Low Gold Concentrations Research Articles

3D printed microstructured Au/TiO2 catalyst for hydrogen photoproduction

We successfully 3D printed Au/TiO2 monoliths for photogenerating hydrogen from water/ethanol gaseous mixtures under dynamic conditions. Monolith designs were printed by additive superposition of microfilaments of titania-based pastes. Factors influencing the efficiency of the photocatalytic reactions, including impregnation of gold nanoparticles (Au NPs), calcination temperature, diameter of microfilaments and monolith design, are investigated. The use of preformed Au NPs assured a constant Au particle size (ca. 4nm) for all samples, which allowed to a precise assessment of the effect of the design of 3D-printed titania monoliths on photocatalytic activity. The impregnation of preformed Au NPs before or after the 3D printing process has a strong influence on the photocatalytic efficiency. The pre-impregnated monoliths have a homogeneous Au NPs distribution throughout the microfilaments, whereas the post-impregnated ones present an asymmetric distribution of Au NPs, observing a high gold concentration at the surface and lower gold concentrations in the inner regions of the printed microfilaments. The gold concentration of the Au-loading suspension was reduced ca. 10 times in post-impregnated samples to ensure a similar amount of Au NPs anchored at the surface of the microfilaments, according to an XPS analysis of the pre- and post-impregnated samples. Although the photocatalytic performance of the pre-impregnated monoliths was improved when samples were calcined at 400°C, due to a stronger contact between the Au NPs and the microfilament supports, the post-impregnated samples with 100 times lower Au concentration (0.005wt.%) exhibited enhanced catalytic performances. Under similar geometric open section and photon absorption conditions, the photoproduction of hydrogen on a weight (or volume) basis increased strongly as the diameter of the filaments decreased, which is explained by a progressive increase of the surface-to-weight and surface-to-volume ratios. The best photoactivity was obtained with a post-impregnated titania monolith 3D printed with microfilaments with 200μm in diameter, which yielded 0.24molH2min−1gAu−1.

Biogeochemical gold cycling selects metal-resistant bacteria that promote gold particle transformation

Bacteria catalyze the dissolution and re-precipitation of gold, thereby driving the biogeochemical cycle of gold. Dissolution of gold/silver and re-precipitation of gold transforms gold particles by increasing gold purity. While soluble gold complexes are highly cytotoxic, little is known about how gold cycling affects bacterial communities residing on gold particles. Micro-analysis of gold particles obtained from Western Australia revealed porous textures and aggregates of pure gold nanoparticles, attributable to gold dissolution and re-precipitation, respectively. By interpreting structure and chemistry of particles, the kinetics of gold biogeochemical cycling at the site was estimated to be 1.60 × 10-9 M year-1. Bacterial communities residing on particles were composed of Proteobacteria (42.5%), Bacteroidetes (20.1%), Acidobacteria (19.1%), Firmicutes (8.2%), Actinobacteria (3.7%) and Verrucomicrobia (3.6%). A bacterial enrichment culture obtained from particles contained a similar composition. Exposure of enrichments to increasing concentrations of soluble gold decreased community diversity and selected for metal-resistant bacteria. Lower gold concentrations, which corresponded well with the concentration from the kinetic rate, provided a selective pressure for the selection of metal-resistant organisms while retaining the overall diversity. In conclusion, biogeochemical gold cycling directly influences bacterial communities on gold particles, thereby contributing to a continuum of particle transformation.

Electrospun Bacteria‐Gold Nanoparticle/Polymer Composite Mesofiber Nonwovens for Catalytic Application

AbstractPolymer composite nonwovens with living Micrococcus luteus (ML), a very common gram‐positive bacterium present on human skin, are prepared by electrospinning followed by coating via the chemical vapor deposition (CVD) of poly(p‐xylylene) (PPX). The encapsulated living ML convert Au(III) ions to gold nanoparticles (AuNPs) when the composite nonwovens are dipped in an aqueous chloroauric acid solution. As a result of this process, AuNPs are formed on the ML. The ML‐immobilized AuNPs can be used for catalytic reactions with acetone as the solvent at a very low gold concentration. Despite the presence of acetone, ML survive the catalytic reaction. Interestingly, the catalytic reactions are possible only when the ML in the nonwovens are alive. In contrast, nonwovens with dead ML do not show any significant catalytic activity.

