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

• Simple in situ AFM imaging and force spectroscopy techniques were used.
• Nanoscale domains were observed in water on PbS and HOPG pre-treated in xanthate solutions.
• The species were attributed to gas nanobubbles.
• Long-range attractive forces were found at the pre-treated surfaces upon tip retraction.
• The force curves were explained by the bridging effect of nanobubbles.

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 0.1 mM and 10 mM potassium n-butyl xanthate (KBX) solutions. Submicrometer domains with the height about 3–8 nm 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 100 nm. 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.