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Understanding bacterial adsorption and the evolution of biofilms on arsenopyrite with different surface structures is of great significance to clarifying the mechanism of microbe-mineral interfacial interactions and the production of acidic mine drainage impacting the environment. In this study, the attachment of Sulfobacillus thermosulfidooxidans cells and subsequent biofilm formation on arsenopyrite with different surface structures in the presence of dissolved As(III) was studied. Arsenopyrite slices with a specific surface were obtained by electrochemical corrosion at 0.26 V. The scanning electronic microscopy-energy dispersion spectra analyses indicated that the arsenopyrite surface deficient in sulfur and iron obtained by electrochemical treatment was not favorable for the initial adsorption of bacteria, and the addition of As(III) inhibited the adsorption of microbial cells. Epifluorescence microscopy showed that the number of cells attaching to the arsenopyrite surface increased with time; however, biofilm formation was delayed significantly when As(III) was added.

Ferric iron has a significant effect on the bioleaching of arsenopyrite, the most efficient way for pretreatment of arsenopyrite-bearing gold ores. Up to date, the differential effect of Fe(III) compounds on that process was rarely studied. Herein, FeCl3, Fe(NO3)3 and Fe2O3 were addressed to unravel their different promotion effects during arsenopyrite biooxidation by Sulfobacillus thermosulfidooxidans, in which the As/Fe/S speciation transformation were comprehensively analyzed mainly with synchrotron radiation-based X-ray diffraction (SR-XRD) and Fe L- and As/S K-edge X-ray absorption near edge structure (XANES) spectroscopy to detect the elimination of passivation, besides the changes in the morphology and the leaching parameters of the mineral. The results showed that, the bioleaching of arsenopyrite was efficiently promoted under addition of the Fe(III) compounds (0.6 g/L), for instance, the extraction rates of As were increased from 55% to 64–77%, the surface of arsenopyrite suffered more serious corrosion and covered with a loose and porous structure, the intermediates S0, thiosulfate and orpiment significantly decreased, and jarosites and schwertmannite increased, the remaining content of arsenopyrite was decreased from 31.5% to 21.7–5.3%. Those results indicated that, the iron/sulfur oxidation activity was enhanced and the transformation of those intermediates was accelerated by the Fe(III) compounds added. Such change intension accompanied with the promotion effect observes the order FeCl3 > Fe(NO3)3 > Fe2O3. These results reveale that the adding Fe(III) compounds, especially for FeCl3, can efficiently promote the biooxidation through removal of some intermediates from the surface of the arsenopyrite and thus optimize the pretreatment of arsenopyrite-bearing gold ores.

Coal fly ash (CFA), a waste byproduct of thermal power plants, is a major dust pollution source and a resource bearing valuable metals, such as Al and Ce. Metal bioleaching from CFA can be cost-effective for disposal with significant economic and environmental benefits. The goal of this study was to evaluate the bioleaching of Al and Ce from CFA by meso-acidophilic Acidithiobacillus ferrooxidans with the addition of pyrite after CFA was activated by roasting with Na2CO3 at a mass ratio 1:0.22 (w/w) to quantitatively transform the principal Al-bearing minerals mullite and sillimanite into nepheline and Al2O3. Optimal leaching of Al (91.2% after 12 days of incubation) and Ce (63.4% after 8 days of incubation) was achieved at a mass ratio of pyrite to activated CFA (a-CFA) 1.5:1, pulp density 20 g/L, initial pH 1.75 and initial inoculum 2 × 108/ml. As pyrite was bioleached, the species S2−, S22− and Sn2− were transformed to S0 and then to SO42−, and pyrite was converted to Fe(III)-containing species. With the accumulation of jarosites and the dissolution of a-CFA, amorphous phases containing Al2SiO5, interconnected [SiO4]-[AlOn] units, and SiO2 gel, mineralogical phases containing beaverite and pyrophyllite were successively generated. These results indicated that the oxidation of pyrite driven by A. ferrooxidans significantly promoted the dissolution of a-CFA for metal extraction. Compared with metal bioleaching from CFA in previous studies, the route of activation combined with bioleaching has resulted in significant progress in metal recovery.

In this study, the mechanisms by which ferric iron promotes bioleaching of arsenopyrite by the moderately thermoacidophilic strain Sulfobacillus thermosulfidooxidans YN-22 was evaluated for the first time by integrating Fe L-edge and As/S K-edge X-ray absorption near edge structure (XANES) spectroscopy with Fourier transform infrared spectroscopy (FT-IR), synchrotron radiation X-ray diffraction (SR-XRD), Raman spectroscopy, and scanning electron microscopy (SEM), and the leaching parameters were also determined. The results showed that the addition of Fe3+ (6 g/L) significantly promoted bioleaching of arsenopyrite by enhancing the cell growth and the (bio)degradation of elemental sulfur (S0) and orpiment (As2S3) intermediates on the mineral surface. In addition, an increased formation of loose particulate structures containing the Fe(III)-containing products jarosite (mainly ammoniojarosite), scorodite (ferric arsenate) and schwertmannite was observed.

