Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrate at 45–47°C and pH 1.8–2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the microorganisms from the experimental and aboriginal communities during the oxidation of sulfide ore flotation concentrate at 47°C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus (the most active sulfur oxidize) and Sulfobacillus thermotolerans (active oxidizer of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrate at high pulp density (S : L = 1 : 4).     

Selective leaching of zinc from copper-zinc concentrate

Biooxidation of copper-zinc concentrate with the use of consortia of mesophilic and moderately thermophilic acidophilic chemolithotrophic microorganisms was studied. Pyrrhotite, sphalerite, and chalcopyrite were the main sulfide minerals of the concentrate. The possibility in principal of complete selective leaching of zinc from sulfide concentrate coupled with minimal recovery of copper (less than 20%) was demonstrated. Selective leaching of zinc could be caused by galvanic interactions between minerals of the concentrate during the biooxidation. The results can be used as the basis for the development of the technologies for production of grade copper concentrate not containing zinc from sulfide copper-zinc concentrate obtained from refractory ores.     

Leaching of nonferrous metals from copper converter slag with application of acidophilic microorganisms

The leaching process of copper and zinc from copper converter slag with ferric iron in sulfuric acid solutions obtained using the association of acidophilic chemolithotrophic microorganisms was investigated. The best parameters of chemical leaching (temperature 70°C, an initial concentration of ferric iron in the leaching solution of 10.1 g/L, and a solid phase content in the pulp of 10%) were selected. Carrying out the process under these parameters resulted in the recovery of 89.4% of copper and 39.3% of zinc into the solution. The possibility of the bioregeneration of ferric iron in the solution obtained after the chemical leaching of slag by iron-oxidizing acidophilic chemolithotrophic microorganisms without inhibiting their activity was demonstrated.     

Biohydrometallurgical technology of a complex copper concentrate process

Leaching of sulfide-oxidized copper concentrate of the Udokan deposit ore with a copper content of 37.4% was studied. In the course of treatment in a sulfuric acid solution with pH 1.2, a copper leaching rate was 6.9 g/kg h for 22 h, which allowed extraction of 40.6% of copper. As a result of subsequent chemical leaching at 80 degrees C during 7 h with a solution of sulphate ferric iron obtained after bio-oxidation by an association of microorganisms, the rate of copper recovery was 52.7 g/kg h. The total copper recovery was 94.5% (over 29 h). Regeneration of the Fe3+ ions was carried out by an association of moderately thermophilic microorganisms, including bacteria of genus Sulfobacillus and archaea of genus Ferroplasma acidiphilum, at 1.0 g/l h at 40 degrees C in the presence of 3% solids obtained by chemical leaching of copper concentrate. A technological scheme of a complex copper concentrate process with the use of bacterial-chemical leaching is proposed.     

Leaching of copper ore of the Udokanskoe deposit at low temperatures by an association of acidophilic chemolithotrophic microorganisms

Pure cultures of indigenous microorganisms Acidithiobacillus ferrooxidans strain TFUd, Leptospirillum ferrooxidans strain LUd, and Sulfobacillus thermotolerans strain SUd have been isolated from the oxidation zone of sulfide copper ore of the Udokanskoe deposit. Regimes of bacterial-chemical leaching of ore have been studied over a temperature range from −10 to +20°C. Effects of pH, temperature, and the presence of microorganisms on the extraction of copper have been shown. Bacterial leaching has been detected only at positive values of temperature, and has been much more active at +20 than at +4°C. The process of leaching was more active when the ore contained more hydrophilic and oxidized minerals. The possibility of copper ore leaching of the Udokanskoe deposit using sulfuric acid with pH 0.4 at negative values of temperature and applying acidophilic chemolithotrophic microorganisms at positive values of temperature and low pH values was shown.     

Microbial communities in four industrial copper dump leaching operations in Bulgaria

Abstract: The microflora of four industrial copper dump leaching operations in Bulgaria was studied in detail. The microbial communities in these operations had a similar species composition but differed from each other with respect to the counts of microorganism related to the different species. It was found that the copper solubilizalion depended mainly on the amount and activity in situ of the mesophilic acidophilic chemolithotrophic bacteria which occurred in the ore dumps, which were the prevailing microorganisms in these engineered environments. On their parts, this amount and activity depended on a complex of environmental factors. These factors varied in the different dumps as well as in different sections of one and the same dump. The attempts to enhance the leaching by improving some of the environmental factors as well as by introducing laboratory-bred strains into the dumps are described.     

