Sulfobacillus Thermosulfidooxidans Research Articles

Bioleaching of a Copper-Zinc Concentrate with High Arsenic Content

The goal of the present work was to study the dependence of the rate of copper and zinc bioleaching from an arsenic-containing copper-zinc concentrate containing 16% Cu, 5.3% Zn, and 1.36% As, on the temperature and the presence of an organic carbon source (yeast extract) in the medium. The main minerals of the concentrate were chalcopyrite (CuFeS2), tennantite (Cu12As4S13), sphalerite (ZnS), and pyrite (FeS2). A mixed culture of moderately thermophilic acidophilic microorganisms oxidizing sulfur and ferrous iron, which was used in the work, consisted of the strains Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans SH-1, and Acidiplasma sp. MBA-1. The experiments were carried out in flasks with 100 mL of mineral medium and 2 g of the concentrate on a rotary shaker for 30 days at temperatures from 40 to 60°C. It was shown that the leaching rate of copper depended both on temperature and on the presence of yeast extract. Copper leaching rate increased with increasing temperature, while zinc leaching was less dependent on the temperature. In the presence of an organic carbon source in the medium, both copper and zinc were actively leached at high temperatures (55 and 60°C), while in experiments with a medium without yeast extract, the activity of non-ferrous metals leaching from the concentrate at these temperatures was much lower. At the same time, at temperatures of 40–50°C, leaching activity was less dependent on the presence of the organic carbon source in the medium.

Enhancement of arsenopyrite bioleaching by different Fe(III) compounds through changing composition and structure of passivation layer

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.

Effect of Sodium Chloride on Pyrite Bioleaching and Initial Attachment by Sulfobacillus thermosulfidooxidans.

Biomining applies microorganisms to extract valuable metals from usually sulfidic ores. However, acidophilic iron (Fe)-oxidizing bacteria tend to be sensitive to chloride ions which may be present in biomining operations. This study investigates the bioleaching of pyrite (FeS2), as well as the attachment to FeS2 by Sulfobacillus thermosulfidooxidans DSM 9293T in the presence of elevated sodium chloride (NaCl) concentrations. The bacteria were still able to oxidize iron in the presence of up to 0.6M NaCl (35 g/L), and the addition of NaCl in concentrations up to 0.2M (~12 g/L) did not inhibit iron oxidation and growth of S. thermosulfidooxidans in leaching cultures within the first 7 days. However, after approximately 7 days of incubation, ferrous iron (Fe2+) concentrations were gradually increased in leaching assays with NaCl, indicating that iron oxidation activity over time was reduced in those assays. Although the inhibition by 0.1M NaCl (~6 g/L) of bacterial growth and iron oxidation activity was not evident at the beginning of the experiment, over extended leaching duration NaCl was likely to have an inhibitory effect. Thus, after 36 days of the experiment, bioleaching of FeS2 with 0.1M NaCl was reduced significantly in comparison to control assays without NaCl. Pyrite dissolution decreased with the increase of NaCl. Nevertheless, pyrite bioleaching by S. thermosulfidooxidans was still possible at NaCl concentrations as high as 0.4M (~23 g/L NaCl). Besides, cell attachment in the presence of different concentrations of NaCl was investigated. Cells of S. thermosulfidooxidans attached heterogeneously on pyrite surfaces regardless of NaCl concentration. Noticeably, bacteria were able to adhere to pyrite surfaces in the presence of NaCl as high as 0.4M. Although NaCl addition inhibited iron oxidation activity and bioleaching of FeS2, the presence of 0.2M seemed to enhance bacterial attachment of S. thermosulfidooxidans on pyrite surfaces in comparison to attachment without NaCl.

Effect of inoculum history, growth substrates and yeast extract addition on inhibition of Sulfobacillus thermosulfidooxidans by NaCl