Bioleaching of chalcopyrite with different crystal structures (α-phase, β-phase and γ-phase) by Acidianus manzaensis was comparatively studied by synchrotron radiation based X-ray diffraction (SR-XRD) and S K-edge X-ray absorption near edge structure (XANES) spectroscopy. The α-phase, β-phase and γ-phase chalcopyrite was prepared by heating original chalcopyrite at 583, 773 and 848 K, respectively. Bioleaching results showed that [Cu2+] in the leaching solution of α-phase, β-phase, γ-phase and original chalcopyrite after 10 days of bioleaching was 1.27, 1.86, 1.43 and 1.13 g/L, respectively, suggesting that β-phase had a better leaching kinetics than others. SR-XRD and XANES results indicated that jarosite and chalcopyrite were the main components in the leaching residues in all cases, and elemental sulfur formed in the early stage of bioleaching. While for β-phase and γ-phase chalcopyrite during bioleaching, bornite was produced in the initial stage of leaching, and turned into chalcocite on day 6.

Mechanical activation as a means of accelerating the mineral dissolution may play an important role in chalcopyrite bioleaching. In the present work, the mechanical activation by ball-milling with 10 min, 30 min, 60 min, 90 min, 120 min and 180 min time periods of bioleaching of chalcopyrite was studied, and then evaluated by a Density Functional Theory (DFT) calculation. The results showed that the specific surface area increased sharply in the very beginning of mechanical activation and then increased slowly until the agglomeration of the particles occurred, while the chalcopyrite lattices increased with the mechanical activation. The reaction activity analyzed by cyclic voltammetry (CV) increased slowly in 30 min, increased quickly in the following 90 min, and then decreased, while the hydrophobicity analyzed by contact angles of the chalcopyrite after activation showed less of a change. The results showed that after 15 days of bioleaching, the Cu leaching by Sulfobacillus thermosulfidooxidans (S. thermosulfidooxidans) increased from 9.39% in the 0 min of mechanical activation to 87.41% in the 120 min of mechanical activation, and the copper leaching rate increased by about 78%. The DFT results provide solid proof that the activated chalcopyrite can be adsorbed more easily by cells with higher adsorption energies and stronger bonds.

Ag+ is one of the efficient and recoverable catalysts to improve chalcopyrite bioleaching. Because of the complexity of the surface reaction during chalcopyrite bioleaching, there is still controversy on catalytic mechanism of Ag+ in improving dissolution of chalcopyrite. In the present study, we studied the catalytic effect of Ag+ on bioleaching of chalcopyrite by extreme thermophile Acidianus manzaensis. Based on synchrotron radiation X-ray diffraction (SR-XRD) and X-ray absorption near edge structure (XANES) spectroscopy, the relevant iron and sulfur speciation of leaching residues was analyzed. Bioleaching experiments showed that copper extraction was significantly promoted by adding Ag+, and the optimum concentration of Ag+ was 0.05% (mass fraction of Ag+ to chalcopyrite). SR-XRD and XANES analyses showed that, during bioleaching in the presence of 0.05% of Ag+ and in the absence of Ag+, the intermediates S0, jarosite and secondary minerals (chalcocite, bornite and covellite) were formed. The linear combination fitting of XANES spectra further revealed that the addition of silver ions remarkably promoted the formation of bornite and covellite, while had no effect on formation of chalcocite, indicating that bioleaching of chalcopyrite should be catalyzed by Ag+ with promoting the generation of bornite and its conversion to covellite. This model suggested that the rapid formation of bornite like species contributed to positive effect of Ag+ on chalcopyrite bioleaching, while the accumulation of covellite slowed leaching rate at the end period of chalcopyrite bioleaching.

The impact of pyrite (FeS2) on the bioleaching of chalcopyrite (CuFeS2) was studied, and related mechanisms were elucidated by combining electrochemical experiments and first-principles density functional theory (DFT) calculations. The bioleaching experimental results show that after mixing with FeS2, the bioleaching rate for CuFeS2 is promoted by more than 3.5 times, and the best mass mixing ratio (FeS2: CuFeS2) is 1:1, which leads to an increase in the CuFeS2 bioleaching rate of 14% to 63%. The electrochemistry results show that after mixing with FeS2, an FeS2-CuFeS2 galvanic cell is formed, the corrosion current density is increased from 0.01997 mA·cm−2 to 0.5813 mA·cm−2, the redox reaction current density is enhanced, and the ion exchange resistance is decreased from 330.2 Ω·cm−2 to 167.4 Ω·cm−2, indicating that the FeS2 promotes the oxidation of CuFeS2, leading to a faster electronic delivery efficiency. The DFT results show that the S-Fe bonding between the CuFeS2 (0 0 1) and FeS2 (1 0 0) surfaces is weak; the work functions of FeS2-CuFeS2 decrease from 330.2 Ω·cm−2 to 167.4 Ω·cm−2, indicating a faster electron transfer; the electrons are transferred from CuFeS2 to FeS2 with the Fe atoms of FeS2 acting as the main electron acceptors; after mixing, glucose can be more easily adsorbed onto the CuFeS2 surface, resulting in stronger bonds, larger adsorption energies, and greater electron transfer, elaborating well on the bioleaching and electrochemical results.

