IN-SITU SCANNING-TUNNELING-MICROSCOPY STUDIES OF GALENA SURFACES UNDER FLOTATION-RELATED CONDITIONS

A scanning tunnelling microscope was used to topographically image the surface of galena under flotation-related conditions. Scanning tunnel ling microscopy (STM) images were determined in situ and accurate pH c ontrol 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 spectrosco py (XPS) confirmed a lead-deficient/sulfur-rich surface, formed throug h an incongruent oxidative dissolution mechanism. With time, the surfa ce projections are less evident and cavities appear in the galena surf ace with depths corresponding to the PbS unit cell dimension, the diss olution 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 atta ched colloidal projections; the rate of their formation and extent of surface coverage is controlled by the ethyl xanthate solution concentr ation. These topographical features give insight into ethyl xanthate a dsorption mechanisms and enhance our understanding of the collector-in duced flotation of galena. No adsorbed colloidal particles were observ ed in the in situ STM images of iron(III)-treated galena surfaces, but rather increased surface dissolution. Adsorbed colloidal particles we re, however, observed in the ex situ STM images of iron(III)-treated g alena surfaces.