Copper Bioleaching Research Articles

Effect of Temperature on Biobeneficiation of Bulk Copper-Nickel Concentrate with Thermoacidophilic Microbial Communities

Bioleaching of the bulk copper–nickel sulfide concentrate was proposed as a method to remove nickel from it and to obtain a concentrate containing copper as chalcopyrite. This approach is based on the different refractoriness of sulfide minerals in ferric sulfate solutions and oxidation by acidophilic microorganisms. The bulk concentrate contained 10.8% copper in the form of chalcopyrite (CuFeS2) and 7.2% nickel that occurred in pentlandite ((Ni,Fe)9S8) and violarite (FeNi2S4). Three microbial communities grown at 35, 40, and 50 °C were used for bioleaching. The microbial community at 40 °C was the most diverse in the genus and species composition. At all temperatures of the process, the key roles in bioleaching belonged to mixotrophic and heterotrophic acidophiles. The highest levels of nickel leaching of 97.2 and 96.3% were observed in the case of communities growing at 40 and 50 °C, respectively. At the same time, the bioleach residue, which could be characterized as a marketable high-grade copper (chalcopyrite) concentrate, was obtained only at 40 °C. This solid contained 15.6% copper and 0.54% nickel. Thus, the biobeneficiation of bulk sulfide concentrates can be a promising field of biohydrometallurgy.

Geological and mineralogical study of ore tailings for bio-leaching

In this paper, the geological conditions of accumulation and the material composition of the ore tailings from the processing plants of Kazakhstan were studied. The results of studying the material of unused tailings are presented. Accumulated tailings were studied on natural exposures and on the materials of cartographic wells. In the three tailing dumps of the Zhezkazgan enrichment plant, after processing, more than 1.2 billion tons of tailings are accumulated in the form of effluent pulp, of which about 1 billion tons are in two inactive tailing dumps, and the third tailing dump is operational. When the content of the main copper ore component in tailing dump is about 0.1-0.3%, the total geological reserves of metals can be at least 2.0 million tons. More than 630 million tons of ground material with a copper content of 0.1 to 0.4% is accumulated in the tailing site of another large facility – Balkhash enrichment plant. Thus, in the tailing ponds of only two considered processing plants, there are more than 1.5 billion tons of technogenic raw ore material, where the geological reserves of copper are about 3 million tons. Mineralogical studies provide a determination of the distribution and content of basic (copper, lead, zinc) and associated (noble and rare metals) useful components in the tailings. The tailings of the processing plant can be considered promising for processing technogenic deposits of mineral raw materials. This type of technogenic ore is underexplored from both a geological and technological point of view. In this regard, it was necessary to conduct full-scale scientific research in order to study the material composition of tailings as technogenic deposits with the establishment of variability in the distribution of useful components in them and the technological properties of their processing. The results of studying the chemical, mineral and granulometric content of the tailings can serve as reliable initial data for technological studies on the extraction of metals from this technogenic raw ore material. The mineral and granulometric content of copper ore processing tailings has been studied. Microscopic descriptions of polished sections made of loose tailings are given. Sulfide ore minerals are microscopic in size, they are distributed mainly inside the grains of the host rocks and are rush in nature. Using the results of geological studies, a methodology for technological research was selected and laboratory experiments were conducted on the bioleaching of copper from the tailings.

Geological and mineralogical study of ore tailings for bio-leaching

In this paper, the geological conditions of accumulation and the material composition of the ore tailings from the processing plants of Kazakhstan were studied. The results of studying the material of unused tailings are presented. Accumulated tailings were studied on natural exposures and on the materials of cartographic wells. In the three tailing dumps of the Zhezkazgan enrichment plant, after processing, more than 1.2 billion tons of tailings are accumulated in the form of effluent pulp, of which about 1 billion tons are in two inactive tailing dumps, and the third tailing dump is operational. When the content of the main copper ore component in tailing dump is about 0.1-0.3%, the total geological reserves of metals can be at least 2.0 million tons. More than 630 million tons of ground material with a copper content of 0.1 to 0.4% is accumulated in the tailing site of another large facility – Balkhash enrichment plant. Thus, in the tailing ponds of only two considered processing plants, there are more than 1.5 billion tons of technogenic raw ore material, where the geological reserves of copper are about 3 million tons. Mineralogical studies provide a determination of the distribution and content of basic (copper, lead, zinc) and associated (noble and rare metals) useful components in the tailings. The tailings of the processing plant can be considered promising for processing technogenic deposits of mineral raw materials. This type of technogenic ore is underexplored from both a geological and technological point of view. In this regard, it was necessary to conduct full-scale scientific research in order to study the material composition of tailings as technogenic deposits with the establishment of variability in the distribution of useful components in them and the technological properties of their processing. The results of studying the chemical, mineral and granulometric content of the tailings can serve as reliable initial data for technological studies on the extraction of metals from this technogenic raw ore material. The mineral and granulometric content of copper ore processing tailings has been studied. Microscopic descriptions of polished sections made of loose tailings are given. Sulfide ore minerals are microscopic in size, they are distributed mainly inside the grains of the host rocks and are rush in nature. Using the results of geological studies, a methodology for technological research was selected and laboratory experiments were conducted on the bioleaching of copper from the tailings.