The differences of superficial (about 10 nm) extracellular polymeric substances (EPS) composition of thermoacidophilic archaea Acidianus manzaensis YN-25 acclimated with different energy substrates (FeS2, CuFeS2, S0, FeSO4) were analyzed in situ for the first time by synchrotron radiation (SR) based carbon K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that there are clear associations between the energy substrates and the changes in organic composition in terms of typical function groups (-C=O, -C-O and -C-N). The archaea acclimated with chalcopyrite and pyrite contain higher proportion of proteins but less polysaccharides compared to cells acclimated with S0.The archaea acclimated with FeSO4 contains the highest proportion of protein which is positively associated with the iron oxidation process, while archaea acclimated with S0 contains more lipids and polysaccharides, which may be favorable to the hydrophobic S0 adsorption and utilization processes.

This article presents as follows the most recent progresses of our group on in-situ characterization and evaluation of the molecular mechanisms of interfacial interaction of minerals and bioleaching microorganisms. (1) By studying the speciation transformation of iron/copper/sulfur on the mineral surface, the evolution of cell surface properties and EPS composition, the evolution of microbial community structure, and the evolution of expression of key oxidase genes during bioleaching, to characterize the adaptation process and therein the effects of it on the specific sulfur oxidation efficiency of bioleaching; (2) by in-situ characterization of the evolution of chalcopyrite surface microstructure, chemical speciation and the biofilm formation, to illustrate the specific adsorption and the relationship between cell growth/biofilm formation and the structure and speciation on the defect mineral surface; (3) by studying the utilization, transformation and activation of S0, which is one of the major intermediates during bioleaching, and the distribution of extracellular thiol groups and iron speciation, to evaluate in situ the sulfur activation mechanism; and (4) by comparative proteomics study of the extracellular and outmembrane proteins and looking up the genome sequence, to screen sulfur activation/transportation relevant proteins and genes.

Adaption to the energy substrates and heavy metals by bioleaching micoorganisms is the prerequisite for efficient microbe-mineral interaction in bioleaching process. It is known extracellular polymer substances (EPSs) take important role in mediating the adaption to and action on energy substrates and heavy metals. This report presents the evolution of compositions and contents of the major components of EPSs of the typical bioleaching microorganisms (Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum, Sulfobacillus thermosulfidooxidans, and Acidianus manzaensis,) exposed to different energy substrates and heavy metal ions. These strains were acclimated firstly to Fe2+ substrate, and then on the substrates elemental sulfur (S0), pyrite and chalcopyrite, respectively. It was found that the major components of capsule and slime EPSs in terms of proteins, polysaccharides, as well as uronic acids were quite different in contents for the Fe2+-acclimated strains, and they even changed more when the Fe2+-acclimated strains were further acclimated to the other substrates. When exposed to heavy metals, all strains demonstrated much decrease in contents of capsule EPSs, and much increase in slime EPSs contents and the heavy metals were found to bound to the slime parts. It was for the first time the EPSs of the bioleaching strains were fractionated into capsule part and slime part, and it was also for the first time we found the differences in evolution of compositions and contents of the major organic components as well as the inorganic matter of capsule EPSs and slime EPSs when the bioleaching strains were exposed to different energy substrates and heavy metals.

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 (

The bioleaching experiments of chalcopyrite were conducted with mixed mesophilic culture (30 degrees C), moderately thermophilic culture (45 degrees C) and extremely thermophilic culture (65 degrees C), respectively. During bioleaching, the S/Fe/Cu speciation was analyzed by synchrotron radiation (SR) based X-ray diffraction (XRD) and S, Fe and Cu K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the chalcopyrite dissolution could be significantly promoted by these mixed cultures, and the promotion effects were enhanced with the increase of bioleaching temperature. For all bioleaching tests, the formation of intermediates S, jarosite and secondary minerals (chalcocite, bornite and covellite) was detected, in which the formation of bornite, chalcocite and covellite was just related with redox potential. The formation of bomite could accelerate chalcopyrite dissolution, while the decrease of bioleaching microorganisms could reduce chalcopyrite dissolution. (C) 2017 Elsevier Ltd. All rights reserved.

The bioleaching of pure chalcopyrite by thermophilic Archaea strain Acidianus manzaensis YN-25 under different constant pH was first comparatively investigated. Then the relevant sulfur speciation was analyzed by synchrotron radiation based X-ray diffraction (SR-XRD) and S K-edge X-ray absorption near edge structure (XANES) spectroscopy. The acidity of the leaching solution was monitored at 3-h intervals to make it steady at pH 1.25, 1.50, 1.75, 2.00, 2.25 and 2.50, respectively. Leaching results showed that the copper ion extraction increased during chemical leaching but decreased during bioleaching when pH value decreased from 2.50 to 1.25. SR-XRD analysis showed that, during bioleaching, new elemental sulfur (S 0 ) phase was detected at all tested pH cases; new jarosite phase was detected at cases of pH 1.50 to 2.50; and jarosite gradually became a major phase when pH value increased. XANES analysis further showed that covellite was detected during bioleaching at cases of pH 1.25 to 2.00 at higher redox potential (ORP) value, while chalcocite and bornite were detected at cases of pH 2.25 and 2.50 at lower ORP value. These results suggested that the formation of S 0 was mainly accounting for hindering the dissolution of chalcopyrite while the formation of bornite could accelerate the dissolution of chalcopyrite by A. manzaensis .

