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A method for leaching rare earth elements from coal ash in the presence of elemental sulfur using communities of acidophilic chemolithotrophic microorganisms was proposed. The optimal parameters determined for rare element leaching in reactors were as follows: temperature, 45 degrees C; initial pH, 2.0; pulp density, 10%; and the coal ash to elemental sulfur ratio, 10 : 1. After ten days of leaching, 52.0, 52.6, and 59.5% of scandium, yttrium, and lanthanum, respectively, were recovered.

Antimony leaching from sulfide ore samples by an experimental consortium of thermoacidophilic microorganisms, including Sulfobacillus, Leptospirillum, and Ferroplasma strains was studied. The ores differed significantly in the content of the major metal sulfides (%): Sb(S), 0.84 to 29.95; Fe(S), 0.47 to 2.5, and As(S), 0.01 to 0.4. Independent on the Sb(S) concentration in the experimental sample, after adaptation to a specific ore and pulp compaction the microorganisms grew actively and leached/oxidized all gold-antimony ores at 39 ± 1 degrees C. The lower was the content of iron and arsenic sulfides, the higher was antimony leaching. For the first time the investigations conducted with the use of X-ray microanalysis research made it possible to conclude that in a natural high-antimony ore Sb inhibits growth of only a part of the cell population and that Ca, Fe, and Sb may compete for the binding centers of the cell.

A community of acidochemolithotrophic microorganisms with a high oxidation rate of pyrrhotite-containing sulphide ore flotation concentrate was selected. The Acidithiobacillus caldus OP-1 and Ferroplasma acidiphilum OP-2 cultures were identified to be dominating members. The presence of the Acidithio- bacillusferrooxidans OP-3, Leptospirillumferriphilum OP-4, and Sulfobacillus thermosulfidooxidans OP-5 cultures in the community's composition was also mentioned. The analysis results of solid residues of the process showed a greater elemental sulfur oxidation level and gold recovery when the initial pH value in tank I was maintained at a level of 1.8-2.0 (90.5%) rather than 1.6-1.8 (86.3%).

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 degrees 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 degrees 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.

Quantitative abundance of microbial species within an association was found to depend on the energy substrate and the oxidation temperature of sulfide minerals. The number of microbial cells varied depending on the position of reactor in the chain, i.e., the stage of the energy substrate oxidation. Microbial associations oxidized the energy substrate more efficiently than any of their individual components. The increase in pulp density up to the solid : liquid ratio of 1 : 2.5 had an unfavorable effect on microorganisms comprising microbial associations.

Quantitative and qualitative changes in the content of elements in the solid and liquid phases occurred as the pulp moved through fermenters during biooxidation of an ore flotation concentrate. The association of microorganisms were adapted for utilizing sulfur-containing substrates; however, the rate of their oxidation was insufficient, which led to an increase in the amount of sodium cyanide required for gold recovery. The replacement of one-fourth of the liquid phase of the pulp (density, 13%) with a mineral medium without an energy source, the fractional addition of FeSO4 x 7H2O (1 g/l per day), and the improvement of pulp aeration made it possible to increase the content of SO4(2-) by 80.7, 86.2, and 58.5%, respectively. When one-fourth of the liquid phasa of the pulp (density, 24%) was replaced with a mineral medium without an energy source, the rate of additional oxidation of sulfide minerals increased, which increased the efficiency of gold extraction into solution and gold recovery on charcoal by 3.4 and 3.6%, respectively, and reduced sodium cyanide consumption by 3 kg/ton.

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.

