Natural Galena Research Articles

Grain size effect on the polarity of seebeck coefficient of natural galena

Thermoelectricity studies on semiconductors in the 1980s have established that pellets made by cold pressing from natural galena particles, followed by sintering, show polarity changes with grain size. At grain sizes < 61 μm, galena shows p-type conduction, while in the 104–124 μm rangem, and n-type conduction is observed at different temperatures up to 570 K. A peculiar behaviour is observed in pellets made from 76–104 μm galena particles, which show n-type conduction at room temperature and become p-type on increasing the temperature. The change of polarity is suspected to be due to surface oxidation effects.

Xanthate adsorption at PbS/aqueous interfaces: Comparison of XPS, infrared and electrochemical results

In order to elucidate the reasons for the difference in results of measurements of adsorption of ethylxanthate (EtX −) ion at the surface of lead sulphide and galena, performed using different methods, measurements by X-ray photoelectron spectroscopy and infrared internal reflection spectroscopy were performed on both natural galena and synthetic PbS. The measurements were performed both at spontaneously established potential and under controlled potential conditions. The results obtained using both methods were very similar, showing the formation of submonolayer perpendicularly oriented adsorbed lead ethylxanthate.

STM investigation of galena surfaces in air

The scanning tunnelling microscope has been used to resolve the surface microstructure of natural galena (PbS), cleaved in air. Large atomically flat (001) planes with single and multiple atom layer steps are common. Cubic (100) facets and dislocations are observed. Surfaces exposed to air for several days have also been imaged and results are compared with oxide depth measurements by XPS. We present evidence for discontinuous oxide layers on these air-exposed surfaces, which may have some implications in the flotation chemistry of minerals of this type.

ChemInform Abstract: CATHODIC REACTIONS OF NATURAL GALENA IN PERCHLORIC ACID

AbstractCyclisch voltammetri‐ sche Untersuchung in l M HClO4 führen im Potentialbereich +O.lO bis ‐ l.25V (SCE) zur Identifizierung von nicht weniger als l l elektrochemischen Reaktionen unter Beteiligung von Spezies wie Pb", Pb, PbS, H2S, S", 5%" und S2′.

Cathodic reactions of natural galena in perchloric acid

The electrochemical behaviour of natural galena electrodes in 1 M perchloric acid was studied using linear sweep voltammetry. In the potential domain of + 0.10 to − 1.25 V vs sce, no fewer than 11 electrochemical reactions were identified, involving species such as Pb 2+, Pb, PbS, H 2S, S 0, S 2− 2 and S 2−. The geological implications of the electrochemical behaviour of natural galena are briefly discussed.

Properties of artificially grown single crystals of galena

The growth of high quality single crystals of PbS from natural galena is reported. From ESR spectra the presence in the lattice of isolated Mn2+ ions and an Fe3+ rich phase for the correspondingly doped crystals is inferred.

ChemInform Abstract: ELECTRON SPECTROSCOPIC STUDIES OF GALENA AND ITS OXIDATION BY MICROWAVE‐GENERATED OXYGEN SPECIES AND BY AIR

AbstractDie Reaktion von (lOO)‐Oberflächen von PbS‐Kristallen (natürlicher Galenit) mit reaktiven Sauerstoff‐Spezies aus Mikrowellen‐Entladung in NO wurde durch Röntgen‐ und UV‐Photoelektronen‐Spektroskopie mit Winkelauflösung untersucht und mit Oxidation durch Luft verglichen.

Experimental studies of some opto-electronic properties of thin films of galena

An experimental investigation into some of the optical and electronic properties of electron beam evaporated thin films of natural galena is presented in this study. In particular, we focus our attention on potentialities of thin films of natural galena for making thin film resistors. The dark (i) I–V characteristics and (ii) sheet resistance and electrical conductivity as a function of temperature, as also (iii) sheet-resistance and I–V characteristics as a function of irradiance constitute the study of the electronic properties while (i) refractive index, (ii) optical density and (iii) transmittance account for the optical properties. The temperature dependent electrical conductivity for these films is shown to obey our studies reported earlier for natural galena crystals. The very large resistivity of these films is accounted for by a very large inter-grain distance as is indicated by the scanning electron micrographs. The energy gap-refractive index values are in complete accord with the Moss relation.

Growth of PbS single crystals from natural galena

Crystal Research and TechnologyVolume 17, Issue 9 p. K100-K102 Short Note Growth of PbS single crystals from natural galena Dr. S. V. Nistor, Dr. S. V. Nistor Central Institute of Physics, IFTM, C.P.MG-7 Mǎgurele –- Bucures̨ti, R-76900 RomaniaSearch for more papers by this authorM. I. Toacsan, M. I. Toacsan Central Institute of Physics, IFTM, C.P.MG-7 Mǎgurele –- Bucures̨ti, R-76900 RomaniaSearch for more papers by this author Dr. S. V. Nistor, Dr. S. V. Nistor Central Institute of Physics, IFTM, C.P.MG-7 Mǎgurele –- Bucures̨ti, R-76900 RomaniaSearch for more papers by this authorM. I. Toacsan, M. I. Toacsan Central Institute of Physics, IFTM, C.P.MG-7 Mǎgurele –- Bucures̨ti, R-76900 RomaniaSearch for more papers by this author First published: 1982 https://doi.org/10.1002/crat.2170170921Citations: 2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume17, Issue91982Pages K100-K102 RelatedInformation

