Moderate Thermophile Sulfobacillus Research Articles

Mechanism by which ferric iron promotes the bioleaching of arsenopyrite by the moderate thermophile Sulfobacillus thermosulfidooxidans

Abstract 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.

Influence of Sulfobacillus thermosulfidooxidans on Initial Attachment and Pyrite Leaching by Thermoacidophilic Archaeon Acidianus sp. DSM 29099

At the industrial scale, bioleaching of metal sulfides includes two main technologies, tank leaching and heap leaching. Fluctuations in temperature caused by the exothermic reactions in a heap have a pronounced effect on the growth of microbes and composition of mixed microbial populations. Currently, little is known on the influence of pre-colonized mesophiles or moderate thermophiles on the attachment and bioleaching efficiency by thermophiles. The objective of this study was to investigate the interspecies interactions of the moderate thermophile Sulfobacillus thermosulfidooxidans DSM 9293T and the thermophile Acidianus sp. DSM 29099 during initial attachment to and dissolution of pyrite. Our results showed that: (1) Acidianus sp. DSM 29099 interacted with S. thermosulfidooxidansT during initial attachment in mixed cultures. In particular, cell attachment was improved in mixed cultures compared to pure cultures alone; however, no improvement of pyrite leaching in mixed cultures compared with pure cultures was observed; (2) active or inactivated cells of S. thermosulfidooxidansT on pyrite inhibited or showed no influence on the initial attachment of Acidianus sp. DSM 29099, respectively, but both promoted its leaching efficiency; (3) S. thermosulfidooxidansT exudates did not enhance the initial attachment of Acidianus sp. DSM 29099 to pyrite, but greatly facilitated its pyrite dissolution efficiency. Our study provides insights into cell-cell interactions between moderate thermophiles and thermophiles and is helpful for understanding of the microbial interactions in a heap leaching environment.

Investigation of copper, iron and sulfur speciation during bioleaching of chalcopyrite by moderate thermophile Sulfobacillus thermosulfidooxidans

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 20days 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 α-S8, jarosite and chalcocite were produced at day 4; the bioleaching residue contained jarosite, covellite and α-S8 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 μ-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, α-S8 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.

Site-specific mutagenesis and functional analysis of active sites of sulfur oxygenase reductase from Gram-positive moderate thermophile Sulfobacillus acidophilus TPY

Sequence alignments revealed that the conserved motifs of SORSa which formed an independent branch between archaea and Gram-negative bacteria SORs according to the phylogenetic relationship were similar with the archaea and Gram-negative bacteria SORs. In order to investigate the active sites of SORSa, cysteines 31, 101 and 104 (C31, C101, C104), histidines 86 and 90 (H86 and H90) and glutamate 114 (E114) of SORSa were chosen as the target amino acid residues for site-specific mutagenesis. The wild type and six mutant SORs were expressed in E. coli BL21, purified and confirmed by SDS-PAGE and Western blotting analysis. Enzyme activity determination revealed that the active sites of SORSa were identical with the archaea and Gram-negative bacteria SORs reported. Replacement of any cysteine residues reduced SOR activity by 53–100%, while the mutants of H86A, H90A and E114A lost their enzyme activities largely, only remaining 20%, 19% and 32% activity of the wild type SOR respectively. This study will enrich our awareness for active sites of SOR in a Gram-positive bacterium.

Study on Comprehensive Utilization of Arsenic from High Arsenic-Bearing Copper Sulphide Concentrate

In this paper a new technology for comprehensive utilization of arsenic in high-arsenic copper sulfide concentrate has been studied out. Firstly,the concentrate was bioleached by moderate thermophile Sulfobacillus thermosulfidooxidans, under the suitable leaching conditions, the experiments results show that the concentrate is bioleached 82% of Cu,78% of As and 40% of Fe. Secondly, removal of Fe3+ by solvent extraction with P204 from bacterial leaching solution are presented, and Fe3+ is extracted up to 93％, and the content of Fe3+ in raffinate is under 9 mg/L. The comprehensive utilizations of most of arsenic from leaching liquor after removal Fe3+ has been carried out. When the temperature is 80 to 90°C, pH at 4.0~5.0 and ammonia as a neutralizer, the results of XRD analysis show that the forming process of copper arsenate is complicated, and the formed molecular formulas are in different types, and they are CuAs2O4, Cu5As2O10•5H2O, C4H6As6Cu4O16, Cu5As4O15•9H2O and Cu2AsO4OH•3H2O. The comprehensive utilizations of most of arsenic are in the form of copper arsenate, and the content of arsenic is 9.11~35.82mg/L in solution after its precipitated. This study provides a new treatments and process for the utilization of arsenic in the high-arsenic copper sulfide concentrate.

Comparison of Bioleaching High Arsenic-Bearing Copper Sulphide Concentrate Using Thiobacillus Ferrooxidans and Sulfobacillus Thermosulfidooxidans

The usage of high-arsenic sulfide copper concentrate were limited because the arsenic in the concentrate harms the qualities of copper product and pollutes the environment. In this paper an innovative process for high-arsenic copper sulfide concentrate with with bio-oxidation respectively Thiobacillus ferrooxidans and moderate thermophile Sulfobacillus thermosulfidooxidans has been studied out, and the influencing factors have been comparative studied during the leaching process, such as concentration particle size, leaching methods, pulp concentration, leaching time and the initial concentration of Fe3+, etc. Under the suitable leaching conditions, the experiments results show that the concentrate is leached 47.13% of Cu,50.09% of As and 52.46% of Fe by Thiobacillus ferrooxidans and 82.39% of Cu,78.21% of As and 40.38% of Fe by moderate thermophile Sulfobacillus thermosulfidooxidans. The high concentration initial Fe3+ has speeded leaching process up in the presence of moderate thermophile Sulfobacillus thermosulfidooxidans, and when the pulp initial concentration of Fe3+ is in the range of 0.08~0.32mol/L, the leaching rate of Cu is 86.34~97.06%, As 89.22~94.13%. It is concluded that Sulfobacillus thermosulfidooxidans have a better effect on bioleaching high-arsenic sulfide copper concentrate than Thiobacillus ferrooxidans.

