Morphology and dissolution processes of metal sulfide minerals observed with the electrochemical scanning tunneling microscope

Abstract

We report the use of a novel electrochemical scanning tunneling microscope (STM) in the study of surface topography and dissolution phenomena on naturally occurring metal sulfide minerals. Real time dissolution studies of galena in sulfate solution showed that at pH=2.7, the step edges are oriented with outward normal vectors parallel to 〈110〉. Atomic resolution images obtained in acidic perchlorate solution showed single vacancy sites, demonstrating the ability of the STM to resolve individual atomic species under electrolyte solutions. A novel syringe pump system was used to directly determine the effect of chloride ions on the surface structure at the onset of the adsorption process. STM images show the chloride ion produces small pits in the outermost layer of the surface. These observations underscore the importance of anionic species and their effects on the surface topography and dissolution rates. Initial investigations on pyrite and covellite suggest a potentially wide application to metal sulfide minerals, while more detailed investigations on galena illustrate some important aspects of the mineral/electrolyte interface.