X-ray Photoelectron Spectroscopy in Mineral Processing Studies

Abstract

Surface phenomena play the crucial role in the behavior of sulfide minerals in mineral processing of base and precious metal ores, including flotation, leaching, and environmental concerns. X-ray photoelectron spectroscopy (XPS) is the main experimental technique for surface characterization at present. However, there exist a number of problems related with complex composition of natural mineral systems, and instability of surface species and mineral/aqueous phase interfaces in the spectrometer vacuum. This overview describes contemporary XPS methods in terms of categorization and quantitative analysis of oxidation products, adsorbates and non-stoichiometric layers of sulfide phases, depth and lateral spatial resolution for minerals and ores under conditions related to mineral processing and hydrometallurgy. Specific practices allowing to preserve volatile species, e.g., elemental sulfur, polysulfide anions and flotation collectors, as well as solid/liquid interfaces are surveyed; in particular, the prospects of ambient pressure XPS and cryo-XPS of fast-frozen wet mineral pastes are discussed. It is also emphasized that further insights into the surface characteristics of individual minerals in technological slurries need new protocols of sample preparation in conjunction with high spatial resolution photoelectron spectroscopy that is still unavailable or unutilized in practice.

Advanced XPS characterization: XPS-based multi-technique analyses for comprehensive understanding of functional materials

“…Similar studies have been carried out on sulfur rich systems such as pyrites and sphalerite, which until recently could not be accurately characterised in a UHV system due to the loss of sulfur species in vacuum. 146,147 Ejtemaei et al 148 combined cryo-XPS and depth profiling to study the activation of metal sulfides through the presence of Cu. Polished mineral samples were submerged in a copper sulfate solution for 10 minutes before being precooled to below À160 1C and maintained at that temperature for analysis by XPS.…”

Reaction surfaces and interfaces of metal sulfides: cryo-XPS meets HAXPES and DFT

“…X-ray absorption spectroscopy (XANES) and some other techniques with probing depths larger than that of conventional XPS have revealed that the non-stoichiometric regions can be essentially, up to dozens and hundreds of nm thick. 25–27 We recently established, by applying synchrotron-based high energy photoemission spectroscopy (HAXPES) together with XANES and DFT+ U calculations, that the metal-deficient sulfide regions formed for the iron sulfides FeS 2 and Fe 9 S 10 (ref. 29) and chalcopyrite, CuFeS 2 , 30 in air or aqueous solutions are stratified into at least three layers (Fig.…”

“…18 and references therein). Metal suldes undergo signicant corrosion upon contact with the atmosphere and aqueous media, which has been studied using XPS methods [12][13][14][15][17][18][19][20][21][22][23][24][25][26][27] but is still far from being completely understood. An important peculiarity of metal sulde reactivity is the preferential release of metal cations into aqueous solution or metal (hydr)oxide or/and another phase, leaving the surface and under-surface layer depleted in metal and enriched in sulfur.…”

“…These phenomena are detectable mainly due to S-S bonding and the formation of di-and polysulde anions. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The nature of the metal-decient structures, which are disordered, non-equilibrium and fairly thick in many cases, and the mechanisms behind their formation and decomposition yielding elemental sulfur as the main S-bearing product, remains poorly understood.…”

“…X-ray absorption spectroscopy (XANES) and some other techniques with probing depths larger than that of conventional XPS have revealed that the nonstoichiometric regions can be essentially, up to dozens and hundreds of nm thick. [25][26][27] We recently established, by applying synchrotron-based high energy Fig. 1 Scheme illustrating a stratified structure of the reaction interfaces at metal sulfides and arbitrary probing depths for their analysis with HAXPES and cryo-XPS.…”