The role of cupric ions in the oxidative dissolution process of marmatite: A dependence on Cu2+ concentration

Inhibition of pyrite oxidation through forming biogenic K-jarosite coatings to prevent acid mine drainage production

This study proposes a novel method by forming biogenic K-jarosite coatings on pyrite surfaces driven by Acidithiobacillus ferrooxidans (A. ferrooxidans) to reduce heavy metal release and prevent acid mine drainage (AMD) production. Different thicknesses of K-jarosite coatings (0.7 to 1.1 μm) were able to form on pyrite surfaces in the presence of A. ferrooxidans, which positively correlated with the initial addition of Fe2+ and K+ concentrations. The inhibiting effect of K-jarosite coatings on pyrite oxidation was studied by electrochemical measurements, chemical oxidation tests, and bio-oxidation tests. The experimental results showed that the best passivation performance was achieved when 20 mM Fe2+ and 6.7 mM K+ were initially introduced with a bacterial concentration of 4 × 108 cells·mL-1, reducing chemical and biological oxidation by 70 % and 98 %, respectively (based on the concentration of total iron dissolved into the solution by pyrite oxidation). Similarly, bio-oxidation tests of two mine waste samples also showed sound inhibition effects, which offers a preliminary demonstration of the potential applicability of this method to actual waste rock. This study presents a new perspective on passivating the oxidation of metal sulfide tailings or waste and preventing AMD.

Utilising the Nanozymatic Activity of Copper-Functionalised Mesoporous C3 N5 for Sensing Biomolecules

Designing unique nanomaterials for the selective sensing of biomolecules is of significant interest in the field of nanobiotechnology. In this work, we demonstrated the synthesis of ordered Cu nanoparticle-functionalised mesoporous C3 N5 that has unique peroxidase-like nanozymatic activity for the ultrasensitive and selective detection of glucose and glutathione. A nano hard-templating technique together with the in-situ polymerisation and self-assembly of Cu and high N-containing CN precursor was adopted to introduce mesoporosity as well as high N and Cu content in mesoporous C3 N5 . Due to the ordered structure and highly dispersed Cu in the mesoporous C3 N5 , a large enhancement of the peroxidase mimetic activity in the oxidation of a redox dye in the presence of hydrogen peroxide could be obtained. Additionally, the optimised Cu-functionalised mesoporous C3 N5 exhibited excellent sensitivity to glutathione with a low detection limit of 2.0 ppm. The strong peroxidase activity of the Cu-functionalised mesoporous C3 N5 was also effectively used for the sensing of glucose with a detection limit of 0.4 mM through glucose oxidation with glucose oxidase. This unique Cu-functionalised mesoporous C3 N5 has the potential for detecting various molecules in the environment as well as for next-generation glucose and glutathione diagnostic devices.

(Bio)dissolution of arsenopyrite coupled with multiple proportions of pyrite: Emphasis on the mobilization and existential state of arsenic

The formation of arsenic-bearing acid mine drainage (AMD) via the oxidation of arsenopyrite refuse ore has attracted significant attention. Pyrite, as main a concomitant mineral, is a crucial factor that affects the (bio)dissolution of arsenopyrite, but there are still some points on the detailed action mechanism under normal environmental conditions that need further study. In this study, the effect mechanism of pyrite with a systematic pyrite content (0, 10, 25, 50, 75, 90, and 100 wt %) on arsenopyrite oxidation and arsenic release in the presence of Acidithiobacillus ferrooxidans was investigated. The X-ray diffraction (XRD), scanning election microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical analyses were also carried out. Results showed that the existence of pyrite and Acidithiobacillus ferrooxidans significantly accelerated the dissolution of arsenopyrite and the oxidation of As (Ⅲ) to As (Ⅴ), resulting from the galvanic effect, an increase in the Fe³⁺/Fe²⁺ ratio and the oxidation-reduction potential (Eh) value, and a decrease in pH level. As the detected main intermediate products, element sulphur was considered as the dominating obstructive factor during arsenopyrite oxidation, while the added pyrite could accelerate its oxidation. Moreover, a close relationship between different mineral proportions and the galvanic effect was also observed and discussed. Finally, suggestions on AMD governance and source control are proposed.

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.

The Interplay of Iron Minerals and Microflora to Accelerate Cr (VI) Reduction

Widespread hexavalent chromium (Cr (VI)) in the environment has become a worldwide problem, and economical and efficient treatment is urgently needed. In this paper, the treatment method of Cr (VI) by microorganisms and iron minerals (pyrite and magnetite) under anaerobic conditions was investigated. Furthermore, the influence of Cr (VI) on the microbial community structure was explored. The reduction test demonstrated that the removal rate of Cr (VI) in a single biological group was 54.96%; however, in the pyrite and biological groups and magnetite and biological groups, the removal rates of Cr (VI) increased to 83.06% and 78.23%, respectively. Microorganisms and iron minerals work together to produce a better removal effect on the removal rate of Cr (VI). Mechanistic studies have found that in the process of Cr (VI) reduction, a passivation layer is formed on the surface of the mineral that hinders the progress of the reaction. The addition of bacteria can reduce the negative impact of the passivation layer. At the same time, iron minerals have better electron-receiving and -conducting ability and can be used as electron carriers for bacteria to reduce Cr (VI). In addition, iron minerals and the disappearance of Cr (VI) will change the structure of the community and affect the expression of its functions, which is more conducive to reducing Cr (VI). This work sheds new light on the treatment of heavy metal pollution and the understanding of the synergistic reduction mechanism of Cr (VI).

