Wenqing Qin

Adhesion forces between cells of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans or Leptospirillum ferrooxidans and chalcopyrite.

The efficiency of copper leaching is improved by bacteria attached to chalcopyrite. Therefore, the study of the attachment mechanism to control leaching is important. The adhesion of three species of leaching microorganisms including Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans to chalcopyrite was investigated by using atomic force microscopy (AFM). The forces were measured with tip-immobilized cells approached to and retracted from the mineral. The results show that both the surface charge and the hydrophobicity of bacteria cells influence the adhesion force. Furthermore, the adhesion force decreased in case the extracellular polymeric substances (EPS) had been removed. In addition, the data indicate that the amount of attached cells increased with increasing adhesion force.

Bioleaching of chalcopyrite by moderately thermophilic microorganisms.

The leaching of chalcopyrite by moderately thermophilic microorganisms was investigated by employing cyclic voltammetry (CV), accompanying with the leaching behavior elucidation. Leaching experiment showed that there was clear benefit in leaching chalcopyrite within the low solution potential (below 400 mV vs. SCE), compared to the high potential leach (above 550 mV vs. SCE). Simultaneous maintenance of an appropriate concentration of total dissolved iron was necessary and also beneficial to leach chalcopyrite. The leaching results showed the existence of an optimum pH in the leaching of chalcopyrite by the moderately thermophilic microorganisms. The analysis of CV results revealed that the chalcopyrite was reduced to a series of intermediate products (such as talnakhite, bornite and chalcocite) in the cathodic, and then the intermediate product (chalcocite) was oxidized in the anodic.

Bioleaching of chalcopyrite by pure and mixed culture

The bioleaching of chalcopyrite in shake flasks was investigated by using pure Acidithiobacillus ferrooxidans and mixed culture isolated from the acid mine drainage in Yushui and Dabaoshan Copper Mine in China, marked as YS and DB, respectively. The mixed culture consisted mainly of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum spp. (Leptospirillum ferriphilum and Leptospirillum ferrooxians). The results show that the mixed culture is more efficient than the pure Acidithiobacillus ferrooxidans because of the presence of the sulfur-oxidizing cultures that positively increase the dissolution rate and the recovery of copper from chalcopyrite. The pH value decreases with the decrease of chalcopyrite leaching rate, because of the formation of jarosite as a passivation layer on the mineral surface during bioleaching. In the bioleaching using the mixed culture, low pH is got from the sulfur oxidizing inhibiting, the formation of jarosite. The copper extraction reaches 46.27% in mixed culture and 30.37% in pure Acidithiobacillus ferrooxidans after leaching for 75 d.

Microwave-assisted synthesis and characterization of ZnO-nanorod arrays

High density ZnO-nanorod arrays (rod length 1.59 μm) were successfully synthesized via a microwave-assisted solution-phase method using zinc chloride and ammonia solution as reactants. The influence of concentration of ammonia solution, work power, and microwave irradiation time on the morphology and size of final products was carefully investigated. The crystal structure, chemical composition and morphologies of final products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The as-synthesized ZnO is composed of single crystalline and possesses three photoluminescence emissions centered at 400, 469 and 534.5 nm, respectively.

Synergistic bioleaching of chalcopyrite and bornite in the presence of Acidithiobacillus ferrooxidans

Bioleaching of chalcopyrite and bornite in the presence of Acidithiobacillus ferrooxidans was carried out to investigate the influences between each other during bioleaching. Bioleaching results indicated that bornite accelerated the dissolution of chalcopyrite, and chalcopyrite also accelerated the dissolution of bornite, it could be described as a synergistic effect during bioleaching, this synergistic effect might be attributed to the galvanic effect between chalcopyrite and bornite, and to the relatively low solution potential as the addition of bornite. Significantly amount of elemental sulfur and jarosite formed on the minerals surface might be the main passivation film inhibiting the further dissolution, and the amount of elemental sulfur significantly increased with the addition of bornite. Results of electrochemical measurements indicated that the oxidation and reduction mechanisms of chalcopyrite and bornite were similar, the addition of bornite or chalcopyrite did not change the oxidative and reductive mechanisms, but increased the oxidation rate.

Effects of pyrite and bornite on bioleaching of two different types of chalcopyrite in the presence of Leptospirillum ferriphilum

The effects of pyrite and bornite on bioleaching of two different chalcopyrite samples by Leptospirillum ferriphilum were studied for the first time. Results showed that bioleaching behaviors of the two chalcopyrite samples were extremely different. Bornite decreased the redox potential (ORP) and maintained it at an appropriate range (380-480 mV vs. Ag/AgCl) to promote chalcopyrite (A) dissolution, but caused the redox potential out of the optimum range and inhibited chalcopyrite (B) dissolution. Large amount of pyrite decreased the redox potential and maintained it at an optimum range to promote chalcopyrite (A) dissolution, while increased the redox potential and kept it at appropriate range for a longer period of time to enhance the dissolution rate of chalcopyrite (B). Chalcopyrite (B) had significantly higher values of conductivity and oxidation-reduction rate when compared with those of chalcopyrite (A). The work is potentially useful in interpreting the inconsistence of the researches of chalcopyrite hydrometallurgy.

