Papers by Keyword: Gold

Abstract: In present article gold cementation features from cyanide solutions using dendritic zinc powders are studied. The powders were obtained by electroextraction from alkaline solutions. Powders with different physical properties were obtained by means of change in current density (from 0.5 to 2 A/m²) and NaOH concentration in solution (from 100 to 400 g/dm³) at the constant zinc concentration (10 g/dm³). The physical properties of mentioned powders were studied using SEM (Jeol JSM-6390LA), BET (Gemini VII 2390) and laser diffraction (Sympatec HELOS & RODOS). It is shown that electrolytic powders have high specific surface area, which is 1.8–2.6 times larger than the surface area of ​​the zinc powder currently used for cementation. At that electrolytic powders particle size is 8-22 times larger than the particle size of powder currently used for cementation. The reason of high specific surface area is the electrolytic zinc powders dendritic structure. It was found that the obtained powders precipitate gold from cyanide solutions with a greater efficiency in a wide range of productivity. Laboratory unit simulating Merrill-Crow technology was used for cementation. Immediately ahead conducting the experiments, Na₂SO₃ was added to the solution in excess to remove dissolved oxygen. Zinc powders were plated by dendritic lead before loading into the laboratory setup by cementation. Lead was added as acetate (Pb (CH₃COO)₂). The consumption of lead acetate was 10% by weight of zinc. Correlation between the powders physical properties and the gold extraction is shown.

Abstract: Inherent problems of oxidized gold-bearing copper ores processing and a comparison of hydrometallurgical methods, applied for such materials, are discussed in this article. Studies on sulfuric acid and cyanide leaching have been carried out, using the following sample of oxidized ore from one of the copper deposits (Kyrgyzstan), %: 15 Mg O, 45.6 SiO2, 0.1 S, 20 Ca O, 12.1 Fe₂O₃, 0.86 Cu, 1.78 Au, 9.61 Ag. Studies have been carried out. Agitation sulfuric acid leaching able to extract up to 29.9% of copper. At the same time, column sulfuric acid leaching able to extract up to 78.5% of total copper and 85.23% of copper presented by acid-soluble compounds. In case of precious metals, the agitation cyanide leaching is able to extract up to 97.6% of gold in 24 h. Increasing the grinding fineness up to 90% - 74 μm reduces cyanidation duration down to 12 h. The consumption of sodium cyanide is 4.8 kg/t of ore. At the same time, column cyanide allows to extract 73.5% Au and 81.9% Ag during 111 days, whereas 52.4% of gold is recovered in the first 10 days. Consumption of sodium cyanide is 5.45 kg/t. The most efficient ways for processing of such materials are proposed.

Abstract: Development of bio-reduction techniques for nanoparticles (NPs) synthesis in medical application remains a challenge to numerous researchers. This work reports a novel technique for the synthesis of gold nanoparticles (AuNP) using palm oil fronds extracts (POFE) in the present of ultrasound radiation. The POFE is a waste material available in abundance in Asia and some African countries. The functional groups in the POFE operate as a persuasive capping and possibly reduced Au³⁺ to Au⁰. The prepared AuNPs were characterized by UV-vis spectrophotometry, FTIR, DLS, FESEM, and XRD. The analysis of FTIR validates the coating of alkynes and phenolic composites on the AuNPs. This shows a feasible function of biomolecules for efficient stabilization of the AuNPs. Field emission scanning electron microscopy (FESEM) clearly show the morphology of the prepared AuNPs. The XRD patterns display the peaks of fcc crystal structures at (111), (200), (220), (311) and (222). A physical and photometric detection effect of ten heavy metals (Pb, Zn, Ni, Co, Cu, Hg, As, Cr, Fe, and Mn) were investigated using the biosynthesized AuNPs and only Cr metal was detected by the AuNPs when it concentration increased from 1 ppm to 50 ppm with a rapit decrease of intensity measured using UV-vis spectrocopy at room temperature. While, almost all metals ions are detected at elevated tempeture (45 – 50 °C).

Abstract: An efficient technology is currently being searched for the processing of aged enrichment gold-containing tailings at the «Solton-Sary» enrichment plant, Kyrgyzstan. In this paper, the effect of microwave-plasma exposure on aged tailings and further gold extraction using froth flotation were investigated. Microwave-plasma treatment of the material was carried out in the presence of the following materials: charcoal, coal/quartz and molybdenum sulfide. Microwave-plasma treatment allowed to improve the quality of flotation concentrates in terms of the gold content from 130 ppm to 227 ppm. The design of plasmatron and methodology of plasma treatment were proposed. The results shown in this paper are valuable for mining organization in terms of searching for new industrial waste processing approaches and for broadening their raw materials base.