This study reports on the effect of inoculum history, growth substrates, and yeast extract on sodium chloride tolerance of Sulfobacillus thermosulfidooxidans DSM 9293T. The concentrations of NaCl for complete inhibition of Fe2+ oxidation by cells initially grown with ferrous iron sulfate, or tetrathionate, or pyrite as energy sources were 525 mM, 725 mM, and 800 mM, respectively. Noticeably, regardless of NaCl concentrations, oxygen consumption rates of S. thermosulfidooxidans with 20 mM tetrathionate were higher than with 50 mM FeSO4. NaCl concentrations of higher than 400 mM strongly inhibited the iron respiration of S. thermosulfidooxidans. In contrast, the presence of NaCl was shown to stimulate tetrathionate oxidation. This trend was especially pronounced in NaCl-adapted cells where respiration rates at 200 mM NaCl were threefold of those in the absence of NaCl. In NaCl-adapted cultures greater respiration rates for tetrathionate were observed than in non-NaCl-adapted cultures, especially at concentrations ≥ 200 mM NaCl. At concentrations of ≤ 200 mM NaCl, cell growth and iron oxidation were enhanced with the addition of increasing concentrations of yeast extract. Thus, cell numbers in cultures with 0.05% yeast extract were ∼5 times higher than without yeast extract addition. At NaCl concentration as high as 400 mM, however, iron oxidation rates improved compared to control assays without yeast extract, but there was no clear dependence on yeast extract concentrations. The initial growth of bacteria with and without yeast extract in the presence of different NaCl concentrations was shown to impact leaching of copper from chalcopyrite. Copper dissolution was enhanced in the presence of 200 mM NaCl and absence of yeast extract, while the addition of 0.02% yeast extract was shown to promote copper solubilization in the presence of 500 mM NaCl.

Mechanical Activation on Bioleaching of Chalcopyrite: A New Insight

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.

Pyrrhotite Biooxidation by Moderately Thermophilic Acidophilic Microorganisms

The goal of the present work was to study the oxidation of sulfide mineral pyrrhotite by members of microbial groups predominant in biohydrometallurgical processes (mixotrophic iron- and sulfur-oxidizing bacterium Sulfobacillus thermosulfidooxidans strain VKMV 1269T, autotrophic sulfur-oxidizing bacterium Acidithiobacillus caldus strain MBC-1, and heterotrophic iron- and sulfur-oxidizing archaeon Acidiplasma sp. strain MBA-1) to evaluate the role of microorganisms with different physiological properties in the leaching of this mineral. It was shown that pyrrhotite was most actively leached by the sulfur-oxidizing strain Acidithiobacillus caldus MBC-1, as well as by mixed cultures in which this strain was present: S. thermosulfidooxidans VKMV 1269T + A. caldus MBC-1 and Acidiplasma sp. MBA-1 + A. caldus MBC-1. These cultures leached 70, 43, and 60% of pyrrhotite, respectively, after 30 days of the experiment. In experiments with pure cultures S. thermosulfidooxidans VKMV 1269T, Acidiplasma sp. MBA-1 and a mixed culture S. thermosulfidooxidans VKMV 1269T + Acidiplasma sp. MBA-1, the rates of pyrrhotite leaching were significantly lower: 29, 37 and 30%, respectively. An experiment on sulfur biooxidation by pure cultures of the studied microorganisms demonstrated that A. caldus strain MBC-1 was the most active sulfur oxidizer. Thus, it was shown that the bioleaching of pyrrhotite was carried out mainly by sulfur-oxidizing microorganisms, with sulfur biooxidation as the most important process. Active biooxidation of the Fe2+ ion by iron-oxidizing microorganisms did not increase activity of pyrrhotite oxidation, but, on the contrary, led to inhibition of pyrrhotite leaching. Thus, active biooxidation of sulfur, which is formed during the leaching of pyrrhotite, was a factor determining the leaching rate for this sulfide mineral.

Микрофлора фосфорсодержащих отходов южного казахстана

The article presents the results of microbiological studies of phosphorus-containing wastes. 70 isolates were isolated, of which 36 isolates were assigned to bacteria, which corresponds to 51% of the total number of isolated microorganisms, 7 isolates were assigned to actinomycetes (10%) and 3 cultures to yeast (4%), 24 isolates were assigned to micromycetes (35%). Based on the screening of microorganisms, 14 of the most active strains that are promising for biogeotechnological purposes were selected. Based on the results of the study of cultural characteristics and PCR analysis data, the isolated strains were assigned to such types of micromycetes as: Aspergillus niger AsIA, Aspergillus tubingensis AsPN, Aspergillus terreus JOM, Aspergillus flavus AsZ, Aspergillus flavus AsF, to denitrifying bacteria Pseudomonas stutzeri NJA, to thermophilic bacteria Methyloversatilis thermotolerans MSO, Nitrosomonas europeae Nit1, Ralstonia pickettii ASA and Ralstonia pickettii TS, Acinetobacter sp. NAO, Alicyclobacillus tolerans ST (Sulfobacillus thermosulfidooxidans), Zoogloea resiniphila NS1, Gallionella capsiferriformans TS2, to acidophilic bacteria strains: Acidithiobacillus ferrooxidans ThIO, Acidithiobacillus thiooxidans ThIO .Key words: phosphorus waste, Acidithiobacillus ferrooxidans, Aspergillus niger, Nitrosomonas europeae, Gallionella capsiferriformans, Sulfobacillus thermosulfidooxidans.

