Min Gan

The nature of Schwertmannite and Jarosite mediated by two strains of Acidithiobacillus ferrooxidans with different ferrous oxidation ability

Jarosite and Schwertmannite are iron-oxyhydroxysulfate materials. These materials gain increasing interest in geological and metallurgical fields. Especially, for it can effectively scavenge heavy metals, less toxic ions and better biocompatibility, the application potential in environment becomes more and more intriguing. In this study, the nature of Jarosite and Schwertmannite mediates synthesized by two strains of Acidithiobacillus ferrooxidans with different ferrous oxidation ability is investigated. The precipitates are characterized by SEM, XRD, FTIR, and TG/DSC analysis. The materials are varied in color, shape, surface area, elemental composition and crystallinity. The crystallinity of precipitate produced by A. ferrooxidans 23270 with lower oxidation ability in optimized medium is significantly better than the precipitate produced by A. ferrooxidans Gf. A. ferrooxidans Gf will tend to mediate the formation of Schwertmannite with the decreasing of monovalent cation concentration in optimized medium. Cr(VI) adsorption capacity difference exists among the four materials. The adsorption efficiency of Schwertmannite is higher than Jarosite. Adsorption capacity of the materials formed by A. ferrooxidans Gf is higher than that of A. ferrooxidans 23270. Adsorption capacity decreases with the increasing of crystallinity.

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.

Bioleaching of multiple metals from contaminated sediment by moderate thermophiles

A moderately thermophilic consortium was applied in bioleaching multiple metals from contaminated sediment. The consortium got higher acidification and metals soubilization efficiency than that of the pure strains. The synergistic effect of the thermophilic consortium accelerated substrates utilization. The utilization of substrate started with sulfur in the early stage, and then the pH declined, giving rise to making use of the pyrite. Community dynamic showed that A. caldus was the predominant bacteria during the whole bioleaching process while the abundance of S. thermotolerans increased together with pyrite utilization. Solubilization efficiency of Zn, Cu, Mn and Cd reached 98%, 94%, 95%, and 89% respectively, while As, Hg, Pb was only 45%, 34%, 22%. Logistic model was used to simulate the bioleaching process, whose fitting degree was higher than 90%. Correlation analysis revealed that metal leaching was mainly an acid solubilization process. Fraction analysis revealed that metals decreased in mobility and bioavailability.

Catalytic effect of light illumination on bioleaching of chalcopyrite

The influence of visible light exposure on chalcopyrite bioleaching was investigated using Acidithiobacillus ferrooxidans. The results indicated, in both shake-flasks and aerated reactors with 8500-lux light, the dissolved Cu was 91.80% and 23.71% higher, respectively, than that in the controls without light. The catalytic effect was found to increase bioleaching to a certain limit, then plateaued as the initial chalcopyrite concentration increased from 2% to 4.5%. Thus a balanced mineral concentration is highly amenable to bioleaching via offering increased available active sites for light adsorption while eschewing mineral aggregation and screening effects. Using semiconducting chalcopyrite, the light facilitated the reduction of Fe(3+) to Fe(2+) as metabolic substrates for A.ferrooxidans, leading to better biomass, lower pH and redox potential, which are conducive to chalcopyrite leaching. The light exposure on iron redox cycling was further confirmed by chemical leaching tests using Fe(3+), which exhibited higher Fe(2+) levels in the light-induced system.

The influence of aluminum chloride on biosynthetic schwertmannite and Cu(II)/Cr(VI) adsorption

The iron oxyhydroxides schwertmannite and akaganeite are recognized as promising absorbents for heavy metal contaminated water treatment. In this study, aluminium chloride modified schwertmannite was biosynthesized using Acidithiobacillus ferrooxidans and characterized using SEM, FTIR, XRD, TGA, potentiometric titrations and XPS. The effect of pH, and the adsorption kinetics, isotherms and mechanism were systematically investigated. With increasing aluminium chloride, the adsorbent transformed from nanoscale villus covered spherical aggregates to rod like structures consisting of globes, and facilitated the decreasing crystallinity and akaganeite formation. The optimum pH for Cr(VI) adsorption was between 6.0 and 7.0, while Cu(II) adsorption was increased over the pH range of 4.0–8.0. The adsorption kinetics varied with pH and the adsorbents. Equilibrium was reached within 30 min for both metals, and the pseudo-second-order model fitted the adsorption process well. The maximum Cu(II) and Cr(VI) adsorption reached 23.95 and 57.60 mg g−1 which occurred at an FeSO4·7H2O/AlCl3 ratio of 15 : 5 and 15 : 10 respectively. As for the binary metal system, the maximum adsorption for Cu(II) and Cr(VI) was 14.10 and 28.89 mg g−1, respectively, achieved with an FeSO4·7H2O/AlCl3 ratio of 15 : 5. The modification enhanced the adsorption capacity effectively. Additionally, the adsorbent could be effectively regenerated through pH 2.0 water washing. FTIR, XPS and released proton correlation analysis revealed that –O–H, O–H–Cl and SO42− were the key groups in adsorption. Heavy metals were adsorbed on schwertmannite through anion-exchange and surface complexation. Heavy metals can be efficiently removed by the modified biosynthetic schwertmannite.

