Adsorption of ionic surfactants in particulate systems: flotation, stability, and interaction forces

The flotation efficiency of silica particles using the ionic surfactants, s odium dodecylbenzenesulfonate (SDbS) and cetyltrimethylammonium bromide (CP B), have been investigated. Results from adsorption, electrophoretic mobili ty, dispersion stability and direct interaction force measurements are used to develop an understanding of the role of ionic surfactants in particulat e flotation. Adsorption and mobility data indicate that SDbS adsorbs at the silica/solution interface, though without improving the flotation efficien cy. CPB was found to adsorb on the silica particles as a result of electros tatic interaction; initially to neutralize the surface charge and destabili ze the suspension, and at higher surfactant concentrations, to reverse the particle charge and re-stabilize the suspension. Direct force measurements in the presence of CPB confirm that the electrostatic interactions between approaching surfaces are neutralized at low CPB concentrations. Additionall y, evidence for a strong adhesive interaction after contact is seen. At hig her concentrations, the surfaces begin to recharge, and the adhesive intera ction decreases in magnitude. The flotation efficiency was found to correla te well with the measured particle interactions, and to be a function of th e particulate electrophoretic mobility. (C) 1999 Elsevier Science B.V. All rights reserved.