Small Amount Of Gold Research Articles

Mineralogy and mineral chemistry of Bi-Te minerals: Constraints on mineralization process of the Dulanggou gold deposit, Dadu River Metallogenic Belt, China

There is a widely recognized association of bismuth (Bi)-tellurium (Te) minerals with gold in many hydrothermal gold deposits. However, the specific process for gold enrichment related to Bi-Te minerals remains enigmatic. The Dulanggou gold deposit, located on the southeastern margin of the Songpan-Garzê orogenic belt, China, provides an opportunity to research this process. Gold in the deposit is mainly associated with coarse-grained Bi-Te minerals and bismuth-rich polyphase metal droplets. Three mineralization stages are identified in the deposit. In Stage 1, a small amount of gold was deposited within dominate pyrrhotite. In Stage 2, a large amount of visible gold grains were precipitated with coarse-grained Bi-Te minerals. The various Bi-Te phases are mainly tsumoite, pilsenite, unnamed minerals (Bi3Te2, Bi2Te), joséite-B and trace hedleyite, which have a common characteristics of 2 ≥ Bi/Te > 1. In stage 3, around the Stage 2 large Bi-Te phase patches, bismuth-rich polyphase metal droplets pervasively occurred with Bi/Te ≥ 2. Other Bi-Te minerals in Stage 3 include hedleyite, unnamed minerals (Bi3Te, Bi8Te3, Bi5Te), joséite-B, and joséite-A, all intergrowth with gold and maldonite in the metal droplets. Mineral chemistry and phase diagrams of the Bi-Te mineral assemblages indicate that the mineralization temperatures at Stages 2 and 3 are > 325 ℃ and around 235 ℃ respectively, and the fTe2 and fS2 gradually decrease from Stage 2 to Stage 3. Importantly, a large amount of native gold was deposited with native Bi during Stage 3 and Bi contents in Bi-Te minerals increase with gold fineness from 799 ∼ 876 at Stage 2 to 833 ∼ 939 at Stage 3. These indicate that the metal droplets could be Bi-rich melts which were separated from Bi-Te phase patches and scavenged gold from earlier mineral assemblages to enhance gold enrichment.

Ultra-Low Loading of Gold on Nickel Foam for Nitrogen Electrochemistry

Ammonia (NH3) is widely used in various fields, and it is also considered a promising carbon free energy carrier, due to its high hydrogen content. The nitrogen reduction reaction (NRR), which converts nitrogen into ammonia by using protons from water as the hydrogen source, is receiving a lot of attention, since effective process optimization would make it possible to overcome the Haber–Bosch method. In this study, we used a solution-based approach to obtain functionalized porous Ni foam substrates with a small amount of gold (<0.1 mg cm−1). We investigated several deposition conditions and obtained different morphologies. The electrochemical performance of various catalysts on the hydrogen evolution reaction (HER) and NRR has been characterized. The ammonia production yield was determined by chronoamperometry experiments at several potentials, and the results showed a maximum ammonia yield rate of 20 µg h−1 mgcat−1 and a Faradaic efficiency of 5.22%. This study demonstrates the potential of gold-based catalysts for sustainable ammonia production and highlights the importance of optimizing deposition conditions to improve the selectivity toward HER.

Gold Nanoparticles Enhance Radiation Therapy at Low Concentrations, and Remain in Tumors for Days.

Gold nanoparticles are a potential method for enhancing radiation therapy, causing extra damage to tumors when irradiated through the Auger effect. One of the major obstacles to using gold nanoparticles in human trials is the relatively large amount of gold required. This paper details an experiment where a relatively small amount of gold (200 μg) was used to significantly reduce tumor volume in mice, as well as the results of an inter-tissue biodistribution experiment. Using a longitudinal analysis, tumor size as a function of time was found to be significantly reduced when mice were given 200 μg of gold nanoparticles and 20 Gray of radiation, compared to radiation alone. 200 μg in a 20-gram mouse would be mass equivalent to 750 mg of gold in a 75 kg person. Biodistribution measurements demonstrated that gold nanoparticles stayed in the tumor for at least one week after injection when targeted to tumors using pH-Low Insertion Peptide and intratumoral injections. These results show gold nanoparticles to be effective at one of the smallest amounts of gold ever attempted in a mouse, and showed that tumor targeting has the potential to keep gold nanoparticles available in tumors long enough to be beneficial to fractionated radiation treatments (a key component of radiation therapy in the clinic).