Isolation and Characterisation of Copper Leaching Microbes from Sanitary Landfill for E-waste Bioleaching

Electronic waste has been the fastest increasing waste generated globally and is predicted to surpass 111 million tons per year by 2050. This trend is concerning, not just due to the growing volume but also due to its high composition of heavy metal elements, leading to potential environmental pollution if not managed properly. However, this issue opens a new prospect in material acquisition through the concept of urban mining via the metal extraction from electronic waste. A conventional method of extraction, i.e., chemical leaching, possesses harmful environmental impact with the production of its residual leachate. Thus, an alternative extraction technique is proposed, known as bioleaching, in which the microbial activity from bacteria mobilized metal into a more soluble form. In this study, bacterial strains were isolated from Malaysia sanitary landfill for bioleaching of copper from waste printed circuit boards (wPCB) with minimal mechanical pre-processing procedure. They were grown in low pH media to utilize their activity for copper bioleaching from the wPCB. Four bacterial strains were successfully isolated. Using 16S rRNA gene sequencing, the isolates were identified as Bacillus sp. strain SE, Bacillus sp. strain SC, Lysinibacillus sp. strain SE2, and Oryzobacter terrae strain S1A. All the isolates showed appropriate bioleaching ability, with strain SC demonstrated the highest copper extraction with up to 23.36 ppm through the two-step bioleaching process. This strain was further evaluated using a copper strip to observe the actual copper extraction and demonstrated a total of 0.80 ±0.02 mg/g copper recovery. These results suggest that copper bioleaching of wPCB is viable as a standalone process.

From Laboratory towards Industrial Operation: Biomarkers for Acidophilic Metabolic Activity in Bioleaching Systems.

In the actual mining scenario, copper bioleaching, mainly raw mined material known as run-of-mine (ROM) copper bioleaching, is the best alternative for the treatment of marginal resources that are not currently considered part of the profitable reserves because of the cost associated with leading technologies in copper extraction. It is foreseen that bioleaching will play a complementary role in either concentration—as it does in Minera Escondida Ltd. (MEL)—or chloride main leaching plants. In that way, it will be possible to maximize mines with installed solvent-extraction and electrowinning capacities that have not been operative since the depletion of their oxide ores. One of the main obstacles for widening bioleaching technology applications is the lack of knowledge about the key events and the attributes of the technology’s critical events at the industrial level and mainly in ROM copper bioleaching industrial operations. It is relevant to assess the bed environment where the bacteria–mineral interaction occurs to learn about the limiting factors determining the leaching rate. Thus, due to inability to accurately determine in-situ key variables, their indirect assessment was evaluated by quantifying microbial metabolic-associated responses. Several candidate marker genes were selected to represent the predominant components of the microbial community inhabiting the industrial heap and the metabolisms involved in microbial responses to changes in the heap environment that affect the process performance. The microbial community’s predominant components were Acidithiobacillus ferrooxidans, At. thiooxidans, Leptospirillum ferriphilum, and Sulfobacillus sp. Oxygen reduction, CO2 and N2 fixation/uptake, iron and sulfur oxidation, and response to osmotic stress were the metabolisms selected regarding research results previously reported in the system. After that, qPCR primers for each candidate gene were designed and validated. The expression profile of the selected genes vs. environmental key variables in pure cultures, column-leaching tests, and the industrial bioleaching heap was defined. We presented the results obtained from the industrial validation of the marker genes selected for assessing CO2 and N2 availability, osmotic stress response, as well as ferrous iron and sulfur oxidation activity in the bioleaching heap process of MEL. We demonstrated that molecular markers are useful for assessing limiting factors like nutrients and air supply, and the impact of the quality of recycled solutions. We also learned about the attributes of variables like CO2, ammonium, and sulfate levels that affect the industrial ROM-scale operation.

