| Description |
Talc is both an important industrial mineral product recovered by flotation, and also in other cases, a gangue mineral of concern in the flotation of certain sulfide ores, such as the PGM ores in South Africa and in the United States. The talc face surface is naturally hydrophobic with a contact angle of nearly 80º, which accounts for its flotation recovery in one case, and its contamination of sulfide mineral concentrates in other instances. High-quality talc structures were investigated using surface analysis techniques including contact angle analysis, high-speed video bubble attachment measurements, atomic force microscopy, molecular dynamics simulation (MDS), microflotation, and film thickness measurements by Synchronized Triwavelength Reflection Interferometry Microscopy (STRIM). The presence of aluminum, which replaces silicon in the silica tetrahedral layer of the talc structure, results in a charge imbalance on the face surface because Si+4 is replaced by Al+3. Experimental sessile drop contact angles were found to decrease with increased aluminum content, decreasing from about 80º for no substitution (talc) to 0º for extensive substitution (phlogopite). For a hydrophilic phlogopite surface, the water film is stable with an equilibrium film thickness (he) of 25 nm. However, for a hydrophobic talc surface, air bubbles readily attach to the talc face surface with a critical rupture thickness (hc) of 56 nm. Further, the wetting characteristics and water film stability at the talc surface have iv been studied, regarding the effect of polysaccharides such as guar gum, starch, and dextrin. In the presence of polysaccharides, there was a significant increase in bubble attachment time at the talc surface but only a slight change in contact angle, which suggests that polysaccharide depression of talc was due to the slow rate of bubble attachment and not due to a change in contact angle. The adsorption state of the polysaccharides can be described as being due to a hydrophobic interaction between the nonpolar mineral surface and the hydrophobic portion of the polysaccharide molecule. Interestingly, it was found that the critical and equilibrium film thickness values do not change significantly with the polysaccharide type or concentration. |