Comparative Leaching Study on Conichalcite and Chalcopyrite Under Different Leaching Systems

Copper leaching from low-grade copper ore samples obtained from two active mines in the US, named conichalcite (sample A) and chalcopyrite (sample B), were studied under different leaching conditions using sulfuric acid and methane sulfonic acid (MSA). The conichalcite, sample A, is calcium-copper arsenite hydroxide [CaCu(AsO4)(OH)] with small amount of gold and other metals. The copper grade is 0.41% with 0.48% arsenic and 2.04% sulfur. The chalcopyrite, sample B, was the main mineral with 0.60% copper grade with 0.73% sulfur and 0.032% molybdenum. Leaching systems utilized two oxidants (ferric ion and hydrogen peroxide) to investigate the kinetics of copper extractions. All leaching tests were performed by bottle roll leaching tests with 6.25% pulp density for 24 hours. Results showed that the leaching kinetics were relatively fast for oxidized sample A. Overall copper recovery was slightly affected by the oxidants and higher than 60% copper extraction was observed. Screen fractioned materials and the leached residue analysis showed that the copper grade in the residues are relatively consistent with 0.14-0.16% copper. This results showed that the ore samples contains readily leachable copper and refractory elements in all size fractions. The refractory portion seems to be relative uniform with wide range of easily leachable copper with 0.30 to 0.54%. Copper extraction from sample B using acids with ferric ion as an oxidant showed around 35% but it significantly increased over 80% using hydrogen peroxide as an oxidant. The copper extraction gradually increased up to 3.0 mol/L hydrogen peroxide content. (Received December 6, 2018; Accepted January 31, 2019)

Smart Golden Leaves Fabricated by Integrating Au Nanoparticles and Cellulose Nanofibers

AbstractA simple processing technology based on spontaneous arrangement of gold nanoparticles (AuNPs) on cellulose nanofibers (CNFs) makes it possible to form a gold leaf with superior mechanical, chemical and electrical characteristics with a small amount of gold (<15 vol.%). The electrical resistivity of the AuNP/CNF hybrid film reached 8.7×10−6 Ω cm at 13 vol.% corresponding to that of a gold plate (2.9×10−6 Ω cm) through a distribution of AuNP inside the film in the form of a band. The AuNPs work not only as linkers between various CNFs in the hybrid structure but also as scaffolds. Self‐assembly allows the formation of leaves on three‐dimensional micrometer‐sized substrates, on which it is impossible to form a uniform flexible metallic layer using conventional techniques such as sputtering, vapor deposition, and electroless plating. The hybrid film holds great promise as a novel gold leaf for a wide range of applications, including coatings, smart papers, electronic skins, and wearable devices owing to its unique combination of superior properties, as well as good productivity, processability, and renewability.

Multi-Mode Elastic Peak Electron Microscopy (MM-EPEM): A new imaging technique with an ultimate in-depth resolution for surface analysis

A non-destructive new imaging technique called Multi-Mode Elastic Peak Electron Microscopy (MM-EPEM), hypersensitive to surface chemistry and with an in-depth resolution of one atomic monolayer was developed. This method consists on performing several MM-EPEM images containing n × n pixels associated to an intensity of the elastic backscattered electrons by varying the incident electron energy in the range 200–2000 eV. This approach allows obtaining depth sampling information of the analyzed structures. Furthermore, MM-EPEM is associated with Monte-Carlo simulations describing the electron pathway in materials in order to obtain very precise quantitative information, for instance the growth mode and the organization of ultra-thin layers (2D materials) or nanoparticules. In this work, we used this new method to study the deposition of very small amount of gold down to one monolayer. Example of 3D reconstruction is also provided.

