Clean-up of Oily Wastewater by Froth Flotation: Effect of Microemulsion Formation III: Use of Anionic/Nonionic Surfactant Mixtures and Effect of Relative Volumes of Dissimilar Phases

ABSTRACT

Froth flotation, a surfactant-based separation process, can be used to remove emulsified oil from water. In previous work, the maximum removal of ortho-dichlorobenzene from water using froth flotation was achieved when a Winsor Type III microemulsion was formed. However, the exact relationship between the equilibrium microemulsion characteristics and the froth flotation operation is still not clear. In the Winsor Type III microemulsion, three phases are present: an excess water phase containing little surfactant or oil, an excess oil phase containing little water or surfactant, and a middle phase containing almost all of the surfactant and large volume fractions of both oil and water (even equal volumes of oil and water). The Winsor Type III microemulsion also corresponds to a minimum in interfacial tension between liquid phases at equilibrium. In order to elucidate which aspect of the microemulsion is responsible for flotation of oil, flotation experiments were performed with three different combinations of phases: water and middle phases (w-m); water and oil phases (w-o); and water, middle, and oil phases (w-m-o). Since it was deduced that most oil being recovered when in the Winsor Type III microemulsion region is in the excess oil phase (not the middle phase), the reason why the Winsor Type III microemulsion results in excellent oil removal in flotation operation is probably the ultralow interfacial tensions present, and the formation of the middle phase is incidental.

Key Words::

• Oily wastewater
• Froth floatation
• Microemulsion