Alexander S. Romanchenko

Ultrafine particles derived from mineral processing: A case study of the Pb-Zn sulfide ore with emphasis on lead-bearing colloids.

Although mining and mineral processing industry is a vast source of heavy metal pollutants, the formation and behavior of micrometer- and nanometer-sized particles and their aqueous colloids entered the environment from the technological media has received insufficient attention to date. Here, the yield and characteristics of ultrafine mineral entities produced by routine grinding of the Pb-Zn sulfide ore (Gorevskoe ore deposit, Russia) were studied using laser diffraction analysis (LDA), dynamic light scattering (DLS) and zeta potential measurement, microscopy, X-ray photoelectron spectroscopy, with most attention given to toxic lead species. It was revealed, in particular, that the fraction of particles less that 1 μm in the ground ore typical reaches 0.4 vol. %. The aquatic particles in supernatants were micrometer size aggregates with increased content of zinc, sulfur, calcium as compared with the bulk ore concentrations. The hydrodynamic diameter of the colloidal species decreased with time, with their zeta potentials remaining about -12 mV. The colloids produced from galena were composed of 20-50 nm PbS nanoparticles associated with lead sulfate and thiosulfate, while the surface oxidation products at precipitated galena were largely lead oxyhydroxides. The size and zeta potential of the lead-bearing colloids decreased with time down to about 100 nm and from -15 mV to -30 mV, respectively. And, conversely, lead sulfide nanoparticles were mobilized before the aggregates during redispersion of the precipitates in fresh portions of water. The potential environmental impact of the metal-bearing colloids, which is due to the large-scale production and relative stability, is discussed.

Specific Characteristics of Noble Metal Nanoparticles on Sulfide Minerals Observed by XPS and STS

Synchrotron radiation X-ray photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy (STM/STS) have been used to characterize gold and silver species spontaneously deposited from HAuCl 4 or AgNO 3 solutions onto sulfide minerals at room temperature. The reacted substrates were studied too. It was found that Au 4f 7/2 binding energies increase up to 1 eV with decrease in the size of Au° nanoparticles in the range 3 to 30 nm. This is attributed to a temporal charging of the particles, lessening kinetic energies of the photoelectrons via interaction with final-state photoholes. STS revealed a positive correlation between the current magnitude and the diameter of Au particles, tentatively explained by Coulomb blockade effects. Silver deposited on the minerals exhibited neither shifts of Ag 5d bands, nor Coulomb blockade in STS. Possible mechanisms behind the suppression of electronic tunneling and its potential role for the charge transfer steps in reactions of gold nanoparticles were considered.

A Transformation of Intermediates of Sulfide Reduction of Gold(III) on the Pyrolytic Graphite

Solid products immobilized from colloids containing intermediates of the reduction of tetrachloroaurate-ions by sodium sulfide on the surface of highly oriented pyrolytic graphite were studied using scanning probe microscopy, cyclic voltammetry and X-ray photoelectron spectroscopy. An evaluation of surface topography and chemical state of both gold and sulfur taking place during colloid’s pre-aging and under electrochemical oxidation in 0.001 M HCl solution were shown.