Abstract
The stability of the liquid surfactant membrane consisting of tri-n-octylamine (TNOA), Span 80 and kerosene as an extractant, surfactant and diluent, respectively, was investigated at mainly 298 K. Emulsions were prepared by extensive mixing of the organic solution with the internal aqueous solution containing 3 mol dm−3 H2SO4 or 1 mol dm−3 HCl using a homogenizer at ambient room temperature. The resultant emulsion was then dispersed in the 1 mol dm−3 H2SO4 aqueous solution with an impeller. The breakdown rate of emulsions was measured using a tracer technique to estimate the stability of liquid membrane when emulsions were dispersed in the external aqueous solution. The stability of emulsions increased with an increase in the rotating speed of the homogenizer or in the mixing time for emulsification. The increase in Span 80 concentration and the decrease in TNOA concentration caused an increase in the stability of emulsions. The breakdown rate of emulsions increased with an increase in the rotating speed of the impeller and with an increase in the temperature of the external solution. The apparent activation energy for the breakdown of emulsions was approximately 60 kJ mol−1. A small droplet size of the internal aqueous phase in W/O emulsions and a narrow distribution of the droplet size were desirable for the stabilization of emulsions. However, the droplet size was not always the determining factor of emulsions stability if the droplet size was smaller than a critical value.
