Abstract
A scanning tunnelling microscope was used to topographically image the surface of galena under flotation-related conditions. Scanning tunnelling microscopy (STM) images were determined in situ and accurate pH control was maintained using a custom-made solution cell. Projections (1–2 nm) developed at the surface of galena during the first 15 min of contact with aqueous solutions at pH 3. X-ray photoelectron spectroscopy (XPS) confirmed a lead-deficient/sulfur-rich surface, formed through an incongruent oxidative dissolution mechanism. With time, the surface projections are less evident and cavities appear in the galena surface with depths corresponding to the PbS unit cell dimension, the dissolution mechanism becoming congruent. At neutral pH, in situ STM shows only cavity formation and XPS shows no sulfur-richness, whereas at pH 10 surface oxidation product growth was apparent. These findings are discussed in the context of the collectorless flotation of galena and the mechanisms of oxidative dissolution. In situ STM images of galena surfaces in the presence of ethyl xanthate showed the presence of attached colloidal projections; the rate of their formation and extent of surface coverage is controlled by the ethyl xanthate solution concentration. These topographical features give insight into ethyl xanthate adsorption mechanisms and enhance our understanding of the collector-induced flotation of galena. No adsorbed colloidal particles were observed in the in situ STM images of iron(III)-treated galena surfaces, but rather increased surface dissolution. Adsorbed colloidal particles were, however, observed in the ex situ STM images of iron(III)-treated galena surfaces.
Published Version
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