Synchrotron PEEM and ToF-SIMS study of oxidized heterogeneous pentlandite, pyrrhotite and chalcopyrite

Flotation Performance and Adsorption Mechanism of a Novel Chelating Collector for Azurite

Thiophosphate compounds have attracted much attention in coordination chemistry, but their deep adsorption mechanism remains underexplored as flotation collectors. The flotation performance and adsorption mechanism of a novel (dibutoxy-thiophosphorylsulfanyl)-acetic acid (CDDP) chelating collector on azurite surfaces were studied by micro-flotation tests, zeta potential measurements, and Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM) analysis. The micro-flotation results indicated that CDDP exhibited superior collecting performances to direct flotation recovery of azurite and floated over 91.44% of azurite at pH 7. For sodium isopentyl xanthate (NaIX) and Benzohydroxamic acid (BHA) collectors, the addition of Na2S still did not show good collection performance. The results of zeta potential, FTIR, XPS and FE-SEM measurements, all confirmed that CDDP showed a better affinity to azurite surfaces than NaIX and BHA. Furthermore, XPS and FE-SEM provided obvious evidence that CDDP could easily react with Cu2+ sites on azurite surfaces. Using the density functional theory (DFT) method, the collection capacity of azurite was CDDP > BHA > NaIX, which exactly matched the micro-flotation results. In addition, this study provided an atomic-scale understanding of the structure–property relationship of CDDP as chelating agents for copper mineral flotation.

X-ray Photoelectron Spectroscopy in Mineral Processing Studies

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.

Energy dispersive spectrometry and first principles studies on the oxidation of pentlandite

Experimental and computational studies were carried out to investigate the oxidation of pentlandite (Fe4.5Ni4.5S8). The oxidation product was first analyzed by energy dispersive spectrometry to reveal the elemental distribution at the cross section. Our experimental study shows that the Fe atoms in pentlandite migrated to the surface and were preferentially oxidized to form a thin layer of Fe2O3, whereas the Ni atoms remained at the center of the grain. Furthermore, density functional theory calculations were performed to investigate the adsorption and diffusion of atomic oxygen as well as the adsorption and dissociation of molecular oxygen on the (001) and (010) surfaces of pentlandite. From the calculated adsorption energies of atomic oxygen at the different sites of the (001) and (010) surfaces, we found that oxidation of the Fe sites was preferable to that of the Ni sites when exposed to an oxidizing atmosphere. For molecular oxygen adsorption on the surfaces of pentlandite, the bridge sites (Fe-Ni and Fe-Fe) were found to be the most favorable adsorption sites. The dissociative adsorption of O2 is thermodynamically more favorable than the molecular adsorption. Calculated dissociation barriers show that the oxidation is feasible during high temperature roasting.

In-situ XRD and EDS method study on the oxidation behaviour of Ni-Cu sulphide ore

The oxidation mechanism of sulfides is the key issue during the sulphide–metallurgy process. In this study, the phase transformation and element migration were clearly demonstrated by in–situ laboratory–based X–ray diffraction (XRD) and energy–dispersive X–ray spectroscopy (EDS), respectively. The reaction sequence and a four–step oxidation mechanism were proposed and identified. The elemental distribution demonstrated that at a low temperature, the Fe atoms diffused outward and the Ni/Cu atoms migrated toward the inner core, whereas the opposite diffusion processes were observed at a higher temperature. Importantly, the unique visual presentation of the oxidation behaviour provided by the combination of in–situ XRD and EDS might be useful for optimising the process parameters to improve the Ni/Cu extraction efficiency during Ni–Cu sulphide metallurgy.

Synchrotron scanning photoemission microscopy of homogeneous and heterogeneous metal sulfide minerals

Scanning photoemission microscopy (SPEM) has been applied to the investigation of homogeneous and heterogeneous metal sulfide mineral surfaces. Three mineral samples were investigated: homogeneous chalcopyrite, heterogeneous chalcopyrite with bornite, and heterogeneous chalcopyrite with pyrite. Sulfur, copper and iron SPEM images, i.e. surface-selective elemental maps with high spatial resolution acquired using the signal from the S 2p and Cu and Fe 3p photoemission peaks, were obtained for the surfaces after exposure to different oxidation conditions (either exposed to air or oxidized in pH 9 solution), in addition to high-resolution photoemission spectra from individual pixel areas of the images. Investigation of the homogeneous chalcopyrite sample allowed for the identification of step edges using the topography SPEM image, and high-resolution S 2p spectra acquired from the different parts of the sample image revealed a similar rate of surface oxidation from solution exposure for both step edge and a nearby terrace site. SPEM was able to successfully distinguish between chalcopyrite and bornite on the heterogeneous sample containing both minerals, based upon sulfur imaging. The high-resolution S 2p spectra acquired from the two regions highlighted the faster air oxidation of the bornite relative to the chalcopyrite. Differentiation between chalcopyrite and pyrite based upon contrast in SPEM images was not successful, owing to either the poor photoionization cross section of the Cu and Fe 3p electrons or issues with rough fracture of the composite surface. In spite of this, high-resolution S 2p spectra from each mineral phase were successfully obtained using a step-scan approach.