Effect of organic nutrients on bioleaching of low-grade copper concentrate at different temperatures

The goal of the present work was to study the effect of different organic nutrients (yeast extract and molasses) on the biooxidation of copper concentrate containing chalcopyrite, tennantite, sphalerite, and pyrite in batch experiments at different temperatures (of 40 to 55°C). For the experiments, representatives of microbial groups predominant in biohydrometallurgical processes, bacterium of the genus Sulfobacillus, Acidithiobacillus caldus, and archaea of the genus Acidiplasma, were used. It was shown that both temperature and addition of organic nutrients in the medium affected the activity of the bioleaching. In the same time, the effect of organic nutrients was significant only at high temperatures (50 and 55°C). In all experiments, biooxidation rate decreased at the highest temperature, 55°C. Since among the strains used in the study, only A. caldus MBC-1 is autotroph, which is able to provide the population with organic nutrients and is not active at 55°C, at this temperature it was not able to maintain activity of other strains. Therefore at 55°C, biooxidation activity strongly depended on the presence of organic nutrients. Despite temperature and presence of organic nutrient affected activity of concentrate biooxidation that was revealed by the differences in pH, Eh values and iron ions concentrations in the medium, copper, zinc and arsenic extraction rates depended on these factors to a lesser extent.

Acid Bioleaching of Copper from Smelter Dust at Incremental Temperatures

ABSTRACT Copper smelters produce solid waste streams that pose potential pollution problems because of the dust and metal content. Dust from flash and electric furnace smelters is normally recycled to the smelting process, but this decreases the capacity for concentrate feed, and increases impurities and carryovers in the dust with time. The purpose of this study was to test an acid bioleaching process for recovering copper from a sample of smelter dust. The dust sample contained delafossite, chalcocyanite, and chalcopyrite as the main Cu-minerals. Smelter dust (10% pulp) in acid leach solution was subjected to three microbial cultures in a sequence of 35°C, 50°C, and 70°C incremental temperatures for 2 days each. Up to 83% copper dissolution from the dust was achieved by the combined action of the three-phase bioleaching and chemical leaching over the contact time of 6 days. Chemical acid demand at 70°C solubilized 68% Cu from smelter dust within 2 h, attributed to chalcocyanite dissolution in the dust. The monovalent copper minerals chalcopyrite and delafossite were more recalcitrant than the sulfate phase chalcocyanite. A 16-day bioleaching experiment at 35°C and 50°C yielded copper recoveries, which were comparable to those obtained in the three-phase bioleaching. It was concluded that further increases in copper yields from smelter dust require extended contact time ideally at the extreme thermophilic temperature range and stirred bioreactor conditions to control key parameters.

A novel approach based on solvent displacement crystallisation for iron removal and copper recovery from solutions of semi-pilot scale bioleaching of WPCBs

Bioleaching of copper from electronic waste (e-waste) in the form of high grade waste printed circuit boards (WPCBs) collected from obsoletemobile phones is assessed using a consortium of iron (Fe2+) & sulfur (S°) oxidizing bacteria in a semi-pilot reactor system. Results from the study indicated that the microorganisms were able to grow in the presence of WPCB and efficiently solubilize Cu from it. At a solid/liquid ratio of 10% (w/v)with a particle size of <250 μm, maximum bioleaching efficiency of around 95% Cu was observed in 8 days of leaching under oxidation-reduction potentials (ORP) of >600 mV and pH 1.8. In order to recover the metallic values, electrowinning (EW) of copper from the bioleach solutions was investigated in detail. Direct EW of the bioleach solution yielded low current efficiencies (66.1% over 4 h.), ascribed due to the high concentrations of iron (i.e., 9.1 g/L). As a novel approach, a downstream purification and concentration process was further tested, that involved ferric hydroxide (Fe(OH)3) precipitation and solvent displacement crystallisation (SDC) to eliminate iron and increase the concentration of copper in solution prior to its application for EW. This significantly improved the current efficiency (by ∼22%) during the EW of copper. A process flow-sheet for Cu recovery from WPCBs was developed and the downstream process was found to be profitable even though its margin was small with techno-economic analysis. It is believed that the two-step hybrid process i.e. bioleaching technique followed by the novel approach proposed (i.e., iron precipitation + SDC) can be suitably employed for the extraction of copper from WPCBs.