Abstract: The objective of this work was to recover gold and silver from the printed circuit board (PCB) of discarded mobile phones by thiourea leaching. Effects of thiourea concentration, leaching temperature, leaching time, and ferric ion (Fe³⁺) concentration on the recovery of gold and silver were investigated. The PCB was pretreated physically to reduce the thiourea consumption and enhance the leaching process. It was found that the percentage of gold leaching was higher than that of silver at different conditions studied. The highest percentages of gold (96%) and silver (90%) leachings were achieved with 20 g/L of thiourea and 8 vol% of Fe³⁺ at 4 h of leaching time and 25°C of leaching temperature.

Abstract: The changes in structural and optical properties of the Cu₂O films obtained on the glass with different concentrations of Au by the chemical bath method were studied in this work. Lattice parameter, crystal size, preferential orientation and surface tension of the films were calculated using X-ray diffraction data which showed that all of the films were in polycrystalline form. It was determined that the structural parameters of all films were changed with the doping ratio. The surface morphology of the films was imaged using a field emission scanning electron microscope. The optical properties of the films were discovered using the optic spectrometer. Changes in the optical properties were discovered as a function of Au ratio. It was determined that the energy band gap value (2.12 eV-2.02 eV), the refractive index, the extinction coefficient, the real and dielectric coefficients, the optical conductivity, and the skin depth of films varied with Au doping ratio.

Abstract: HAuCl₄ was reduced by glucose as reducing agent and dispersant under UV radiation and acetone as photo sensitizer. The experimental samples were characterized by the transmission electron microscopy and UV-visible spectrophotometer, and the results show that these gold nanoparticles’ size is uniform, monodisperse distribution of spherical particles of average diameter of 5.8 nm, and gold nanowires with two-dimensional network structure were successfully prepared. The influence of glucose concentration on reaction under this condition and the mechanism of nucleation and growth of the photochemical reduction were discussed.

Abstract: A simple method to synthesized nanoparticles was satisfied by reduction of tetrachloroauric acid in the presence of palm oil fronds extracts as capping and reduced agents. The as-synthesized gold nanoparticles structures have a triangular and hexagonal shape that are of tens of nanometre in size. It was realized that good control shape of nano-hexagonal gold nanoparticles were obtained from nano-triangular gold nanoparticles in the absence of any soft template. The production techniques of the gold nanoparticles were examined by using UV-vis spectroscopy, EFTEM and XRD patterns, which showed peaks at (111), (200), (220), (311) and (222), that described the preferential structure of the AuNPs as face-centered cubic crystal

Abstract: This article covers acid nitric leaching of Olympiada deposit refractory gold-bearing concentrate after alkaline leaching of stibnite. Thermodynamic analysis of the reaction pyrite and arsenopyrite with nitric acid chemical equations was performed. Equilibrium Eh-pH Pourbaix diagrams of heterogeneous systems studied, containing iron and arsenic were charted. Investigation of elemental and species analyses was maintained. The analysis of the main elements distribution and their combining over grains with the help of electron-probe microanalysis (EPMA) was investigated. It is established, that the material mainly consists of compounds of quartz, dolomite and calcite, as well as pyrite and arsenopyrite. Pre-treatment decarbonization operation of the feed material was proposed with the aim to reduce nitric acid consumption. The dependences of effects of the nitric acid concentration and L/S ratio on iron and arsenic dissolving were determined.

Abstract: In this paper, we propose preparation of PEGylated AuNPs by direct sputtering of Au into pure PEG with subsequent addition of amine terminated PEG. Effect of post-deposition amine addition on properties, aging and thermal stability will be discussed. Transmission electron microscopy and dynamic light scattering measurements showed that we have prepared non-agglomerated spherical NPs with size ranging from 2.9 to 5.9 nm depending on parameters of the preparation. Aging and thermal stability results revealed significant changes in the spectra after addition of PEG–NH₂. Differences in the optical absorption spectra can be assigned to change of refractive index (concentration of amine groups on NPsʼ surface) on the metal core and solvent interface with time and temperature.