Confirmation of the heterocoagulation theory of flotation

To model the flotation process, we have used the microscopic method develop ed by Scheludko et al.,(11) to study the stability of an aqueous thin film containing tetradecyltrimethylammonium bromide (C(14)TAB) between an air bu bble and a silica substrate. The experiments were performed at a range of C (14)TAB concentrations and pH values. Spontaneous rupture of the thin aqueo us film was interpreted in terms of the earlier proposed heterocoagulation mechanism and resulted From the preferential adsorption of relatively low s urfactant concentrations at the vapor/solution interface causing a net posi tive charge while the solution/silica interface remained negatively charged . This attractive electrostatic interaction was sufficient to overcome the van der Waals repulsion. At higher amine concentrations, the negative charg e at the solution/silica interface was reversed. Finally, on approaching th e critical micelle concentration (cmc), both interfaces were sufficiently p ositively charged to cause the restabilization of the film by electrostatic repulsion. In addition, in dilute solution, during the three-phase-contact (TC) expansion or dewetting step following film rupture, it was suggested that the movement of TPC across the silica substrate leads to transfer of a mine from the vapor/solution interface to the vapor/silica. This process re sembles a Langmuir-Blodgett deposition process and emphasizes the importanc e of the solution/vapor interface in the dewetting process.