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[Display omitted] • CRGO-Au (Au = 1 %) shows selectivity to CH 4 gas and CRGO-Au (Au = 50 %) shows selectivity towards CO gas at temperatures > 50◦C. • TRGO-Au (Au = 50 %) shows selectivity to H 2 gas at temperatures > 50◦C. • There exists an intricate interplay between oxygen functionalities of rGO and Au oxidation states, which effectively tunes the gas sensor selectivity for detecting reducing gases. Catalyst-loaded reduced graphene oxide (rGO) is a promising material for developing high-performance gas sensors. In this work, surface functionalization is achieved by loading different quantities of nanogold (Au) on chemically and thermally reduced graphene oxide (CRGO and TRGO). These materials showed selective gas response toward reducing gases such as hydrogen (H 2), carbon monoxide (CO), and methane (CH 4) in the temperature range RT to 150 °C. The quantity of Au catalysts and their oxidation states in the films influenced the selectivity attributes of the studied sensors. The surface oxidation states of the Au catalyst are different for CRGO-Au and TRGO-Au films. It is apparent from the results that the difference in the Au oxidation states is due to the variation in surface oxygen functionalities of the base matrix CRGO and TRGO. The experimental results are tallied with the proposed gas selectivity mechanism of CRGO-Au and TRGO-Au films. Novelty of the Work: In reduced graphene oxide based gas sensors, the combined influence of the graphene oxide reduction method, gold (Au) catalyst quantity, and valence oxidation states (in the Au catalyst) on the gas selectivity is rarely reported. The available reports only focus on examining the metallic gold (Au0) phase of the catalyst. However, it is necessary to note that Au can also exist in various higher oxidation states (Au+1, Au+2, Au+3, etc.), which provide selective gas adsorption sites. Therefore, this work addresses the above issue by employing chemically reduced graphene oxide (CRGO) and thermally reduced graphene oxide (TRGO) decorated with Au nanoparticles (Au wt% = 1 %, 50 % & 90 %) for the selective sensing of reducing gases. [ABSTRACT FROM AUTHOR]

In this work, a gold biosensor has been constructed and characterised in Escherichia coli (E. coli). Though gold biosensors have been previously reported, a NOT gate gold biosensing genetic circuit was constructed using an orthogonal inverter system as an alternative to a circuit where output is contingent solely on input. This enables the detection of changes in gold concentration whereby circuit remains OFF in presence of inducer and ON in absence of inducer. The proposed biosensor is an alternative to conventional forms of gold detection such as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The constructed biosensor is a collection of components – golTSB operon (isolated from Salmonella enterica), mf-Lon protease (isolated from Mesoplasma florum) and associated ssrA degradation tag with GFP acting as a reporter. The minimum time and concentration required by the biosensor gol-mflon-GFP (GMG) to achieve the ON output is characterised here using plate reader data derived from a single multi-stage assay.

The prospects for extracting finely dispersed gold and other useful components from the magnetic tailings of gold recovery plants and other sources are shown. This is achieved by using the process of leaching these particles and their extraction by sorption on metastable nanocrystalline water structures. A gold simulator, a colloid of molecular copper, is passed through the sorbent of a metastable nanocrystalline water structure. After three passes through the sorbent, the copper appears to be completely sorbed. Thus, according to the qualitative analysis of copper sorption, the possibility of extracting gold using this technology is confirmed. [ABSTRACT FROM AUTHOR]

When gold occurs in mining waste for a long time, it becomes coated with dense films of hydroxide of iron, manganese, copper and silver sulfides, hydromica powder and clayey particles, which greatly complicate concentration of such gold by gravity. An efficient method to remove such coatings from gold is treatment of waste using chemical reagents based on halogen-containing compounds. The article presents experimental results on extraction of fine gold from tailings of sluice boxes and dredging classifiers using such chemical reagents. [ABSTRACT FROM AUTHOR]

