solvent extraction (PDSE) process are proposed in this paper. Solvent extraction using polyaphrons provides enhanced mass transfer (extraction) of solute through larger interfacial areas of micron-sized predispersed solvent. Increased rise velocity is needed for subsequent phase separation (flotation) of dispersed polyaphrons through attachment onto micron-sized gas dispersions called colloidal gas aphrons (CGAs). PDSE experiments were conducted in both batch and continuous countercurrent modes to remove a hydrophobic organic dye (Solvent Red 27) from water into kerosene, Sodium dodecylbenzenesulfonate was used as the water-soluble surfactant and Tergitol-15-S-3 as the kerosene-soluble surfactant to form polyaphrons. The CGAs were prepared using hexadecyltrimethyl ammonium bromide in water. Results from batch experiments showed that the efficiency of dye removal depended not only on the duration of flotation but also on the settling time after flotation. Longer settling times increased the process efficiency, indicating gradual removal of the smaller polyaphrons. In the continuous countercurrent mode, the mathematical model predicts that the process efficiency is a function of the flow rates of CGA and polyaphrons relative to feed water flow rate, the partition coefficient of the solute, relative sizes of polyaphrons to CGAs, and the attachment efficiency of polyaphrons to CGAs. Experimental results in the continuous countercurrent mode are tested against the proposed model.