Microbial functional genes enriched in the Xiangjiang River sediments with heavy metal contamination

BackgroundXiangjiang River (Hunan, China) has been contaminated with heavy metal for several decades by surrounding factories. However, little is known about the influence of a gradient of heavy metal contamination on the diversity, structure of microbial functional gene in sediment. To deeply understand the impact of heavy metal contamination on microbial community, a comprehensive functional gene array (GeoChip 5.0) has been used to study the functional genes structure, composition, diversity and metabolic potential of microbial community from three heavy metal polluted sites of Xiangjiang River.ResultsA total of 25595 functional genes involved in different biogeochemical processes have been detected in three sites, and different diversities and structures of microbial functional genes were observed. The analysis of gene overlapping, unique genes, and various diversity indices indicated a significant correlation between the level of heavy metal contamination and the functional diversity. Plentiful resistant genes related to various metal were detected, such as copper, arsenic, chromium and mercury. The results indicated a significantly higher abundance of genes involved in metal resistance including sulfate reduction genes (dsr) in studied site with most serious heavy metal contamination, such as cueo, mer, metc, merb, tehb and terc gene. With regard to the relationship between the environmental variables and microbial functional structure, S, Cu, Cd, Hg and Cr were the dominating factor shaping the microbial distribution pattern in three sites.ConclusionsThis study suggests that high level of heavy metal contamination resulted in higher functional diversity and the abundance of metal resistant genes. These variation therefore significantly contribute to the resistance, resilience and stability of the microbial community subjected to the gradient of heavy metals contaminant in Xiangjiang River.

Biosynthesis of bifunctional iron oxyhydrosulfate by Acidithiobacillus ferroxidans and their application to coagulation and adsorption

Coagulation and adsorption are important environmental technologies, which were widely applied in water treatment. In this study, a type of villous iron oxyhydrosulfate with low crystallinity, high content iron, sulfate and hydroxyl was synthesized by Acidithiobacillus ferrooxidans, which possessed coagulation and heavy metal adsorption ability simultaneously. The results showed that the Cu(II) adsorption capacity increased within a small range over the pH range of 3.0-5.0 but increased evidently over the range of 6.0-8.0. The maximal Cu(II) adsorption capacity of sample Af and Gf reached 50.97 and 46.08mg/g respectively. The optimum pH for Cr(VI) adsorption was 6.0, and the maximal adsorption capacity reached 51.32 and 59.57mg/g. The Langmuir isotherm can better describe the adsorption behavior of Cr(VI). Coagulation performance of the iron oxyhydrosulfate (Sh) has been significantly enhanced by polysilicic acid (PSA), which was mainly determined by PSA/Sh ratio, pH and coagulant dosage. Coagulation efficiency maintained approximately at 98% when the PSA/Sh ratio ranged from 0.4/0.1 to 1.0/0.1. Polysilicic acid worked efficiently in wide pH range extending, from 2 to 3.5. Coagulation performance improved significantly with the increasing of the coagulant dosage at lower dosage range, while, at higher dosage range, the improvement was not evident even with more coagulant addition.

Synchrotron-Based XRD and XANES Study of Bornite Leached by Mesophilic Mixed Bacteria

In this study, bioleaching experiments, synchrotron X-ray Diffraction (SR-XRD), X-ray absorption near edge structure (XANES) and X-ray Photoelectron Spectroscopy (XPS) were conducted to investigate the intermediates and surface species of bornite leached by mesophilic mixed bacteria of Leptospirillum ferriphilum, Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. CuS, Cu9Fe9S16 and S8 were the main intermediate species during bornite bioleaching by mesophilic mixed bacteria, and CuFeS2 was also detected. The surface species of S2− and S2 2− would be polymerized to S n 2− during bioleaching. The formation of element sulfur and the increase of its content were confirmed by the fitted results of XPS spectra. The presence of polysulfide and element sulfur did not inhibit the bornite bioleaching. The formations of CuS and CuFeS2 were confirmed by the results of Cu K-edge XANES spectra.

Investigation of Controlled Redox Potential with Pyrite during Chalcopyrite Bioleaching by Mixed Moderately Thermophiles

Various methods of controlling redox potential (ORP) with electrochemical bioreactor and others have been investigated to increase copper extraction of chalcopyrite in bioleaching,but less attention has been paid to reducing ferric to ferrous ions. Therefore, in this work, the redox potential of chalcopyrite bioleaching system in the presence of mixed moderately thermophiles containing Leptospirillum. ferriphilum,Acidithiobacillus. caldus and Sulfobacillus.thermosulfidooxidans has been controlled by pyrite. It was found that at a constant pH of 2.0, the addition of pyrite can reduce ferric to ferrous ion to a large extent, and the lower ORP values can be obtained. Bioleaching experiments indicated that the time for adding pyrite caused different bioleaching behaviors of chalcopyrite. The high copper extraction can be obtained by added pyrite at a low ORP values (<420 mV vs. Ag/AgCl). The XRD tests and SEM images showed that the amounts of formed jarosite increased as the pyrite addition, and the loose and porous jarosite can be found at low ORP values.

Introduction to High-Throughput Sequencing Technologies and Review of its Application in Bioleaching

Over the past years, the traditional cultivation-independent genomic approaches which rely on the preexisting knowledge about gene sequence, have significantly promoted our understanding of the structural and functional diversity of bioleaching microorganisms in extremely acidic environments. However, high-throughput sequencing technology as a comprehensive and rapid method is now being ported to bioleaching systems for microbial community and gene expression analysis. Years of research have demonstrated that high-throughput sequencing technology has the potential to dramatically accelerate biological research, by enabling the comprehensive analysis of genomes and transcriptomes. This paper aims to introduce the high-throughput sequencing methodology, particularly focusing on the application of high-throughput sequencing technology on bioleaching microorganisms and the challenges associated with its applications.