Control of slime coatings by the use of anionic phosphates: A fundamental study

A model system comprising of chemically-dissimilar and oppositely-charged metal oxides has been used to investigate the removal of small particles from surfaces and, particularly, the role of interaction forces in this process. Techniques including reflectometry, rheology, microelectrophoresis, acoustophoresis and atomic force microscopy have been utilised. Silica particles adsorbed onto titania surfaces were removed by the addition of phosphate. The phosphate was shown to adsorb selectively to the titania. Desorption of the silica particles has been attributed to the ability of the phosphate to modify the interaction forces between the metal oxides. Phosphate was found to alter the electrostatic force between silica and titania from attractive to repulsive. It also introduced an additional repulsive force, which has been ascribed to the presence of a steric barrier. In addition, significant reductions in the adhesive and frictional forces acting between silica and titania were observed. The implications of the findings for ‘slimes’ control during the separation of mineral ores are discussed.