Electron spectroscopic studies of galena and its oxidation by microwave-generated oxygen species and by air

The reaction of (100) surfaces of PbS crystals (natural galena) with reactive oxygen species generated by microwave discharge in NO has been compared with aerial oxidation in studies using angle-resolved X-ray and ultraviolet photoelectron spectroscopies. Reaction with the discharge products was much faster, facilitating the study of this process in a controlled environment. The final products of the two processes were similar.Initial attack by atomic oxygen at Pb sites led to the formation of oxide species with the liberation of free sulphur, most of which was lost from the surface. Some, however, remained trapped under an oxidized layer. Sulphate species were also formed, probably by direct attack on PbS. Surfaces of good crystallinity (assessed via their photoelectron diffraction patterns) and chemical purity could be regenerated from oxidized surfaces by 800 eV argon-ion bombardment followed by annealing at ca. 350 °C.Core-level binding energies (Eb) for bulk PbS, PbSO4, PbO, PbCO3, PbS2O3 and 5Pb(OH)2· Pb(NO3)2 were obtained via gold decoration and confirmed by reference to adventitious carbon. The Eb of the surface sulphate and oxide differed from those of the individual bulk lead salts, and they were inferred to coexist in an intimate mixture which probably also contained hydroxide. After the oxidized surfaces were heated to ca. 350 °C only the sulphate and some of the oxide remained.

A kinetic study of nonoxidative dissolution of galena in aqueous acid solution

This paper presents the results obtained through a kinetic study of the nonoxidative dissolution of natural galena in hydrochloric acid and perchloric acid solutions with and without the addition of sodium chloride. Under the experimental conditions employed in this study, the dissolution rates were controlled by a chemical reaction on the surface of the galena sample. The galena dissolution rate is of the first order with respect to hydrochloric ion activity in hydrochloric acid and perchloric acid solutions. The addition of sodium chloride to the acid solutions greatly enhanced the dissolution rate. The effect of sodium chloride has two possible interpretations: First, it may be the result of an increase in hydrogen ion activity. Second, the enhancement of the dissolution rate observable at high sodium chloride concentration may be due to the specific adsorption of chloride ions or the surface complexing of chloride ions on the galena surface.

Auger analysis of the PbS-Si heterojunction

The chemical structure of the solution-grown PbS-Si hetero-junction was studied by Auger Electron Spectroscopy. Auger depth profiles indicate a PbS film of uniform composition. No major contaminants were observed in the bulk of the PbS film. At the PbS-Si interface the only impurity observed was an oxygen peak, corresponding to approximately 1% atomic concentration. Heating the growth solution enhances the chemical reaction and deposition rates without altering the profiles of the elements at the interface. Similar oxygen peaks were detected at the Au-PbS interface and at the interface between consecutive PbS films. The interface oxygen concentration in the PbS-Si (100) structure is roughly twice that present in the PbS-Si (111) structure. Heat treatment in air increased the interface and surface oxygen concentration by a factor of 2 to 5. The same treatment in N2} ambient had only a slight effect on the surface oxygen concentration but enhanced the interface oxygen concentration. The oxygen at the Au-PbS interface showed similar sensitivity to heat treatment. Oxygen content at the interface of HJs formed on unpolished Si was double that in HJs formed on polished Si. The relative intensity of the S to Pb peaks in the bulk of the PbS film compares closely with that measured on the cleaved surface of natural single crystal galena. The Pb: S peak ratio was roughly constant throughout the PbS film and at the PbS-Si interface. Fe and Cl contaminants were observed at the surface of the PbS film, along with significant changes in the Pb:S ratio. The simultaneous detection of Pb, S and Si near the interface is attributed to the presence of surface irregularity caused by a secondary PbS macrostructure consisting of isolated chain-like clusters.

Magnetic susceptibility of lead sulphide

Magnetic susceptibility measurements were carried out on lead sulphide in the form of natural galena crystals, and in the form of crushed powder. The experimental molecular diamagnetic susceptibility value was found to be 93·27×10−6 (in e.m.u./gm.mol.) for the single crystal and 81·84×10−6 for the powdered material. Calculations based on a modified Slater-Angus method showed that the type of bonding is mainly covalent with a partial ionic character.

Flotation related ESCA studies on PbS surfaces

The oxidation of galena is known to play an important role in the beneficiation of lead sulfide by xanthate flotation. We have used electron spectroscopy for chemical analysis (ESCA) to characterize the nature of chemical species on PbS surfaces exposed to air and aqueous environments. PbS samples were in the form of thin sublimed films, natural galena crystals, and commercially available powdered material. Based on these photoelectron measurements, it may be concluded that lead sulfate is the major product of oxidation of PbS in air and aqueous environments. The presence of small amounts of elemental sulfur in the early stages of oxidation suggests that the initial oxidation step may differ from the major oxidation process. Galena occurs naturally in a wide range of stoichiometries. Oxidation was initially much slower in lead rich samples. In fact, the induction period exceeds the initial conditioning period in a typical separation plant. ESCA spectra of lead-rich sulfides confirms that the first step is the oxidation of Pb to PbO. Evidence is presented indicating that the interaction between lead sulfate and xanthates may be controlled by the semiconducting properties of the material.

