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Abstract

Effects from adsorption of organic species on the surface of nanomaterials have been investigated. Exposure to organic contaminants during material processing, handling and environmental exposure is unavoidable during the manufacturing process of nanoscale materials. In addition, at the nanoscale, surface area to volume ratios increase and surface effects will have an increasing influence on the material properties. Experimentally measured electrical properties of gold nanowires and composition will be presented. The results indicated that C, C—O—C and C=O are adsorbed at the surface of the gold nanowires. These surface contaminants are believed to cause the increase in measured resistivity. A theoretical study was performed to investigate diffusion of these contaminants into the first surface layer, which may act as scattering mechanisms for current flow.
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Abstract

At present, with the increase of production capacity and the promotion of production, the reserves of most mining enterprises under the original industrial indexes are rapidly consumed, and the full use of low-grade resources is getting more and more attention. If mining enterprises want to make full use of low-grade resources simultaneously and obtain good economic benefits to strengthening the analysis and management of costs is necessary. For metal underground mines, with the gradual implementation of exploration and mining projects, capital investment and labor consumption are dynamic and increase cumulatively in stages. Consequently, in the evaluation of ore value, we should proceed from a series of processes such as: exploration, mining, processing and the smelting of geological resources, and then study the resources increment in different stages of production and the processing. To achieve a phased assessment of the ore value and fine evaluation of the cost, based on the value chain theory and referring to the modeling method of computer integrated manufacturing open system architecture (CIMOSA), the analysis framework of gold mining enterprise value chain is established based on the value chain theory from the three dimensions of value-added activities, value subjects and value carriers. A value chain model using ore flow as the carrying body is built based on Petri nets. With the CPN Tools emulation tool, the cycle simulation of the model is carry out by the colored Petri nets, which contain a hierarchical structure. Taking a large-scale gold mining enterprise as an example, the value chain model is quantified to simulate the ore value formation, flow, transmission and implementation process. By analyzing the results of the simulation, the ore value at different production stages is evaluated dynamically, and the cost is similarly analyzed in stages, which can improve mining enterprise cost management, promote the application of computer modeling and simulation technology in mine engineering, more accurately evaluate the economic feasibility of ore utilization, and provide the basis for the value evaluation and effective utilization of low-grade ores.
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Abstract

Nanoparticles are very fascinating area of science not only due to their unique properties but also possibility of producing new more complex materials, which may find an application in modern chemistry, engineering and medicine. In process of nanoparticles formation very important aspect is a rate of individual stage i.e. reduction, nucleation and autocatalytic growth, because this knowledge allows for proper materials design, morphology manipulation, stability. The last one aspect can be realized using proper electrostatic, steric and electrosteric stabilization. However until now nobody reports and measures kinetic rates of all stages during process of particles formation in the presence of steric stabilizers. Thus, the main contribution of this paper is determination of individual rate constants for nanoparticles formation in the presence of steric stabilizers and their comparison to the system without stabilizer. For this purpose, an aqueous solution of Au(III) and Pt(IV) ions were mixed with steric stabilizers like PVA and PVP, and reduced using L-ascorbic acid as a mild and sodium borohydride as a strong reductant. As a results stable nanoparticles were formed and process of their formation was registered spectrophotometrically. From obtained kinetic curves the values of observed rate constants for reduction metal ions, slow nucleation and fast autocatalytic growth were determined using Watzky-Finke model. It was found that the addition of polymer affects the rate of the individual stages. The addition of steric stabilizers to gold ions reduced with L-ascorbic acid causes that the process of nucleation and autocatalytic growth slows down and the value of observed rate constants for nucleation changes from 3.79·10–3 (without polymer) to 7.15·10–5s–1 (with PVA) and for growth changes from 1.15·103 (without polymer) to 0.48·102s–1M–1 (with PVA). However, the rate of the reduction reaction of Au(III) ions is practically unchanged. In case of using strong reductant the addition of polymer effects on the shape of kinetic curve for reduction of Au(III) and it suggests that mechanism is changed. In case of Pt(IV) ions reduction with L-ascorbic acid, the process speeds up a little when PVA was added. Determined values of observed rate constants for nucleation and growth platinum nanoparticles decrease twice comparing to the system without polymer. The reduction of Pt(IV) ions with sodium borohydride accelerates when PVP was added and slows down when PVA was used. Moreover, the size of obtained colloidal gold and platinum was also analysed using DLS method. Obtained results (rate constants) may be useful in the process of nanomaterials synthesis, in particular in microflow.
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Abstract

To improve bioremediation of arsenic (As) contamination in soil, the use of microorganisms to efficiently reduce As and their assessment of genetic erosion by DNA damage using genomic template stability (GTS) evaluation and using RAPD markers were investigated. The five sites examined for microorganisms and contaminated soils were collected from affected gold mining areas. The highest As concentration in gold mining soil is 0.72 mg/kg. Microorganism strains isolated from the gold mining soil samples were tested for As removal capacity. Two bacterial isolates were identified by 16S rRNA gene sequence analysis and morphological characteristics as Brevibacillus reuszeri and Rhodococcus sp. The ability to treat As in nutrient agar (NA) at 1,600 mg/L and contaminated soil samples at 0.72 mg/kg was measured at 168 h, revealing more efficient As removal by B. reuszeri than Rhodococcus sp. (96.67% and 94.17%, respectively). Both species have the capacity to remove As, but B. reuszeri shows improved growth compared to the Rhodococcus sp. B. reuszeri might be suitable for adaptation and use in As treatment. The results are in agreement with their genetic erosion values, with B. reuszeri showing very little genetic erosion (12.46%) of culture in As concentrations as high as 1,600 mg/L, whereas 82.54% genetic erosion occurred in the Rhodococcus sp., suggesting that Rhodococcus sp. would not survive at this level of genetic erosion. Therefore, B. reuszeri has a high efficiency and can be used for soil As treatment, as it is capable to tolerate a concentration of 0.72 mg/kg and as high as 1,600 mg/L in NA.
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