Process mineralogy of refractory gold ore in thiosulfate solutions

A mineralogical characterization was carried out in samples of refractory gold ore with 59 g/ton, according to fire assays, which were taken from a previous leaching process with ammonium thiosulfate. The potential window used to evaluate the cathodic and anodic processes was chosen knowing that gold and copper reduction, and thiosulfate and Cu(I) species oxidation occurs in it. The leaching process consisted of a pretreatment of the mineral (in ammonium hydroxide and copper sulfate during 12 h with and without air bubbling) followed by leaching (in ammonium thiosulfate solution and EDTA at a pH ∼ 10 during 24 h with mechanical stirring at a rate of 250 rpm) which rendered a gold-release of 81.57%. When oxidants and stabilizers like Cu(II), NH3 and EDTA are present in thiosulfate based leaching solutions, the chemistry turns complex, and the partial reduction of copper, and redissolution of gold may occur. This fact and the low gold concentration make the electrowinning process especially difficult. Characterization techniques such as polarized light microscopy, X-Ray Diffraction, Rietveld quantification, and Automated Digital Imaging System, were chosen to track the process mineralogy of the sample, and the results prior to the leaching revealed association, size, and shape of each mineral occurrence; it was found that the mineral composition was pyrite crystals, exhibiting subhedral and inequigranular morphology (75%); galena crystals (10%); sphalerite (1.8%); chalcopyrite and arsenopyrite crystals (<3%); and free gold (<1%). The rest of the sample was comprised of aluminosilicate phases such as quartz and muscovite. After the leaching process, the main feature found was some accumulation of individual pyrite grains with corrosion grooves, and decrease in the particle size; on the other hand, the dissolution of the accompanying phases, with respect to the galvanic interactions, evidenced the next sequence of dissolution: I/E = pyrite > galena > M3 > sphalerite. Rietveld quantification suggested changes in the ratio of the main phases: pyrite decreased from 75.6% up to 65.7%; quartz increased from 21.1% up to 31.3%; galena decreased from 10.4% up to 7.6%; sphalerite decreased from 1.8% up to 1.1%. It is worth saying that the presence of precipitated amorphous phases was not observed.

Application of geostatistical analyst methods in discovering concealed gold and pathfinder elements as geochemical anomalies related to ore mineralisation

Abstract The study area in the West Junggar Basin is known to be rich in hydrothermal gold deposits and occurrences, even though there has been minimum exploration in the area. It is here hypothesised that this area could host more gold deposits if mineral exploration methods were to be reinforced. This research is aimed at identifying geochemical anomalies of Au, and determining possible factors and conditions which facilitate the formation of anomalies by referring to As and Hg as gold pathfinders. Geostatistical analyst techniques have been applied to 9,852 stream sediments and bedrock data collected on a total surface of 1,280 km2 of West Junggar, Xinjiang (northwest China). The kriging interpolation and quantile-quantile plot methods, combined with statistical methods, successfully identified both Au and its pathfinders’ anomalies. In the present study, median was considered as background values (10.2 ppm for As, 9.13 ppb for Hg and 2.5 ppb for Au), whereas the 95th percentile were threshold values (28.03 ppm for As, 16.71 ppb for Hg and 8.2 ppb for Au) and values greater than thresholds are geochemical anomalies. Moreover, the high concentrations of these three discovered elements are caused primarily by hydrothermal ore mineralisation and are found to be controlled mainly by the Hatu and Sartohay faults of a northeast-southwesterly direction as well as their related secondary faults of variable orientation, which facilitate the easy flow of hydrothermal fluids towards the surface resulting in the formation of geochemical anomalies. Most of anomalies concentration of Au are found near the mining sites, which indicates that the formation of new Au anomalies is influenced by current or previous mining sites through geological or weathering processes. In addition, the low concentration of gold and its pathfinders found far from active gold mine or faults indicates that those anomalies are formed due to primary dispersion of hosting rock.