Sulfobacillus thermosulfidooxidans: a new lineage of bacterial evolution?

The nucleotide sequence of 5 S ribosomal RNA (rRNA) of type strain Sulfobacillus thermosulfidooxidans VKM B-1269 was determined. This organism represents a group of moderately thermophilic acidophilic chemolithotrophic bacteria, able to use ferrous and sulfur compounds as the sole energy source. 5 S rRNA of this bacterium is drastically different from all other known bacterial 5 S rRNA sequences. It is suggested that S. thermosulfidooxidans represents a new lineage of bacterial evolution, that diverged from other bacteria at an early step of their evolution.     

Characterization of iron- and sulphide mineral-oxidizing moderately thermophilic acidophilic bacteria from an Indonesian auto-heating copper mine waste heap and a deep South African gold mine

Iron- and chalcopyrite-oxidizing enrichment cultures were obtained at 50°C from acidic, high-temperature, copper/gold mine environments in Indonesia and South Africa. Over 90% copper yield was obtained from chalcopyrite concentrate with the Indonesian enrichment in 3 months with 2% solids concentration, when pH was maintained at around 2. Neither addition of silver cations nor an enhanced nutrient concentration influenced chalcopyrite leaching. Excision and sequencing of bands from denaturing gradient gel electrophoresis of the amplified partial 16S rRNA gene showed that the enrichment cultures from different environments in South Africa and Indonesia were very simple, and similar. Chalcopyrite concentrate supported a simpler and different community than Fe²⁺. The members of the enrichment cultures were closely related to Sulfobacillus yellowstonensis and Sulfobacillus acidophilus.     

Bioleaching of chalcopyrite concentrate by a moderately thermophilic culture in a stirred tank reactor

A mixed culture of moderately thermophilic microorganisms was enriched from acid mine drainage samples collected from several chalcopyrite mines in China. Such mixed culture can be used to effectively extract copper from chalcopyrite. Furthermore, after being adapted to gradually increased concentration of chalcopyrite concentrate, the tolerance of the mixed culture to chalcopyrite concentrate was brought up to 80 g/L. The effects of several leaching parameters on copper recovery in stirred tank reactor also had been investigated. The results of the investigation show that it was possible to achieve a copper extraction rate of 75% in 44 days at a pulp density of 8%. The leaching rate of chalcopyrite concentrate tended to increase with dissolved total iron concentration. At low pH ranges, more microscopic counts of microorganisms were found in the solution. Furthermore, the analysis of leached residues indicates that the passivation of chalcopyrite concentrate was mainly due to a mass of jarosite and PbSO(4) on the mineral surface, other than the elemental sulphur layer. The bacterial community composition was analyzed by using Amplified Ribosomal DNA Restriction Analysis. Two moderately thermophilic bacteria species were identified as Leptospirillum ferriphilum and Acidithiobacillus caldus with abundance of 67% and 33% in the bio-pulp, respectively.     

Changes in the composition of an acid mine drainage microbial community upon successive transfers in medium containing low-grade copper sulfide

A consortium of microorganisms from acid mine drainage samples was cultured in modified 9 K medium containing low-grade copper sulfide. The culture was maintained for sixty days and then transferred to fresh medium. This process was repeated three more times and a final consortium exhibiting a copper extraction rate of 89.3% was obtained. RFLP and microarrays analysis of 16S rRNA sequences retrieved from the consortia showed that Acidithiobacilluscaldus, Leptospirillumferriphilum, Sulfobacillus sp., Acidiphilium sp., and Sulfolobus spp. were represented in higher numbers in the consortia obtained in the copper-containing medium than in the original consortium. In contrast, a decrease in Acidithiobacillus ferrooxidans, Alicyclobacillus sp., Pseudomonas sp., and Sulfobacillus thermosulfidooxidans was observed. The abundance of genes related to sulfur metabolism from At. caldus and Sulfolobus spp., iron oxidation from Leptospirillum sp. and metal resistance from most of the detected microorganisms increased as the consortium was successively transferred into fresh medium.     

