A thermoacidophilic consortium of chemolithotrophic microorganisms oxidizing the concentrate of high-pyrrhotite pyrite−arsenopyrite ore at 38–40°C was isolated. The most active members of the consortium were identified as Leptospirillum ferriphilum, Acidithiobacillus thiooxidans, Ferroplasma acidiphilum, and Sulfobacillus thermotolerans. Leptospirillum and Thiobacillus species were the most numerous members of the consortium and had the highest activity of ferrous iron and sulfur oxidation, respectively. The optimal temperature values for the growth of both isolates were within 35–38°C. The optimal ranges of initial pH were 1.0–1.2 and 1.75–1.85 for leptospirilla and 1.7–3.3 for thiobacilli with the pH optimum of 1.9. Significant polymorphism and specific cyclic growth with formation of vibrios, spirilla, rods with different end shape, spiral filaments, numerous “pseudococci,” and densely packed spiral filaments surrounded by a sheath were revealed for the Leptospirillum isolate. Two latter morphoforms of L. ferriphilum were not previously described. Differences in ability of the morphoforms to oxidize Fe2+ were revealed. For the first time, the possibility of growth in the presence of organic substances was demonstrated for A. thiooxidans. The rates of growth and substrate oxidation, cell size, and the maximal cell yield decreased insignificantly in comparison with the lithoautotrophic strain.

The efficiency of biooxidation for treatment of a double-refractory gold-bearing sulfide ore concentrate from the Bakyrchik deposit (East Kazakhstan) was defined. The experiments were conducted in two different modes, i.e., with the standard liquid medium and the medium imitating the chemical composition of the Bakyrchik deposit groundwater and containing high concentrations of sodium, magnesium, and chloride. The concentrate contained 17.5% of organic carbon, 6% of pyrite, and 13% of arsenopyrite. Gold content was 57.5 g t–1. Direct gold recovery by cyanidation was very low (2.8%). While biooxidation was efficient in both cases (approximately 90% of sulfide sulfur was oxidized), the efficiency of cyanidation was low (39 and 32%, respectively). This fact suggests high efficiency of biooxidation is insufficient for efficient treatment of double-refractory gold-bearing sulfide ore concentrates.

Определена эффективность процесса биоокисления концентрата двойной упорности сульфидной руды месторождения Бакырчик (Восточный Казахстан) в двух режимах: при использовании стандартной минеральной среды и среды, состав которой соответствовал составу подземной воды месторождения Бакырчик, содержащей высокие концентрации натрия, магния и хлорид-иона. Концентрат содержал большое количество углистого вещества (17.5%), 6% пирита, 13% арсенопирита и до 57.5 г/т золота. Прямым цианированием из концентрата извлекалось только 2.8% золота. В обоих режимах обработки биоокисление проходило с высокой эффективностью (окислено около 90% сульфидной серы), но извлечение золота цианированием было низким, 39 и 32% соответственно. Это свидетельствовало о том, что эффективного биоокисления может быть недостаточно для достижения высокой степени извлечения золота.

Out of two communities of acidophilic chemolithotrophic microorganisms (ACM), a mesophilic and a thermophilic ones, the latter was selected due to its higher rate of sulfur oxidation and pH decrease to >1 in the presence of coal ashes (CA). The structure of ACM communities was retained. Sulfur-oxidizing activity of the microorganisms from the thermophilic community was observed at pH from 1.8 to 2.6 at sulfur concentrations of 0.6–1.0%. Efficient production of acidic solutions with pH 0.69–0.86 was observed after single CA introduction in the amount corresponding to 5–30% pulp density and in the course of pulp density increasing daily from 1 to 50%. Leaching of rare earth elements from 30% coal ash pulp (pH 0.76) was 15 to 30% of their initial content. No sorption of metals on the biomass was observed.

We examined the ferric leaching and biooxidation steps in a two-step biooxidation process of a gold-bearing sulfide concentrate containing pyrrhotite, arsenopyrite and pyrite. Ferric leaching of the concentrate (pulp density at 200 g/L) for 2 hours at 70°C at pH 1.4 by ferric sulfate solution (initial concentration at 35.6 g/L), which was obtained by microbial oxidation of ferrous sulfate allowed to oxidize 20.4% of arsenopyrite and 52.1% of sulfur. The most effective biooxidation of ferric leached concentrate was observed at 45°C in the presence of yeast extract. Oxidation of the sulfide concentrate in a two-step process proceeded more efficiently than in one-step. In a two-step mode, gold extraction from the residue was 10% higher and the content of elemental sulfur was two times lower than in a one-step process.

