Hong-chang Liu

Thermophilic archaeal community succession and function change associated with the leaching rate in bioleaching of chalcopyrite.

The community succession and function change of thermophilic archaea Acidianus brierleyi, Metallosphaera sedula, Acidianus manzaensis and Sulfolobus metallicus were studied by denaturing gradient gel electrophoresis (DGGE) analysis of amplifying 16S rRNA genes fragments and real-time qPCR analysis of amplifying sulfur-oxidizing soxB gene associated with chalcopyrite bioleaching rate at different temperatures and initial pH values. The analysis results of the community succession indicated that temperature and initial pH value had a significant effect on the consortium, and S. metallicus was most sensitive to the environmental change, A. brierleyi showed the best adaptability and sulfur oxidation ability and predominated in various leaching systems. Meanwhile, the leaching rate of chalcopyrite closely related to the consortium function embodied by soxB gene, which could prove a desirable way for revealing microbial sulfur oxidation difference and tracking the function change of the consortium, and for optimizing the leaching parameters and improving the recovery of valuable metals.

Effect of surfactant Tween-80 on sulfur oxidation and expression of sulfur metabolism relevant genes of Acidithiobacillus ferrooxidans

Abstract The effects of surfactant Tween-80 on the growth, sulfur oxidation, and expression of selected typical sulfur metabolism relevant genes of Acidithiobacillus ferrooxidans ATCC 23270 were investigated. The results showed that in the presence of 10 −2 g/L Tween-80, the growth of A. ferrooxidans and its metabolism on the insoluble substrate S 0 and CuFeS 2 were promoted. After 24 d of bioleaching, the copper extraction yield of chalcopyrite at 10 −2 g/L Tween-80 increased by 16% compared with the bioleaching experiment without Tween-80. FT-IR spectra analysis revealed that the result was probably caused by the extracellular polymeric substances whose composition could be changed by the surfactant addition. RT-qPCR was used to analyze the differential expressions of 17 selected sulfur metabolism relevant genes in response to the addition of Tween-80. Down-regulation of the extracellular protein genes indicated the influence of Tween-80 on bacteria-sulfur adsorption. Variation of the expression level of the enzymes provided a supplement to sulfur metabolism investigation.

Synchrotron radiation based STXM analysis and micro-XRF mapping of differential expression of extracellular thiol groups by Acidithiobacillus ferrooxidans grown on Fe2 + and S0

The differential expression of extracellular thiol groups by Acidithiobacillus ferrooxidans grown on substrates Fe(2+) and S(0) was investigated by using synchrotron radiation based scanning transmission X-ray microscopy (STXM) imaging and microbeam X-ray fluorescence (μ-XRF) mapping. The extracellular thiol groups (SH) were first alkylated by iodoacetic acid forming Protein-SCH2COOH and then the P-SCH2COOH was marked by calcium ions forming P-SCH2COOCa. The STXM imaging and μ-XRF mapping of SH were based on analysis of SCH2COO-bonded Ca(2+). The results indicated that the thiol group content of A. ferrooxidans grown on S(0) is 3.88 times to that on Fe(2+). Combined with selective labeling of SH by Ca(2+), the STXM imaging and μ-XRF mapping provided an in situ and rapid analysis of differential expression of extracellular thiol groups.

Differential utilization and transformation of sulfur allotropes, μ-S and α-S8, by moderate thermoacidophile Sulfobacillus thermosulfidooxidans.

The utilization of amorphous μ-S and orthorhombic α-S8 by thermoacidophile Sulfobacillus thermosulfidooxidans was firstly investigated in terms of cell growth and sulfur oxidation behavior. The morphology and surface sulfur speciation transformation were evaluated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Raman spectroscopy and sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the strain grown on μ-S entered slower (about 1 day later) into the exponential phase, while grew faster in exponential phase and attained higher maximal cell density and lower pH than on α-S8. After bio-corrosion, both sulfur samples were evidently eroded, but only μ-S surface presented much porosity, while α-S8 maintained glabrous. μ-S began to be gradually converted into α-S8 from day 2 when the bacterial cells entered the exponential phase, with a final composition of 62.3% μ-S and 37.7% α-S8 on day 4 at the stationary phase. α-S8 was not found to transform into other species in the experiments with or without bacteria. These data indicated S. thermosulfidooxidans oxidized amorphous μ-S faster than orthorhombic α-S8, but the chain-like μ-S was transformed into cyclic α-S8 by S. thermosulfidooxidans.

