Influence of sodium dodecyl sulphate and Dowfroth frothers on froth stability

Surfactants significantly influence froth stability. Detailed theoretical analysis of this influence is deficient at present. This paper presents an experimental investigation into the influence of surfactants on froth stability measured by the foam lifetime. The surfactants studied include sodium dodecyl sulphate (SDS) and the Dowfroth frothers. The foaming experiments were carried out in a laboratory flotation column by blowing air through a sparger. The physical properties of the foaming systems versus the surfactant concentration were experimentally determined for the surface tension, bubble size, and interfacial viscosity. The pendant drop method was used for surface tension measurement for various concentrations of SDS and Dowfroth frothers. The bubble size was determined using a photography technique. The interfacial viscosity was determined with a deep-channel interfacial viscometer. The obtained physical parameters of foams were not able to describe the dependence of the foam lifetime on the surfactant concentration. As the interfacial shear viscosity, which significantly influences the liquid drainage in foam, is not directly correlated with the foam lifetime it is possible that the froth stability is to a great extent controlled by the rupture of the intervening liquid films residing between bubbles.