Bioprocessing of oxidized platinum group element (PGE) ores as pre-treatment for efficient chemical extraction of PGE

Platinum-group elements (PGE) are relevant for many high technology applications, prompting the search for potential alternative resources and environmentally friendly processing technologies. The largest deposit of PGE worldwide is the Bushveld Complex in South Africa. The pristine sulfide-bearing ore is mined using conventional metallurgical methods, while the near-surface oxidized PGE ore is currently stockpiled. Economic extraction of PGE from these stockpiles using conventional technologies is not feasible to date. Hence, biohydrometallurgical approaches to recover valuable transition metals and liberate platinum-group minerals for subsequent chemical PGE extraction have been considered. The four stockpile samples taken from a heap of oxidized PGE ores from the Platreef formation showed a similar mineralogical composition with >90 wt% silicates and minor amounts of Fe-(oxy)/hydroxides, both associated with Ni, Mn and Cu. Platinum-group minerals were present as sperrylite (PtAs2), cooperite (PtS low Pd), native platinum and Pd‑bismuthotellurides and mostly associated with silicates. Stirred tank bioleaching under various conditions was proven to be most feasible for an oxidative process at moderately-high temperatures using a consortium of iron- and sulfur-oxidizing acidophiles dominated by Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. Bioleaching achieved up to 86% total metal recovery (including Co, Cu, Mn and Ni) and led to a liberation of platinum-group minerals. The bioleach residues were subsequently chemically leached by a HNO3/NaCl and a cyanide leach, allowing for the enhanced extraction of up to 89% Pt and 96% Pd after bioleaching. Chemical and mineralogical analysis validated the potential of oxidative bioleaching as a promising processing option for a pre-treatment of oxidized PGE ore, allowing separate and efficient recovery of valuable base metals and enhancing the subsequent chemical PGE extraction.

Bioleaching of Enargite and Tennantite by Moderately Thermophilic Acidophilic Microorganisms

The goal of the present work was to study the bioleaching of chalcopyrite (CuFeS2), enargite (Cu3AsS4), and tennantite (Cu12As4S13) by pure and mixed cultures of moderately thermophilic microorganisms belonging to the groups predominant in technological processes (Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans SH-1, and Acidiplasma sp. MBA-1) under different conditions (temperature of 40 to 60°C, presence of Fe2+ ions, pyrite (FeS2), and pyrrhotite (FeS)). Bioleaching of copper from chalcopyrite and enargite was shown to depend on temperature and to be almost independent of the composition of microbial culture. Under optimal conditions (50–55°C), after 30 days 25–27 and 14% of copper was leached from chalcopyrite and enargite, respectively. Increase in the temperature up to 60°C led to the inhibition of copper bioleaching from both minerals. The optimal temperature for tennantite bioleaching was 45°C, while the rate of bioleaching was significantly dependent on the composition of the microbial culture. In an experiment with a mixed culture of all three strains, 26% of copper was leached, while in experiments with pure cultures of A. caldus MBC-1, S. thermosulfidooxidans SH-1, and Acidiplasma sp. MBA-1, after 30 days 12, 21, and 18% of copper was leached, respectively. Addition to the medium of Fe2+ as ferrous sulfate resulted in an increased rate of copper leaching from enargite and tennantite, which may be explained by the fact that Fe3+ ions are generated during microbial Fe2+ biooxidation to Fe3+, which is a strong oxidizing agent and plays an important role in the leaching of sulfide minerals. In the presence of pyrite and pyrrhotite, the rates of enargite and tennantite leaching increased, probably due to the presence of Fe3+ ions in the medium, which were generated during the biooxidation of iron sulfide minerals. The results of the work demonstrated that different environmental factors affected the bioleaching of copper minerals in different ways, which is of practical importance, in particular, for planning the trials for bioleaching of mineral raw materials.