Red mud (RM) is a typical mass quantity of solid waste generated from industrial alumina production and usually consists of valuable metals such as Al and rare earths (REs). This work mainly investigated the extraction of Al and REs from RM via aerobic and anaerobic bi-stage bioleaching by Acidianus manzaensis with the addition of pyrite, by monitoring the morphology, phase and speciation transformations of Al, Si, S and Fe using primarily SEM-EDS, XRD, XPS, and XANES. The results showed that during the aerobic bioleaching stage with increase in mass ratios of pyrite/RM, the extraction rates of Al and REs increased; the highest rates for Al (85.1%), Ce (82.4%), Gd (86.8%), Y (85.3%) and Sc (78.6%) were achieved at pyrite/RM mass ratio 2:1 after 22 d of bioleaching. A slight decrease then occurred because that the complexes formed from jarosites, hematite, diaspore and SiO2-gel can adsorb small amounts of the dissolved elements. Under anaerobic conditions, the additive S0 gradually oxidized to sulfate, and the jarosites gradually dissolved into Fe2+ and disappeared at day 10 with maximal bioleaching rate for Al, Ce, Gd, Y and Sc as 52.5%, 86.3%, 93.7%, 90.2% and 74.9%, indicating that the residues from the first stage were dissolved with the dissimilatory reduction of jarosites by A. manzaensis using S0 as an electron donor. These results suggested a new method for the efficient recovery of valuable metals from RM.

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).

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 (S(0))) 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 S(0). 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.

The bioleaching experiments of chalcopyrite were conducted with single and mixed mesophiles (30 °C) and moderate thermophiles (45 °C) and extreme thermophile (65 °C), respectively, and analyzed by synchrotron radiation (SR) based X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the copper extraction of chalcopyrite could be significantly promoted by bioleaching microorganisms, and the promotion effects for both the mixed cultures grown at different temperature and the different cells grown at the same temperature were significantly different. The surface of chalcopyrite after bioleached by the mixed or sole cultures are serious corroded and became complicated. More S0 was found to form in the sole cultures of specific iron-oxidizing microorganism L. ferrooxidans and L. ferriphilum and sulfur-oxidizing microorganisms A. thiooxidans and A. caldus cultures. Jarosite and secondary minerals (chalcocite and covellite) were detected for the mixed cultures and sole cultures of iron/sulfur-oxidizing microorganisms. The evolution of chalcocite and covellite were just relevant to the potential of leaching solution, no matter which cultures were used, where chalcocite could be formed at Eh value less than 500 mV and then converted to covellite at Eh value ~550 mV.

The in situ relevance of micro- structure and electrochemical properties of chalcopyrite to adsorption of thermoacidophilic bioleaching Archaea Acidianus manzaensis was studied. In this study, the electrochemical behavior of chalcopyrite was first investigated by cyclic voltammetry (CV) to get suitable initial reduction and oxidation potentials, at which electrochemical corrosions of chalcopyrite for several time were performed, respectively, to get specific surface micro-structures. The specific adsorption of A. manzaensis on the electrochemically corroded chalcopyrite surface was then comparatively studied. The changes of microstructure and chemical composition/speciation on the surface of chalcopyrite before and after electrochemical treatment and bio-adsorption was characterized by scanning electron microscopy/electron dispersive spectroscopy (SEM/EDS), and synchrotron radiation-based X-ray diffraction (SR-XRD) and Fe, Cu K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the suitable initial oxidation and reduction of chalcopyrite electrode were at 0.67 V for 1h and -0.54 V for 10 min, respectively. After treated at 0.67V the surface of chalcopyrite became Cu-deficient with a composition of CuFe1.02S2.15, and bornite (Cu5FeS4) was detected. While after treated at -0.54V, the surface became Fe/S-deficient, with a composition of CuFe0.33S0.81, and a mass of chalcocite and some covellite were detected. Comparing to the original chalcopyrite, the adsorption capacity of A. manzaensis was increased on the surface of oxidation-treatment at 0.67 V, and decreased on the surface of reduction-treatment at -0.54 V. It clearly demonstrates the bornite-containing copper deficient chalcopyrite surface was more preferably adsorbed, whereas the chalcocite-containing Fe/S deficient chalcopyrite surface was less adsorbed by A. manzaensis, indicating the dependence of the specific adsorption of A. manzaensis upon the secondary minerals as well as Fe/S availability in the microstructure of chalcopyrite.