A thermotolerant, Gram-positive, aerobic, endospore-forming, acidophilic bacterium (strain Kr1T) was isolated from the pulp of a gold-containing sulfide concentrate processed at 40 degrees C in a gold-recovery plant (Siberia). Cells of strain Kr1(T) were straight to slightly curved rods, 0.8-1.2 microm in diameter and 1.5-4.5 microm in length. Strain Kr1T formed spherical and oval, refractile, subterminally located endospores. The temperature range for growth was 20-60 degrees C, with an optimum at 40 degrees C. The pH range for growth on medium containing ferrous iron was 1.2-2.4, with an optimum at pH 2.0; the pH range for growth on medium containing S0 was 2.0-5.0, with an optimum at pH 2.5. Strain Kr1T was mixotrophic, oxidizing ferrous iron, S0, tetrathionate or sulfide minerals as energy sources in the presence of 0.02 % yeast extract or other organic substrates. The G+C content of the DNA of strain Kr1T was 48.2+/-0.5 mol%. Strain Kr1T showed a low level of DNA-DNA reassociation with the known Sulfobacillus species (11-44 %). 16S rRNA gene sequence analysis revealed that Kr1T formed a separate phylogenetic group with a high degree of similarity between the nucleotide sequences (98.3-99.6 %) and 100 % bootstrap support within the phylogenetic Sulfobacillus cluster. On the basis of its physiological properties and the results of phylogenetic analyses, strain Kr1T can be affiliated to a novel species of the genus Sulfobacillus, for which the name Sulfobacillus thermotolerans sp. nov. is proposed. The type strain is Kr1T (=VKM B-2339T=DSM 17362T).

In the course of pilot industrial testing of a biohydrometallurgical technology for processing goldarsenic concentrate obtained from the Nezhdaninskoe ore deposit (East Siberia, Sakha, Yakutiya), a new gram-positive rod-shaped spore-forming moderately thermophilic bacterium (designated as strain N1) oxidizing Fe2+, S0, and sulfide minerals in the presence of yeast extract (0.02%) was isolated from a dense pulp. Physiologically, strain N1 differs from previously described species of the genus Sulfobacillus in having a somewhat higher optimal growth temperature (55 degrees C). Unlike the type strain of S. thermosulfidooxidans, strain N1 could grow on medium with 1 mM thiosulfate or sodium tetrathionate as a source of energy only within several passages and failed to grow, in the absence of an inorganic energy source, on media with sucrose, fructose, glucose, reduced glutathione, alanine, cysteine, sorbitol, sodium acetate, or pyruvate. The G + C content of the DNA of strain N1 was 48.2 mol %. The strain showed 42% homology after DNA-DNA hybridization with the type strain of S. thermosulfidooxidans and 10% homology with the type strain of S. acidophilus. The isolate differed from previously studied strains of S. thermosulfidooxidans in the structure of its chromosomal DNA (determined by the method of pulsed-field gel electrophoresis) which remained stable as growth conditions were changed. According to the results of the 16S rRNA gene analysis, the new strain forms a single cluster with the bacteria of the species Sulfobacillus thermosulfidooxidans (sequence similarity of 97.9-98.6%). Based on these genetic and physiological features, strain N1 is described as a new species Sulfobacillus sibiricus sp. nov.

The thermoacidophilic iron-oxidizing chemolithotroph Sulfobacillus sibiricus N1T is characterized by steady growth and amplified cell yield when grown in vigorously aerated medium containing Fe2+, glucose, and yeast extract as energy sources. In this case, carbon dioxide, glucose, and yeast extract are used as carbon sources. Glucose is assimilated through the fructose-bisphosphate pathway and the pentose-phosphate pathway. Glyoxylate bypass does not function in S. sibiricus, and the tricarboxylic acid cycle is disrupted at the level of 2-oxoglutarate dehydrogenase. The presence of ribulose-bisphosphate carboxylase indicates that carbon dioxide fixation proceeds through the Calvin cycle. The activity of ribulose-bisphosphate carboxylase is highest in autotrophically grown cells. The cells also contain pyruvate carboxylase, phosphoenolpyruvate carboxylase, phosphoenolpyruvate carboxykinase, and phosphoenolpyruvate carboxytransphosphorylase.