Green Synthesis of Gold Nanoparticles Using Upland Cress and Their Biochemical Characterization and Assessment

This research focuses on the plant-mediated green synthesis process to produce gold nanoparticles (Au NPs) using upland cress (Barbarea verna), as various biomolecules within the upland cress act as both reducing and capping agents. The synthesized gold nanoparticles were thoroughly characterized using UV-vis spectroscopy, surface charge (zeta potential) analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results indicated the synthesized Au NPs are spherical and well-dispersed with an average diameter ~11 nm and a characteristic absorbance peak at ~529 nm. EDX results showed an 11.13% gold content. Colloidal Au NP stability was confirmed with a zeta potential (ζ) value of −36.8 mV. X-ray diffraction analysis verified the production of crystalline face-centered cubic gold. Moreover, the antimicrobial activity of the Au NPs was evaluated using Gram-negative Escherichiacoli and Gram-positive Bacillus megaterium. Results demonstrated concentration-dependent antimicrobial properties. Lastly, applications of the Au NPs in catalysis and biomedicine were evaluated. The catalytic activity of Au NPs was demonstrated through the conversion of 4-nitrophenol to 4-aminophenol which followed first-order kinetics. Cellular uptake and cytotoxicity were evaluated using both BMSCs (stem) and HeLa (cancer) cells and the results were cell type dependent. The synthesized Au NPs show great potential for various applications such as catalysis, pharmaceutics, and biomedicine.

Uncertainty Evaluation for Determination of Gold in High-Purity Gold by LA-ICP-MS

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a new analytical method developed in recent years. The LA-ICP-MS is a quasi-non-destructive multi-elemental analytical method with low detection limits, high sensitivity and specificity. In this study, this method is applied to detecting high-purity gold. The micro-region information of high-purity gold can be analysed, and the original position information of the sample can be obtained in real time and accurately. In this study, the content of impurity elements in high-purity gold were determined by LA-ICP-MS, and the accuracy and reliability of the test results were improved by calculating the uncertainty. According to the test and analysis, the gold content of the high purity gold sample is (999.995 ± 0.003) ‰, so the gold content of the sample is more than 999.99 ‰. The result shows that the LA-ICP-MS has the advantages of fast, accurate and green, which is conducive to the rapid development of jewellery industry technology, and puts forward guiding suggestions for the production development direction, and promotes the green and healthy development of jewellery industry.

Baikal–Vilyui Paleoproterozoic Belt of The Siberian Platform: Regional Gold-Controlling Structure

The article demonstrates that the placer gold content of the Vilyui Syneclise is governed by the regional structure of the crystalline basement of the Siberian Platform—the Baikal–Vilyui Paleoproterozoic belt, the boundaries and tectonics of which are substantiated by analysis of the gravitational field structure. The belt includes a system of basement blocks with a common northeastern strike, which form horsts (of the Suntar type) and grabens (of the Kempendyai type). The gold-bearing placers of the Vilyui Syneclise are mainly confined to the Suntar, Tyukyan, and Chybyda blocks of the belt, the metamorphic and igneous rocks of which were the primary gold sources in the sedimentary cover. The suture zone of the Baikal–Vilyui belt was very permeable to deep fluids responsible for gold migration. The types of possible primary gold sources (gold–platinoid, low-sulfidation gold-quartz, and gold–silver) reflect the peculiarities in the evolution of Early Precambrian gold during sedimentation in the Vilyui Syneclise. The areas controlled by the Suntar, Kempendyai, Tyukyan, Chybyda, and Khapchagai blocks of Early Precambrian rocks, which may contain gold objects, should be considered promising for buried gold placers in the Vilyui Syneclise.