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.

Effect of Organic Nutrients and Elevated Temperature on Bioleaching of Sulfide Copper Concentrate

The goal of the work was to study the effect of addition of organic carbon source required for microorganisms oxidizing sulfide minerals in the nutrient medium on the rate of copper concentrate bioleaching. The concentrate containing 31.6% Fe, 19.2% Cu, and 2.9% Zn was bioleached in a batch mode for 30 days using mixed culture of acidophilic microorganisms. In the first reactor, biooxidation was performed at 45°C without additional carbon sources. In the second and in the third reactors, biooxidation was performed at 45°C and 55°C and nutrient medium was supplemented with 0.02% of yeast extract. Biooxidation without yeast extract allowed extracting 47 and 92% of copper and zinc. During biooxidation at 45°C using the medium supplemented with yeast extract, 54 and 94% of copper and zinc were extracted. During bioleaching at 55°C, 48% and 84% of copper and zinc were extracted. Thus, yeast extract allowed increasing copper bioleaching rate at 45°C, but temperature increase up to 55°C led to decrease in bioleaching efficiency. It may be explained by the fact that yeast extract increased activity of acidophilic microorganisms, which may consume organic carbon sources, while high temperature may inhibit some microorganisms and, therefore, does not allow increasing bioleaching rate.

Effect of water salinity on the bioleaching of copper, nickel and cobalt from the sulphidic tailing of Golgohar Iron Mine, Iran

This study investigates the influence of salinity on the bioleaching efficiency of a copper‑nickel‑cobalt bearing sulphidic tailing obtained from Golgohar iron ore desulphurization plant (Sirjan, Iran). The effects of several critical parameters including, suspension pH, nutrient medium, microorganism type, and pulp density were investigated on the extraction of copper, cobalt and nickel from the sulphidic tailing at different levels of sodium chloride concentration. Bioleaching efficiency was also evaluated in the presence of saline local and process waters. Results showed that maximum extraction of nickel (87%) and cobalt (69%) was achieved at the initial pH of 1.8, the pulp density of 10%, Norris nutrient medium containing 10 g/L sodium chloride, and using moderately thermophilic microorganisms. However, maximum copper extraction (~90%) was obtained in the presence of local water. It was also found that the local and process waters containing around 15.5 and 8.3 g/L chloride ions, respectively, increased metal extraction about 25% and 10% in comparison to distilled water at the first two days. Nevertheless, the metal extraction decreased at the end of the process in both water types mainly due to the formation of gypsum and jarosite precipitates, which were found by SEM/EDS analyses. Furthermore, at the initial pH of 1.5, the extraction of valuable metals was significantly improved (20–60% increase at first 9 days) in the presence of 5 g/L sodium chloride; whereas a further increase (to 10 g/L sodium chloride) had a negative effect on the extractions. Increasing the pulp density from 5% (w/v) to 10% decreased the nickel and cobalt extraction about 26% and 21%, respectively; however, copper extraction increased around 5% which could be related to the lower level of oxidation-reduction potential of the suspension at the higher pulp density. It can be concluded that the low levels of salinity (up to 5 g/L sodium chloride addition) could have a positive effect on the efficiency of the bioleaching process.

Intensified Bioleaching of Copper from Chalcopyrite: Decoupling and Optimization of the Chemical Stage

A one-stage process for the bioleaching of copper from chalcopyrite has a low leaching rate compared to the conventional smelting, pressure oxidation, and roasting routes, thus reducing the economic viability of the process. It is, therefore, crucial to optimize the process and the associated rate-influencing factors to make it competitive with the traditional, proven technologies. A strategy to intensify the extraction process is the decoupling of the chemical and biological stages, which expands the attainable region for the optimization of the variables. In the present research, the decoupled optimization of the chemical stage in the copper bioleaching of a chalcopyrite ore from the Iranian Sungun mine at East Azerbaijan was investigated. The factors affecting the rate of oxidation of chalcopyrite were determined and optimized with a (realistic) priori prepared bio-related medium. The optimized variables included the reaction temperature of 70 °C, the ore particle size of 0.65 μm, pH of 1.8 in the leaching solution, ferric ion concentration of 0.1 of the stoichiometric value (0.0022 mol per gram of chalcopyrite), and redox potential ~406 mV. Overall, the effect of redox potential on the extraction rate was the most pronounced such that the leaching rate was increased by about three times in the potential range of 401.0–405.8 mV relative to other ranges.