Gold in Plant: A Biogeochemical Approach in Detecting Gold Anomalies Undercover- A Case Study at Pelangio Gold Project at Mamfo Area of Brong Ahafo, Ghana

Many plants have the ability to take up gold from soils and accumulate them in their tissues. Their concentrations and distributions reflect the nearby gold deposits masked by complex regolith. The 50 vegetation samples collected at Pelangio Tepa concession recorded low and subtle gold (Au) concentrations of 0.2 to 10.4 ppb at Pokukrom target, 0.3 to 28.3 ppb at Nfante East target and 0.1 to 1.7 ppb at Subriso target. Each target area had different concentration populations enough to distinguish the anomalous areas from the background contrary to Au-geochemical expressions derived from the gold in soils. So many uncertainties were placed on the soil-Au-geochemistry because the defined anomalies were not strong and generally appear patchy, weak and subtle that led to the assumption of no associated bedrock mineralisation. The gold in plant samples confirmed the Pokukrom anomaly that has been drilled and known to relate to underlying mineralisation. Much better and robust anomaly was defined by the biogeochemical Au data in plants sampled and analysed for Au at Nfante East target and isolated high patchy anomalies were identified at Subriso area. The case study at Pelangio Mamfo project reveals and recommends the significant application of biogeochemistry in mineral exploration particularly in the field of gold prospecting at the regional exploration stage and endorses it as being practically feasible in regolith-dominated terrains where regolith-landform modifications may impact on the true geochemistry in anomaly delineation. Keywords: Biogeochemistry, Regolith-Dominated-Terrain, Plant, Gold, Pelangio

The source and evolution of ore fluids in the Heiniuwa gold deposit, Baoshan block, Sanjiang region: Constraints from sulfide trace element, fluid inclusion and stable isotope studies

The Heiniuwa gold deposit is located in the northwestern segment of the Longyang Au–Fe–Pb–Zn polymetallic ore cluster in the northern Baoshan block, Sanjiang region, SW China. This ore cluster is characterized by skarn Fe–Pb–Zn mineralization (∼120 Ma) in the central part and Au mineralization in the distal part. The genesis of the Heiniuwa deposit and its relationship with the skarn deposits remain unclear. All orebodies in Heiniuwa are hosted in the Upper Cambrian calcareous slate and siltstone of the Hetaoping Formation, and are controlled by the NS-striking faults. Three main paragenetic stages of mineralization have been recognized based on petrographic observation including, from early to late, a pyrite – arsenopyrite – quartz stage (stage I), a pyrite – pyrrhotite – sphalerite – galena – chalcopyrite – quartz – calcite stage (stage II), and a quartz – calcite – chlorite stage (stage III). Three types of fluid inclusions were identified in the quartz and calcite from the stage I to III in Heiniuwa, including liquid-rich (L-type), vapor-rich (V-type) and solid-bearing (S-type) inclusions. The S-type inclusions only occur in stage I quartz. The fluid inclusions from stage I homogenized at 185–326 °C (concentrating at 220–250 °C), with eutectic temperatures of −48.5 °C to −36.7 °C, final ice-melting temperatures of −11.34 °C to −0.8 °C and salinities ranging from 1.4 to 17.2 wt% NaCl equiv. The inclusions from stage II homogenized at 155–281 °C (concentrating at 190–230 °C), with eutectic temperatures of −51.6 °C to −37.5 °C, final ice-melting temperatures of −10.6 °C to −0.5 °C and corresponding salinities ranging from 0.9 to 14.6 wt% NaCl equiv. The inclusions from stage III homogenized at 116–202 °C (concentrating at 150–170 °C), with eutectic temperature of −45.5 °C to −37.5 °C, final ice-melting temperatures of −4.3 °C to −0.6 °C and salinities ranging from 1.3 to 7.2 wt% NaCl equiv. The microthermometry reveals that the ore-forming fluid of Heiniuwa gold deposit is a typical H2O–NaCl–CaCl2 fluid system. The carbon and oxygen isotopes of calcite show that δ13CPDB and δ18OSMOW values respectively range from −13.4‰ to −6.8‰ and 9.1‰ to 9.6‰ in stage II, and from −8.1‰ to −1.5‰ and 6.4‰ to 8.2‰ in stage III. The bulk marble and calcareous slate samples have δ13CPDB and δ18OSMOW values from −3.0‰ to −0.7‰ and 7.8‰ to 11.9‰, respectively. This suggests that the carbon in the ore-forming fluid was probably from a magmatic source. The δ18Ofluid values of ore-forming fluid vary from 1.6‰ to 2.5‰ in stage I, from −6.2‰ to 0.6‰ in stage II and from −10.8‰ to −2.5‰ in stage III. This indicates that the fluid in stage I is dominantly magmatic, whereas the fluid in stage III is close to meteoric water. The decrease of Na/Ca ratios of ore-forming fluid from stage I to stage III suggests that the interaction with carbonate wallrock is significant during fluid evolution. The sulfide δ34S values range from −5.7‰ to +4.6‰ (mean = +0.3‰, n = 19), agreeing with the explanation based on C–O isotopes and fluid inclusions that the ore-forming fluids are mainly magmatic in origin. In addition, LA-ICP-MS analysis of sulfides also supports this opinion. The stage I pyrite has Cu/Ni ratios greater than 1, and a high concentration of gold; in contrast, the stage II pyrrhotite samples display a very low concentration of gold. This suggests that gold mineralization mainly occurred in stage I. The mixing between magmatic hydrothermal fluid and meteoric water is considered to be a key factor controlling the gold deposition.