Chitosan-based hybrid nanocomposite on aluminium for hydrogen production from water

The activity of the hydrogen evolution reaction (HER) has been investigated on a polypyrrole-chitosan composite film decorated with a small amount of gold (Au) nanoparticles coated on an aluminium electrode. The facile aluminium modified with such a hybrid nanocomposite and its performance was investigated for hydrogen evolution for the first time. A simple two-step approach was applied, including the first co-electrodeposition of polypyrrole and chitosan at a constant current electrolysis accompanied by the electrodeposition of Au nanoparticles via cyclic voltammetry. The chitosan (Chi), which is available in abundant quantities as a raw material, was incorporated into polypyrrole (PPy) chains, and it plays a key role in keeping metal nanoparticles highly dispersed and interconnected through the formation of a collaborative hybrid network. The low loading (≈2 wt%) of Au on this composite film favoured the related reaction more with a high cathodic current density and reduced the Tafel slope (−152 mV dec−1) confirming that the reaction proceeded via the Volmer-Heyrovsky mechanism with a rate control step by the Volmer reaction (proton discharge step). In addition, the long-term durability over 8 h achieved this hybrid composite as a promising nano-electrocatalyst for HER.

Catalytic cracking of light diesel over Au/ZSM-5 catalyst for increasing propylene production

The catalytic cracking of light diesel oil (235–337 °C) over gold-modified ZSM-5 was investigated in a small confined fluidized bed at 460 °C and ambient pressure. Different Au/ZSM-5 catalysts were prepared by a modified deposition-precipitation method by changing the preparation procedure and the amount of gold loading and were characterized by X-ray diffraction, N2 adsorption-desorption, temperature-programmed desorption of NH3, transmission electron microscopy and inductively coupled plasma spectrometer. It was found that a small amount of gold had a positive effect on the catalytic cracking of light diesel oil and increased propylene production at a relatively low temperature. The maintenance of the ZSM-5 MFI structure, pore size distribution and the density of weak and strong acid sites of the Au/ZSM-5 catalysts depended on the preparation parameters and the Au loading. Simultaneous enhancement of the micro-activity and propylene production relies on a synergy between the pore size distribution and the relative intensity of the weak and strong acid sites. A significant improvement in the micro-activity index with an increase of 4.5 units and in the propylene selectivity with an increase of 23.2 units was obtained over the Au/ZSM-5 catalyst with an actual Au loading of 0.17 wt%.

Paper-Based Sensor for Electrochemical Detection of Silver Nanoparticle Labels by Galvanic Exchange

Here we report a three-dimensional paper fluidic device configured for electrochemical detection of biomolecules labeled with silver nanoparticles (AgNPs). This new sensor, which we call a NoSlip, represents a major improvement of our previously reported oSlip system. Specifically, detection of AgNPs in the NoSlip is based on galvanic exchange rather than a chemical oxidant (bleach or MnO4– in the oSlip). Galvanic exchange is implemented by depositing a very small amount of gold onto the working electrode. Once the AgNP labels are brought into the proximity of the electrode through the use of magnetic force, a fraction of the Au0 is electrochemically oxidized to Au3+. The Au3+ reacts with the AgNPs to form Ag+ and Au0. The Ag+ is then detected by anodic stripping voltammetry. This new methodology resolves three shortcomings of the oSlip while simultaneously simplifying the basic sensor form factor. First, the NoSlip resolves an oxidant instability issue because of the inherent stability of the Au0 coating...

Self Healing of Creep Damage by Gold Precipitation in Iron Alloys

In the present study we demonstrate that autonomous repair of high‐temperature creep damage can be achieved in iron by alloying with a small amount of gold. Adopting a heat treatment that provides mobile gold within the iron matrix is found to significantly extend the creep lifetime at a temperature of 550 °C. Combined electron‐microscopy techniques demonstrate that the improved creep properties originate from selective precipitation of gold atoms within early‐stage creep cavities, before they can merge into micro‐cracks along the grain boundaries. The selective precipitation of gold atoms at the free surface of a creep cavity results in pore filling, and as a result autonomous repair of the creep damage. Grain boundaries and dislocations act as fast routes for solute gold transport from the matrix to the creep damage. Pore filling preferentially takes place at the highest loaded grain boundaries oriented perpendicular to the applied load. The efficiency to heal creep damage is found to depend strongly on the applied stress. For lower stress levels filling fractions of up to 80% of the open‐volume creep damage have been observed.