Genotypic and phenotypic polymorphism of environmental strains of the moderately thermophilic bacterium Sulfobacillus sibiricus

Five cultures of moderately thermophilic spore-forming acidophilic chemolithotrophic bacteria were isolated from the zones of spontaneous heating of pyrrhotine-containing pyrite-arsenopyrite gold-arsenic sulfide ores in an operating open pit (strains B1, B2, B3, OFO, and SSO). Analysis of the chromosomal DNA structure revealed differences between these cultures at the strain level (apart from B3 and SSO, which had identical restriction profiles). All the strains had a similar G + C DNA molar content (47.4-48.3%). The level of DNA reassociation was 85 to 95%. The similarity between the DNA of the type strain Sulfobacillus sibiricus N1 isolated from arsenopyrite ore concentrate and that of these strains (83-93%) indicates that they belong to the same species. The strains had similar values of pH and temperature optimal for growth on ferrous iron (1.6-2.0 and 45-55 degrees C, respectively). They were mixotrophs; Fe(II), S0, and sulfide minerals along with organic compounds were used as energy sources and electron donors. However, the kinetic parameters of growth and substrate oxidation varied from strain to strain. Genetic variety of the strains from diverse ecosystems and environments is possibly the result of the different rates of microevolution processes.     

Two-stage process of bacterial-chemical oxidation of refractory pyrite-arsenopyrite gold-bearing concentrate

A technology for tank biooxidation of refractory gold-bearing concentrate under variable temperature conditions has been improved: the temperature of the first of two stages was changed from 30°C to 34–36°C. Gold in this concentrate is mainly associated with sulfide minerals: arsenopyrite and pyrite, which underlies a low gold recovery (16.68%) as a result of cyanidation. To resolve the problem, an association of mesophilic acidophilic chemolithotrophic microorganisms and moderately thermophilic bacteria of the Sulfobacillus genus were used for the concentrate oxidation. The composition of the used microbial association was studied; it was shown that it depends upon temperature: at 42°C, the population of the mesophilic thiobacteria decreased, whereas that of thermophilic sulfobacilli enhanced as compared to 36°C. The accepted scheme of the process ensures a high extent of gold recovery (94.6%) within a short space of time for biooxidation (96 h).     

Selective extraction of metals from zinc concentrate by association of chemolithotrophic bacteria

Ability for selective extraction of copper and zinc from zinc concentrate using association of chemolithotrophic bacteria was investigated. In the presence of bacterial association, the rate of leaching of zinc, copper, and iron was increased 3-fold, 4–5-fold, and 2-fold, respectively. The results indicate the maximum dissolution rate for zinc, then followed by copperand iron. It was revealed that addition of Fe³⁺ 2 g/l resulted in reduction of iron leaching and in 3-fold increase of leaching rate of copper at constant dissolution rate of mineral zinc. It is suggested that the intensification of copper leaching is connected with the activity of sulfur-oxidizing bacteria able to activate the mineral surface via elimination of passivation layer of elemental sulfur. It was concluded that sulfur-oxidizing bacteria play a significant role in copper leaching from zinc concentrate. A unique strain of mesophile sulfur-oxidizing bacteria was isolated from leaching pulp of zinc concentrate; in the perspective, it may serve as efficient candidate for performing of selective extraction of copper from zinc concentrate.     

Bioregeneration of the pregnant leach solutions obtained during the leaching of nonferrous metals from slag waste by acidophilic microorganisms

The bioregeneration of the solutions obtained after the leaching of copper and zinc from slag waste by sulfuric acid solutions containing ferric iron was examined. For bioregeneration, associations of mesophilic and moderately thermqophilic acidophilic chemolithotrophic microorganisms were made. It has been shown that the complete oxidation of iron ions in solutions is possible at a dilution of the pregnant leach solution with a nutrient medium. It has been found that the maximal rate of oxidation of iron ions is observed at the use of a mesophilic association of microorganisms at a threefold dilution of the pregnant leach solution with a nutrient medium. The application of bioregeneration during the production of nonferrous metals from both copper converter slag and its waste would make it possible to approach the technology of their processing using the closed cycle of workflows.     

Biohydrometallurgical technology of copper recovery from a complex copper concentrate

Leaching of sulfide-oxidized copper concentrate of the Udokan deposit ore with a copper content of 37.4% was studied. In the course of treatment in a sulfuric acid solution with pH 1.2, a copper leaching rate was 6.9 g/kg h for 22 hours, which allowed extraction of 40.6% of copper. At subsequent chemical leaching at 80°C during 7 hours with a solution of ferric sulfate obtained after biooxidation by an association of micro-organisms, the rate of copper recovery was 52.7 g/kg h. The total copper recovery was 94.5% (over 29 hours). Regeneration of the Fe³⁺ ions was carried out by an association of moderately thermophilic microorganisms, including bacteria of genus Sulfobacillus and archaea Ferroplasma acidiphilum, at 1.0 g/L h at 40°C in the presence of 3% solids obtained by chemical leaching of copper concentrate. A flowsheet scheme of a complex copper concentrate process with the use of bacterial-chemical leaching is proposed.     

