Adsorptive Bubble Separation for Oil Removal

Abstract

This present work emphasized on the current knowledge regarding (i) feasibility of multi–stage forth flotation operation for oil removal, and (ii) comprehension of dynamic surface tensions of surfactant solutions in relation to foam characteristics. A multi–stage forth flotation efficiency depends on the enhancement of interfacial adsorption and the number of bubble caps and tray. The operational parameters including foam height, air flow rate and feed flow rate were controlled to obtain the optimum process performance. Under the optimum conditions—a number of trays of 4, a foam height of 60 cm, an air flow rate of 40 L/min, a feed flow rate of 60 mL/min, a surfactant concentration of 0.3% (w/v), and an NaCl concentration of 1.5% (w/v)—the enrichment ratio and the removal of motor oil could reach as high as 16.3 and 97.9%, respectively. Furthermore, the effects of surfactant structure on the equilibrium and dynamic surface tension were investigated and discussed to correlate with foam properties. For all studied surfactant solutions, the equilibrium experimental data were well fitted with the Langmuir adsorption isotherm, while the dynamic surface tension data were used to calculate diffusivity values of all studied surfactants by using Word-Tordai equation. It was found that a surfactant having longer alkyl group has a lower diffusivity value, whereas a surfactant having larger head group size has a higher diffusivity. The adsorption process of surfactant onto the air/water interface of generated bubbles was controlled by the diffusion.