The effect of impurities and cleavage characteristics on talc hydrophobicity and polymer adsorption

We have investigated three natural talc samples from different geographical locations (Rhode Island (USA), Delaware (USA), and Flinders Range (Australia)) to determine the effect of impurities and cleavage characteristics on hydrophobicity and polymer adsorption. Bulk (electron microprobe) and surface (X-ray photoelectron spectroscopy) composition measurements have indicated that the Rhode Island and Delaware talcs have the lowest level of Al atoms substituted within the talc structure (0.008%), and detectable at the cleaved basal plane surface (1.5 and 1.7%), and that the Flinders Range talc has the highest level of Al atoms (8.5% bulk; 8.2% surface). Contact angle measurements have highlighted the role of Al atom substitution and step-edge density (as revealed by AFM imaging) on the measured hydrophobicity of the cleaved surfaces, with the Flinders Range talc and the Rhode Island talc having significantly lower contact angles than the Delaware talc (65° and 83°, respectively, versus 90° for the Delaware). In addition, we have characterised the adsorption of two polysaccharide polymers on the three talc samples (CMC and Dextrin TY) using in situ tapping mode AFM. CMC adsorbs with the same morphology on all three talc samples, whereas Dextrin TY presents three different morphologies on the talc surfaces. The potential implications of the observed variation in adsorption behaviour on mineral flotation are discussed.

AFM images of Rhode Island talc (top left) and Delaware talc (bottom left) - insets show advancing water contact angles of the 2 samples. On the right, for each talc sample, is the polymer layer formed when Dextrin TY adsorbs.Figure optionsDownload as PowerPoint slideHighlights
► Natural talc samples from different geographical locations.
► Talc surfaces have been characterized by XPS, AFM, and contact angle measurements.
► Hydrophobicity is altered by impurity ions and cleavage/fracture characteristics.
► Dextrin is responsive to altered surface chemistry; CMC is not.