Phenomics is originally a biological concept. In the most recent years, the studies of plant and human phenomics have started, and show a strong momentum and trend of development. In this paper, based on the related research on bioleaching/acid mine drainage (AMD), we put forward the relevant concepts and methodology of phenomics of microbe-mineral interaction (MMI) in bioleaching/AMD environments. It refers to the systematic study on phenotypes of MMI on both levels of microbiome and mineralome under various environmental conditions, by which it gives the relationship between microbial/mineral genome and phenome of MMI responding to the varying environmental conditions. The pertinent methodology is of mainly (meta)-omics, synchrotron radiation-based techniques and supercomputing-based density function theory (DFT) calculation.

The impact of mechanical activation on the bioleaching of pyrite was studied, and the mechanisms were elucidated by DFT (density functional theory). The characterization result of the pyrite that were mechanically activated showed that the average diameter of the pyrite particles decreased sharply when the activation time was up to 80 min and remained constant from 80 min to 120 min due to the sample agglomeration effect. The change in the specific surface area exhibited the opposite trend, and the contact angles of the pyrite particles decreased gradually as the grinding time increased from 0 to 120 min, which implied that the hydrophilic property of the pyrite increased. The pyrite lattices increased after mechanical activation, indicating the presence of S defect sites on the pyrite surface. Notably, all these changes favored the increase in the bioleaching rate of pyrite. The result showed that the leaching rate of pyrite increased noticeably after mechanical activation by Sulfobacillus thermosulfidooxidans (S.t), and the cell exhibited enhanced adsorption on the activated pyrite surface. The DFT result proved that the activated pyrite could be easily adsorbed by H2O and cells, with relatively large adsorption energies, strong bonds, and an increased number of electron transfers.

The bio-oxidative dissolution of arsenopyrite, the most severe arsenic contamination source, can be mediated by organic substances, but pertinent studies on this subject are scarce. In this study, the bio-oxidative dissolution of arsenopyrite by Sulfobacillus thermosulfidooxidans and arsenic immobilization were evaluated in the presence of humic acid (HA). The mineral dissolution was monitored through analyses of the parameters in solution, phase and element speciation transformations on the mineral surface, and arsenic immobilization on the surfaces of cells and jarosites-HA. The results show that the presence of HA enhances the dissolution of arsenopyrite, e.g., 7.1% of arsenopyrite was in the residue after 12 d of bio-oxidation compared to 19.3% in the absence of HA. Meanwhile, the presence of HA led to changes of the fates of As and Fe and no accumulation of elemental sulfur (S0) or ferric arsenate on the mineral surface. Moreover, a flocculent porous structure was formed on the surfaces of both microbial cells and jarosites, on which a large amount of arsenic was adsorbed. These results clearly indicate that HA can simultaneously promote the dissolution of arsenopyrite and arsenic immobilization, which may be significant for bioleaching of arsenopyrite-bearing contaminated sites.

The catalytic mechanism of Ag+ for chalcopyrite bioleaching by mesophilic culture (at 30 &deg, C) and thermophilic culture (at 48 &deg, C) was investigated using synchrotron radiation-based X-ray diffraction (SR-XRD) and S K-edge and Fe L-edge X-ray absorption near edge structure (XANES) spectroscopy. Bioleaching experiments showed that copper extraction from chalcopyrite bioleaching by both cultures was promoted significantly by Ag+, with more serious corrosion occurring on the minerals surface. SR-XRD and XANES analyses showed that the intermediates S0, jarosite and secondary minerals (bornite, chalcocite and covellite) formed for all bioleaching experiments. For these secondary minerals, the formation of bornite and covellite was promoted significantly in the presence of Ag+ for both cultures, while Ag+ has almost no effect on the formation of chalcocite. These results provided insight into the catalytic mechanisms of Ag+ to chalcopyrite bioleaching by the mesophilic and thermophilic cultures, which are both probably due to the rapid formation of bornite by Ag+ and the conversion of bornite to covellite.

The adsorption of cysteine on the pyrite (1 0 0) surface was evaluated by using first-principles-based density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) measurements. The frontier orbitals analyses indicate that the interaction of cysteine and pyrite mainly occurs between HOMO of cysteine and LUMO of pyrite. The adsorption energy calculation shows that the configuration of the -OH of -COOH adsorbed on the Fe site is the thermodynamically preferred adsorption configuration, and it is the strongest ionic bond according to the Mulliken bond populations. As for Fe site mode, the electrons are found transferred from cysteine to Fe of pyrite (1 0 0) surface, while there is little or no electron transfer for S site mode. Projected density of states (PDOS) is analyzed further in order to clarify the interaction mechanism between cysteine and the pyrite (1 0 0) surface. After that, the presence of cysteine adsorption on the pyrite (1 0 0) surface is indicated by the qualitative results of the XPS spectra. This study provides an alternative way to enhance the knowledge of microbe&ndash, mineral interactions and find a route to improve the rate of bioleaching.

