Bioleaching System Research Articles

Bioleaching of Industrial Metallic Steel Waste by Mixed Cultures of Thermoacidophilic Archaea

Different mixed cultures of extremely thermoacidophilic microorganisms were used for bioleaching of metalliferous industrial dust waste derived from the basic oxygen furnace (BOF) steelmaking process. Such mixed cultures can extract various metals from multi-metallic BOF-dust waste, improving the metal dissolution and bioleaching performance in frames of metal recycling processes to assist circular economies and waste management. The results of the investigation showed that mixed cultures of thermoacidophilic archaea of the order Sulfolobales (Acidianus spp., Sulfolobus spp., and Metallosphaera sedula) during their growth in laboratory glass bioreactors provided a superior bioleaching system to Acidianus manzaensis alone. Depending on the composition of mixed thermoacidophilic cultures, extraction of various metals from BOF-dust could be achieved. Among the three different types of mixed cultures tested, the mixed culture system of A. manzaensis, A. brierleyi, and S. acidocaldarius was most effective for extraction of major elements (Fe, Ca, Zn, Mn, and Al). The mixed culture of A. manzaensis, A. brierleyi, and M. sedula showed high performance for bioleaching of most of the minor elements (Cu, Ni, Pb, Co, Mo, and Sr). The efficient ability of mixed cultures to colonise the mineral matrix of the metal waste product was observed via scanning electron microscopy, while their metal extraction capacities were analysed by inductively coupled plasma mass spectrometry. These investigations will promote the further design of microbial consortia in order to break down the solid matrix and efficiently extract metals from metalliferous waste materials.

Moderate permeability enhanced microbial community turnover and copper extraction during bioleaching of low-grade copper ores

Heap bioleaching is one of the most promising technologies for extracting valuable metals from low-grade ores. However, the effects of permeability of the heap on microbial community and bioleaching efficiency remain unclear. In this study, heap bioleaching systems with different permeability were constructed. Despite the high content of larger particles had better permeability (0.25 cm/s) and oxygen transfer efficiency (0.14), there was a 25 % decrease in copper extraction compared with the moderate permeability group (81.2 %), while low permeability (0.025 cm/s) could cut the extraction in half (48.5 %). The fine profiles of microbial communities based on relatively and absolutely quantitative technologies suggested that permeability significantly affected microbial diversity, biomass, and composition. Microbial community evenness was crucial to improving extraction than biomass. Additionally, Thermoplasmatales except for Acidiplasma and Ferroplasma played vital roles in bioleaching. This study highlighted the delicate trade-off of particle size-mediated permeability for intensifying bioleaching efficiency of low-grade copper ores.

Increase in energy efficiency of tunnel composting by bio leaching and biogas production

Bio waste treatment can be done by composting or by digestion. Both ways of treatment have their advantages and disadvantages. The increase in energy efficiency of tunnel composting approached by a bio leaching system and bio gas production is one part of the EnBV research project. The reduction of organic matter by bio leaching and the enrichment of carbons in the leachate water can be used for increasing the energy efficiency.

The role of microstructure of extracellular proteins in dewaterability of alkaline pretreatment sludge during bioleaching

Alkaline pre-treatment is known to enhance the acid production efficiency of sludge but adversely affects its dewatering performance. In this study, the improvement of sludge dewaterability by a novel bioleaching system with inoculating domesticated acidified sludge (AS) and its underlying mechanism were investigated. The results showed that although the addition of Fe2+ and the reduction of pH improved the dewatering performance of sludge, their effects were inferior to that of AS + Fe. The addition of AS and Fe2+ significantly reduced the specific resistance to filtration and capillary suction time of the sludge by 98.6 % and 95.5 %, respectively. This improvement in dewatering performance was achieved through the combined actions of bio-acidification, bio-oxidation, and bio-flocculation. Remarkably, under alkaline pH, microorganisms in AS remained active, leading to the formation of iron-based bioflocculants, along with a rapid pH decrease. These bioflocculants, in combination with protein (PN) in tightly bound extracellular polymeric substances (TB-EPS) through amide bonding, transformed TB-EPS from extractable to non-extractable form, reducing PN content from 12.1 mg g−1DS to 5.09 mg g−1DS and altering the protein's secondary structure. Consequently, the gel-like TB-EPS matrix effectively broke down, releasing cellular water and significantly enhancing sludge dewaterability.

