Bioleaching of chalcopyrite with thermophiles: Temperature–pH–ORP dependence

Extremely thermoacidophilic archaea for metal bioleaching: What do their genomes tell Us?

Elevated temperatures favor bioleaching processes through faster kinetics, more favorable mineral chemistry, lower cooling requirements, and less surface passivation. Extremely thermoacidophilic archaea from the order Sulfolobales exhibit novel mechanisms for bioleaching metals from ores and have great potential. Genome sequences of many extreme thermoacidophiles are now available and provide new insights into their biochemistry, metabolism, physiology and ecology as these relate to metal mobilization from ores. Although there are some molecular genetic tools available for extreme thermoacidophiles, further development of these is sorely needed to advance the study and application of these archaea for bioleaching applications. The evolving landscape for bioleaching technologies at high temperatures merits a closer look through a genomic lens at what is currently possible and what lies ahead in terms of new developments and emerging opportunities. The need for critical metals and the diminishing primary deposits for copper should provide incentives for high temperature bioleaching.

Bioleaching Mercury from Coal with Aspergillus flavus M-3

This study focuses on the utilization of Aspergillus flavus(M-3) for the bioleaching mercury from coal, offering an alternative and environmentally to its clean utilization. The fungus was isolated from the soil near a high mercury coal mine in Lao Ying Shan (LYS), Guizhou. Utilizing direct mercury analysis, X-ray diffraction (XRD), and Fourier Transform-Infrared (FT-IR) analysis techniques, the transformation of mercury speciation, mineral components, and organic groups in the coal were analyzed before and after the bioleaching process. The findings of the study illustrated that the fungus M-3 exhibited a remarkable capacity for coal bioliquefaction and mercury leaching from LYS coal. Following a 15-day bioleaching process, a remarkable mercury leaching rate of 83.79% was achieved. Various forms of mercury speciation, including residue, organic matter, sulfide-bound, oxide-bound, exchangeable, and carbonate-bound forms, were released from the coal, with leaching rates ranging from 80.41% to 92.60%. XRD analysis indicated that the M-3 strain facilitated the dissolution of coal pyrite and the degradation of macromolecules, effectively loosening the coal structure. FT-IR analysis of raw and residual coal demonstrated the breakdown of the aromatic ring structure and introduced oxygen-containing functional groups by M-3. Overall, this study highlights the efficacy of bioliquefying coal using Aspergillus flavus (M-3) as a method for clean coal utilization while simultaneously bioleaching mercury.

Comparative Genomic Analysis of a Thermophilic Protease-Producing Strain Geobacillus stearothermophilus H6

The genus Geobacillus comprises thermophilic gram-positive bacteria which are widely distributed, and their ability to withstand high temperatures makes them suitable for various applications in biotechnology and industrial production. Geobacillus stearothermophilus H6 is an extremely thermophilic Geobacillus strain isolated from hyperthermophilic compost at 80 °C. Through whole-genome sequencing and genome annotation analysis of the strain, the gene functions of G. stearothermophilus H6 were predicted and the thermophilic enzyme in the strain was mined. The G. stearothermophilus H6 draft genome consisted of 3,054,993 bp, with a genome GC content of 51.66%, and it was predicted to contain 3750 coding genes. The analysis showed that strain H6 contained a variety of enzyme-coding genes, including protease, glycoside hydrolase, xylanase, amylase and lipase genes. A skimmed milk plate experiment showed that G. stearothermophilus H6 could produce extracellular protease that functioned at 60 °C, and the genome predictions included 18 secreted proteases with signal peptides. By analyzing the sequence of the strain genome, a protease gene gs-sp1 was successfully screened. The gene sequence was analyzed and heterologously expressed, and the protease was successfully expressed in Escherichia coli. These results could provide a theoretical basis for the development and application of industrial strains.