Cancer cells biomineralize ionic gold into nanoparticles-microplates via secreting defense proteins with specific gold-binding peptides

Cancer cells have the capacity to synthesize nanoparticles (NPs). The detailed mechanism of this process is not very well documented. We report the mechanism of biomineralization of aqueous gold chloride into NPs and microplates in the breast-cancer cell line MCF7. Spherical gold NPs are synthesized in these cells in the presence of serum in the culture media by the reduction of HAuCl4. In the absence of serum, the cells exhibit gold microplate formation through seed-mediate growth albeit slower reduction. The structural characteristics of the two types of NPs under different media conditions were confirmed using scanning electron microscopy (SEM); crystallinity and metallic properties were assessed with transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). Gold-reducing proteins, related to cell stress initiate the biomineralization of HAuCl4 in cells (under serum free conditions) as confirmed by infrared (IR) spectroscopy. MCF7 cells undergo irreversible replicative senescence when exposed to a high concentration of ionic gold and conversely remain in a dormant reversible quiescent state when exposed to a low gold concentration. The latter cellular state was achievable in the presence of the rho/ROCK inhibitor Y-27632. Proteomic analysis revealed consistent expression of specific proteins under serum and serum-free conditions. A high-throughput proteomic approach to screen gold-reducing proteins and peptide sequences was utilized and validated by quartz crystal microbalance with dissipation (QCM-D). Statement of significanceCancer cells are known to synthesize gold nanoparticles and microstructures, which are promising for bioimaging and other therapeutic applications. However, the detailed mechanism of such biomineralization process is not well understood yet. Herein, we demonstrate that cancer cells exposed to gold ions (grown in serum/serum-free conditions) secrete shock and stress-related proteins with specific gold-binding/reducing polypeptides. Cells undergo reversible senescence and can recover normal physiology when treated with the senescence inhibitor depending on culture condition. The use of mammalian cells as microincubators for synthesis of such particles could have potential influence on their uptake and biocompatibility. This study has important implications for in-situ reduction of ionic gold to anisotropic micro-nanostructures that could be used in-vivo clinical applications and tumor photothermal therapy.