Microbial immobilisation and adaptation to Cu2+ enhances microbial Fe2+ oxidation for bioleaching of printed circuit boards in the presence of mixed metal ions

A circular economy requires effective re-use of finite resources, such as metals from waste electrical and electronic equipment (WEEE). Bioleaching for extraction and recovery of base metals from printed circuit boards (PCBs) before recovering precious metals has potential to increase metal circularity. However, inhibition by base metals released from the PCBs and accumulated in PCB leachates on microbial Fe2+ oxidation, a critical bioleaching sub-process for Fe3+ regeneration, can limit this approach. Here, we explore the potential of microbial immobilisation on polyurethane foam (PUF) and adaptation to cupric ions to minimise inhibition by mixed metals released from PCBs, particularly zinc, nickel, and tin, and enhancing Fe2+ oxidation rates in PCB bioleaching systems. A mixed mesophilic culture dominant in Leptospirillum ferriphilum, Acidiplasma cupricumulans and Acidithiobacillus caldus was immobilised on PUF and adapted to 6 g/L Cu2+. Tolerance of Cu-adapted immobilised cells to the inhibitory metal ions Zn2+, Ni2+, and Sn2+, as individual (0–10 g/L) and mixed metal ions at concentrations typically leached from PCBs at solids loadings of 0–20% (mass/volume) was compared to that of non-adapted immobilised cells. Further, the impact of solutes from PCB leachates was evaluated. Inhibition by individual metal ions decreased in the order Sn2+ > Ni2+ > Zn2+. Inhibition of ferrous iron oxidation by mixed metal ions was synergistic with respect to individual metal ions. PCB leachates were more inhibitory than both mixed and individual metal ions even where metal concentration was low. Cu-adapted immobilised cells exhibited higher tolerance to increasing concentrations of inhibitory metal ions than non-adapted cells. These results are promising for the application of Cu-adapted cells in the bioleaching of PCBs and multi-metal concentrates.

Evaluation of manganese bioleaching and silver extraction in mining tailings by native bacteria using a flooded system

During the silver extraction process in mining, the generated residues (called tailings) still contain approximately 100-140 g/ton of silver due to the presence of refractory materials that trap this metal and prevent its solubilization by conventional methods. These residues can be treated by biohydrometallurgical processes allowing, together with the cyanidation process, an increase in the efficiency of silver extraction by eliminating refractory materials such as manganese, which is present as pyrolusite (MnO2, 3.78 %). Pyrolusite can change from manganese (IV) to manganese (II) when solubilized by bioleaching. This research analyzed the effects of bioleaching using native bacteria on the concentration of silver extraction from the removal of manganese in mining tailings. The native bacteria ITDBC2, ITDBC5, and ITDBC6 were identified as Leptospirillum ferriphilum by amplification of the 16S gene corroborated by bioinformatic analysis. The experimentation was carried out using a flooded bioleaching system (9.43 L) to resemble the industrial geometry with the following variables: concentration of ferrous ions (2, 7, and 14 g/L), pH (2, 4, and 6) and agitation time at 100 rpm (2, 4 and 6 min/day). The experimentation lasted 18 days. The removal of manganese and silver extraction was 71.84 and 55.53 %, respectively. The scaled-up of the evaluated bioprocess could reduce energy consumption and process larger amounts of pulp than the reported at the laboratory scale.