Mercury capture by a regenerable sorbent under oxycoal combustion conditions: Effect of SO2 and O2 on capture efficiency

The present study evaluates an Au/C sorbent based on the direct reduction of a gold salt on a carbon coated structured cordierite monolith for mercury capture under oxyfiring conditions. Both mercury retention efficiency and mercury retention capacity were tested in a bench scale plant under different conditions. The influence of gas temperature (50–150°C) and gas composition (CO2, N2, SO2, and O2) on sorbent performance for mercury capture is evaluated and discussed. The amount of mercury captured did not vary significantly with temperature under a CO2 atmosphere. These results were compared with those obtained under N2 atmosphere with no remarkable differences found between them. High retention efficiencies were obtained despite the small amount of gold used. The presence of SO2 and O2 in the flue gas led to mercury oxidation that seemed to be mainly promoted by SO2 under the presence of the Au-sorbent.

Facile fabrication of large-area and uniform silica nanospheres monolayer for efficient surface-enhanced Raman scattering

• Large-area monolayers were fabricated by Langmuir–Blodgett (LB) assembly and sputter coating process. • The diameter of nanospheres and the surface pressures have an effect on ordered arrangement monolayers. • Study of the uniformity enhancement of the Raman signal across the entire surface. A large-area efficient surface enhanced Raman scattering (SERS) substrate was deposited by Langmuir–Blodgett (LB) assembly and followed by sputter coating process. The interparticle distance of silica nanospheres was convenient and readily regulated by controlling the surface pressure. After sputter coating with a small amount of gold, the nanocomposite film was formed. The surfaces of nanostructures were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The applicability of the nanostructures as SERS substrates was investigated by adsorption of crystal violet (CV) molecules. Different SERS effects were observed on deposited gold nanostructure upon large-area silica nanospheres monolayer with diameter of 250, 570 and 800 nm. It was also discussed the nanospheres with diameter of 250 nm for the fabrication of ordered arrangement of monolayers at surface pressures of 10–30 mN/m. These substrates with the close-packed nanospheres and sputtering of gold were found to exhibit high and uniform enhancement of the Raman signal across the entire surface. The averaged surface enhancement factor (ASEF) was calculated and discussed. The fabricated nanocomposite structures could be utilized as low-cost SERS-active substrates for biomedical and analytical chemistry field.

Oxide Catalysts for Rechargeable High‐Capacity Li–O2 Batteries

AbstractNano‐crystalline mixed metal oxides with an expanded pyrochlore structure are synthesized by a chemical precipitation route in alkaline media. The high concentration of surface active sites afforded by their high surface area, intrinsically variable oxidation state and good electron transport lead to promising electrocatalytic properties for oxygen evolution in Li‐O2 cells, yielding rechargeable discharge capacities over 10 000 mAh g−1 and lowering anodic overpotentials significantly. The discharge capacity of the Li‐O2 cell is increased further when a small amount of gold is deposited on the pyrochlore oxide, which serves as a more efficient oxygen reduction catalyst. The amount of catalyst necessary for oxygen evolution performance is reduced to as little as 5 wt% by supporting the highly‐divided pyrochlore oxide crystallites on carbon using in‐situ deposition methods.

Charge referencing issues in XPS of insulators as evidenced in the case of Al‐Si‐N thin films