Current Trends in Metal Biomining with a Focus on Genomics Aspects and Attention to Arsenopyrite Leaching-A Review

The presented review is based on scientific microbiological articles and patents in the field of biomining valuable metals. The main attention is paid to publications of the last two decades, which illustrate some shifts in objects of interest and modern trends both in general and applied microbiology. The review demonstrates that microbial bioleaching continues to develop actively, despite various problems in its industrial application. The previous classic trends in the microbial bioleaching persist and remain unchanged, including (i) the search for and selection of new effective species and strains and (ii) technical optimization of the bioleaching process. Moreover, new trends were formed during the last decades with an emphasis on the phylogeny of leaching microbiota and on genomes of the leaching microorganisms. This area of genomics provides new, interesting information and forms a basis for the subsequent construction of new leaching strains. For example, this review mentions some changed strains with increased resistance to toxic compounds. Additionally, the review considers some problems of bioleaching valuable metals from toxic arsenopyrite.

Kinetics, Thermodynamics, and Mechanism of Cu(II) Ion Sorption by Biogenic Iron Precipitate: Using the Lens of Wastewater Treatment to Diagnose a Typical Biohydrometallurgical Problem

The feasibility of improving typical biohydrometallurgical operation to minimize copper losses was investigated by the use of biogenic iron precipitate for the uptake of Cu(II) ions from aqueous solutions. The iron precipitate was obtained from mineral sulfide bioleaching and characterized using SEM/EDS, XRD, FTIR, BET, TGA, and pHpzc analyses. The results show that the precipitate is highly heterogeneous and that Cu(II) ion adsorption can be described by both Freundlich and Langmuir adsorption isotherms, with a maximum adsorption capacity of 7.54 mg/g at 30 °C and 150 mg/L. The sorption followed pseudo-second-order kinetics, while the major presence of -OH and -NH2 functional groups initiated a chemisorption mechanism through an ion-exchange pathway for the process. Ionic Cu(II) (radius (0.72 Å)) attached easily to the active sites of the precipitate than hydrated Cu(II) (radius (4.19 Å)). With an estimated activation energy of 23.57 kJ/mol, the obtained thermodynamic parameters of ΔS° (0.034-0.050 kJ/mol K), ΔG° (8.37-10.64 kJ/mol), and ΔH° (20.07-23.81 kJ/mol) indicated that the adsorption process was chemically favored, nonspontaneous, and endothermic, respectively. The 43% Cu(II) removal within 60 min equilibrium contact time at pH 5 was indicative of the reduced efficiency of copper extraction observed in a real-life biohydrometallurgical process due to sorption by the iron precipitate. The result of this study might provide an insight into the management of the biohydrometallurgical process to minimize copper losses. It may also help mitigate environmental pollution caused by the disposal of these biogenic iron precipitate residues.

Active destruction of pyrite passivation by ozone oxidation of a biotic leaching system

Although pyrite bio-dissolution plays an important role in the processing of sulfide ores, the formation of passivation film inhibited the further dissolution of sulfide ores. In order to enhance the dissolution of sulfide ores, a novel method for destroying the passivation film using ozone was proposed and verified. The generated passivation film inhibiting pyrite dissolution in the presence of Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans was studied. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results indicate that a passivation film mainly consisting of jarosite and polysulfide (S_n^n-/S⁰) might be formed during biotic stage, which can be eliminated with the introduction of ozone (2 g/min) in 30 min. Electrochemical results show that ozone significantly increased the electrochemical reactivity of passivated pyrite, further proving that ozone enhanced the dissolution of passivated pyrite through destroying the passivation layer. Hence, a bi-stage method for dissolution of sulfide ores can be proposed.

Progress, Challenges, and Perspectives of Bioleaching for Recovering Heavy Metals from Mine Tailings

The accumulation of mine tailings on Earth is a serious environmental challenge. The importance for the recovery of heavy metals, together with the economic benefits of precious and base metals, is a strong incentive to develop sustainable methods to recover metals from tailings. Currently, researchers are attempting to improve the efficiency of metal recovery from tailings using bioleaching, a more sustainable method compared to traditional methods. In this work, the research status of using biological leaching technologies to recover heavy metals from tailings was reviewed. Furthermore, CiteSpace 5.7.R2 was used to visually analyze the keywords of relevant studies on biological leaching of tailings to intuitively establish the current research hotspots. We found that current research has made recent progress on influencing factors and microbial genetic data, and innovations have also been made regarding the improvement of the rate of metal leaching by biological leaching combined with other technologies. This is of great significance for the development of bioleaching technologies and industrial production of heavy metals in tailings. Finally, challenges and opportunities for bioleaching provide directions for further research by the scientific community.