A Bioleaching Process for Sustainable Recycling of Complex Structures with Multi-Metal Layers

Industrial waste is accumulating, while primary metal resources are depleting. Bioleaching has been shown to be a cost-effective and environmentally friendly approach to metal recovery from waste, but improved designs are needed for large-scale recycling. Metal components that are manufactured by electrodeposition over a mandrel can be difficult to recycle using conventional techniques due to their complex geometry and inner Ag coating. A sustainable biotechnology for separating Cu and Ag from waste electrodeposited components is presented. Two-step bioleaching experiments were performed, during which Cu was solubilized by Fe3+ regenerated by Acidithiobacillus (At.) ferrooxidans CF3 and a consortium of ten acidophilic Fe2+-oxidizers. High Cu recovery rates were achieved in agitated flasks (22 °C, pH 1.9), with At. ferrooxidans solubilizing 94.7% Cu in 78 days and the consortium 99.2% Cu in 59 days. Copper bio-solubilization was significantly accelerated in a laboratory-scale bioreactor (32 °C, 1 L air min−1) using the bacterial consortium adapted to elevated Cu concentrations, reaching >99.6% Cu extraction in only 12 days. The bioreactor was dominated by Leptospirillum and Acidithiobacillus, with their proportions changing (from 83.2 to 59% of total reads and from 3.6 to 29.4%, respectively) during the leaching process. Dissolved Cu was recovered from the bioleachates (containing 14 to 22 g Cu L−1) using electrowinning; >99% of the Cu was deposited (with Cu purity of 98.5 to 99.9%) in 3.33 h (at current efficiency between 80 and 92%). The findings emphasize the importance of a bioleaching system design to achieve economical separation of base and precious metals from industrial wastes. The presented technology minimizes waste generation and energy consumption. On a larger scale, it has the potential to contribute to the development of industrial recycling processes that will protect natural resources and contribute to the Net Zero target.

Bioleaching rare earth elements from coal fly ash by Aspergillus niger

Rare earth elements (REEs) are abundant in certain mining coal, and further enriched in coal fly ash (CFA) after coal combustion. If the appropriate leaching technology is chosen, the CFA can be used as an unconventional source of REEs. In this paper, culture conditions and bioleaching process of Aspergillus niger (A. niger) were optimized, the mechanism of acid production and factors of the bioleaching process of A. niger were discussed, and the bioleaching mechanism of REEs from CFA by A. niger was expounded. The results showed that organic nitrogen sources affected the morphology and acid production capacity of A. niger, and the A. niger used in this study mainly secreted oxalic acid (4.05 mg/L). Secondly, the initial pH value, the most influential factor, further affected the bioleaching process by affecting the acid production of A. niger. Therefore, by optimizing the initial pH value to enhance the acid production capacity of A. niger and developing the best bioleaching system, the CFA can reach a leaching rate of 30.91 % for total REEs. Finally, based on the test results of organic acids and pH, combined with previous studies, we speculated the main mechanism of REES bioleaching from CFA by A. niger as proton exchange and organic ligand complexation. Microbial leaching (e.g., A. niger) integrates economic, environmental, and resource use values.

Bidirectional effects of sulfur-oxidizer Acidithiobacillus thiooxidans in uranium bioleaching systems with or without sulfur by mixed acidophilic bacteria

Bidirectional effects of sulfur-oxidizer Acidithiobacillus thiooxidans in uranium bioleaching systems with or without sulfur by mixed acidophilic bacteria

Responses of microbial community to geochemical parameters on vertical depth in bioheap system of low-grade copper sulfide

