Preparation and application of colloidal liquid aphron for predispersed solvent extraction

Abstract

Aphron is defined as a distinct unit of fluid, encapsulated by a thin film of another fluid. There are two types of very small and highly stable aphrons. Colloidal Gas Aphrons, CGAs, were first manufactured by Sebba, by utilizing a modified venturi device under the name of microfoams. The Colloidal Liquid Aphrons, CLAs, differ from CGA in that, instead of a gas in the hole, there is a liquid that is insoluble in the water, which is the continuous phase. Both CGA and CLA possess unique characteristics that make them extremely useful for a wide range separation application. CLAs can be produced with a very high phase volume ratio without phase inversion or coalescence. When CLAs are dispersed in a bulk aqueous phase, they show a remarkable resistance to coagulation, remaining as discrete entities over long periods of time, with only minimal agitation and without undergoing coalescence as dose a conventional emulsion. Despite their potential uses in a wide variety of applications, very little work has been carried out to investigate the CLA’s structures, preparation and on the stability of CLA. A basic knowledge about stability of aphrons would be very valuable for the optimization of aphron-based processes and provide useful information for the design of process equipment. In this study, the preparation of CLA with various solvents, surfactants and phase volume ratios (PVRs) were investigated. Several solvents commonly used in extraction process were tested to form CLAs. CLAs can be prepared with a high PVR using non-polar solvents that are insoluble in water. According to the solvent and surfactant used to prepare CLAs, obtainable PVR was changed. Although CLAs were not formed at the time when anionic surfactant was used as water-soluble surfactant, stable CLAs could be produced with cationic or non-ionic water-soluble surfactant in case of a basic solvent. In addition, the stability measurements for CLA were presented in terms of solvent volume release from ...