Pyrite-promoted dissolution of arsenopyrite in the presence of Sulfobacillus thermosulfidooxidans

The weathering of arsenopyrite in mine wastes is crucial for the formation of arsenic-containing acid mine drainage (AMD). Arsenopyrite is always associated with pyrite. In this study, the influence of pyrite on the biooxidation of arsenopyrite in the presence of Sulfobacillus thermosulfidooxidans was investigated by leaching experiments and surface characterizations. Bioleaching experiments of 5 days showed that the presence of pyrite increased the ferric concentration, and then accelerated arsenopyrite bioleaching, but increasing the mass ratio of pyrite to arsenopyrite above 1 had no obvious impact on further arsenopyrite dissolution. Synchrotron X-ray diffraction (S-XRD) and scanning electron microscopy (SEM) provided a direct understanding of arsenopyrite-pyrite galvanic interaction, and confirmed the formation of elemental sulfur and jarosite clusters, which did not passivate the arsenopyrite surface. Iron arsenate was detected by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). Additionally, the bioleaching experiments of 18 days indicated that the presence of pyrite facilitated the oxidation of As(III) to As(V) since most of arsenopyrite had been bioleached, and the increase of pyrite addition triggered the further oxidation of As(III).

Effect of introduction of exogenous strain Leptospirillum ferriphilum YSK on functional gene expression, structure, and function of indigenous consortium during pyrite bioleaching

Leptospirillum ferriphilum YSK was added to a native consortium of bioleaching bacteria including Acidithiobacillus caldus, A. thiooxidans, A. ferrooxidans, Sulfobacillus thermosulfidooxidans, Acidiphilium spp., and Ferroplasma thermophilum cultured in modified 9K medium containing 0.5% (W/V) pyrite. The bioleaching efficiency markedly increased. Changes in community structure and gene expression were monitored with real-time PCR and functional gene arrays. Dynamic changes that varied in different populations in the consortium occurred after the addition of L. ferriphilum YSK, with growth of A. caldus S1, A. thiooxidans A01, Acidiphillum spp. DX1-1 promoted the growth of Ferroplasma L1, inhibited that of S. thermosulfidooxidans ST, and exerted little effect on that of A. ferrooxidans CMS. Genes encoding ADP heptose, phosphoheptose isomerase, glycosyltransferase, biotin carboxylase, and protoheme ferrolyase from L. ferriphilum, acetyl-CoA carboxylase from Acidiphillum spp., and doxD from A. caldus were up-regulated in 0–20 h. Genes encoding lipid A disaccharide synthase LpxB, glycosyl transferase, and ADP heptose synthase from A. ferrooxidans were up-regulated in 0–8 h and then down-regulated in 8–20 h. Genes encoding ferredoxin oxidoreductase from Ferroplasma sp. were up-regulated in 0–4 h, down-regulated in 4–16 h, and again up-regulated in 16–20 h. CbbS from A. ferrooxidans was down-regulated in 0–20 h.

Comparison of leaching of bornite from different regions mediated by mixed moderately thermophilic bacteria

Bioleaching experiments combined with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted to investigate three kinds of bornites from different regions leached by moderately thermophilic mixed bacteria of Leptospirillum ferriphilum YSK, Acidithiobacillus caldus D1 and Sulfobacillus thermosulfidooxidans ST. The results of bioleaching experiments showed that the leaching efficiency and the redox potential were significantly increased. The copper extraction efficiencies of three kinds of bornite maintained rapid growth until around the 12th day and no longer increased after the 18th reaching 83.7%, 96.5% and 86.6%, respectively. The XRD results of the leaching residue indicated that three kinds of bornites all produced jarosite in the late stage of leaching, and the leaching residues from of Daye Museum and Yunnan Geological Museum contained a mass of elemental sulfur. XPS analysis and scanning electron microscopy experiments showed that the surface of mineral particles was jarosite and the copper in the leaching residue was almost dissolved.

Influence diversity of extracellular DNA on bioleaching chalcopyrite and pyrite by Sulfobacillus thermosulfidooxidans ST

In this paper, Sulfobacillus thermosulfidooxidans ST was selected for use in bioleaching of pyrite and chalcopyrite. The adsorption experiments revealed that more cells were adsorbed on the surface of pyrite than on the surface of chalcopyrite. The role of extracellular DNA (eDNA) in the bioleaching process was investigated by depletion of eDNA using DNase I. The number of cells attached on the chalcopyrite and pyrite surfaces decreased on a large scale, and the lag phase of cell growth increased, causing the leaching percentages of pyrite and chalcopyrite to decrease by approximately 11.6% and 20.5%, respectively. The formation and distribution of eDNA secreted during bioleaching was assessed by a fluorescent dye-based method and visualized by confocal laser scanning microscopy (CLSM). The content of eDNA increased with bioleaching time. Furthermore, ST showed a stronger capacity to produce eDNA on the surface of pyrite than on the surface of chalcopyrite. These results showed that the removal of eDNA has a more significant effect on the bioleaching of chalcopyrite than on pyrite.