Monitoring of the microbial community in bioleaching system is essential for control process parameters and enhance the leaching efficiency. Due to the difficulty of sampling, microbial distribution, community succession and bioleaching activity along the vertical depth of bioleaching heaps remain unresolved. This study investigated the geochemical parameters and microbial community structure along a depth profile in a bioleaching heap and leachate. 80 ore samples at different heap depths and 9 leaching solution samples from three bioheaps of Zijin Copper Mine were collected. Microbial composition, mineral types and geochemical parameters of these samples were analyzed by 16S rRNA high-throughput sequencing and a series of chemical measurement technologies. The results revealed that the pH, Cu, Fe and the total sulfur contents were the major factors shaping the composition of the microbial communities in the bioleaching system. The extent of mineral oxidation increased as the sample depth increases, followed by the increasing of sulfur oxidizers. The abundance of sulfur and iron oxidizers including members of Acidithiobacillus, Sulfobacillus and Acidiferrobacter were significantly higher in the leaching heap than in the leaching solution, meanwhile, they showed strong positive interactions with other members within the same genera and iron oxidizer Leptospirillum and Ferroplasma. Besides, Acidithiobacillus negatively interacted with heterotrophs such as Sphingobium, Exiguobacterium, Brevundimonas and so on. On the contrast, members of Leptospirillum and unclassified Archaea were significantly abundant in the leaching solution and revealed strong interactions with members of Thermoplasmatales. The main conclusion of this study, especially the leaching potential of microorganisms prevailing in bioheaps and their relationships with geochemical factors, provides theoretical guidance for future process design such as the control of processing parameters and microbial community in heap leaching.

Synergistic enhancement of metal extraction from spent Li-ion batteries by mixed culture bioleaching process mediated by ascorbic acid: Performance and mechanism

Pure and mixed cultures of microorganisms are used to leach spent Li-ion batteries (LIBs) to extract high-value metals. However, a low metal leaching efficiency is a general problem, hindering the commercialization of spent LIBs bioleaching. Therefore, a mixed culture bioleaching (MCB) process, mediated by ascorbic acid (AA), is proposed to promote the leaching of spent LIBs. Results show that the AA-MCB process leaches 94% Co and 95% Li at a pulp density of 20 g L−1, realizing 54% Co and 31% Li enhancement. Mass spectrometry analysis showed that a reduced bioleaching system is constructed by the mixed culture, AA, and AA products. In this system, bacteria promote LiCoO2 exposure on spent LIB surface by producing bioacid. Therefore, the refractory Co(III) easily reduces to soluble Co(II) by AA and its products, leading to the destruction of the crystalline structure of LiCoO2. Furthermore, bioacid facilitates easy leaching of Co and Li from structurally damaged LiCoO2. Ultimately, the AA-MCB process transforms spent LIBs from hazardous to general solid waste, exhibiting no biotoxicity to Escherichia coli growth. Therefore, bioleaching process intensification by adding a green organic reducing agent is a promising alternative for effective metal extraction from spent LIBs, enriching the current recycling technologies of spent LIBs.

Enhanced copper extraction in the chalcopyrite bioleaching system assisted by microbial fuel cells and catalyzed by silver-bearing ores

Chalcopyrite is the most abundant copper ores in nature and the main source of copper resources. Low energy consumption but slow kinetics occurred in the microbial fuel cell (MFC)-assisted chalcopyrite bioleaching process. High price and low recovery limited the use of silver-bearing chemicals as catalysts for the chalcopyrite bioleaching. Besides, the process of extracting silver-bearing chemicals from silver-bearing ores was complex and energy-intensive. Silver-bearing ores were low-cost and could release Ag+, which could be used as the alternative to silver-bearing chemicals in the chalcopyrite bioleaching. This study proposed the catalytic effect and catalytic pathway of silver-bearing ores on copper extraction in the MFC-assisted chalcopyrite bioleaching. After 216 days bioleaching, the maximum Cu2+ leaching efficiency of 10.03% was achieved in column reactor mixed with silver-bearing ores. Replacing silver-bearing chemicals (Ag2SO4) with silver-bearing ores in MFC-assisted bioleaching processes promoted the copper extraction efficiency by 1.5 times (10.03 % vs. 6.63 %). In contrast, the Cu2+ leaching efficiency was observed to be 5.37 % in the absence of silver. Compared with the regeneration of Ag+ only from Ag2S in the system mixed with Ag2SO4, the continuous release of Ag+ from silver-bearing ores maintained an appropriate concentration, which facilitated the bacterial growth and chalcopyrite dissolution. Ag+ promoted the formation of porous surfaces and increased surface roughness, which enhanced the adsorption of bacteria on chalcopyrite surface. Additionally, both Ag+ and MFC better reduced passivation and maintained the optimum ORP, which facilitated the continuous dissolution of chalcopyrite.