Study on Gold and base metal occurrence in Uluwai Prospect, Western Latimojong Mountain, South Sulawesi

Uluwai Prospect is located in the northern part of South Arm of Sulawesi along the eastern part of the Kalosi Fold Belt and Latimojong Mountain. The area is generally characterized by moderate to rugged topography area with elevation in the range of 700 to 1400 m above sea level in the mountainous complex called Latimojong Mountain Complex. The mineralization is characterized by a relatively simple sulphide ore mineral assemblage consists of pyrite, sphalerite and chalcopyrite. Samples were collected in areas showing abundant sulphide minerals where younger faults cut the bedding and foliation of country rocks. A number of silicified zones have been observed, as well as float material containing disseminated pyrite, chalcopyrite, and sphalerite with hematite, goethite and limonite. Some alteration types have been observed including sericitization, albitization, carbonatization and silisification. The samples collected indicated that the mineralisation is contained within metasedimentary (sandstone to mudstone) and greenschist. Geochemical analyses from 16 samples including 5 stream sediment samples indicated that the most promising mineralization occur in the prospect area are copper (Cu) and zinc (Zn). This is also supported by the abundance of chalcopyrite and sphalerite in some highly altered samples. Assaying of the collected samples revealed most of samples contain relatively low gold (Au) concentration. However, two samples contain 0.007 and 0.01 ppm of Au. In the mineralized area, Zn concentrations are up to 134 ppm, Cu up to 120 ppm and Pb up to 18 ppm and As up to 70 ppm. There is no clear relationship that exists between Au and the base metals except that one of the samples with highest Au values tend to have high Zn and As. This unclear pattern also shown by Cu, Pb and Zn. Base metal concentration in stream sediment samples show a relatively stable pattern than in rock samples. Arsenic tends to be elevated in base metal rich samples. Sb and Mo are relatively low in all sample type. However, Mo values will be high in the samples which contain highest Cu and Zn.

Surface functionalized biomass for adsorption and recovery of gold from electronic scrap and refinery wastewater

Abstract In this study, polyethylenimine (PEI) modified Lagerstroemia speciosa leaves powder (PEI-LS) as low-cost and eco-friendly biosorbent was efficiently applied for gold recovery from acidic solution. Our experimental data show that PEI-LS is effective in complete recovery of gold at pH 1, compared to the raw L. speciosa leaves powder (raw LS) biomass. The adsorption kinetic results show gold adsorption reaches equilibrium in 6 h and follows a pseudo-second order kinetic. The adsorption isotherm data were best explained by Freundlich model and the monolayer adsorption capacity of PEI-LS for gold are in the range 286–313 mg/g. Thermodynamic parameters suggest that gold adsorption on PEI-LS was spontaneous and endothermic in nature. The developed PEI-LS was reusable up to 4 cycles with ∼98% gold recovery. Further, the calculated separation factor values suggest the PEI-LS shows high selectivity for low concentration of gold over the other co-existing metal ions in binary mixtures. Various instrumental characterization of raw LS and PEI-LS confirms the successful grafting of PEI on biomass surface. Surface analytical techniques like X-ray photoelectron spectroscopic (XPS) analysis confirms the adsorption-reduction mechanism of gold ions on PEI-LS leading to the formation of zero-valent gold on the biosorbent surface. The XPS was also used to characterize the PEI-LS surface functional groups (N1s) responsible for gold adsorption-reduction mechanism. The PEI-LS was successfully applied for quantitative gold recovery (≥95%) from an acidic solution of electronic scrap, gold refining sludge and wastewater.

Electrochemical Recovery of Gold from Waste Electric and Electronic Equipment Using Circulating Particulate Bed Reactor (CPBE)

The utilization of electrochemical process recovery involving low reactant concentrations of metal requires electrodes with high mass transport rates and specific surface areas. This is essential to increase cross-sectional current densities whilst optimizing the capital and operating costs. Experimental results demonstrated that Circulating Particulate Bed Reactor (CPBE) is suitable for the recovery of low concentrations of gold from aqueous chloride solution containing and of less than 0.5 mol m-3(< 102 g m-3). Elemental gold was successfully obtained on 0.5-1 mm gr particles in an electrochemical reactor incorporating a cation- permeable membrane and operated in bath recycle mode. Depletion to concentration < 5 × 10-3 mol m-3 (< 1 g m-3) appeared to be mass transport controlled at an applied potential of +0.20 V (SCE), specific electrical energy consumption (SEEC) of ca. 800-1300 kWh h (tonne Au)-1 for cell voltages (U) of 2.0-3.0 V, and fractional current efficiencies of ca. 0.95. However, atomic absorption and UV spectrophotometry established that as the concentration decayed, the molar ratio changed. A multi-step mechanism for reduction of ions explained this behavior in terms of changing overpotentials for and reduction as total dissolved gold concentration decreased. In addition, SEM images confirmed that adherent and coherent Au deposits were achieved with CPBE for Au deposition under mass transport control at 0.20 V (SCE).