Habituation of Sulfobacillus thermosulfidooxidans to 4-nonylphenol in ferrous ion growth medium

The aim of this study was to resolve the apparent inconsistency between the prevalence of the moderate thermophile Sulfobacillus thermosulfidooxidans in copper sulfide heaps and the sensitivity of this bacterium to the solvent extraction (SX) reagent used to concentrate and purify the copper in solution prior to metal production. More than 1 year was required to achieve habituation to the most inhibitory component of the SX reagent, 4-nonylphenol (4-NP; 2 mg L −1), when S. thermosulfidooxidans was grown in ferrous ion medium. However, habituation to 4-NP did not confer the ability to tolerate higher 4-NP concentrations and those characteristics acquired by the cells during habituation were rapidly lost when grown for a short period in 4-NP-free medium. The culture habituated to the presence of 2 mg L −1 4-NP exhibited differences in cell morphology, cell ultrastructure and membrane fatty acid composition compared with the untreated culture subjected to a similar subculture regime. It is concluded that, where S. thermosulfidooxidans is prevalent in copper sulfide heaps associated with SX-EW plants, this species has become habituated through continuous long-term exposure to low concentrations of 4-NP derived from entrained SX reagent in the recycled leach solutions.

Investigation of the sulfur speciation during chalcopyrite leaching by moderate thermophile Sulfobacillus thermosulfidooxidans

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.

Comparative Leaching of Chalcopyrite by Selected Acidophilic Bacteria and Archaea

A systematic study of the bioleaching of chalcopyrite (CuFeS 2 ) was conducted using axenic cultures of 11 species of acidophilic Bacteria and Archaea to obtain a direct comparison of the microbial chalcopyrite leaching capabilities of the different cultures and to determine the factors that affect Cu release. The characteristics of chalcopyrite leaching by the moderate thermophile Sulfobacillus thermosulfidooxidans , the mesophile Acidithiobacillus ferrooxidans , and the thermophile Acidianus brierleyi were used to elucidate the leaching process. Moderately thermophilic cultures of Sulfobacillus acidophilus, Acidimicrobium ferrooxidans , and Acidithiobacillus caldus were used to study the effects of different metabolic capabilities and relate those to leaching efficiency. The greatest rate of Cu solubilization from chalcopyrite was achieved at high temperatures (up to 70°C) at redox potentials below +550 mV (Ag/AgCl). The enhanced Cu solubilization observed at high temperatures resulted from accelerated chemical reaction rates, rather than from the rates at which individual acidophiles generated the mineral leaching reactants such as Fe 3+ .

Bioleaching of Ok Tedi copper concentrate in oxygen- and carbon dioxide-enriched air

Bacterial leaching of sulphide minerals is fairly well established in heap, dump and in-situ leaching and the primary bacterial treatment of refractory gold concentrate using CSTRs has gained industrial prominence in recent years. Three cultures, a mesophile T.ferrooxidans (DSM 583), a moderate thermophile Sulfobacillus accidophilus (YTF1) and an extreme thermophile (Sulfolobus BC65) were used to bioleach the Ok Tedi copper concentrate under the optimal O 2 and CO 2 enriched air in laboratory CSTRs (2L) at 30% O 2 and 10% CO 2 by volume. The positive effect of using oxygen and carbon dioxide enriched air to bioleach the copper mineral was clearly demonstrated where increases in Cu leaching rate by factors of 2.8, 2.1 and 1.9 for DSM 583, YTF1 and Sulfolobus respectively were observed compared with shake flask tests. The lag phase observed in shake flasks or in CSTR with air, was eliminated when the mineral was leached under optimal gas enrichment and ≈80% of the Cu was extracted in the first 120 to 150 hours of leaching for all three cultures. The average observed dissolved oxygen concentrations in the pulp were 11.8, 8.0 and 7.2 mg/l for DSM 583, YTF1 and Sulfolobus respectively, indicating that O 2 was not limiting in these tests. The Fe released during the bioleaching of copper was non stiochiometric for a predominantly chalcopyrite concentrate and the low redox potential values (max 638mV) suggested galvanic interaction during the leaching of copper where chalcopyrite was leached preferentially in the presence of pyrite. Bioleaching of copper under optimum gas enrichment at different pulp densities showed that near total copper extraction occurred at pulp densities of 3, 10 and 20% (w/v). At high pulp densities, more so at 40% than 30% (w/v), the leaching rate decreased rapidly for experiments with YTF1 and Sulfolobus. Monitoring of dissolved O 2 shows that the O 2 demand increased with increasing pulp density and the average dissolved O 2 concentrations observed for DSM 583, YTF1 and Sulfolobus at 40% solids concentration were 3.0, 2.6 and 2.4 mg/l respectively, suggesting that oxygen and carbon dioxide are not limiting. The decrease in leaching rate observed at high pulp densities (30 & 40%) under optimum gas enrichment was accompanied by low metal dissolution and low redox potential values which was attributed to shear stress due to attrition of cells at high solids concentration. The toxicity of metal ions especially Ag, Fe and Cu, and the formation of precipitates and jarosites was confirmed from XRD analysis of leach residues. These factors appeared to impede the leaching process rather than limiting O 2 and CO 2 conditions.