AbstractAccurate charge referencing in XPS of insulating specimens is a delicate issue. This difficulty is illustrated in the case of Al‐Si‐N composite thin films deposited by reactive magnetron sputtering with variable composition from pure aluminum nitride to pure silicon nitride. The samples were mounted with Au‐coated metallic clamps. Argon sputter cleaning was required to remove a surface native oxide before analysis. For charge referencing implanted argon atoms from the sputter gas and a small amount of gold re‐deposited from the metallic clamps onto the specimen surface during sputter cleaning were evaluated. For the argon atoms, a surprisingly large chemical shift (∼1 eV) and a significant peak broadening (0.6 eV) of the Ar 2p3/2 photoelectron line were found with varying the Si content of the films. This could be related to chemical and structural changes of the Al‐Si‐N films. Hence implanted argon could not be used for charge referencing of Al‐Si‐N samples. In contrast to the implanted argon, the Au 4f7/2 line width of the gold re‐deposited onto the sample surface did not depend on the Si content of Al‐Si‐N films. A constant energy shift (∼1.2 eV) of the Au 4f7/2 line as compared with bulk gold was, however, found, which was related to the size of gold particles formed on the insulating films. Therefore gold could be reliably used to study chemical shifts of sample‐relevant species in Al‐Si‐N films, but the absolute binding energies of Al 2p, Si 2p and N 1s photoelectrons could not be determined. Copyright © 2011 John Wiley & Sons, Ltd.

Hydrodechlorination of CCl4 on Pt–Au/Al2O3 Catalysts

A series of Pt/Al2O3 catalysts were prepared by the impregnation method and were characterized by TEM, XRD, H2 and CO chemisorptions, and investigated in the hydrodechlorination of tetrachloromethane. Three Pt-rich, Pt–Au/Al2O3 catalysts (Pt100, Pt95Au5 and Pt90Au10) showed a similar metal particle size (~2.5–2.7 nm), so observed changes in the catalytic behavior are ascribed to alloying effect, especially because a considerable degree of Pt–Au mixing was achieved in the bimetallic samples. It appeared that by introducing very small amount of gold (10 at.%) to platinum, the catalytic activity is increased. It is argued that the occurrence of this moderate synergistic effect is associated with a decreased tendency of surface chloriding when platinum is alloyed with gold.

RBS investigation of annealed thin gold layers on crystalline germanium

In this work we report firstly on the behaviour of Schottky barrier diodes (SBD's) when subjected to thermal treatment after metallization. To better understand this, a systematic study of the interaction between thin gold films and crystalline germanium substrates was undertaken. Gold metal films having thicknesses of 30 and 100 nm have been prepared by means of thermal evaporation on bulk-grown (111) n-type germanium doped with Sb to a level of 2.5×1015 cm-3. Before metallization the samples were first degreased and then etched in a mixture of H2O2:H2O (1:5) for one minute. Subsequently the samples have been thermally treated in Ar-atmosphere for 10 minutes and at temperatures ranging from 300 to 600°C. Rutherford backscattering spectrometry (RBS) has been performed to estimate the composition of the as-deposited and thermally treated films. It was found, that the composition of the as-deposited film remains unchanged under thermal treatment up to 340°C. Between 340°C and 360°C a gold-rich layer containing a very small amount of germanium is formed. At 361°C this layer suddenly converts to a germanium-rich layer with a small amount of gold. This transition is accompanied by the formation of agglomerates on the surface of the substrate.

Preferential catalytic oxidation of carbon monoxide in presence of hydrogen over bimetallic AuPt supported on zeolite catalysts

A series of AuPt/A zeolite and Pt/A zeolite catalysts prepared by incipient wetness impregnation are investigated for the preferential oxidation (PROX) of carbon monoxide in the presence of hydrogen over the temperature range of 50–310 °C under atmospheric pressure. The results indicate that when a small amount of gold is added to the Pt/A zeolite catalyst, the CO selectivity is improved at low temperatures, and 1% AuPt/A zeolite (at a weight ratio of Au:Pt = 1:2) gives the best performance, which provides a high CO conversion in combination with a high CO selectivity. In more realistic simulated reformate gases containing 10% CO 2 and 10% H 2O, there is not much difference between those in the presence and the absence of CO 2 and H 2O. Transmission electron microscopic and X-ray diffraction studies show that the two metals, Au and Pt, appear to be severely phase separated, which is confirmed by energy dispersive investigations.