Bioregeneration of Leaching Solutions during Two-Step Processing of Copper-Zinc Concentrate

A comparative study of the oxidation of ferrous iron ions by various cultures of acidophilic chemolithotrophic microorganisms in solutions obtained after ferric leaching of copper-zinc concentrate at 80°C has been carried out. It was shown that the use of a moderately thermophilic culture for bioregeneration of leaching solutions was preferable. At the same time, the oxidation rate of Fe²⁺ ions reached 0.88 g/(L h), or 21.1 g/(L day). We propose that the activity of the moderately thermophilic culture was due to the presence of the mixotrophic bacteria Sulfobacillus spp., which used organic products of the microbial lysis for their growth. These products were formed during high-temperature ferric leaching of the copper-zinc concentrate with the biosolution.     

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+ .     

Significance of microbial communities and interactions in safeguarding reactive mine tailings by ecological engineering

Pyritic mine tailings (mineral waste generated by metal mining) pose significant risk to the environment as point sources of acidic, metal-rich effluents (acid mine drainage [AMD]). While the accelerated oxidative dissolution of pyrite and other sulfide minerals in tailings by acidophilic chemolithotrophic prokaryotes has been widely reported, other acidophiles (heterotrophic bacteria that catalyze the dissimilatory reduction of iron and sulfur) can reverse the reactions involved in AMD genesis, and these have been implicated in the "natural attenuation" of mine waters. We have investigated whether by manipulating microbial communities in tailings (inoculating with iron- and sulfur-reducing acidophilic bacteria and phototrophic acidophilic microalgae) it is possible to mitigate the impact of the acid-generating and metal-mobilizing chemolithotrophic prokaryotes that are indigenous to tailing deposits. Sixty tailings mesocosms were set up, using five different microbial inoculation variants, and analyzed at regular intervals for changes in physicochemical and microbiological parameters for up to 1 year. Differences between treatment protocols were most apparent between tailings that had been inoculated with acidophilic algae in addition to aerobic and anaerobic heterotrophic bacteria and those that had been inoculated with only pyrite-oxidizing chemolithotrophs; these differences included higher pH values, lower redox potentials, and smaller concentrations of soluble copper and zinc. The results suggest that empirical ecological engineering of tailing lagoons to promote the growth and activities of iron- and sulfate-reducing bacteria could minimize their risk of AMD production and that the heterotrophic populations could be sustained by facilitating the growth of microalgae to provide continuous inputs of organic carbon.     

Characteristics of a moderately thermophilic and acidophilic iron-oxidizing Thiobacillus

Summary Thiobacillus TH1 is an acidophilic chemolithotrophic heterotroph growing at temperatures up to about 50°C on media containing ferrous iron or pyrite when supplemented with yeast extract or glutathione. Virtually no carbon dioxide fixation occurred during growth on iron with yeast extract. Its DNA contains 48 mol % guanine + cytosine. The organism effects the thermophilic leaching of metals from pyrite, chalcopyrite, CuS, and copper concentrates. Oxidation of soluble ferrous iron at pH 1.6 was competitively inhibited by ferric iron and had a K_m of 7.3 mM FeSO₄.     

Genotypic and phenotypic polymorphism of environmental strains of the moderately thermophilic bacterium <Emphasis Type="Italic">Sulfobacillus sibiricus</Emphasis>

Five cultures of moderately thermophilic spore-forming acidophilic chemolithotrophic bacteria were isolated from the zones of spontaneous heating of pyrrhotite-containing pyrite-arsenopyrite gold-arsenic sulfide ores in an operating open pit (strains B1, B2, B3, OFO, and SSO). Analysis of the chromosomal DNA structure revealed the differences between these cultures at the strain level (apart from B3 and SSO, which had identical restriction profiles). All the strains had a similar G+C DNA molar content (47.4–48.3%). The level of DNA reassociation was 85 to 95%. The similarity between the DNA of the type strain Sulfobacillus sibiricus N1 isolated from arsenopyrite ore concentrate and that of these strains (83–93%) indicates that they belong to the same species. The strains had similar values of pH and temperature optimal for growth on ferrous iron (1.6–2.0 and 45–55°C, respectively). They were mixotrophs; Fe(II), S^o, and sulfide minerals along with organic compounds were used as energy sources and electron donors. However, the kinetic parameters of growth and substrate oxidation varied from strain to strain. Genetic variety of the strains from diverse ecosystems and environments is possibly the result of the different rates of microevolution processes.