Iron L-edge and sulfur K-edge XANES spectroscopy analysis of pyrite leached by Acidianus manzaensis

Iron L-edge and sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy analysis of pyrite leached by extreme thermophilic Archaea strain Acidianus manzaensis (A. manzaensis) was carried out. Leaching experiments show that the oxidation of pyrite can be accelerated by A. manzaensis. Leaching results show that with the increase of leaching time, pH value in the leaching solution gradually decreases, redox potential increases rapidly from day 0 to day 3, and then increases slowly. The SEM results show that the pyrite surfaces are corroded gradually by A. manzaensis, and the XRD results show that the leaching residues contain new compositions of jarosite and elemental sulfur (S-0). The iron L-edge XANES spectroscopy analysis of pyrite during biooxidation indicates that pyrite is gradually converted to Fe(III)-containing species. The sulfur K-edge XANES spectroscopy analysis indicates that elemental sulfur is produced during bioleaching and maintains mass fractions of 3.2%-5.9%. Sodium thiosulfate was also detected from day 2 to day 4, indicating the existence of thiosulfate during biooxidation of pyrite.

Differential utilization of cyclic, orthorhombic α- and chain-like polymeric μ-sulfur by Acidithiobacillus ferrooxidans

Abstract The differential utilization of cyclic, orthorhombic α-sulfur (α-S) and chain-like polymeric μ-sulfur (μ-S) by Acidithiobacillus ferrooxidans was investigated. The growth and sulfur oxidation results indicated that utilization of μ-S by A. ferrooxidans was clearly different from α-S. Even if the planktonic cells were produced, the fall of pH and the rise of sulfate concentration were the same after 300 h on each substrate, the speeds of the planktonic cells increase, pH decrease and sulfate concentration increase in the earlier cultivation stage were faster on polymeric sulfur compared with the orthorhombic form. The adsorption capacity of the cells was higher on μ-S than on α-S. The results of SEM, DRIFTS and XRD analyses indicated that the surfaces of α-S and μ-S were modified differently by cells. Differential expression of 11 selected sulfur adsorption-activation and metabolism relevant genes was detected by RT-qPCR. The results showed that the expression of the hydrophobic substrate transport proteins and the sulfur metabolism related proteins was up-regulated, and the adsorption and activation related proteins were down-regulated when the cells were grown on μ-S, suggesting that μ-S could be more easily bio-adapted and activated than α-S.

Evidence of cell surface iron speciation of acidophilic iron- oxidizing microorganisms in indirect bioleaching process

While indirect model has been widely accepted in bioleaching, but the evidence of cell surface iron speciation has not been reported. In the present work the iron speciation on the cell surfaces of four typically acidophilic iron-oxidizing microorganism (mesophilic Acidithiobacillus ferrooxidans ATCC 23270, moderately thermophilic Leptospirillum ferriphilum YSK and Sulfobacillus thermosulfidooxidans St, and extremely thermophilic Acidianus manzaensis YN25) grown on different energy substrates (chalcopyrite, pyrite, ferrous sulfate and elemental sulfur (S0)) were studied in situ firstly by using synchrotron-based micro- X-ray fluorescence analysis and X-ray absorption near-edge structure spectroscopy. Results showed that the cells grown on iron-containing substrates had apparently higher surface iron content than the cells grown on S0. Both ferrous iron and ferric iron were detected on the cell surface of all tested AIOMs, and the Fe(II)/Fe(III) ratios of the same microorganism were affected by different energy substrates. The iron distribution and bonding state of single cell of A. manzaensis were then studied in situ by scanning transmission soft X-ray microscopy based on dual-energy contrast analysis and stack analysis. Results showed that the iron species distributed evenly on the cell surface and bonded with amino, carboxyl and hydroxyl groups.