The technology of gold extraction to lead from its mixture with the sample powder during lowtemperature alkaline fusion is developed. The optimal ratios of masses for the sample, lead, and alkali, as well as heating conditions, temperature, and fusion duration, are determined for satisfactory gold recovery. A low temperature of fusion makes it possible to lighten the structure of furnaces, to decrease energy consumption, and to shorten the duration of the entire cycle from the beginning of fusion until the next set of crucibles is loaded. Using the modular approach, a furnace can be assembled in a small area for the simultaneous fusion of a great number of samples. The results of determining gold by the X-ray fluorescence method obtained by using the proposed concentration technology satisfy the regulatory requirements with respect to accuracy. [ABSTRACT FROM AUTHOR]

Abstract: Economic concentrations of detrital gold are rare in young foreland basins due to paucity of significant gold sources, and a paucity of sediment recycling processes during filling of the foreland basin. Gold shed into the foreland basins is typically widely dispersed in an overwhelming volume of immature basin-fill detritus of no economic significance. In the actively forming Canterbury Basin of New Zealand, minor gold concentration occurs at the mountain front in the bed of the Rakaia River, and 60 km downstream on beaches and the crest of foredunes at the river mouth. The Cretaceous–Tertiary Denver and Western Canada Basins in North America also have minor gold concentrations at the mountain front, and minor gold dispersal into the basin. Tectonic quiescence in the middle Tertiary in the Denver Basin kept gold within 20 km of the mountain front, where renewed uplift in late Tertiary caused minor economic concentrations to form in modern streams. Gold has been transported ca. 200 km across the Western Canada basin by progressive recycling of gravel during slow (ca. 10 to 50 m/Ma) middle Tertiary–Recent regional uplift and tilting, but little concentration has occurred. Development of significant placers in a foreland basin, the generally accepted setting for the Witwatersrand Au-U palaeoplacers, appears to require specific tectonic conditions during and/or after basin evolution to drive the sedimentary recycling necessary for significant placer development. Such tectonic conditions have not occurred in an any of the three young foreland basins examined in this study. [Copyright &y& Elsevier]

We report a complete set of strategies for characterization and an accurate determination of gold in metallic nanoparticles. For this, gold nanorods (AuNR) were synthesized by using the surfactant hexadecyltrimethylammonium bromide (CTAB) as the stabilizer and shape-directing agent. The surfactant CTAB forms a bilayer structure around the nanoparticles and became a challenge for the development of the microwave-assisted decomposition of the AuNR colloid. The bilayer structure of CTAB prevents the Au3+ release for the acidic media during the decomposition procedure. To overcome this limitation, a combination of low sample volume consumption (only 200 μL), an acidic mixture of reverse aqua regia (1:3 v/v, HCl:HNO 3), and sulfuric acid, and a microwave program was used. The gold quantification by ICP-MS and checked through the ICP OES, demonstrated that the seed-mediated growth method used for the AuNR synthesis has a high yield, presenting ca. 100% of gold content (ca. 100 mg L−1 of gold concentration) in the post-synthesis colloid (AuNR-total) as well as in the colloid after a washing step (AuNR-res). The microwave-assisted decomposition procedure also demonstrated to be efficient in the acidic decomposition of the gold-silver core-shell nanoparticle (Au@AgNR), which presents a high content of polyvinylpyrrolidone (PVP) (Mw ~55000 g mol−1) acting as a stabilizer, in addition to the matrix with CTAB. The results demonstrated an accurate recovery of ca. 100% of gold content for the Au@AgNR regarding the gold nanorod before the growth of the silver shell (AuNR_Core). The proposed microwave-assisted decomposition platform demonstrated to be an efficient, reliable, and robust characterization tool for the gold quantification in metallic nanoparticles, presenting no interference of the complex matrix with high organic content. Image 1 • Total gold concentration in single- and multi-elemental metallic nanoparticles. • Microwave-assisted decomposition of matrices with a high content of organic matter. • Accurate gold quantification by ICP-MS and ICP OES. • Evaluation of synthesis yield of gold nanorod growth. • Recovery of ca. 100% of gold content with no interference of the complex matrix. [ABSTRACT FROM AUTHOR]