Role of humic acid in bioleaching of copper from waste computer motherboards

In recent years, an increasing attention has been paid to the bioleaching of copper from waste computer motherboards. Here, we investigate the effect of humic acid on the bioleaching of waste computer motherboards using the mixed culture HQ0211. For this, the response surface methodology (RSM) is employed to investigate the effect of pulp density, initial pH and humic acid content on copper recovery. Samples leached at optimized experimental conditions according to RSM were analyzed by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The results show that under optimum conditions; the initial pH = 1.53, pulp density = 1.35% (w/v) and humic acid addition = 0.31 g/L, a complete the copper leaching could be achieved. According to the results, the effectiveness of the bacterial and its capability to oxidize humic acid was proved. Overall, the biological leaching was found to be more effective than the chemical leaching. Humic acid can promote the bioleaching of waste computer motherboards, reducing its environmental hazards.

Optimized bioleaching of copper by indigenous cyanogenic bacteria isolated from the landfill of e-waste

In this study, indigenous cyanogenic bacterial strains were isolated on nutrient, minimal salt, and soil extract media at various culture conditions from two distinct landfills of e-waste, Iran. Based on their cyanide formation profiles, five most potent isolates were selected for optimization and to this end, the influence of the most effective factors on cyanide production including pH, glycine concentration and temperature were assessed using one-factor at a time method (OFAT). Initial pH of 7, glycine concentration of 2 g/L and temperature of 30°C were obtained as optimal conditions for most of the isolates. Additionally, two bioleaching processes were applied for each bacteria to detect the effect of optimal conditions on bioleaching and to assay their potential in the mobilization of copper. Under optimal conditions and pulp density of 1 g/L, copper recoveries were recorded as 96.73%, 82.49%, 81.17%, 41.72%, and 31.52% by S22, N13, N37, N23, and N41 respectively during 10 days which is approximately 1.5–5 times higher than the recovery obtained without optimization. During the optimization and the bioleaching process, the pH fluctuation of the flasks was monitored which validated the activity of the microorganisms.

Advances in bioleaching of copper and nickel from electronic waste using Acidithiobacillus ferrooxidans: evaluating daily pH adjustment

The waste stream of electrical and electronic equipment is three times faster than other municipal waste streams. Recycling of electronic waste is necessary for both reducing environmental pollution and saving natural ores. Bioleaching is known as an efficient technology for metal leaching. In most of the previous studies on the bioleaching of electronic waste, the pH of the process was adjusted daily under the optimal pH of the bacterium growth. Using acid causes increasing process costs and unsustainability of the process. In this work, the effect of daily pH adjustment on the bioleaching efficiency of electronic waste using adapted Acidithiobacillus ferrooxidans was studied. Simultaneously, Cu and Ni leaching efficiency, bacterial growth characteristics, and chemical characteristics (including field emission scanning electron microscopy, Fourier transform infrared spectrometer, and X-ray diffraction) were discussed. The results showed that at a pulp density of 1.5% (w/v) with pH adjustment, the maximum leaching efficiency of Cu and Ni was, respectively, about 90% and 88%, while for the sample without pH adjustment, the maximum leaching efficiency of Cu and Ni was, respectively, 100% and 92%. All the results confirmed pH adjustment of the bioleaching solution is not necessary and even reduces the process efficiency.

Effect of Graphite on Copper Bioleaching from Waste Printed Circuit Boards

The efficient extraction of copper as a valuable metal from waste printed circuit boards (WPCBs) is currently attracting growing interest. Here, we systematically investigated the impact of bacteria on the efficiency of copper leaching from WPCBs, and evaluated the effect of graphite on bioleaching performance. The HQ0211 bacteria culture containing Acidithiobacillus ferrooxidans, Ferroplasma acidiphilum, and Leptospirillum ferriphilum enhanced Cu-leaching performance in either ferric sulfate and sulfuric acid leaching, so a final leaching of up to 76.2% was recorded after 5 days. With the addition of graphite, the percentage of copper leaching could be increased to 80.5%. Single-factor experiments confirmed the compatibility of graphite with the HQ0211 culture, and identified the optimal pulp density of WPCBs, the initial pH, and the graphite content to be 2% (w/v), 1.6, and 2.5 g/L, respectively.

