Effect of adsorption of butyl xanthate on galena, PbS, and HOPG surfaces as studied by atomic force microscopy and spectroscopy and XPS

Abstract

Atomic force microscopy (AFM) and force spectroscopy techniques have emerged as powerful tools for in situ studies of interactions between solid surfaces, reactants and air bubbles which are of fundamental importance for understanding the mechanisms and increasing the efficiency of froth flotation. Such studies, however, have very rarely involved real mineral sulfides and flotation collectors to date. Here, the tapping mode AFM, force spectroscopy with conventional silicon cantilevers, and ex situ XPS were used to characterize surfaces of single crystals of natural PbS and, for comparison, highly oriented pyrolytic graphite (HOPG) in pure water before and after their pre-treatment in 0.1mM and 10mM potassium n-butyl xanthate (KBX) solutions. Submicrometer domains with the height about 3–8nm were observed on the PbS surfaces with chemisorbed xanthate. The force–distance curves measured upon retraction of the tip from PbS and HOPG surfaces pre-treated in KBX solutions revealed the attraction forces, often with two sudden pull-off steps, acting at the separation distances longer than 100nm. We attributed the soft domains to gas nanobubbles; the long-range attraction was explained in terms of the capillary forces induced by a vapor cavity arising between the tip and the hydrophobic substrates upon their disconnection, and coalescence of the cavity with the pre-existing nanobubbles. The role of these phenomena in flotation is briefly discussed.