Vacuum metal deposition: Visualisation of gold agglomerates using TEM imaging

Vacuum metal deposition (VMD) is a well-established technique that can be used for the development of latent fingermarks on a range of polymer surfaces, including polyethylene (PE) bags exposed to harsh environmental conditions. The technique has also proved to be effective on difficult semi-porous surfaces such as the polymer banknotes in circulation in Australia and in an increasing number of other countries. VMD is a two-stage technique. In the first stage, a small amount of gold is deposited under high vacuum onto the exhibit. This is then followed by the deposition, onto the gold layer, of a much thicker layer of zinc. Normal VMD development is characterised by zinc depositing all over the surface except on the fingermark ridges themselves. A phenomenon of reverse development (zinc on the ridges but not on the surface) has been reported by many authors. Recent studies indicated that this phenomenon might occur on low-density polyethylene (LDPE) when the amount of deposited gold is above an optimum quantity. The results suggested that the size of the gold agglomerates formed on the surface of the polymer plays a critical role. This preliminary study was aimed at visualising, by transmission electron microscopy (TEM), the formation of gold agglomerates on polymer surfaces to gain an appreciation of how the density and size of these agglomerates changes with an increasing amount of evaporated gold.

Characterization of Au–YBa 2Cu 3O 7− y composites by paraconductivity analysis with a short-wavelength cutoff

Bulk composites of Au–YBa 2Cu 3O 7− y are characterized by means of paraconductivity analyses by taking account of a short-wavelength cutoff in the fluctuation spectrum. General expressions for the Aslamazov–Larkin, Maki–Thompson and density of state terms are derived in the momentum-cutoff regime, which are found to describe fairly well observed paraconductivity at overall temperatures investigated. From the theoretical fittings, we estimate several parameters, including the anisotropy parameter, fluctuation amplitude, scattering lifetime, and phase-breaking time. A normalized absorption of AC susceptibility is also investigated. It is found that many of these parameters exhibit rapid variations with a small amount of gold, which may be attributed to enhanced disorder upon doping, while behavior in those parameters at higher doping levels is related to a percolative nature of the composites. We could observe evidence of a pronounced two-dimensional character due perhaps to better crystallinity upon Au doping.

Ammoniacal thiosulfate and sodium cyanide leaching of preg-robbing Goldstrike ore carbonaceous matter

The aim of this work was to establish a relationship between the preg-robbing behavior of Goldstrike ore and the leaching behavior of carbonaceous matter within the ore. Carbonaceous matter obtained by acid demineralization of Goldstrike ore was leached using either an ammoniacal thiosulfate system or a sodium cyanide system. Leaching of the carbonaceous matter was conducted in batch experiments, as well as in columns at various flow rates to compare the mass of gold leached from the carbonaceous matter to its initial gold content. Ammoniacal thiosulfate leaching of carbonaceous matter from autoclaved Goldstrike ore resulted in 90–100% solubilization of the gold initially present regardless of the preg-robbing behavior of the parent ore. For carbonaceous matters from non-autoclaved ores, ammoniacal thiosulfate leaching only solubilized about 40% of the gold initially present in the carbonaceous matter, indicating that approximately 60% of the gold was encapsulated in sulfides. The percentage of gold leached by ammoniacal thiosulfate was found to depend on the initial gold content of the carbonaceous matter since an equivalent, small amount of gold was taken up by all carbonaceous matters examined. Gold leaching was primarily limited by the volume of lixiviant contacting the carbonaceous matter; however, a slight kinetic limitation was observed in ammoniacal thiosulfate leaching at higher flow rates. The percentage of gold leached by sodium cyanide from carbonaceous matter demineralized from autoclaved Goldstrike ore was inversely related to the preg-robbing behavior of the parent ore, suggesting that preg-robbing is controlled by the retention of gold by carbonaceous matter during leaching. Similarities between the naturally occurring carbon and commercial activated carbon suggest that the mechanism of gold retention by the naturally occurring carbon during leaching is the same as gold cyanide complex adsorption by commercial activated carbon. Similar to leaching with ammoniacal thiosulfate, kinetics of sodium cyanide leaching also depended primarily on the volume of lixiviant contacting the carbonaceous matter; however, the kinetics of sodium cyanide leaching were also influenced by the preg-robbing behavior of the ore.