Specific mechanism of Acidithiobacillus caldus extracellular polymeric substances in the bioleaching of copper-bearing sulfide ore

This study aimed to reveal the specific mechanism of extracellular polymeric substances (EPS) in the bioleaching of copper-bearing sulfide ore by moderately thermophilic bacterium Acidithiobacillus caldus. The bioleaching performance of blank control (BC), planktonic cell deficient (PD), attached cell deficient (AD), and EPS deficient (ED) systems were compared, to investigate the specific functions of "non-contact" and "contact" (including direct contact and, EPS-mediated contact) mechanisms. The detailed mechanics of bioleaching were studied using μx of cell growth, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The μx of cell growth demonstrated that EPS favors planktonic and attached cell growth. SEM observation revealed that intensive micro-pores on slag benefitted from the "EPS-mediated contact" mechanism. XRD identification indicated that additional chemical derivatives were produced via "EPS-mediated contact" mechanism, because of the active iron/sulfur metabolism. FTIR analysis revealed that the absorption peaks of C-O-S, sulfate, and S = O, which are closely associated with sulfur metabolism, have significant influences of EPS secretion. Taken together, the "EPS-mediated contact" mechanism contributed to almost half of the "contact" mechanism efficiency and a quarter of the total bioleaching efficiency. The proposed specific mechanism of EPS can deepen our understanding of similar bioleaching processes.

Bioleaching of two different genetic types of chalcopyrite and their comparative mineralogical assessment

The bioleaching of two different genetic types of chalcopyrite by the moderate thermophile Sulfobacillus thermosulfidooxidans was investigated by leaching behaviors elucidation and their comparative mineralogical assessment. The leaching experiment showed that the skarn-type chalcopyrite (STC) revealed a much faster leaching rate with 33.34% copper extracted finally, while only 23.53% copper was bioleached for the porphyry-type chalcopyrite (PTC). The mineralogical properties were analyzed by XRD, SEM, XPS, and Fermi energy calculation. XRD indicated that the unit cell volume of STC was a little larger than that of PTC. SEM indicated that the surface of STC had more steps and ridges. XPS spectra showed that Cu(I) was the dominant species of copper on the surfaces of the two chalcopyrite samples, and STC had much more copper with lower Cu 2p_3/2 binding energy. Additionally, the Fermi energy of STC was much higher than that of PTC. These mineralogical differences were in good agreement with the bioleaching behaviors of chalcopyrite. This study will provide some new information for evaluating the oxidation kinetics of chalcopyrite.

Kinetics of pyrite, pyrrhotite, and chalcopyrite dissolution byAcidithiobacillus ferrooxidans

The main objective of this study was to investigate the dissolution kinetics of pyrite, pyrrhotite, and chalcopyrite. Crushed minerals were reacted with Acidithiobacillus ferrooxidans (25 °C). The kinetics of dissolution was investigated by monitoring pH and Fe2+and Fe3+ion concentrations in the leaching solutions. Pyrite, pyrrhotite, and chalcopyrite dissolution by A. ferrooxidans was found to be a chemically controlled process. With bacteria, the dissolution rates of the minerals increased in the order of pyrrhotite, pyrite, and chalcopyrite. The number of cells attached to mineral surfaces increased in the same order. Acidithiobacillus ferrooxidans was found to enhance the dissolution rates of the minerals. The acid-insoluble trait of pyrite and acid-soluble trait of the other 2 minerals affected the pH changes in the leaching solutions.

Effects of pyrite and bornite on bioleaching of two different types of chalcopyrite in the presence of Leptospirillum ferriphilum

The effects of pyrite and bornite on bioleaching of two different chalcopyrite samples by Leptospirillum ferriphilum were studied for the first time. Results showed that bioleaching behaviors of the two chalcopyrite samples were extremely different. Bornite decreased the redox potential (ORP) and maintained it at an appropriate range (380-480 mV vs. Ag/AgCl) to promote chalcopyrite (A) dissolution, but caused the redox potential out of the optimum range and inhibited chalcopyrite (B) dissolution. Large amount of pyrite decreased the redox potential and maintained it at an optimum range to promote chalcopyrite (A) dissolution, while increased the redox potential and kept it at appropriate range for a longer period of time to enhance the dissolution rate of chalcopyrite (B). Chalcopyrite (B) had significantly higher values of conductivity and oxidation-reduction rate when compared with those of chalcopyrite (A). The work is potentially useful in interpreting the inconsistence of the researches of chalcopyrite hydrometallurgy.