Из ацидофильных микробных сообществ месторождений сульфидных руд Казахстана были выделены штаммы A. ferrooxidans и изучены их физиологические свойства, важные с позиции биотехнологии – определены оптимальная и предельные температуры роста, исследована устойчивость штаммов к NaCl. Показано, что оптимумы температуры у штаммов совпадали (30–32°C), но диапазоны толерантности различались: при 37°C штамм TFBK практически не окислял железо, тогда как скорость окисления железа при 37°C штаммом TFV была лишь незначительно ниже, чем при более низких температурах. Хлорид натрия ингибировал окислительную активность обоих штаммов. Окисление железа штаммом TFV ингибировалось 5 г/л NaCl, а при концентрации NaCl 20 г/л подавлялось практически полностью. Окисление железа штаммом TFBK ингибировалось NaCl в меньшей степени: при концентрации NaCl 10 г/л скорость окисления железа была достаточно высокой, при концентрации NaCl 20 г/л железо окислялось с незначительной скоростью, но полностью окисление не подавлялось. Окисление штаммами серы подавлялось хлоридом натрия в меньшей степени, чем окисление двухвалентного железа. Окисление серы штаммом TFV заметно ингибировалось только при концентрации NaCl 20 г/л, но не подавлялось полностью. Окисление серы штаммом TFBK ингибировалось NaCl в большей степени. При концентрации NaCl 10 г/л скорость окисления была значительно ниже, чем при меньших концентрациях NaCl (после 6 сут окисления при концентрации NaCl до 5 г/л в среде было около 130 мМ сульфата, а при концентрации 10 г/л – примерно 100 мМ). Окисление серы штаммом TFBK заметно ингибировалось при концентрациях NaCl 10 и 20 г/л, но также как и в случае штамма TFV не было ингибировано полностью. Результаты, полученные в данной работе, позволяют сделать вывод о приспособленности вида A. ferrooxidans к широкому диапазону условий роста.

A method for leaching rare earth elements from coal ash in the presence of elemental sulfur-oxidizing communities of acidophilic chemolithotrophic microorganisms was proposed. The optimal parameters determined for rare element leaching in reactors were as follows: temperature, 45°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.

Acidithiobacillus ferrooxidans strains were isolated from acidophilic microbial communities of Kazakhstan sulfide ore deposits. Their biotechnologically important properties (optimal and maximal growth temperatures and resistance to NaCl) were determined. While temperature optima of the strains were the same (30–32°C), temperature ranges were different. Thus, strain TFBK oxidized iron very poorly at 37°C, while for strain TFV the iron oxidation rate at this temperature was insignificantly lower than at lesser temperatures. NaCl inhibited the oxidative activity of both strains. Iron oxidation by strain TFV was inhibited at 5 g/L NaCl and was suppressed almost completely at 20 g/L. Iron oxidation by strain TFBK was inhibited by NaCl to a lesser degree, so iron oxidation rate was relatively high at 10 g/L, while at 20 g/L NaCl the process was not suppressed completely, although the oxidation rate was low. Sulfur oxidation by these strains was less affected by NaCl than oxidation of ferrous iron. Sulfur oxidation by strain TFV was inhibited considerably, albeit not suppressed completely, only at 20 g/L NaCl, but was not suppressed completely. Sulfur oxidation by strain TFBK was more affected by NaCl. At 10 g/L NaCl the oxidation rate was much lower than at lower NaCl concentrations (sulfate concentrations after 6 days of oxidation at 5 and 10 g/L NaCl were~130 and~100 mM, respectively). While sulfur oxidation by strain TFBK was considerably inhibited at 10 and 20 g/L NaCl, similar to strain TFV it was not suppressed completely. Our results indicate the adaptation of the species A. ferrooxidans to a broad range of growth conditions.