The use of an electrogenerative process as a greener method for recovery of gold(III) from the E-waste

Abstract In this present work, an electrogenerative flow-through reactor with an activated reticulated vitreous carbon (RVC) cathode was developed and used in recovering gold from an E-waste. The system resulted in more than 99% gold being recovered within 2 h of operation for 100 mg L −1 of initial gold(III) chloride concentration. Besides, the flow cell system in series shows around 98% gold being recovered within 4 h. From three different cathodes studied, activated RVC serves as the best cathode material having the highest recovery rate with more than 99% of gold from E-waste being recovered in 2 h of operation. It has an exceptional high void volume, highly porous surface structure, rigid structure and low resistance to fluid flow. It can be seen that the developed electrogenerative method is environmentally friendly and could recover the gold fully (>99%), even at a low concentration of gold. Finally, the morphology of gold deposits on an activated RVC cathode was also investigated.

Laser Ablation ICPMS Analysis of Pyrite and U-Pb Zircon Dating of Host Rocks From the Tersang Gold Deposit, Malaysia

The Central gold belt of peninsular Malaysia comprises a number of gold deposits located in the east of the N-S striking Bentong-Raub Suture Zone. The Tersang gold deposit is a mesothermal, orogenic gold deposit, which is hosted in sandstone, shale, rhyolite and breccia. The deposit has an inferred and indicated resource of 120,000 ounces of gold in the JORC category. Detrital zircon grains from the host sandstones returned a maximum depositional age ranging from Early Carboniferous to Early Permian (333.5 ± 2.5 Ma-261.5 ± 4.9 Ma) and those of the rhyolite indicated a crystallization age of 218.8 ± 1.7 Ma. Pyrite trace element mapping has revealed four pyrite phases. Laser Ablation ICPMS analyses on pyrite has shown that pyrite phase 1 has the lowest Au concentration (mean 0.4 ppm) and is interpreted to have preceded the main Au mineralisation stage. Pyrite phases 2 and 3 are the main Au mineralisation stage with Au mean range from 1.5 to 4.5 ppm and contributed most of the invisible gold to the ore-forming system. Pyrite phase 4 has low gold concentrations (mean 0.5 ppm) and post-dated the main Au mineralisation stage recorded in pyrite phases 2 and 3. The trace element chemistry of pyrite indicates that Au mineralisation recorded in pyrite is likely a product of four stages ore forming system centred on the rhyolite corridor. In terms of gold exploration, gold has a positive correlation with As, Ag, Cu, Se, Sb, Pb and Tl in pyrite. These metals can be used as pathfinders to detect proximity to ore for orogenic gold deposit type in the central gold belt of Peninsular Malaysia.

Selective Electrochemical Gold Recovery from Leaching Solutions of Thiosulfate

This work presents a study of the selective electrowinning of gold from thiosulfate electrolyte, taking into account difficulties related with low gold concentration and metal impurities that usually limit gold recovery. The cathodic and anodic processes were evaluated in a potential window where gold and copper reduction and the oxidation of thiosulfate and Cu (I) species occurs. Three materials with different reactivity were evaluated as cathode: Pt, Ti and DSA. It was possible to define the effect of each material in the electrochemical reactions involved and to identify three potential regions where selective electrodeposition happens: the first one involves selective deposition of gold, the second accounts for the co-deposit formation of copper and gold and the last one for the massive copper electrodeposition. The use of DSA as cathode electrode showed an intermediate electrochemical behavior between Pt and Ti and good selectivity. For these reasons DSA is proposed as a good cost/benefit option for gold electrowinning process from thiosulfate solutions.