A moderately thermophilic mixed microbial culture for bioleaching of chalcopyrite concentrate at high pulp density

Three kinds of samples (acid mine drainage, coal mine wastewater, and thermal spring) derived from different sites were collected in China. Thereafter, these samples were combined and then inoculated into a basal salts solution in which different substrates (ferrous sulfate, elemental sulfur, and chalcopyrite) served as energy sources. After that, the mixed cultures growing on different substrates were pooled equally, resulting in a final mixed culture. After being adapted to gradually increasing pulp densities of chalcopyrite concentrate by serial subculturing for more than 2 years, the final culture was able to efficiently leach the chalcopyrite at a pulp density of 20% (wt/vol). At that pulp density, the culture extracted 60.4% of copper from the chalcopyrite in 25 days. The bacterial and archaeal diversities during adaptation were analyzed by denaturing gradient gel electrophoresis and constructing clone libraries of the 16S rRNA gene. The results show that the culture consisted mainly of four species, including Leptospirillum ferriphilum, Acidithiobacillus caldus, Sulfobacillus acidophilus, and Ferroplasma thermophilum, before adapting to a pulp density of 4%. However, L. ferriphilum could not be detected when the pulp density was greater than 4%. Real-time quantitative PCR was employed to monitor the microbial dynamics during bioleaching at a pulp density of 20%. The results show that A. caldus was the predominant species in the initial stage, while S. acidophilus rather than A. caldus became the predominant species in the middle stage. F. thermophilum accounted for the greatest proportion in the final stage.

A review of the structure, and fundamental mechanisms and kinetics of the leaching of chalcopyrite

Most investigators regard CuFeS2 as having the formal oxidation states of Cu(+)Fe(3+)(S(2-))2. However, the spectroscopic characterisation of chalcopyrite is clearly influenced by the considerable degree of covalency between S and both Fe and Cu. The poor cleavage of CuFeS2 results in conchoidal surfaces. Reconstruction of the fractured surfaces to form, from what was previously bulk S(2-), a mixture of surface S(2-), S2(2) and S(n)(2-) (or metal deficient sulfide) takes place. Oxidation of chalcopyrite in air (i.e. 0.2 atm of O2 equilibrated with atmospheric water vapour) results in a Fe(III)-O-OH surface layer on top of a Cu rich sulfide layer overlying the bulk chalcopyrite with the formation of Cu(II) and Fe(III) sulfate, and Cu(I)-O on prolonged oxidation. Cu2O and Cu2S-like species have also been proposed to form on exposure of chalcopyrite to air. S2(2-), S(n)(2-) and S(0) form on the chalcopyrite surface upon aqueous leaching. The latter two of these species along with a jarosite-like species are frequently proposed to result in surface leaching passivation. However, some investigators have reported the formation of S(0) sufficiently porous to allow ion transportation to and from the chalcopyrite surface. Moreover, under some conditions both S(n)(2-) and S(0) were observed to increase in surface concentration for the duration of the leach with no resulting passivation. The effect of a number of oxidants, e.g. O2, H2O2, Cu(2+), Cr(6+) and Fe(3+), has been examined. However, this is often accompanied by poor control of leach parameters, principally pH and E(h). Nevertheless, there is general agreement in the literature that chalcopyrite leaching is significantly affected by solution redox potential with an optimum E(h) range suggesting the participation of leach steps that involve both oxidation and reduction. Three kinetic models have generally been suggested by researchers to be applicable: diffusion, chemical reaction and a mixed model containing diffusion and chemical components which occur at different stages of leaching. Passivation effects, due to surface diffusion rate control, may be affected by leach conditions such as pH or E(h). However, only initial conditions are generally described and these parameters are not controlled in most studies. However, at fixed pH, E(h) and temperature, it appears most likely that leaching in sulfuric acid media in the presence of added Fe(3+) is surface reaction rate controlled with some initial period, depending on leach conditions, where the leach rate is surface layer diffusion controlled. Although bioleaching of some copper ores has been adopted by industry, bioleaching has yet to be applied to predominantly chalcopyrite ores due to the slow resulting leach rates. Mixed microbial strains usually yield higher leach rates, as compared to single strains, as different bacterial strains are able to adapt to the changing leach conditions throughout the leach process. As for chemical leaching, passivation is also observed on bioleaching with jarosite being likely to be the main contributor. In summary, whilst much has been observed at the macro-scale regarding the chalcopyrite leach process it is clear that interpretation of these phenomena is hampered by lack of understanding at the molecular or atomic scale. Three primary questions that require elucidation, before the overall mechanism can be understood are: 1. How does the surface of chalcopyrite interact with solution or air borne oxidants? 2. How does the nature of these oxidants affect the surface products formed? 3. What determines whether the surface formed will be passivating or not? These can only realistically be tackled by the application of near atomic-scale analytical approaches, which may include quantum chemical modelling, PEEM/SPEM, TEM, AFM etc.