Extended Abstract Mining and metallurgical treatment of sulfide ores is characterized by significant losses of nonferrous and precious metals into the various wastes. Flotation of sulfide ores yields formation of sulfide flotation tailings. These wastes pose a problem not just because of their sheer volume, but some of them may affect local ecosystems. Nowadays, mining wastes can be considered as technogenic source of metals for biohydrometallurgy in particular. The solubilization of metals by acidophilic chemolithotrophic microorganisms is widely and successfully used in the industrial process of bioleaching or biomining to extract non-ferrous and precious metals. Acidophilic microorganisms that are able to oxidize sulfide minerals are phylogenetically heterogeneous and include representatives of several bacterial and archaeal phyla, such as mesophilic (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans), thermotolerant (Leptospirillum ferriphilum, Ferroplasma acidiphilum, Acidiferrobacter thiooxydans), and moderately thermophilic species (At. caldus, Sulfobacillus spp., Acidimicrobium spp., and Acidiplasma spp.). A sample of old pyrite flotation tailings from the concentrator contained 11.4% sulfidic iron, 14.5% sulfidic sulfur, 0.26% copper, 0.22% zinc, and 0.67 g/t gold. Pyrite was the main sulfide mineral (31%). The gold recovery from the unoxidized flotation tailings was 50%. Recently, it has been proposed to recover copper and zinc from this waste by the treatment with sulfuric acid solution (Bulaev et al., 2014). A biooxidation of the mining waste is proposed for the recovery of gold. The biooxidation of the waste was conducted in a few bioreactors that were connected in series under continuous conditions with periodic feeding and with effluent removal. Biooxidation was carried out in 2.0 L reactors that contained 1 L of pulp. A microbial consortium containing Acidithiobacillus caldus INMI-10, Sulfobacillus thermosulfidooxidans strains HT-4 and HT-1, Leptospirillum and Acidithiobacillus strains, and the indigenous culture obtained from the pyrite tailings was used as an inoculum for the biooxidation experiments. The pulp density was maintained at 20% (w/v). The effects of temperature, pH, and duration of the biooxidation of old pyrite flotation tailings on the recovery of gold by carbon-in-pulp cyanidation were investigated. The best technological parameters of the biooxidation step for recovery of gold from the leach residue were the temperature of 35°C, pH 1.2– 1.5, biooxidation for 12 days. Under these conditions, the sulfidic iron and sulfidic sulfur oxidation levels were 88.9% and 92.3%, respectively, and the gold recovery level was 92%. The extraction of copper into the liquid phase was 68.2%, and zinc extraction was 76.8%. Gold recovery after 6 days of biooxidation was 87% while copper and zinc extraction was 57.5% and 60.5%, respectively. Thus, it was shown that biooxidation of old pyrite flotation tailings with application of acidophilic chemolithotrophic microorganisms for recovery of copper, zinc, and gold could be a promising technique for the treatment of these wastes.

Исследован процесс окисления флотоконцентрата сульфидной руды с высоким содержанием пирротина сообществами ацидофильных хемолитотрофных микроорганизмов при 35, 40 и 45°C. Физико-химические параметры жидкой фазы пульпы, результаты анализа твердых остатков после биоокисления и цианирования свидетельствовали о том, что с большей скоростью процесс вело сообщество микроорганизмов, сформировавшееся при 40°C. Степень извлечения золота при 35°C составила 89.34%, при 40°C – 94.59%, при 45°C – 83.25%. При 40°C в жидкой фазе пульпы отмечена самая высокая численность микроорганизмов – 6.01 ? 109 кл/мл. Изменение температуры почти не сказалось на видовом составе сообществ микроорганизмов, за исключением отсутствия Leptospirillum ferriphilum при 35°C, но соотношение видов в сообществах заметно различалось. При 40°C в сообществе микроорганизмов отмечена относительно большая численность Sulfobacillus thermosulfidooxidans, окисляющих с более высокой скоростью железо и элементную серу, чем представители других видов ацидофильных хемолитотрофных микроорганизмов.

A community of thermoacidophilic chemolithotrophic microorganisms was shown to exhibit enhanced efficiency of leaching and biooxidation of the gold-bearing pyrite-arsenopyrite flotation concentrate in continuous mode of cultivation. Under the optimal values of growth parameters, the degree of oxidation of sulfide arsenic, iron, sulfur, and antimony in the line of three laboratory reactors (D = 0.004 h −1 ) was 99.55, 98.87, 99.65, and 97.08%, respectively, while gold recovery from the solid biooxidation residue was 97.4%.