Effect of Organic Carbon Source on Pyrite Biooxidation by Moderately Thermophilic Acidophilic Microorganisms

Iron- and sulfur-oxidizing auto-, mixo- and heterotrophic bacteria and archaea dominate in the bioleaching of pyrite from sulfide ores and concentrates both in natural conditions and in biohydrometallurgical processes. The goal of the present work was to study the oxidation of pyrite, the most widespread sulfide mineral, by representatives of microbial groups predominant in biohydrometallurgical processes (mixotrophic iron- and sulfur-oxidizing bacterial strain Sulfobacillus thermosulfidooxidans VKMB1269T, autotrophic sulfur-oxidizing bacterial strain Acidithiobacillus caldus MBC-1, and heterotrophic iron- and sulfur-oxidizing strain of archaea Acidiplasma sp. MBA-1) to evaluate the potential importance of different groups of microorganisms, and to determine the role of interspecies interactions in the population during pyrite oxidation. It was shown that pyrite was most actively leached by the strain of the mixotrophic bacterium S. thermosulfidooxidans VKMB 1269T, in the case when the medium was supplemented with organic substrates. In the experiment with a pure culture of strain VKMV 1269T in a medium with 0.02% yeast extract, 17% of pyrite was leached in 30 days, while in experiments with pure cultures of A. caldus MBC-1 and Acidiplasma sp. MBA-1, less than 1.5% of pyrite were leached. Significantly better results were obtained using mixed cultures of iron-oxidizing strains and A. caldus MBC-1: the rate of pyrite leaching was 26–28%. Moreover, in experiments with a mixed culture of S. thermosulfidooxidans VKMB 1269T and A. caldus MBC-1, addition of an organic carbon source (yeast extract) did not affect the rate of pyrite leaching (25–26%). The highest (38%) leaching rate was in the experiments with a pure culture of S. thermosulfidooxidans VKMV 1269T with periodic addition of yeast extract to the medium: 0.02% at the beginning of the experiment, as well as on days 10 and 20. Thus, in laboratory conditions it was shown that the greatest role in the process of pyrite oxidation was played by the bacterial strain of the genus Sulfobacillus, but its activity was largely dependent on availability of an organic carbon source in the medium, which may be represented by yeast extract or exometabolites of autotrophic bacteria present in the community of microorganisms performing pyrite leaching from sulfide ores and concentrates.

Mechanisms of NaCl-tolerance in acidophilic iron-oxidizing bacteria and archaea: Comparative genomic predictions and insights

For most acidophilic iron-oxidizing bioleaching microorganisms, chloride ions are toxic even at low concentrations since they are able to induce an acidification of the cytoplasm and osmotic stress. To identify molecular determinants for osmotic tolerance of these microorganisms, a genomic analysis based on the complete genomes of twelve iron oxidizers was carried out. Genes for a complete or partial repertoire of K+ transporters Kdp and Ygg were found in most of the genomes. Representatives of Nitrospirae, Firmicutes and Actinobacteria harbor genes for the biosynthesis of (5-hydroxy)ectoine and trehalose. Members of the phylum Nitrospirae appeared to be better equipped with classical mechanisms for osmotic tolerance than representatives of other phyla. The moderately halotolerant bacteria Acidihalobacter prosperus V6 and Leptospirillum ferriphilum Sp-Cl did not show overrepresentation of these mechanisms. In agreement with the bioinformatics results, minimal inhibitory concentrations (MICs) of NaCl showed that Sulfobacillus thermosulfidooxidans, Ferrimicrobium acidiphilum and Leptospirillum ferriphilum were more tolerant than Acidithiobacillus ferrooxidans. Furthermore, external supplementation of ectoine led to an increase in NaCl MIC for L. ferriphilum and F. acidiphilum. These results may provide useful insights for designing chloride-based technologies to bioprocess minerals.