The effect of the surface microstructure and chemical speciation of chalcopyrite on the attachment behaviors of thermoacidophilic archaeon Sulfolobus metallicus was evaluated for the first time by using integrated techniques including epifluorescence microscopy (EFM) and sulfur K-edge X-ray absorption near edge structure (S K-edge XANES) spectroscopy, as well as scanning electron microscopy with energy dispersive spectrometry (SEM/EDS) and Fourier transform infrared (FT-IR) spectroscopy. In order to obtain the specific surface, the chalcopyrite slices were electrochemically oxidized at 0.87 V and reduced at −0.54 V, respectively. The EFM analysis showed that the quantity of cells attaching on the mineral surface increased with time, and the biofilm formed faster on the electrochemically treated slices than on the untreated ones. The SEM-EDS analysis indicated that the deficiency in energy substrate elemental sulfur (S0) in the specific microsize of local defect sites was disadvantageous to the initial attachment of cells. The XANES and FT-IR data suggested that the elemental sulfur (S0) could be in favor of initial attachment, and surface jarosites inhibited the adsorption and growth of S. metallicus. These results demonstrated that not only the surface microstructure but also the chemical speciation defined the initial attachment behaviors and biofilm growth of the extreme thermophilic archaeon S. metallicus.

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.

The relatedness of copper and iron speciation to chalcopyrite bioleaching by acidophilic Acidithiobacillus ferrooxidans was analyzed by synchrotron radiation-based X-ray diffraction (SR-XRD) and Cu, Fe K-edge X-ray absorption near edge structure (XANES) spectroscopy, accompanying with the determination of leaching parameters and the observation of chalcopyrite surface modification by scanning electron microscopy. The results showed that chalcopyrite was leached gradually by A. ferrooxidans , with ~ 70.58% of Cu 2 + dissolution after 30 days of bioleaching when the mineral surface was evidently attacked. During the bioleaching, bornite and chalcocite were detected at day 3 and day 9 when the redox potential was less than 500 mV, but they disappeared at day 18 and day 30 when covellite was detected and the redox potential was about 550 mV. The linear fitting of Cu and Fe XANES spectra quantitatively demonstrated the composition of leaching residue: the copper species comprised ~ 84.8% of chalcopyrite, ~ 10.2% of bornite and ~ 5.0% of chalcocite at day 3, then changed to ~ 90.1% of chalcopyrite, ~ 6.5% of bornite and ~ 3.4% of chalcocite at day 9; the composition became ~ 89.8% of chalcopyrite and ~ 10.2% of covellite at day 18, and ~ 80.3% of chalcopyrite and ~ 19.7% of covellite at day 30. The iron species comprised ~ 26% of chalcopyrite and ~ 74% of jarosite at day 30. Elemental sulfur and jarosite were detected from day 3 but without evident negative effect on the copper extraction.

The copper, iron and sulfur speciation of chalcopyrite leached by moderate thermophile Sulfobacillus thermosulfidooxidans was investigated by combining synchrotron radiation X-ray diffraction (SR-XRD) and X-ray absorption near edge structure (XANES) spectroscopy. Leaching experiment showed that the leaching rate of copper was 73.6% after 20 days bioleaching. Results of scanning electron microscopy of leaching residues showed that the surface of chalcopyrite was gradually corroded. Results of SR-XRD showed that orthorhombic form alpha-S-8, jarosite and chalcocite were produced at day 4; the bioleaching residue contained jarosite, covellite and alpha-S-8 besides chalcopyrite from day 8. The Cu, Fe and S K-edge XANES spectra quantitatively analyzed the copper, iron and sulfur species compositions of leaching residues, and the fitted results showed similar trend to SR-XRD results. According to both SR-XRD and XANES study, bornite and amorphous elemental sulfur mu-S were not found during bioleaching of chalcopyrite by S. thermosulfidooxidans. By conclusion, it indicated that iron-deficiency sulfide chalcocite first formed at the initiation of bioleaching with a low Eh value, and it then gradually transformed to covellite at a high Eh value. Meanwhile, alpha-S-8 and jarosite were produced as the predominant intermediates. By combining SR-XRD and XANES, it was useful for better understanding the dissolution mechanism of chalcopyrite during bioleaching by qualitatively and quantitatively analyzing in situ the surface chemical composition of the minerals. (C) 2015 Elsevier B.V. All rights reserved.

The influence of initial pH on the chalcopyrite oxidation dissolution at 65 °C was investigated by bioleaching and cyclic voltammetry experiments, and the oxidation products were investigated by XRD and Raman spectroscopy. Bioleaching results show that chalcopyrite dissolution rate increases with the decrease of the initial pH in chemical leaching, while the influence of initial pH on bioleaching is on the contrary. The presence of Acidianus manzaensis does not promote chalcopyrite dissolution under initial pH 1.0, which mainly results from serious inhibition of high acidity to the growth of Acidianus manzaensis. Electrochemical experiments results show that anodic oxidation currents of electrolyte with or without Acidianus manzaensis both increase with the increase of initial pH, and covellite and sulfur are detected on the electrode surface. The results confirm that chalcopyrite dissolution in chemical leaching is under the combined action of oxidation and non-oxidation of proton, with conversion of chalcopyrite to covellite and elemental sulfur.