Bioleaching of Non-Ferrous Metals from Arsenic-Bearing Sulfide Concentrate

Tank bioleaching of substandard arsenic-bearing sulfide copper–zinc concentrate, containing 1.70, 6.22, and 7.30% of arsenic, copper, and zinc, was performed. The concentrate contained pyrite, chalcopyrite, tennantite, and sphalerite. Bioleaching was performed at 40°C using a mixed culture of acidophilic microorganisms in two modes. In the first mode, pulp density was 10%, while in the second it comprised 15%. Bioleaching made it possible to extract 17 and 70% of copper and zinc in the first mode, and 15 and 72% of copper and zinc in the second mode. The results obtained that bioleaching can be an effective approach to remove zinc from substandard copper-zinc concentrates. At the same time, copper minerals, including arsenic-bearing mineral tennantite, may be comparatively resistant to bioleaching, so requires the development of novel hydrometallurgical approaches for effective processing.

Simultaneously enhanced Cu bioleaching from E-wastes and recovered Cu ions by direct current electric field in a bioelectrical reactor

In this study, a proof-of-concept of bioleaching and recovery of copper (Cu) from E-wastes assisted by direct current (DC) electric field was proved in a bioelectrical reactor. Results showed that 40 mA electric current application could not only significantly shorten the leaching time of Cu from 5 (control) to 3 days with 100% leaching efficiency, but also recover about 97% leached Cu ions within 4 days. DC electric field improved the activity and growth of iron oxidizing bacteria and facilitated Fe2+ oxidation, which resulted in effective leaching of Cu from printed circuit boards (PCBs). The functional Acidithiobacillus was selectively enriched by DC electric field for enhancing the efficiency of bioleaching. At the same time, the leached Cu ions were rapidly electrodeposited on the cathode, achieving the recovery of Cu. Hence, this work provided a novel strategy for metals bioleaching and recovery from E-wastes.

Research progress in enhanced bioleaching of copper sulfides under the intervention of microbial communities

Compared with the traditional pyrometallurgical process, copper bioleaching has distinctive advantages of high efficiency and lower cost, enabling efficiently extracts of valuable metal resources from copper sulfides. Moreover, during long-term industrial applications of bioleaching, many regulatory enhancements and technological methods are used to accelerate the interfacial reactions. With advances in microbial genetic and sequencing technologies, bacterial communities and their mechanisms in bioleaching systems have been revealed gradually. The bacterial proliferation and dissolution of sulfide ores by a bacterial community depends on the pH, temperature, oxygen, reaction product regulation, additives, and passivation substances, among other factors. The internal relationship among the influencing factors and the succession of microorganism diversity are discussed and reviewed in this paper. This paper is intended to provide a good reference for studies related to enhanced bioleaching.

Validation of Genetic Markers Associated to Oxygen Availability in Low-Grade Copper Bioleaching Systems: An Industrial Application.

Forced aeration is one of the major energy consumption factors of the bioleaching process of run-of-mine ore. The effect of aeration in the microbial community has scarcely been studied at industrial level. Leptospirillum ferriphilum is one of the most representative species of the Fe3+ producing population in this kind of systems. We analyzed the effect of oxygen availability on L. ferriphilum by growth activity and transcriptional dynamics of its two terminal oxidases (cbb3 and bd complexes) under different experimental test: culture reactor, bioleaching column, and industrial heap tests. Relatively low O2 availability triggered important changes in the microbial community composition, cell growth, microbial activity and cydAB genes transcription in all cases of study. We assessed the potential role of the terminal oxidases on the adaptation to variable aeration conditions in different lifestyles of L. ferriphilum and identified transcriptional markers associated to oxygen metabolism in an industrial system. An interesting hypothesis about the possible role of the cbb3 complex in the response to oxidative stress as well as their role as a high oxygen-affinity oxidase in L. ferriphilum is proposed and discussed. This study successfully proves the function of the cydAB genes as valid genetic markers for low-grade copper industrial bioleaching systems.