Ultrasound-assisted production of W/O emulsions in liquid surfactant membrane processes

Liquid surfactant membrane (LSM) process is a novel and effective method for the recovery and separation of heavy metals and amino acids from aqueous solutions. Repeated production and destruction of W/O emulsions plays a crucial role in the LSM process. The aim of this work was to study the efficiency of emulsification with horn ultrasound (20 kHz), in which the organic phase contained the surfactant Span 80 and the acidic carrier di(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene. The (internal) aqueous phase consisted of divalent Cu(II)-EDTA chelated anions as the tracers. All experiments were performed as a function of emulsification time, surfactant and carrier concentrations, ultrasonic power, and volume ratio of the internal aqueous phase to organic phase. It was shown that in most cases the emulsification was finished with 1 min. With ultrasound, the droplet sizes of W/O emulsions (Sauter diameter, d32) were much smaller than those reported previously by mechanical agitation. The effect of ultrasonic power and surfactant concentration on the droplet size was also investigated. Finally, the possibility of ultrasound demulsification was evaluated and discussed.