Differential utilization and speciation transformation of orthorhombic α-S8 and amorphous μ-S by substrate-acclimated mesophilic Acidithiobacillus ferrooxidans

The utilization and speciation transformation of alpha-S-8 and mu-S by the typical mesophilic acidophilic strain Acidithiobacillus ferrooxidans ATCC 23270 were investigated. A. ferrooxidans cells first acclimated to the energy source alpha-S-8 or mu-S, respectively. The results of cell growth and sulfur oxidation behavior showed that the strain grown on alpha-S-8 entered slowly (about 1 d later) into the exponential phase, while grew faster in the exponential phase and attained higher maximal cell density and lower pH value than that on mu-S. After bio-corrosion, both of the two sulfur samples were evidently eroded and modified by A. ferrooxidans cells. After growth of A. ferrooxidans, the surface composition of amorphous mu-S became 63.1% mu-S and 36.9% alpha-S-8, and that of orthorhombic alpha-S-8 became 68.3% alpha-S-8 and 31.7% mu-S, while the surface compositions of alpha-S-8 and mu-S in sterile experiment were not changed, indicating that these two elemental sulfur species can be interconverted by A. ferrooxidans.

Relatedness between catalytic effect of activated carbon and passivation phenomenon during chalcopyrite bioleaching by mixed thermophilic Archaea culture at 65 °C

The relatedness between catalytic effect of activated carbon and passivation phenomenon during chalcopyrite bioleaching by mixed thermophilic Archaea culture (Acidianus brierleyi, Metallosphaera sedula, Acidianus manzaensis and Sulfolobus metallicus) at 65 °C was studied. Leaching experiments showed that the addition of activated carbon could significantly promote the dissolution of chalcopyrite for both bioleaching and chemical leaching. The results of synchrotron-based X-ray diffraction, iron L-edge and sulfur K-edge X-ray absorption near edge structure spectroscopy indicated that activated carbon could change the transition path of electrons through galvanic interactions to form more readily dissolved secondary mineral chalcocite at a low redox potential (<400 mV) and then enhanced the copper dissolution. Jarosite accumulated immediately in the initial stage of bioleaching with activated carbon but copper dissolution was not hindered. However, much jarosite precipitated on the surface of chalcopyrite in the late stage of bioleaching, which might account for the decrease of copper dissolution rate. More elemental sulfur (S0) was also detected with additional activated carbon but the mixed thermophilic Archaea culture had a great sulfur oxidation activity, thus S0 was eliminated and seemed to have no significant influence on the dissolution of chalcopyrite.

Formation and evolution of secondary minerals during bioleaching of chalcopyrite by thermoacidophilic Archaea Acidianus manzaensis

Abstract The formation and evolution of secondary minerals during bioleaching of chalcopyrite by thermoacidophilic Archaea Acidianus manzaensis were analyzed by combining synchrotron radiation X-ray diffraction (SR-XRD) and S, Fe and Cu Kα X-ray absorption near edge structure (XANES) spectroscopy. Leaching experiment showed that 82.4% of Cu2+ was dissolved by A. manzaensis after 10 d. The surface of chalcopyrite was corroded apparently and covered with leaching products. During bioleaching, the formation and evolution of secondary minerals were as follows: 1) little elemental sulfur, jarosite, bornite and chalcocite were found at days 2 and 4; and 2) bornite and chalcocite disappeared, covellite formed, and jarosite gradually became the main component at days 6 and 10. These results indicated that metal-deficiency sulfides chalcocite and bornite were first formed with a low redox potential value (360–461 mV), and then gradually transformed to covellite with a high redox potential value (461–531 mV).