Bio-modification and application of coal fly ash in cementitious composites

Coal fly ash (CFA), an industrial solid waste, has been predominantly used a substitute for material in the concrete industry. Its reactivity is usually a crucial factor for use in cementitious composites. Conventionally physical and chemical treatments have been used to modify CFA for improving reactivity, but there still are some limitations such as easy agglomeration of particles, high cost, high energy-consumption, environmental pollution, etc. Herein, a feasible bio-modification treatment on CFA using Paenibacillus mucilaginosus is proposed. Adhesion and desilication of the bacteria & metabolites change the morphology, size distribution and surface properties of CFA. Compared with CFA, the bio-modified CFA (BCFA) has coarser surface, finer particle size, larger specific surface area (SSA), higher surface calcium content and lower surface Si/Al ratio. The characteristic changes contribute to enhancing the reactivity of BCFA relating to morphological, pozzolanic, micro-aggregate and interfacial effects in cementitious composites. The strength activity index (SAI) of BCFA reaches 90.8% at 28 d and increases 27.7% compared to that of CFA. Soluble silicon content in the bioleaching system shows significantly positive correlations with the SSA and SAI of BCFA (P < 0.05). The cementitious composites containing 30% BCFA show higher mechanical properties, lower early hydration heat and denser microstructure compared to those containing 30% CFA. This work could provide a promising green and low-carbon way to produce highly active BCFA for concrete industry and other fields.

Heterotrophic Bioleaching of Vanadium from Low-Grade Stone Coal by Aerobic Microbial Consortium.

Bioleaching is a viable method that assists in increasing the vanadium output in an economical and environmentally friendly manner. Most bioleaching is conducted by pure cultures under autotrophic conditions, which frequently require strong acidity and produce acid wastewater. However, little is known about heterotrophic bioleaching of vanadium by mixed culture. This study investigated the bioleaching of vanadium from low-grade stone coal by heterotrophic microbial consortium. According to the results, vanadium was efficiently extracted by the employed culture, with the vanadium recovery percentage in the biosystem being 7.24 times greater than that in the control group without inoculum. The average vanadium leaching concentration reached 680.7 μg/L in the first three cycles. The kinetic equation indicated that the main leaching process of vanadium was modulated by a diffusion process. Scanning electron microscopy revealed traces of bacterial erosion with fluffy structures on the surface of the treated stone coal. X-ray photoelectron spectroscopy confirmed the reduction of the vanadium content in the stone coal after leaching. Analysis of high-throughput 16S rRNA gene sequencing revealed that the metal-oxidizing bacteria, Acidovorax and Delftia, and the heterotrophic-metal-resistant Pseudomonas, were significantly enriched in the bioleaching system. Our findings advance the understanding of bioleaching by aerobic heterotrophic microbial consortium and offer a promising technique for vanadium extraction from low-grade stone coals.

Comparison of extraction methods for extracellular polymeric substances (EPS) and dynamic characterization of EPS from sessile microorganisms during pyrite bioleaching