Из пробы сульфидного золотосодержащего флотоконцентрата пиритно-арсенопиритной руды при температуре 45–47°C и рН 1.8–2.0 выделено аборигенное сообщество термофильных ацидофильных хемолитотрофных микроорганизмов (АХМ). Сравнение его с экспериментально созданным термоацидофильным консорциумом микроорганизмов, сформировавшимся при культивировании в параллельных биореакторах, показало, что организмы консорциума активнее выщелачивали и окисляли железо, уступая аборигенному в активности окисления серы. Новое термофильное aцидофильное хемолитотрофное сообщество получено путем взаимообогащения микроорганизмами экспериментально созданного консорциума и аборигенного сообщества в ходе окисления флотоконцентрата сульфидной руды при 47°C. В новом сообществе АХМ доминирующими были штаммы видов бактерий: Acidithiobacillus caldus, наиболее активно окисляющие серу, и Sulfobacillus thermotolerans, активно окисляющие и железо, и серу, в меньшем количестве – железоокисляющие археи семейства Ferroplasmaceae и гетеротроф Alicyclobacillus tolerans. Показана перcпективность использования нового сообщества АХМ для выщелачивания/окисления сульфидов концентрата при высокой плотности пульпы (Т : Ж = 1 : 4).

Oxidation of flotation concentrate of a pyrrhotite-rich sulfide ore by acidophilic chemolithoautotrophic microbial communities at 35, 40, and 45°C was investigated. According to the physicochemical parameters of the liquid phase of the pulp, as well as the results of analysis of the solid residue after biooxidation and cyanidation, the community developed at 40°C exhibited the highest rate of oxidation. The degree of gold recovery at 35, 40, and 45°C was 89.34, 94.59, and 83.25%, respectively. At 40°C, the highest number of microbial cells (6.01 × 109 cells/mL) was observed. While temperature had very little effect on the species composition of microbial communities (except for the absence of Leptospirillum ferriphilum at 35°C), the shares of individual species in the communities varied with temperature. Relatively high numbers of Sulfobacillus thermosulfidooxidans, the organism oxidizing iron and elemental sulfur at higher rates than other acidophilic chemolithotrophic species, were observed at 40°C.

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.

Optimal aeration conditions were determined and the effect of yeast extract on biooxidation of high-pyrrhotite sulfide ore flotation concentrate in the course of continuous cultivation of an acidophilic chemolithotrophic microbial community was studied in a line of four sequential laboratory reactors; the aeration rate was 3 L/(L min), yeast extract concentration was 0.02%. The gold recovery level was 96.45% at 2.23% elemental sulfur content in the solid residue. The dominant strains identified in the community responsible for biooxidation were Acidithiobacillus caldus OL13-1, At. caldus OL13-3 = At. caldus OL12-3, and an ‘Acidiferrobacter’ strain. Strains Sulfobacillus thermosulfidooxidans OL13-2 = S. thermosulfidooxidans OL12-1 and Ferroplasma acidiphilum OL13-4 = F. acidiphilum OL12-4 were isolated in pure culture and identified.

Оптимизированы условия биоокисления золотосодержащего упорного пиритно-арсенопиритного флотоконцентрата и охарактеризована численность доминирующих групп организмов в сообществе термофильных ацидофильных хемолитотрофных микроорганизмов (АХМ) на разных этапах процесса биовыщелачивания. В периодическом режиме процесса оптимальными параметрами роста сообщества и выщелачивания/окисления минеральных компонентов концентрата были: рН 1.4–1.8; температура 47.5°С; соотношение солей при приготовлении жидкой фазы пульпы (г/л) – К2НРО4 · 3Н2 – 0.53, (NH4)2SO4 – 1.6 и MgSO4 · 7H2O – 2.5 (или (NH4)2SO4 – 1.23, аммофос – 0.41 и КОН – 0.1) с 0.03% дрожжевого экстракта (ДЭ). Оптимальные условия обеспечивали наиболее высокие: скорость роста сообщества АХМ; степень выщелачивания из концентрата железа и мышьяка; степень окисления Fe2+ и S2/S0 и доминирование в сообществе микроорганизмов Acidithiobacillus caldus, Sulfobacillus spp. и Ferroplasma spp.

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).