Inﬂuence of sodium dodecyl sulphate and Dowfroth frothers on froth stability P.A. Harvey, A.V. Nguyen * , G.J. Jameson, G.M. Evans Discipline of Chemical Engineering and Centre for Multiphase Processes, The University of Newcastle, University Drive, Callaghan, New South Wales 2308, Australia Received 19 May 2004; accepted 21 June 2004 Abstract 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 surf- actants 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 concen- tration. 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. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Flotation froths; Flotation frothers; Flotation collectors; Flotation reagents; Froth ﬂotation 1. Introduction Froths, foams, and emulsions are well known to sci- entists as well as the general public in every day life (PrudÕhomme and Khan, 1996; Exerowa and Kruglya- kov, 1997; Weaire and Hutzler, 1999). Some common examples include foams used for washing dishes and clothes, and pouring beer. In addition, many industrial applications involve foams, which can either be desir- able or undesirable depending on the system. In indus- try, foams are immediately related to froth ﬂotation, which is a very important unit operation, in particular in the minerals processing industry (Ross, 1998; Ata et al., 2002). The knowledge of the physicochemical properties of foams, particularly the factors which inﬂu- ence the foam stability, is very important in optimising the operating eﬃciency for a plant or system. Until now many aspects of this problem are not clear. There still does not exist a general theory to describe the foam behaviour (Weaire and Hutzler, 1999). The stability of foam may be inﬂuenced by many factors, but is primar- ily linked to the liquid drainage in the foam and the rupture of the intervening liquid ﬁlms. Stable foams will drain slowly and may persist for hours, whereas foams produced with pure liquids may only have a life- time of milliseconds and can be regarded as unstable foams. Foam is a dispersion of gas bubbles in a relatively smaller volume of liquid with surface-active agents 0892-6875/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2004.06.011 * Corresponding author. Tel.: +61 249 216 189; fax: +61 249 216 920. E-mail address: anh.nguyen@newcastle.edu.au (A.V. Nguyen). This article is also available online at: www.elsevier.com/locate/mineng Minerals Engineering 18 (2005) 311–315