The apparent sulfur oxidation activities of four pure thermophilic archaea, Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared, which were characterized indirectly by the evolution of the cells concentration, pH value and sulfate ions concentration in solution. The results show that the mixed culture contributed significantly to the raising of leaching rate, which suggests that the mixed culture had a higher sulfur oxidation activity than the pure culture. Meanwhile, the results also indicate that the changes of parameters characterizing the sulfur oxidation activity of thermophilic archaea are often influenced by many factors, so it is hard to reflect accurately the specific sulfur oxidation activities among the different sulfur-oxidizing microbes when bioleaching chalcopyrite at different conditions. Accordingly, an efficient method to characterize microbial sulfur oxidation activity appears to be desirable.

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.

Sulfur speciation transformation during bioleaching of pyrite-containing sphalerite concentrate by thermophile Sulfolobus metallicus (S. metallicus) at 65 A degrees C was investigated by X-ray diffraction (XRD), diffuse reflectance Fourier transform infrared spectroscopy (FT-IR) and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). The results show that the presence of S. metallicus effectively enhances the dissolution of the mineral. The yield of zinc increases from 0.5 g/L in sterile control to 2.7 g/L in bioleaching. The pyrite in the concentrate facilitates zinc dissolution in the early stage, but has hindrance role in the late stage for the formation of jarosite. Sulfur speciation analyses show that jarosite and elemental sulfur are main products in bioleaching process, and the accumulation of jarosite is mainly responsible for the decline of leaching efficiency.

To estimate the relationships among bioleaching performance, additional elemental sulfur (S0), microbial population dynamics and its energy metabolism, bioleaching of chalcopyrite by three typical sulfur- and/or iron-oxidizing bacteria, Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum and Acidithiobacillus thiooxidans with different levels of sulfur were studied in batch shake flask cultures incubated at 30°C. Copper dissolution capability (71%) was increased with the addition of 3.193 g/L S0, compared to that (67%) without S0. However, lower copper extraction was obtained in bioleaching with excessive sulfur. Microbial population dynamics during chalcopyrite bioleaching process was monitored by using PCR-restriction fragment length polymorphism (PCR-RFLP). Additional S0 accelerated the growth of sulfur-oxidizing bacteria, inhibited the iron-oxidizing metabolism and led to the decrease of iron-oxidizing microorganisms, finally affected iron concentration, redox potential and bioleaching performance. It is suggested that mixed iron and sulfur-oxidizing microorganisms with further optimized additional S0 concentration could improve copper recovery from chalcopyrite.

The sulfur oxidation activities of four pure thermophilic archaea Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared. Meanwhile, the relevant surface sulfur speciation of chalcopyrite leached with the mixed thermophilic archaea was investigated. The results showed that the mixed culture, with contributing significantly to the raising of leaching rate and accelerating the formation of leaching products, may have a higher sulfur oxidation activity than the pure cultures, and jarosite was the main passivation component hindering the dissolution of chalcopyrite, while elemental sulfur seemed to have no influence on the dissolution of chalcopyrite. In addition, the present results supported the former speculation, i.e., covellite might be converted from chalcocite during the leaching experiments, and the elemental sulfur may partially be the derivation of covellite and chalcocite.

The effect of activated carbon on chalcopyrite bioleaching by extreme thermophile Acidianus manzaensis YN25 at 65 °C was evaluated, together with the investigation of the sulfur speciation transformation on the mineral by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. Bioleaching experiments show activated carbon significantly accelerated the dissolution of copper from chalcopyrite concentrate. The optimum concentration of activated carbon enhancing copper dissolution is 2 g/L, under which the copper yields increased from 64% to 95%. The catalysis could mainly be attributed to the galvanic interaction between activated carbon and chalcopyrite. Jarosite, elemental sulfur and chalcocite were detected in the solid phase, and the formation of potassium jarosite was prior to ammonio-jarosite. Activated carbon did not change the species of sulfur-containing compounds, but accelerated the formation of them.

The original strains Acidithiobacillus ferrooxidans GF and Acidiphilium cryptum DX1-1 were isolated from the drainage of some caves riched in chalcopyrite in Dexing Mine in Jiangxi Province of China. The optimum temperature and pH for growth were 30°C and 3.5 for Ac. cryptum DX1-1, and 30°C and 2.0 for At. ferrooxidans GF, respectively. For Ac. cryptum DX1-1, the optimum UV radiating time was 60 s and the positive mutation rate was 22.5%. The growth curves show that Ac. cryptum after mutagenesis reached stationary phase within 60 h, which was 20 h earlier than the original strain. For At. ferrooxidans GF, the optimum mutation time was 60 s and the positive mutation rate was 35%. The most active UV-mutated strain At. ferrooxidans GF oxidized all the ferrous after 48 h. The bioleaching experiments showed that bioleaching with the mixture of UV-mutated strains of At. ferrooxidans GF and Ac. cryptum DX1-1(1:1) could extract 3.01 g/L of copper after 30 d, while the extracted copper was 2.63 g/L with the mixture of the original strains before UV-mutation. At the end of the bioleaching experiments, the proportion of the cell density in the cultures of Ac. cryptum DX1-1 and At. ferrooxidans GF was approximately 1:5.