Comparison of the adhesion of Streptococcus sanguinis to commonly used dental alloys stratified by gold content

Background/purposeStreptococcus sanguinis is an early colonizer of biofilm and plays a key role in the process of adhesion to prosthetic surfaces by facilitating the adhesion of later colonizers. The main aim of this study was to determine if S. sanguinis is affected by the gold concentration dental prosthetic alloys. Materials and methodsFive commonly used alloys with varying degrees of gold concentration were selected for this study. We evaluated the ability of S. sanguinis ATCC strain 10556 to adhere to each of these alloys by counting the number of cells that adhered to each of the tested alloys. Each alloy was also assessed for cell adherence using scanning electron microscopy. One-way analysis of variance and Student–Newman–Keuls comparison test were used for statistical analysis based on cell counts from each well for the test and control groups. ResultsThe highest concentration of bacterial cells adhered best to pure gold alloy (458±8) followed by 88.4% gold Je alloy (382.33±2), 56% gold Wi alloy (269±4), 2% gold Es alloy (212.33±2), and nongold Re alloy (183±3). Based on the cell counts and scanning electron microscopy observations, there was a clear correlation between gold concentration and S. sanguinis adherence. ConclusionThe findings of this study suggest that alloys with a lower gold concentration may result in lower bacterial colonization rates and may reduce the risk of invasive infections. When choosing an alloy, low gold concentrations may be a better clinical choice.

Ion-association dispersive liquid–liquid microextraction of ultra-trace amount of gold in water samples using Aliquat 336 prior to inductively coupled plasma atomic emission spectrometry determination

Gold is a rare and noble metal with atomic number of 79. Several techniques including both spectrometric and electrochemical methods are widely used to determine gold level in real samples. As a result of low concentration of gold in environmental samples, sample preparations such as extraction, clean-up, and pre-concentration before instrumental analysis are mandatory. Thus, a pre-treatment method (dispersive liquid–liquid microextraction (DLLME)) for gold pre-concentration and inductively coupled plasma optical emission spectrometry (ICP-OES) determination is proposed. An extraction method employing DLLME and ICP-OES has been developed for rapid separation, pre-concentration, and determination of ultra-trace amount of Au (III). The extraction of the analyte was performed in the presence of a quaternary ammonium cation, N-methyl-N,N,N-trioctylammonium chloride, (Aliquat 336) as an extractant based on ion-association extraction system. 1-Octanol and acetonitrile were used as extraction and disperser solvents, respectively. The variables affecting the extraction conditions were optimized. A calibration curve in the range of 0.3–100 ng mL−1, the detection limit of 0.09 ng mL−1, an enrichment factor of 150, and an extraction recovery of 74 % were obtained. The precision (RSD %) of the method was 6 % for five replicates and recoveries of 10 ng mL−1 Au(III). The combined DLLME method with ICP-OES can readily determine Au(III) at trace (μg L−1) level using only 10 mL of sample solution (tap, lake, and mining water) without interference by the matrices. This methodology is simple, fast, and low cost which can be used in routine analytical laboratories.

Effective and selective recovery of gold and palladium ions from metal wastewater using a sulfothermophilic red alga, Galdieria sulphuraria

The demand for precious metals has increased in recent years. However, low concentrations of precious metals dissolved in wastewater are yet to be recovered because of high operation costs and technical problems. The unicellular red alga, Galdieria sulphuraria, efficiently absorbs precious metals through biosorption. In this study, over 90% of gold and palladium could be selectively recovered from aqua regia-based metal wastewater by using G. sulphuraria. These metals were eluted from the cells into ammonium solutions containing 0.2M ammonium salts without other contaminating metals. The use of G. sulphuraria is an eco-friendly and cost-effective way of recovering low concentrations of gold and palladium discarded in metal wastewater.

