[Show abstract][Hide abstract] ABSTRACT: In this work, the interactions between one sample of silver-bearing tailing (223 g/t silver) and chalcopyrite during bioleaching by mixed moderately thermophilic culture were investigated. Bioleaching results showed that copper can be almost totally extracted from chalcopyrite as the result of addition of the silver-bearing tailing, and silver (Ag) extraction can be significantly improved with the addition of chalcopyrite. Hence, cooperative bioleaching process of chalcopyrite and the chosen silver-bearing tailing was feasible. Ag mainly occurred as silver sulfate (Ag2SO4), and further work of enhancing the Ag extraction and its recovery is currently in progress. The catalytic effect of the silver-bearing tailing on chalcopyrite dissolution was investigated mainly with X-ray photoelectron spectroscopy (XPS) and electrochemical analysis. Results proved that the presence of the silver-bearing tailing enhanced the oxidation rate of chalcopyrite and also eliminated the passivation effect of polysulfide, thus resulting in an extremely high copper extraction.
[Show abstract][Hide abstract] ABSTRACT: A facile solvothermal method is developed for synthesizing layered Co-Ni hydroxide hierarchical structures by using hexamethylenetetramine (HMT) as alkaline reagent. The electrochemical measurements reveal that the specific capacitances of layered bimetallic (Co-Ni) hydroxides are generally superior to those of layered monometallic (Co, Ni) hydroxides. The as-prepared Co0.5Ni0.5 hydroxide hierarchical structures possesses the highest specific capacitance of 1767 F g-1 at a galvanic current density of 1 A g-1 and an outstanding specific capacitance retention of 87% after 1000 cycles. In comparison with the dispersed nanosheets of Co-Ni hydroxide, layered hydroxide hierarchical structures show much superior electrochemical performance. This study provides a promising method to construct hierarchical structures with controllable transition-metal compositions for enhancing the electrochemical performance in hybrid supercapacitors.
Journal of Physics and Chemistry of Solids 09/2015; 88. DOI:10.1016/j.jpcs.2015.09.006 · 1.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, gallium (Ga) microspheres were successfully prepared on silicon substrate by a chemical vapor deposition method and used as templates to fabricate Au nanoparticle-coated Ga (Ga/Au) composite microspheres using an oxidation-reduction reaction between Ga and HAuCl4. The morphology and composition of the Ga microspheres were characterized by scanning electron microscope and energy-dispersive X-ray. It was found that Ga microspheres were partly embedded in the Si substrate. The possible formation mechanism was discussed. The content of Au in the composites could be modulated by controlling the reaction time. SERS measurement shows that the content of Au element in Ga/Au composite microspheres has a great effect on SERS activity. The SERS signals collected by point-to-point and SERS mapping image showed that as-prepared composites exhibit good spatial uniformity and reproducibility. Detection of malachite green molecules with a low concentration (1.0 × 10-10 M) was used as an example to show the possible application of such substrate.
[Show abstract][Hide abstract] ABSTRACT: Sulfate adenylyltransferase gene and 4Fe-4S ferredoxin gene are the key genes related to sulfur and iron oxidations during bioleaching system, respectively. In order to better understand the bioleaching and microorganism synergistic mechanism in chalcopyrite bioleaching by mixed culture of moderate thermophiles, expressions of the two energy metabolism genes and community dynamics of free and attached microorganisms were investigated. Specific primers were designed for real-time quantitative PCR to study the expression of these genes. Real-time PCR results showed that sulfate adenylyltransferase gene was more highly expressed in Sulfobacillus thermosulfidooxidans than that in Acidithiobacillus caldus, and expression of 4Fe-4S ferredoxin gene was higher in Ferroplasma thermophilum than that in S. thermosulfidooxidans and Leptospirillum ferriphilum. The results indicated that in the bioleaching system of chalcopyrite concentrate, sulfur and iron oxidations were mainly performed by S. thermosulfidooxidans and F. thermophilum, respectively. The community dynamics results revealed that S. thermosulfidooxidans took up the largest proportion during the whole period, followed by F. thermophilum, A. caldus, and L. ferriphilum. The CCA analysis showed that 4Fe-4S ferredoxin gene expression was mainly affected (positively correlated) by high pH and elevated concentration of ferrous ion, while no factor was observed to prominently influence the expression of sulfate adenylyltransferase gene.