Study on Vacuum Roasting Pretreatment of Carbonaceous Gold Concentrates Based on Nonoxidation Technology

Carbonaceous gold ores are difficult to treat because of the “preg-robbing” by carbonaceous matters and locking by minerals. Roasting is the most commonly used method that is useful in dealing with carbonaceous gold ores. In this study, flotation gold concentrates containing sulfides and carbonaceous matters were investigated to ascertain the reaction process and the matters’ transformation characteristics in different temperatures by vacuum roasting pretreatment. Calcine and volatile condensates were characterized with several techniques. In the process of vacuum roasting, the main chemical reactions were decomposition reaction and carbothermic reduction reactions of sulfide ores, carbothermic reduction reactions of SiO2, and thermal decomposition reactions of organic carbon. The bad effects of “preg-robbing” by carbonaceous matters were greatly weakened by the thermal decomposition and carbothermal reduction. The gold locking minerals were mainly removed by reduction reactions. The sulfides were removed in ways that did not produce SO2. The removal of sulfur and carbonaceous matters during the vacuum roasting process was 95.83% and 65.38%, respectively. Direct cyanidation of the calcine extracted from 2.13% to 88.37% of the gold content with a vacuum degree of 10 Pa and roasting from 25°C to 1,200°C for 30 min.

Developing the technology of associated gold recovery when concentrating copper-pyrite ore

Research objective is to address an up to date task of developing the technology of associated gold recovery from complex ore. Object of research is the gold-bearing copper-pyrite ore. Gold was recovered in laboratory conditions with the use of gravity methods of mineral separation. Research tools. Rational modes of machinery operation have been determined through mathematical planning of experiments including the obtained results processing by mathematical and statistical methods. Methods of research. Gold was recovered in the grinding-classification circuit based on a seriesinstalled short-cone hydrocyclone, a jigging machine and a shaking table. Research results. The developed jig mode differs from the existing ones by the closed-circuit of jig machine chambers: from the feed of the second (in the direction of the light fraction travel) jig chamber, the light fraction (tailings) and undersize product – fraction with the increased content of accessory minerals (rough concentrate) are separated. The rough concentrate in the second chamber is directed to the first chamber of the machine, where the finished jig concentrate is obtained in the form of an undersize product. The light fraction moves from the first chamber to the second and is removed from the machine through the tail board. When fine-tuning the heavy fraction of jigging on a shaking table, it is recommended to mix 1/2 part of the initial feed of the tables with the rough concentrate isolated from the other 1/2 of the original feed. The new jigging mode and the scheme of concentration on the tables provide an increase in the gold content in the initial feed of the apparatus, which is the reason for a decrease in gold losses with the tails of the gravity circuit. Research relevance. Gold recovery increment by 4.77% was obtained due to the use of all three recommended scientific and technical measures, namely sands concentration in a short head cone crusher on a jig, switching the jig chambers to a closed circuit, and jet motion of concentrates on shaking tables. Scope of the results. The results should be applied when concentrating ore containing free (amalgamable) gold, as well as gold-bearing pyrite.

Application of a nanosecond corona discharge generator for electrical separation of ores

The use of a pulsed nanosecond voltage source in a corona separator was investigated. Measurements of the distribution of corona discharge current were obtained. The influence of the interelectrode distance on the distribution of the corona discharge current was investigated. Experiments with gold-bearing quartz-sulfide ore and ilmenite ore were carried out. A concentrate was obtained with a gold content of 48 g/t, a mass equal to 18.7% of the original, which corresponds to the extraction of 92% of gold. The titanium content of ilmenite was enriched from 2.87% to 18.1%.

Typomorphism of Placer Gold and Prerequisites for the Discovery of Gold Ore Occurrences in the Southern Part of the Lena-Anabar Trough (North-East of The Siberian Platform)