Detection of gold nanoparticles with different sizes using absorption and fluorescence based method

Growing world demand for gold and decreasing discovery rates of ore deposits necessitates new techniques for gold exploration. Current techniques for the detection of ppb level of gold, such as inductively coupled plasma mass spectrometry (ICP-MS) are not field-deployable. By contrast, current portable device such as X-ray fluorescence (XRF) based sensors are not sufficiently sensitive. Thus, there is growing interest in developing a new, easy-to-use and fast method for detection of low concentrations of gold at the site of an exploration drilling rig.Two optical methods, absorption and fluorescence, are examined for their suitability for low gold concentration detection. Absorption study is based on the analysis of localised surface plasmon resonance peak. For fluorescence analysis, the ability of gold nanoparticles to specifically catalyse the conversion of the non-fluorescent compound (I-BODIPY) to the fluorescent derivative (H-BODIPY) is used. For both absorption and fluorescence methods, the limit of quantification (LOQ) of gold nanoparticles (NPs) was found to be dependent on the NP size (71ppb of 5nm and 24.5ppb of 50nm NPs for absorption and 74ppb of 5nm and 1200ppb of 50nm NPs for fluorescence). The LOQ for fluorescence for 50nm NPs measured in a suspended core optical fibre was almost twice lower than in a cuvette. The field deployment potential of these methods was also determined using a portable set up.

Tectonic evolution of the Gaoua region, Burkina Faso: Implications for mineralization

The interpretation of high-resolution airborne geophysical data integrated with field structural and lithological observations were employed in the creation of a litho-structural framework for the Gaoua region, Burkina Faso. The granite-greenstone domain of Paleoproterozoic age was affected by multiple deformation and mineralization events. The early tectonic phase is characterized by the emplacement of voluminous tholeiitic and calc-alkaline lavas, probably in a volcanic arc setting. The copper mineralization in Gongondy, Dienemera and Mt Biri is concentrated in a diorite/andesite breccia, and is interpreted as porphyry-copper style formed at an early stage of the evolution of the area. Evidence for the first deformation event D1Ga corresponding to N–S shortening was only found in the E–W trending mafic unit bordering the Gaoua batholith to the south. A second deformation phase D2Ga occurred under greenschist facies conditions and lead to a development of more or less penetrative metamorphic foliation and its subsequent folding under overall E–W compression. At later stages, the D2Ga switched to a transcurrent regime characterized by intense N–S to NW-trending steeply dipping shear zones. The first significant gold mineralization event is related to this transcurrent tectonic phase. During subsequent D3Ga, intense network of brittle to brittle–ductile NW and NE faults developed. Economic gold concentrations are attributed to the D3Ga event and are associated with the remobilization of early disseminated low grade gold concentrations. Significant deposits in the area are Nassara, Gomblora, Batié West and Kampti. The last deformation event D4Ga resulted in E–W trending thrust faults and crenulation cleavage planes, under overall N–S compression. No mineralization events related to this stage have been seen.

Experimental validation of L-shell x-ray fluorescence computed tomography imaging: phantom study.

Thanks to the current advances in nanoscience, molecular biochemistry, and x-ray detector technology, x-ray fluorescence computed tomography (XFCT) has been considered for molecular imaging of probes containing high atomic number elements, such as gold nanoparticles. The commonly used XFCT imaging performed with K-shell x rays appears to have insufficient imaging sensitivity to detect the low gold concentrations observed in small animal studies. Low energy fluorescence L-shell x rays have exhibited higher signal-to-background ratio and appeared as a promising XFCT mode with greatly enhanced sensitivity. The aim of this work was to experimentally demonstrate the feasibility of L-shell XFCT imaging and to assess its achievable sensitivity. We built an experimental L-shell XFCT imaging system consisting of a miniature x-ray tube and two spectrometers, a silicon drift detector (SDD), and a CdTe detector placed at [Formula: see text] with respect to the excitation beam. We imaged a 28-mm-diameter water phantom with 4-mm-diameter Eppendorf tubes containing gold solutions with concentrations of 0.06 to 0.1% Au. While all Au vials were detectable in the SDD L-shell XFCT image, none of the vials were visible in the CdTe L-shell XFCT image. The detectability limit of the presented L-shell XFCT SDD imaging setup was 0.007% Au, a concentration observed in small animal studies.