Current Microbiology 05/2015; 71(1). DOI:10.1007/s00284-015-0817-7 · 1.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Needle-like CoO nanowires grown on carbon cloth have been successfully fabricated by a controllable hydrothermal method followed via annealing process. The as-fabricated nanostructure showed enhanced specific capacitances and excellent cycling stability in supercapacitors.
[Show abstract][Hide abstract] ABSTRACT: Bio-hydrometallurgy technology was applied for the extraction of copper from the raw ores of Chambishi Mine in Zambia. A copper extraction of 93.29% was obtained for small scale column bioleaching within 63 days, while a copper extraction of 89.05% was achieved for large scale column bioleaching in 90 days, thus confirming the amenability of the raw ores for effective extraction via bioleaching. The bacteria were cultured in a 6-stage enlarge cultivation. The bacterial cultures with cell concentration of more than 1×10 8 cells/mL were added into a spray pond of sulfuric acid to be applied in the dump leaching, and a copper extraction of about 50% was achieved within 2 months. The production report revealed that the copper extraction increased by approximate 20%, and the acid consumption was reduced to around 35% as a consequence of adding the bacteria. The industrial demonstration of the bio-hydrometallurgy technique is now well established in Zambia, and further applications of bio-hydrometallurgy in both Zambia and Congo are currently in progress.
[Show abstract][Hide abstract] ABSTRACT: Double-shell cobalt monoxide (CoO) hollow particles were successfully synthesized by a facile and effective one-pot solution-based synthetic route. The inner architecture and outer structure of the double-shell CoO hollow particles could be readily created through controlling experimental parameters. A possible formation mechanism was proposed based on the experimental results. The current synthetic strategy has good prospects for the future production of other transition-metal oxides particles with hollow interior. Furthermore, double-shell cobalt oxide (Co3O4) hollow particles could also be obtained through calcinating corresponding CoO hollow particles. The magnetic measurements revealed double-shell CoO and Co3O4 hollow particles exhibit ferromagnetic and antiferromagnetic behaviour, respectively.
[Show abstract][Hide abstract] ABSTRACT: Hollow BiVO4 microspheres are prepared in the presence of ethylenediaminetetraacetic acid (EDTA) through a hydrothermal method, and used as a template for the fabrication of Ag-nanoparticle-decorated BiVO4 (BiVO4/Ag) composite microspheres. The morphology and structure are characterized by transmission electron microscopy and scanning electron microscopy. It is found that EDTA plays an important role in the formation of the hollow microspheres, and the possible formation mechanism is discussed. UV/visible spectrometry analysis shows that the BiVO4/Ag composite microspheres exhibit a distinct surface plasmon absorption band compared with pure BiVO4 microspheres. The photocatalytic activities of the BiVO4/Ag composite microspheres are examined by studying the degradation of rhodamine 6G (R6G) solutions under visible-light irradiation (>400 nm). The results show clearly that the BiVO4/Ag composite microspheres possess a much higher photocatalytic activity than pure BiVO4 microspheres and P25. In addition, Raman analyses show that the BiVO4/Ag composite microspheres exhibit an excellent surface-enhanced Raman scattering (SERS) performance.