Extracellular polymeric substances (EPS) have many beneficial functions in the bioleaching process. A mixed culture of moderate thermophilic microorganisms was used to bioleach pyrite concentrate in a stirred tank reactor at a pulp density of 6%. Three physical methods (heating, ultrasound and vibration with glass beads) and three chemical methods (NaOH, H2SO4 and formaldehyde) were assessed for the extraction of EPS from sessile microorganisms. The parameter conditions for each method were optimised to obtain the optimal settings. The EPS content of each extract varied depending on the extraction method used. Cell lysis can be minimised by optimizing the extraction conditions. Results indicated that heating method outperformed other methods with low cell lysis and yielded 355.56 ± 116.56 ug/108 cells of protein and 16.72 ± 1.45 ug/108 cells of polysaccharides. Thereafter, this method was applied to extract EPS from pyrite surface during the bioleaching process. During pyrite bioleaching, extracellular proteins were the major component of EPS extracted from sessile strains. Confocal laser scanning microscope and scanning electron microscope showed that pyrite grains were wrapped by many extracellular proteins. Therefore, this research can provide a reference for the extraction of EPS from moderate thermophilic bioleaching systems by analysing the potential impact of extraction methods.

Biolixiviación de As de jales mineros utilizando una cepa Nativa de Bacillus cereus

Contamination of heavy metals has been a serious environmental problem due to increasing anthropogenic activities such as mining, smelting, livestock, landfills, waste dumps, and agriculture. Bioleaching experiments were conducted using native Bacillus cereus MAMPE19 BCG, isolated and characterized from previous research, to test removal of arsenic (As) from actual mining waste. Mineralogical characterization by XRD was performed to identify mineral associations with As. The experimental design included a bioleaching system with agitated flasks (triplicate) and the effects of pH (5, 7, and 9) and pulp density (10, 15, and 20%) were evaluated. Finally, based on the results of the ANOVA, the system that achieved the highest percentage of As dissolution was selected and scaled to a stirred tank bioreactor. The composition of the mineral was mainly calcite (CaCO3), gismondine (CaAl2Si2O8·4(H2O)), akermanite (Ca2MgSi2O7), and silicon oxide (SiO2). Native Bacillus cereus dissolved 40.6 ± 4.9 and 37.4 ± 2.7 % of As in 10 d, in agitated flasks at a pH of 5 and a pulp density of 10 and 15%, respectively; and a 27.5 ± 2.9% dissolution of As was achieved in the stirred tank bioreactor at pH 5 and pulp density of 15%, supported by significant statistical differences.

Optimized biogenic sulfuric acid production and application in the treatment of waste incineration residues

The biological leaching of metals from different waste streams by bacteria is intensively investigated to address metal recycling and circular economy goals. However, usually external addition of sulfuric acid is required to maintain the low pH optimum of the bacteria to ensure efficient leaching. Extremely acidophilic Acidithiobacillus spp. producing sulfuric acid and ferric iron have been investigated for several decades in the bioleaching of metal-containing ores. Their application has now been extended to the extraction of metals from artificial ores and other secondary sources. In this study, an optimized process for producing biogenic sulfuric acid from elemental sulfur by two sulfur-oxidizing species, A. thiooxidans and A. caldus and their combinations, was investigated in batch and stirred tank experiments. Using a combined culture of both species, 1.05 M and 1.4 M biogenic sulfuric acid was produced at 30 °C and 6% elemental sulfur in batch and semi continuous modes, respectively. The acid produced was then used to control the pH in a heap bioleaching system in which iron- and sulfur-oxidizing A. ferrooxidans was applied to biologically leach metals from waste incineration residuals. Metals like Cu, Ni, Al, Mn, and Zn were successfully recovered by 99, 93, 84, 77 and 68%, respectively within three weeks of heap bioleaching. Overall, a potential value recovery of incorporated metals >70% could be achieved. This highlights the potential and novelty of applying extremely acidophilic sulfur-oxidizing bacteria for cheap and efficient production of biogenic sulfuric acid and its use in pH control.