Sulfobacillus thermosulfidooxidans: an acidophile isolated from acid hot spring for the biosorption of heavy metal ions

Heavy metal contaminations in acid mine drainage (AMD) have posed a serious health and environmental risk. Biosorption is a promising in situ remediation technique to remove heavy metals from AMD. In this study, the potential of thermophilic acidophilus Sulfobacillus thermosulfidooxidans was used as biosorbent to remove heavy metal ions (Cd2+, Cu2+, Zn2+ and Ni2+) from acidic solution. The results indicated that the maximum adsorption capabilities of S. thermosulfidooxidans in the order of Ni2+ > Cd2+ > Zn2+ > Cu2+ at initial heavy metal concentrations range from 0.5 to 6 mM in single-metal system while showed an extremely high affinity toward Cu2+ in quaternary metal coexisting system. pH was positively related to adsorption capacity, and isothermal models also indicated monolayer adsorption played a major role in the biosorption process. Additionally, the deprotonation of carboxyl and phosphoryl contributed to the adsorption of heavy metal ions which were identified by ProtoFit analysis. Fourier transform infrared spectroscopy (FTIR) further proved these two kinds of functional groups as well as amino groups participated in the biosorption process. This study provided a new strategy for in situ bioremediation of heavy metal ions in AMD.

Impact of mechanical activation on bioleaching of pyrite: A DFT study

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.

Developing Methods of Biological Delivery of Sulfane Sulfur

Two laboratory-scale bioreactors, operated in flow-through mode at fixed pH values, were set up to generate sulfuric acid from elemental sulfur at different temperatures using consortia of sulfur-oxidizing acidophilic prokaryotes. One bioreactor, maintained at 30 °C, was dominated by Acidithiobacillus albertensis when operated at pH 1.0 and by Sulfobacillus thermosulfidooxidans at pH 0.8. Acidibacillus ambivalens (an obligately heterotrophic iron/sulfur-oxidizer) was present at ~10–20% relative abundance at both pH values but Acidithiobacillus caldus was only detected as a minor member of the consortium. In contrast, the other bioreactor, maintained at 50 °C, was populated by At. caldus and the thermophilic archaeon Sulfolobus metallicus at both pH values. Operating both reactors at pH 0.8 was less successful than at pH 1.0, due to the acid-sensitivities of the microbial consortia. However, the total acidities of the sulfuric acid solutions generated could be increased by >90% by increasing sulfate concentrations in the feed liquors, which resulted in most of the acidity generated being in the form of bisulfate (HSO4−) rather than hydronium (H3O+) ions, and obviating, at least partially, the limitations caused by inhibition of the extreme acidophiles to highly elevated concentrations of the latter. Fastest rates of sulfuric acid production under the conditions tested were found when operating the bioreactors at pH 1.0 and 30 °C, with a pH 3.0 influent liquor supplemented with 200 mM magnesium sulfate. This work demonstrated the feasibility of using an empirical flow-through bioreactor to generate a sulfuric acid lixiviant that could be used alone or in tandem with other (microbially-generated) liquors to accelerate the dissolution of minerals and metallic waste materials in bio-processing operations.

Humic acid promotes arsenopyrite bio-oxidation and arsenic immobilization

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.

Microbial generation of sulfuric acid from granular elemental sulfur in laboratory-scale bioreactors

Two laboratory-scale bioreactors, operated in flow-through mode at fixed pH values, were set up to generate sulfuric acid from elemental sulfur at different temperatures using consortia of sulfur-oxidizing acidophilic prokaryotes. One bioreactor, maintained at 30 °C, was dominated by Acidithiobacillus albertensis when operated at pH 1.0 and by Sulfobacillus thermosulfidooxidans at pH 0.8. Acidibacillus ambivalens (an obligately heterotrophic iron/sulfur-oxidizer) was present at ~10–20% relative abundance at both pH values but Acidithiobacillus caldus was only detected as a minor member of the consortium. In contrast, the other bioreactor, maintained at 50 °C, was populated by At. caldus and the thermophilic archaeon Sulfolobus metallicus at both pH values. Operating both reactors at pH 0.8 was less successful than at pH 1.0, due to the acid-sensitivities of the microbial consortia. However, the total acidities of the sulfuric acid solutions generated could be increased by >90% by increasing sulfate concentrations in the feed liquors, which resulted in most of the acidity generated being in the form of bisulfate (HSO4−) rather than hydronium (H3O+) ions, and obviating, at least partially, the limitations caused by inhibition of the extreme acidophiles to highly elevated concentrations of the latter. Fastest rates of sulfuric acid production under the conditions tested were found when operating the bioreactors at pH 1.0 and 30 °C, with a pH 3.0 influent liquor supplemented with 200 mM magnesium sulfate. This work demonstrated the feasibility of using an empirical flow-through bioreactor to generate a sulfuric acid lixiviant that could be used alone or in tandem with other (microbially-generated) liquors to accelerate the dissolution of minerals and metallic waste materials in bio-processing operations.