Papers by Keyword: Gold

Abstract: The paper shows fundamental possibility of processing of gold-bearing technogenic raw materials using the method of electric explosion. A series of experiments using a laboratory and pilot-production high-voltage pulsed discharge (HVPD) installation for the processes of enrichment of gold-bearing mineral raw materials of Komsomolsk mine tailings in Kemerovo region is conducted with a relatively low energy electrical discharge in the pulse of up to 112.5 Joules and the cost of electric power of about 1.5 kW/ton of raw material, that allows complete destruction of clay components agglomerations to less than 0.045 mm (micron and submicron sizes). Solid minerals such as quartz are simultaneously destroyed by defects in the grains and withdrawn from the installation with water, thus increasing gold degree of the concentrate. The results of particle-size and X-ray structural analyses of gold-bearing mineral raw materials of Komsomolsk mine tailings in Kemerovo region obtained by the method of electric explosion are discussed.

Abstract: In this work, Au-TiO₂ nanoparticles (NPs) were synthesized in a single step by flame spray pyrolysis (FSP) method. X-ray diffraction (XRD) results indicated that phase structures of all samples TiO₂ were the mixture of anatase and rutile phases. High resolution transmission electron microscopy (HRTEM) showed that dark spots of Au NPs deposited on larger TiO₂ nanoparticles. HRTEM results indicated TiO₂ NPs were average crystallite size in the range of 10–30 nm whereas the average diameter of Au NPs was about 5–10 nm. UV–Vis absorption spectroscopy technique showed peaks attributable of surface plasmon resonance (SPR) to Au NPs loaded on TiO₂ in the wavelength of 500–630 nm. The Au-TiO₂ NPs showed excellent photocatalytic activity for the degradation of methylene blue (MB) under UV-Vis irradiation. It was found that 0.25 mol% Au-TiO₂ which was a better photocatalyst than others under the same reaction conditions. The results showed that Au NPs-loading could effectively improve the photocatalytic activities of TiO₂.

Abstract: Gold nanoparticles and silicate microsheet modified TiO₂ photoanode with various decoration amount of gold solution have been successfully synthesized. The gold nanoparticles were prepared using Turkevich method and silicate microsheet was using silica gel. The sample were characterized by XRD, SEM, and FTIR. The DSSC performance were evaluated by photocurrent-voltage measurement. The results show the increasing decoration amount of gold nanoparticles, increase the intensity of diffraction peaks. The gold nanoparticles size is 20-35 nm. Comparing with pristine TiO₂ photoanode, the efficiency of DSSC using modified photoanode increase up to 31%.

Abstract: In the present work, gold electroextraction technological features on three-dimensional cathode are studied. Zinc powders are used as cathode. Similar ones are used to gold cementation from cyanide solutions. The studies object was production of cyanide solution of following composition, mg/dm³: 7 Au. 123.65 Zn, 670 CN-; pH 10.3. Electroextraction laboratory studies were carried out in cylindrical electrolyzer with a horizontal arrangement of current-carrying electrode. It has been found that zinc powders polarization contributes to more complete gold deposition from cyanide solutions. Moreover, it allows to reduce zinc transition into spent solution, as a consequence, zinc consumption reduces. At the same time, under investigated conditions, significant cyanide oxidation does not occur.

Abstract: This paper details the hydrometallurgical method of processing of refractory gold antimony flotation concentrate. Investigation of feed material has been occurred. Mineralogical analyses (XRD, SEM-EDS) and chemical analyses of the concentrate have been studied. Mainly, the material consists of compounds of antimony, silicon, calcium, sulfur and iron. The main phases are quartz, stibnite, calcium carbonate and ankerite, pyrite and arsenopyrite have been found as well. The feature of antimonite’s dissolving in alkaline solutions has been reviewed. The dependences of effects of the temperature, time, L/S ratio and NaOH concentration on the antimony and sulfur extraction from the feed flotation concentrate have been determined. During alkaline sulphide leaching of the starting material several physicochemical characteristics of gold dissolution have been identified. Agitated cyanide gold leaching test of the pre-treated cake was conducted. Gold recovery was 32.2%. The obtained low indexes of gold recovery are based on cyanidation. A nitric acid leaching of disantimonied cake was proposed.

Abstract: The present work relates to hydrometallurgy, in particular, to gold-bearing clay ores leaching processes. The initial and agglomerated material filterability was studied. Filterability varies in different agglomeration conditions. Influence of cement, lignosulfonate, plastizer (Cemmix CemPlast), lime consumption was investigated. The negative effect of organic reagents additives, such as plasticizer (Cemmix CemPlast) and lignosulfonate, on the filtration process was established. Colmatation of agglomerated ore minimizes at CaO and Ca (OH)2 using as a modifier of the system, also phase separation in the percolation regime and under pressure proceeds without difficulty. Lime and cement joint use in the optimum proportion at clay ore agglomeration under the studied conditions reduces the filtration duration from a few hours to 2-5 minutes.