The role of Acidithiobacillus ferrooxidans in Fe(II) oxidation of pyrite in bioleaching processes

AbstractBACKGROUNDMicrobial leaching is an emerging ore extraction technology, especially for low‐grade ores. In sulfide and oxide ore bioleaching systems, Acidithiobacillus ferrooxidans is becoming a widely applied microorganism for mineral processing. Many studies are currently focusing on the vital role of A. ferrooxidans in facilitating the efficiencies of sulfur and iron species transformation for sulfide ore bioleaching. Existing research usually investigates the composite action of A. ferrooxidans and Fe(III) for ore bioleaching, the effect of A. ferrooxidans alone being investigated to a lesser extent. An important effect is the role of A. ferrooxidans in the oxidative conversion of Fe(II) in pyrite bioleaching.RESULTSThe oxidative dissolution of pyrite in an imitated A. ferrooxidansbioleaching system was investigated in this work, particularly concerning the effects of bacteria on Fe(II) oxidation of the pyrite. Results of the dissolution performance test, cyclic voltammetry and polarization analysis indicated that the preceding oxidation of Fe(II) has control over the pyrite dissolution rate in the imitated bioleaching system. The semiconductor properties and carrier density of the passivation films of pyrite formed under a variety of conditions indicated that the oxidative leaching of ferrous disulfide is subject to the movement of the holes of the Fe2+species and the oxygen vacancy of H2O at the interface. Acidithiobacillus ferrooxidans promotes pyrite bioleaching by accelerating the preferential oxidation of Fe(II) caused by movement of the electron hole of Fe2+ to H2O at the solid–liquid interface.COCLUSIONThe oxidation process of pyrite in this study turns out to involve hole movement. © 2022 Society of Chemical Industry (SCI).

Effect of diurnal temperature range on bioleaching of sulfide ore by an artificial microbial consortium

Temperature is considered to be one of the main factors affecting bioleaching, but few studies have assessed the effects of diurnal temperature range (DTR) on the bioleaching process. This study investigates the effects of different bioleaching temperatures (30 and 40 °C) and DTR on the bioleaching of metal sulfide ores by microbial communities. The results showed that DTR had an obvious inhibitory effect on the bioleaching efficiency of the artificial microbial community, although this effect was mainly concentrated in the early and middle stages (0–18 days) of exposure, gradually decreasing until almost disappearing in the late stage (18–24 days). Extracellular polymeric substance (EPS) analysis showed that DTR did not change the composition of the EPS matrix (humic acid-like substances, polysaccharides and protein-like substances), but had a significant effect on the generative behavior of EPS, inhibiting the secretion of EPS during the early and middle stages of the bioleaching process. However, the continual increase in EPS secretion in the bioleaching system gradually reduced the adverse effects of DTR on mineral dissolution. X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Scanning electron microscopy- energy dispersive spectrometry (SEM-EDS) analysis of the bioleached residue showed that DTR had no obvious effect on the mineralogical characteristics of sulfide ore. Therefore, in industrial sulfide ore bioleaching applications, in order to accelerate the artificial microbial community start-up process, temperature control measures should be increased in the bioleaching process to reduce the adverse effects of DTR on mineral dissolution.

Responses of bacterial community to potential heap construction methods of fine-grained copper tailings in column bioleaching system

The column bioleaching of copper flotation tailings was comparatively investigated using layered heap construction method (LM), agglomerate heap construction method (AM), and pellets-sintering heap construction method (PM). The bacterial communities of free, attached, weakly-attached, and strongly-attached microbes in the later bioleaching stage were investigated. In AM group, the addition of lump sulphide ore resulted in the low leachate pH, high ferric iron concentration, and rapid microbial adsorption, which obtained the maximum copper extraction (60.1%) compared with LM (54.6%) and PM (43.9%) groups. The relative abundance of dominant genera and microbial communities of different microbiota underwent changes in three heap construction methods. The alpha-diversity indexes of attached, weakly-attached, and strongly-attached microbes were different, while no significant change was observed in free bacteria. The variation of whole bacterial community was significantly associated with solution pH, total iron, and ferric iron concentrations. Pearson correlation analysis and partial least square path model both indicated that attached bacteria made larger contribution to the copper extraction of tailings.