Thermophilic archaeal community succession and function change associated with the leaching rate in bioleaching of chalcopyrite

The community succession and function change of thermophilic archaea Acidianus brierleyi, Metallosphaera sedula, Acidianus manzaensis and Sulfolobus metallicus were studied by denaturing gradient gel electrophoresis (DGGE) analysis of amplifying 16S rRNA genes fragments and real-time qPCR analysis of amplifying sulfur-oxidizing soxB gene associated with chalcopyrite bioleaching rate at different temperatures and initial pH values. The analysis results of the community succession indicated that temperature and initial pH value had a significant effect on the consortium, and S. metallicus was most sensitive to the environmental change, A. brierleyi showed the best adaptability and sulfur oxidation ability and predominated in various leaching systems. Meanwhile, the leaching rate of chalcopyrite closely related to the consortium function embodied by soxB gene, which could prove a desirable way for revealing microbial sulfur oxidation difference and tracking the function change of the consortium, and for optimizing the leaching parameters and improving the recovery of valuable metals.

Bioleaching of chalcopyrite by moderately thermophilic microorganisms

The leaching of chalcopyrite by moderately thermophilic microorganisms was investigated by employing cyclic voltammetry (CV), accompanying with the leaching behavior elucidation. Leaching experiment showed that there was clear benefit in leaching chalcopyrite within the low solution potential (below 400 mV vs. SCE), compared to the high potential leach (above 550 mV vs. SCE). Simultaneous maintenance of an appropriate concentration of total dissolved iron was necessary and also beneficial to leach chalcopyrite. The leaching results showed the existence of an optimum pH in the leaching of chalcopyrite by the moderately thermophilic microorganisms. The analysis of CV results revealed that the chalcopyrite was reduced to a series of intermediate products (such as talnakhite, bornite and chalcocite) in the cathodic, and then the intermediate product (chalcocite) was oxidized in the anodic.

Effect of sodium chloride on sulfur speciation of chalcopyrite bioleached by the extreme thermophile Acidianus manzaensis

The influence of sodium chloride on dissolution of chalcopyrite and surface sulfur speciation during bioleaching of chalcopyrite with the extreme thermophile Acidianus manzaensis YN-25 was studied. The addition of sodium chloride accelerated the dissolution of chalcopyrite by reducing the accumulation of elemental sulfur layers on the mineral surface, resulting in an increase in the concentration of copper ions from 2.37g/L to 2.67g/L. Jarosite and elemental sulfur were found in the bioleached residues, while the amount of elemental sulfur accumulating on the mineral surface decreased drastically from 25.4% to 3.0% when 0.66g/L of sodium chloride was present during bioleaching. Therefore, the accumulation of elemental sulfur on the mineral surface is likely mainly responsible for the slowdown in the dissolution rate. The results indicated that bioleaching chalcopyrite with extreme thermophiles possessing high sulfur oxidation activity likely enhances dissolution of chalcopyrite by effectively removing elemental sulfur accumulating on the mineral surface.