Mixed potentials and local cells in flotation systems

The results obtained in earlier potential measurements at galena electrodes under various experimental conditions and measurements of local potentials on polished mineral plates of natural galena and copper sulphide specimens shown the presence of corrosive micro-cells on the mineral surface. The measured local potentials had a mixed potential character. The results obtained seemed to agree with the following electrochemical scheme of reactions involving xanthate ion (X −) reactions with the freshly ground sulphide mineral in an aerated water suspension. The fast surface reaction of binding of xanthate ions 2X − + H 2 O + 1 2 O 2 + srufac → 2 X-surface + 20 H − can be followed by a slow formation of metal xanthate (MeX) as a bulk product 2 2X−surface + Me 2S → S 0− surface + 2 MeX(bulk) The formation of excess elementary sulphur at the surface (S 0-surface) must be balanced by a slow diffusion of metal ions in the crystal lattice, changing the character and number of lattice defects in the mineral.

Growth of fcc Metals on Lead Sulfide

The growth of evaporated Au and Ag films on air- and vacuum-cleaved natural galena is studied in situ by RHEED, LEED, and with conventional electron microscopy after removal from the PbS substrates. Au was observed to grow with two equivalent (110) orientations. This predominant orientation occurs over the entire substrate temperature range studied (25 °–400 °C). Ag forms with a (111)-one deg orientation at 25 °C; (100)-oriented Ag becomes evident at 100 °C and increases with temperature to nearly perfect epitaxy at 200 °C. The orientation of both Au and Ag is the same on air- and vacuum-cleaved surfaces and is not influenced by electron irradiation.

Natural galena whiskers

Natural galena whiskers have been observed in the hydrothermal polymetal deposit of “Mogilata”, Madan ore district, Bulgaria. Using optical goniometric and X-ray techniques there have been determined [100] and [110] whiskers, as well as different kinked whiskers connected with the change of the growth direction. The average thickness of the well shaped whisker is about 10–15 μm. There have been observed together with them dendritic and needle-like galena crystals. On some whiskers are overgrowing small cubic galena crystals. The conditions of formation of natural galena whiskers are being discussed.

Sulfur isotope fractionation in the Pb-S system

Sulfur isotope fractionation among phases of the Pb-S system was investigated by silica tube experiments. Strong kinetic effects were observed when Pb reacts with S to form PbS. The difference in reaction rates of 32S and 34S gives lead sulfide enriched in the light S-isotope. The most pronounced effect was recorded at the moment when all Pb had reacted. After establishment of phase equilibrium a period of sulfur isotope homogenization follows and an equilibrium fractionation factor of 1.0025 results at 300°C. Isotopic equilibrium at this temperature was reached three orders of magnitude more slowly than was phase equilibrium. The reaction rate of isotope homogenization is strongly dependent on temperature and is for instance 100 times faster at 500°C than at 400°C. Experiments showed that natural galena rapidly exchanges its sulfur with sulfur vapor. Galenas in ore may exchange isotopes with vapors or gases that contain sulfur and lose their initial isotope ratios.

EXPERIMENTAL INVESTIGATION OF CHALCOCITE: ANNEALING AND PLASTIC DEFORMATION AT ELEVATED TEMPERATURES

The recrystallization behavior and deformation of synthetic chalcocite (Cu2S) in the temperature range 400–725 °C was studied microscopically after the compound was annealed in evacuated silica glass capsules and heated under differential pressures in sealed gold capsules. The temperature of recrystallization and grain growth ascribed to the hexagonal cubic inversion, at sulfur vapor pressures much less than 1 atmosphere, was determined at 465 ± 5 °C, with annealing time of [Formula: see text].Experiments involving differential pressures of 8 000 p.s.i. show that chalcocite in the solid state becomes considerably more mobile above 563 ± 10 °C and can readily be injected as a plastic mass to form veins without preservation of deformational textures.Natural bornite and natural galena may also be injected under differential pressure at 640 °C, but some unhealed fractures remain. Flow structure is well-preserved in galena and, under certain conditions, in bornite.Mixtures of bornite and pyrite flowed and recrystallized to chalcopyrite and bornite with exsolved chalcopyrite. No evidence of flowage remained.Chalcopyrite and pyrrhotite are resistant to injection under similar differential pressures and temperatures.

The ternary system Ag 2 S-Bi 2 S 3 -PbS

Phase equilibria in the systems Bi-S, Ag 2 S-PbS, Ag 2 S-Bi 2 S 3 , PbS-Bi 2 S 3 , AgBiS 2 -PbS, and Ag 2 S-Bi 2 S 3 -PbS have been studied by thermal analysis and quenching methods. The high solid solubility of Bi and Ag in the synthetic galena-type structures is correlated with the common occurrence of these elements in natural galena.