[Show abstract][Hide abstract] ABSTRACT: Thermodynamic calculations and electrochemical measurements were employed to establish a mathematic model for predicting the optimum redox potential in chalcopyrite leaching at 318 K. The proposed model revealed that the optimum redox potential mainly depended on the temperature as well as the concentrations of Cu2+ and Fe2+. Chemical leaching (ferric leaching) of chalcopyrite indicated that the proposed model was accurate, from which the optimum redox potential of bioleaching of chalcopyrite can also be accurately predicted. Based on the model, the redox potential should be maintained at an optimum potential range (E-L-E-H) to obtain a high leaching efficiency. Moreover, the addition of Cu2+ and Fe2+ accelerated the dissolution of chalcopyrite remarkably at the initial stage of bioleaching, but the further dissolution was inhibited owing to the jarosite formed during the bioleaching process. Therefore, Cu2+ and Fe2+ should be added periodically to prevent the rapid formation of jarosite and enhance the bioleaching efficiency. (C) 2014 Elsevier B.V. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Assistance of introduction of Ferroplasma thermophilum in improving copper concentrate bio-dissolution was investigated. Results in pH-controlled stirred tank reactors showed that addition of F. thermophilum into the defined microbial consortium (Acidithiobacillus caldus and Leptospirillum ferriphilum) improved the dissolution and conversion of iron and meanwhile caused significant difference in the planktonic and attached population dynamics. Thereby, copper extraction was accelerated and increased by 22.7% after 24 days in comparison to the control without F. thermophilum. The intensive study of relationships between the modified bioleaching performance and augmentation of F. thermophilum conducted in shake flasks indicated that (1) F. thermophilum was capable of bio-catalytically regenerating the sulfide-attacking agent—ferric iron in bioleaching; (2) more importantly, mixed cultures involving F. thermophilum collaboratively resisted the inhibitory effects of environmental stress conditions on cells, such as 0.04% yeast extract, 5 g L−1 Cu2+ and low initial pH 1.2 demonstrated in the simple growth medium, and furthermore increased the total cell numbers and accelerated the iron or sulfur oxidation compared to pure cultures. In conclusion, these findings revealed that there were synergetic acts between F. thermophilum and At. caldus or L. ferriphilum, which contributed to an improvement in copper leaching rate and level.
[Show abstract][Hide abstract] ABSTRACT: Copper Sulfide (CuS) hollow spheres could be successfully synthesized in large quantities through a facile biomolecule-assisted hydrothermal synthetic method. The as-fabricated CuS hollow spheres showed specific capacitances and excellent cycling stability in supercapacitors.
[Show abstract][Hide abstract] ABSTRACT: In this work, a new stirred reactor was designed and then a comparative study of bioleaching using stirred reactor and shake flask was carried out to investigate the bioleaching performance of the new stirred reactor. Results showed that variations of redox potentials and acid consumptions during were similar in the two systems, and about 15% more copper extraction can be obtained by stirred reactor. Bacterial concentration increased more sharply in the initial stage of bioleaching in stirred reactor. Analytical results showed that a worse passivation caused by larger amount of jarosite and elemental sulfur on the minerals surface leaded the lower copper extraction in shake flask. Electrochemical analysis revealed that the conductivity of bioleaching residues of shake flasks is lower than that of bioleaching residues of stirred reactor. Stirred reactor possesses significant advantages over shake flask in bioleaching of chalcopyrite concentrates can be caused mainly by better mass transfer effect, better air inflation effect and stronger shear force. Therefore, the stirred reactor can be used for both enlarge cultivation of bacteria and tank bioleaching of ores. Electrochemical measurements revealed that chalcopyrite dissolution was preferred to be a continuous reduction-oxidation pathway, in which chalcopyrite was initially reduced and then oxidized, and the initial reduction reaction was the rate-limiting step.
International journal of electrochemical science 01/2015; 10(1):848-858. · 1.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The dissolution process of chalcopyrite in the presence of mesophilic microorganisms was investigated by electrochemical measurements. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis, accompanied by leaching experiments. Results proved that the presence of Acidithiobacillus ferrooxidans enhanced the initial reduction of chalcopyrite to intermediate species (Cu2S), thus promoting the dissolution of chalcopyrite in the initial stage of bioleaching. However, chalcopyrite tended to be directly oxidized to polysulfide (Sn2−) and CuS in the later stage of bioleaching when redox potential was higher than 0.5 V (vs. Ag/AgCl), the formed polysulfide and jarosite can be responsible for the passivation of chalcopyrite in the later stage of bioleaching by A.ferrooxidans. On the contrary, Chalcopyrite was mainly directly oxidized to polysulfide and CuS in the presence of sterile 9K medium or Acidithiobacillus thiooxidans, and the initial reduction reaction was still the rate-limiting step, thus resulting in low copper extraction rate.