Abstract: The Samolazovskoye deposit (Central Aldan ore region, Russia) is confined to the porphyry syenite lopolith (J₃-K₁), localized between the granitic gneiss Archean basement and the series of the Vendian-Lower Cambrian carbonate cover rocks. Four hydrothermal-metasomatic parageneses have been identified within the deposit: skarn paragenesis, developed on the syenites and carbonate cover rocks contact; so called «gumbaite» paragenesis (kalifeldspar + fluorite + carbonate ± quartz), superimposed on the intrusive massif rocks; feldspatholitic paragenesis (quartz + feldspar), developed in the granitic gneisses of the crystalline basement; ore-bearing fluorite-roscoelite-carbonate-quartz paragenesis, superimposed on all of the above. The article compares ores evolved within gumbaitic syenites, basement feldspatholites and breccias, composed of all the above-mentioned rocks clasts. The geochemical study of given ores, resulted in two identified elements associations: gold-telluride (Au, Sb, As, V, Tl, Te, Hg, W) related to the fluorite-roscoelite-carbonate-quartz hydrothermal-metasomatic paragenesis and (uranium)-polymetallic (Bi, Cu, Pb, Zn, Mo, Se, Li, U), associated with the syenites gumbaitization (). There is only gold-telluride association within the basement ore bodies, while the ore bodies localized in the syenites intrusion hold both associations, along with the Au and Ag contents being an order of magnitude higher. Breccia ores are characterized by the maximum concentrations of the ore elements. Gold-telluride association of the Samoazovsky deposit ores is specific to epithermal Au-Te mineralization associated with alkaline (A-type) magmatism.

Abstract: Composites of Au supported on the TiO₂-nanofibers (Au/NF-TiO₂) were synthesized and tested in glycerol oxidation processes. TiO₂-nanofibers were prepared by a microwave-assisted hydrothermal synthesis method. Chemical deposition method was used for nanofibers modification with Au nanoparticles. Oxidation of aqueous glycerol solutions by molecular oxygen in the presence of Au/NF-TiO₂ nanocomposites was performed. It was found that Au/NF-TiO₂ composites are catalytically active in alkaline glycerol water solutions. The main product of glycerol catalytic oxidation was glyceric acid, by-products were – tartronic, lactic, glycolic, oxalic, acetic and formic acid. It was shown that Au/NF-TiO₂ catalysts’ activity and selectivity depend on Au weight loading, glycerol/Au molar ratio, oxygen pressure and NaOH initial concentration. The best result was achieved using the 0.5 wt%Au/NF-TiO₂ catalyst: selectivity by glyceric acid was 76% with glycerol conversion 100%.

Abstract: This study investigated the biooxidation of a high-grade refractory gold ore from the Zarshouran mine (West Azarbaijan, Iran) in shake flasks and a stirred tank bioreactor (STBR) using a mixed culture of moderately thermophilic microorganisms. The influence of four critical parameters including, pH, biooxidation time, nutrient medium type and pulp density on the iron and arsenic extraction as well as gold cyanidation were evaluated in a full factorial design in shake flasks at 45 °C. Maximum iron extraction was obtained in M9K medium, pulp density of 5% (w/v), 15 days of biooxidation time and the pH of 1.6. Biooxidation in the STBR was carried out at the pulp densities of 10% and 20% (w/v), the pH of 1.7 in the M9K medium, in which dissolved oxygen, pH, redox potential, iron and arsenic concentrations were measured during the process. It was found that 61% decrement of sulphur content in the STBR led to recover 80% of gold, which was 43% higher than that in the conventional cyanidation process. It can be concluded that the oxidation of refractory arsenopyrite gold ore can achieved using a moderately thermophilic biooxidation culture.

Abstract: A sulphide concentrate containing 31.4% total sulphur (in which 30.7% was sulphidic), 31.8% iron, 8.0% arsenic, 18.5 g/t gold and 32.9 g/t silver finely disseminated in pyrite and arsenopyrite as the most essential components was subjected to microbial pretreatment to expose the precious metals from the sulphide matrix. Three different types of microbial cultures were tested for their ability to oxidize the sulphides and to expose the precious metals for the subsequent chemical leaching: mesophilic chemolithotrophic bacteria with a temperature optimum for their growth and activity at about 32 – 37°C, moderate thermophilic bacteria with the relevant optimum at 53 – 59°C, and hyperthermophilic archaea at 75 – 84°C. The microbial pretreatment of the concentrate was carried out in reactors with mechanical stirring and enhanced aeration by air enriched in CO_2. It was found that sulphide oxidation of about 40 – 45 % was sufficient for achieving gold extraction higher than 90% during the subsequent leaching of the pretreated concentrate by different gold-solubilizing reagent (cyanide, thiourea, thiosulphate). The highest rate of sulphide oxidation was achieved by a mixed culture of hyperthermophilic archaea at 82°C but at relatively low pulp densities (within 7 – 9%). At higher pulp densities (within 10 – 25%) the highest rates were achieved by means of moderate thermophilic bacteria at 57 – 59°C.