The article examines the results of exploratory work carried out in the southern part of the Lena-Anabar trough in the north-eastern part of the Siberian platform. Alluvial deposits of the Polovinnaya river, which belongs to the Uele-Udzhinsky placer cluster, were sampled for predictive assessment of commercial prospects for placer occurrences of gold. The mineralogical-geochemical features of the placer gold were studied in order to identify potential primary sources. It is proved that the Mesozoic and Cenozoic deposits are the main sources of gold. Its typomorphic features are small size (-0.5 mm), toroidal and flake shape, shagreen surface with casts of pressing of the minerals, and high fineness (950-999 %). The internal structures of gold particles are represented by thick high-grade shells, translation lines and high-grade intergranular veinlets. Along with this, the discovery of the autochtonous gold of ore habit in the studied gold area suggested the presence of an additional primary source. Very small size (-0.2 mm) and angular-lumpy shapes of the individuals, almost unrounded surface and low fineness are typical features of slightly altered gold. The discovery of small (3-4mm) fragments of hydrothermal-metasomatic rocks in the alluvium of the Polovinnaya river confirms the above assumption. The epigenetic mineral composition of these fragments is represented by pyrite, potassium feldspar, fluorapatite, and quartz. Micro-X-ray spectral analysis determined the smallest (first microns) mineral phases of native gold, argentite, galena, sphalerite and greenockite in them. It is worth noting that the described fragments are quite fragile, and they are destroyed with a slight impact with a steel needle. The fragility of these fragments indicates the close proximity of the rewashed ore occurrences. In addition, increased gold content in small classes of heavy concentrate material of small-volume samples was determined according to atomic absorption analysis. All this together is a prerequisite for the discovery of ore occurrences with finely-dispersed and fine gold. It is assumed that the ore occurrences can be localized in the Anabar-Eekit fault zone, which extends parallel to the Pronchishchev ridge, through the Anabar-Olenek trough, to the Sololiy uplift of the Olenek arch. In the area of the Olenek arch, this zone is associated with superimposed gold-bearing low-temperature hydrothermal mineralization, expressed by K-feldspathization and sulfidization of the Permian deposits.

Geological structure and gold content of the eluvial-deluvial placer of the deposit “Golets Visochayshiy”.

The article describes geological structure, characteristics and goldcontent of eluvium-talus deposit of “Golets Visochayshiy” field, according to data from previous geological reports and data, received by author during his work on this deposit.

Geological structure of the gold deposit "Ojerelie" and adjacent territories.

The article considers the structure, characteristics and gold content of the "Ojerelie" deposit according to the data of geological reports, published articles, fund materials and internal documents, which allowed to summarize and briefly present the geological structure of this area.

Gold in Ferromanganese Deposits from the NW Pacific

Ferromanganese crusts from four different areas of the North-West Pacific Ocean—the Detroit (northern part of the Imperial Ridge) guyot, the Zubov (Marshall Islands) guyot, the “Gummi Bear” seamount (an intraplate volcano near the Krusenstern FZ), and Belyaevsky volcano (the Sea of Japan)—were studied. Samples from the Detroit and Zubov guyots and the “Gummi Bear” seamount have similar chemical and mineral compositions of hydrogenetic cobalt-rich ferromanganese crusts. Crust from the Sea of Japan seems to reflect a hydrothermal influence. The gold content in most samples from the Detroit guyot was 68 ppb and from the Zubov guyot varied from 180 to 1390 ppb, which is higher than the average for the Pacific crusts (55 ppb). Gold content in two other samples was less than 10 ppb. Based on the electron microscopic studies, aggregation of gold particles with a size of 680 μm were identified in the Detroit guyot crust. The sizes of the Au particles are up to 10–15 μm, which has not been previously noted. Gold particles similar in morphology and size were also found in the Zubov guyot crust, which is located far from the Detroit guyot. The largest particle of gold (≈60 μm), represented by electrum, was found in the clay substrate from the “Gummi Bear” seamount. The lamellar, rudaceous morphology of the gold particles from the Detroit and Zubov guyots reflects their in situ formation, in contrast to the agglutinated, rounded with traces of dragging gold grain found in the substrate of the sample from the “Gummi Bear” seamount. Three-component (Ag-Au-Cu) gold particles were found in the hydrothermal crust from the Belyaevsky underwater volcano. Grains similar in composition were also found in Co-rich crust. The research results show that the gold was probably added to by hydrothermal fluid in the already-formed hydrogenetic ferromanganese crusts during rejuvenated volcanic stages. Biogeochemical processes may have played a major role in the formation of submicron solid-phase gold particles.