The surface sulfur speciation of chalcopyrite leached by moderately thermophilic Sulfobacillus thermosulfidooxidans was investigated by employing scanning electron microscopy (SEM), X-ray diffraction (XRD) and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES), accompanying with the leaching behavior elucidation. Leaching experiment showed that there was an optimum range of the redox potential for chalcopyrite dissolution. Leaching products were found accumulating during the leaching process, which might be jarosite according to the XRD analysis. The sulfur K-edge spectra indicated that chalcocite might be the intermediate sulfur compound under a critical redox potential, which might explain the existence of optimum range of the redox potential and provide an evidence for the two-step leaching model of chalcopyrite at low Eh. In addition, the results of sulfur K-edge spectra showed jarosite would accumulate on mineral surface, which might be the main component of the passivation layer.

One bioleaching bacterium, named as strain DXS, was isolated from acid mine drainages (AMDs) of Dongxiangshan Mine of Hami, Xinjiang Province, China. The strain DXS is gram-negative and rod-shaped with a size of (0.40±0.05) μm×(1.3±0.5) μm. The optimal temperature and pH for growth are 30 °C and pH 2.0, respectively. It can grow autotrophically by using ferrous iron, elemental sulfur and NaS2O3 as sole energy sources. In the phylogenetic tree, strain DXS has similarity with Acidithiobacillus ferrooxidans type strain ATCC 23270 with 99.57% sequence similarity. The cloning and sequencing of Iro protein gene (iro) and tetrathionate hydrolase gene (tth) reveal that strain DXS is completely identical in iro gene sequence to A. ferrooxidans LY (DQ166841), and almost identical in tth gene sequene to A. ferrooxidans (AB259312) (only two nucleotides change). The bioleaching experiments of marmatite and pyrite reveal that the leached zinc and iron concentrations reach 3.01 g/L and 2.75 g/L, respectively. The strain has a well potential application in industry bioleaching.

Sulfur speciation on the surface of pyrite leached by extreme thermophile Acidianus manzaensis YN-25 was investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). SEM micrographs showed leaching products with numerous holes were formed into the surface of leached pyrite. XRD spectra indicated that the leach residues were mainly composed of pyrite and jarosite. The sulfur K-edge XANES indicated that elemental sulfur, thiosulfate and/or thiosulfate-like species and jarosite were formed on the mineral surface. Raman spectroscopy further verified the presence of jarosite. elemental sulfur and thiosulfate. Jarosite formed in pyrite leaching appeared much later than in chalcopyrite leaching by the same strain. Jarosite on the mineral surface may account for the passivation of pyrite oxidation, with the passivation effect of elemental sulfur which is less important. In addition, the thiosulfate detected in this study provided novel evidence for surface-bound thiosulfate involved in the stepwise oxidation of pyrite by the extreme thermophile A. manzaensis. (C) 2009 Elsevier B.V All rights reserved

The growth and surface properties of new thermoacidophilic Archaea strain Acidianus manzaensis YN-25 isolated from an acid hot spring in Tengchong, Yunnan Province, China were investigated cultured on different substrates including soluble substrate ferrous sulfate and nonsoluble solid substrates S 0 , pyrite and chalcopyrite. The growth characteristics of the cells in each substrate were characterized with the changes in cell number, pH, E h , and concentrations of Fe 2+ or SO 4 2− , or ratios of [Fe 2+ ] to [Fe 3+ ], and the surface properties were characterized and analyzed in terms of Zeta-potential, hydrophobicity, and surface FT-IR spectra of the cells. The results show that the cells grown on solid substrates have higher value of isoelectric points. They are more hydrophobic and express more surface proteins than ferrous sulfate grown cells.

Bio-oxidation of elemental sulfur (S0) is very important in bioleaching and sulfur cycle. S0 was proposed to be first activated by reacting with reactive thiol groups (–SH) of outer membrane proteins, forming –S n H (n ≥ 2) complexes. The differential expression of –SH of moderately thermophilic Sulfobacillus thermosulfidooxidans and extremely thermophilic Acidianus manzaensis grown on Fe2+ and S0 was investigated by synchrotron radiation-based scanning transmission X-ray microscopy (STXM) imaging and micro-beam X-ray fluorescence (μ-XRF) mapping. The STXM imaging and μ-XRF mapping of extracellular –SH were based on the analysis of Ca2+ bound on the cell. By comparing Ca2+ of the cells with and without labeling by Ca2+, the distribution and content of thiol groups were obtained. The results showed that, for both S. thermosulfidooxidans and A. manzaensis, the expression of extracellular –SH of S0-grown cells was higher than that of Fe2+-grown cells. Statistical analysis indicated that the expression of extracellular –SH for S. thermosulfidooxidans and A. manzaensis grown on S0 was 2.37 times and 2.14 times, respectively, to that on Fe2+. These results evidently demonstrate that the extracellular thiol groups are most probably involved in elemental sulfur activation and oxidation of the acidophilic sulfur-oxidizing microorganisms.