Insights into the relation between adhesion force and chalcopyrite-bioleaching by Acidithiobacillus ferrooxidans.

This paper presents a study on the relation between bacterial adhesion force and bioleaching rate of chalcopyrite, which sheds light on the influence of interfacial interaction on bioleaching behavior. In our research, Acidithiobacillus ferrooxidans (A. ferrooxidans) were adapted to grow with FeSO4 · 7H2O, element sulfur or chalcopyrite. Then, surface properties of Acidithiobacillus ferrooxidans and chalcopyrite were analyzed by contact angle, zeta potential and Fourier transform infrared spectroscopy (FTIR). Adhesion force between bacteria and chalcopyrite was measured by atomic force microscopy (AFM). Attachment and bioleaching behaviors were also monitored. The results showed that A. ferrooxidans adapted with chalcopyrite exhibited the strongest adhesion force to chalcopyrite and the highest bioleaching rate. Culture adapted with sulfur bacteria took second place and FeSO4 · 7H2O-adapted bacteria were the lowest. Bioleaching rate and bacterial attachment capacity were positively related to bacterial adhesion force, which is affected by the nature of energy source. According to this work, the attachment of bacteria to chalcopyrite surface is one of the most important aspects that influence the bioleaching process of chalcopyrite.

Solution chemistry and utilization of alkyl hydroxamic acid in flotation of fine cassiterite

Solution chemistry and ?otation of cassiterite in the presence of alkyl hydroxamic acid collector were investigated. Results show that the alkyl hydroxamic acid is able to float fine cassiterite very well at relatively alkaline conditions, and the pH range of better flotability broadens with the increase of chain length of the collector. Moreover, the metal cations influence the flotation mostly depending on the pH of the medium and to some extent on the concentration of metal cations. Theoretical calculation on the group electronegativity indicates that the alkyl chain length of about seven is of great superiority in the synthetization of hydroxamic acid collector for cassiterite flotation. A co-adsorption between molecules and ions onto cassiterite surface is considered according to the lg c—pH diagram analysis. In terms of zeta potential and infrared spectra, the main interaction involves electric charge interaction, hydrogen bonding interaction and complexation, with the proposed formation of an O, O-five membered rings chelate compound .

Bacterial leaching of chalcopyrite and bornite with native bioleaching microorganism

Abstract A native mesophilic iron-oxidizing bacterium, Acidithiobacillus ferrooxidans , has been isolated (30°C) from a typical, lead-zinc concentrate of Dachang Mine in the region of Liuzhou located in the southwest of China. Two typical copper sulfide minerals, chalcopyrite and bornite, were from Meizhou Copper Mine in the region of Guangdong Province, China. Variation of pH and cell growth on time and effects of some factors such as temperature, inoculation cell number, and pulp density on the bioleaching of chalcopyrite and bornite were investigated. The results obtained from the bioleaching experiments indicate that the efficiency of copper extraction depends on all of the mentioned variables, especially the pulp density has more effect than the other factors on the microorganism. In addition, the results show that the maximum copper recovery was achieved using a mesophilic culture. The copper dissolution reached 51.34% for the chalcopyrite while it was 72.35% for the bornite at pH 2.0, initial Fe(II) concentration 9 g/L and pulp density 5%, after 30 d.

Comparison of electrochemical dissolution of chalcopyrite and bornite in acid culture medium

Abstract The electrochemical dissolution process of chalcopyrite and bornite in acid bacteria culture medium was investigated by electrochemical measurements and X-ray photoelectron spectroscopy (XPS) analysis. Bornite was much easier to be oxidized rather than to be reduced, and chalcopyrite was difficult to be both oxidized and reduced. The relatively higher copper extraction of bornite dissolution can be attributed to its higher oxidation rate. Covellite (CuS) was detected as the intermediate species during the dissolution processes of both bornite and chalcopyrite. Bornite dissolution was preferred to be a direct oxidation pathway, in which bornite was directly oxidized to covellite (CuS) and cupric ions, and the formed covellite (CuS) may inhibit the further dissolution. Chalcopyrite dissolution was preferred to be a continuous reduction–oxidation pathway, in which chalcopyrite was initially reduced to bornite, then oxidized to covellite (CuS), and the initial reduction reaction was the rate-limiting step.