Intensification of Nickel Bioleaching with Neutrophilic Bacteria Guyparkeria halophila as an Approach to Limitation of Sulfuric Acid Pollution

Hydrometallurgical production of valuable and non-ferrous metals is traditionally accompanied with acid waste effluents/acid mine drainage leading to acidification of the mining areas. The traditional cause of this pollution is the well-known technology based on the recovery of metals with acid solutions and the application of strong acidophilic leaching bacteria for the oxidation of sulfide ores. In our experiments, we used neutrophilic autotrophic bacteria (NAB) stimulated with formic acid or coupled with acidophilic bacteria. The first approach was based on using formic acid as an energetic substrate by autotrophic bacteria. In the second case, the NAB provided initial biogenic acidification for the following growth of the inoculated acidophilic bacteria. Our experiments resulted in increased nickel recovery from the low-grade sulfide ores, which was provided by the NAB in a medium supplemented with formic acid. Bioleaching resulted in 1116 mg Ni/L (69.75%) in the medium with formate and only 35.4 mg Ni/L without formate in 43 days. As a whole, our bench scale experiments showed that the stimulated NAB can be effective at pH 7–5. Partially replacing sulfuric acid with formic acid could also give benefits via the following natural degradation of acid wastes. As a whole, this approach is more environmentally friendly than conventional bioleaching techniques.

Combined effect of silver ion and pyrite on AMD formation generated by chalcopyrite bio-dissolution

Chalcopyrite is a crucial contributor causing acid mine drainage (AMD). Silver and pyrite are commonly co-existed with chalcopyrite, and can significantly affect the copper release from chalcopyrite bio-dissolution process. However, the combined effect of them on chalcopyrite bio-dissolution has not been illustrated up to now. To fill this knowledge gap, the combined effect of silver and pyrite on chalcopyrite dissolution with Acidithiobacillus ferrooxidans was investigated in this study. The copper extraction reached the maximum value (62.3 ± 0.1%) with the presence of silver and pyrite, which was 43.8 ± 0.1% higher than the control group (without addition). This suggested more copper ions and acids were released under this circumstance. According to bio-dissolution results, SEM, XRD and XPS analyses, the promotion effect of silver and pyrite on chalcopyrite bio-dissolution was mainly attributed to the increase of ferric ions in solution and the reduction of passivation layer (S_n^2-/S⁰) on chalcopyrite surface. The investigation into the bio-dissolution of chalcopyrite is important for controlling the generation of copper ions and acids. Silver or pyrite bearing chalcopyrite should be carefully treated to avoid the pollution of heavy metal copper and acid in the mining environment.

Simultaneously enhance iron/sulfur metabolism in column bioleaching of chalcocite by pyrite and sulfur oxidizers based on joint utilization of waste resource

In chalcocite (Cu₂S) bioleaching, the lack of iron metabolism is a key restricting factor. As the most common sulfide mineral, pyrite (FeS₂) can release Fe(Ⅱ) and compensate for the iron metabolism deficiency in chalcocite bioleaching. The bioleaching of chalcocite in an imitated industrial system was improved by enhancing the iron-sulfur metabolism simultaneously using pyrite and sulfur oxidizers based on the joint utilization of waste resources, while the bioleaching performance and community structure in the leachate were systematically investigated. Due to the active sulfur/iron metabolism, the pH reached 1.2, and Fe³⁺ was increased by 77.78%, while the biomass of planktonic cells was improved to 2.19 × 10⁷ cells/mL. Fourier transform infrared reflection (FTIR) and X-ray diffraction (XRD) analysis results showed that more iron-sulfur crystals were produced due to more active iron-sulfur metabolism. Scanning electron microscopy (SEM) revealed that many derivative particles and corrosion marks appeared on the surface of the ore, implying that the mineral-microbe interaction was strengthened. Confocal laser scanning microscopy (CLSM) showed the accumulation of cells and extracellular polymeric substances (EPS) on the ore surface, indicating a stronger contact leaching mechanism. Furthermore, the community structure and canonical correspondence analysis (CCA) demonstrated that the introduction of sulfur-oxidizing bacteria and pyrite could maintain the diversity of dominant leaching microorganisms at a high level. Sulfobacillus (27.75%) and Leptospirllillum (20.26%) were the dominant sulfur-oxidizing and iron-oxidizing bacteria during the bioleaching process. With the accumulation of multiple positive effects, the copper ion leaching rate was improved by 44.8%. In general, this new type of multiple intervention strategy can provide an important guide for the bioleaching of low-grade ores.

Mineralogical phase transformation of Fe containing sphalerite at acidic environments in the presence of Cu2

Dissolution of the exposed sphalerite (marmatite) in abandoned mining sites and tailings may exacerbate acid and metalliferous drainage (AMD) hazards. Cupric ions are inevitable ions in AMD systems but its action mechanism on the dissolution of sphalerite is still unclear. In this work, the possible phase transition from sphalerite to chalcopyrite is firstly discovered in acidic cupric ions solution according to the results of Raman and (synchrotron radiation-based) X-ray (micro-) diffractometer spectra, which should be an important reason that mediates the dissolution of sphalerite. Results of DFT calculations reveal the underlying mechanism that Cu²⁺ can selectively replace zinc in marmatite lattices and further diffuse into the matrix. Additionally, a strong correlation between the cupric ion consumption with the pH value variation is discussed and the effects of the formed new phase on the dissolution kinetics of marmatite were researched. According to this work, the action mechanism of cupric ions on sphalerite dissolution in acidic environments is furtherly clarified.

The use of biochar for controlling acid mine drainage through the inhibition of chalcopyrite biodissolution

Although chalcopyrite biodissolution plays an important role in the formation of acid mine drainage (AMD), the control of AMD through inhibiting the biodissolution of chalcopyrite has not been studied until now. In order to fill this knowledge gap, a novel method for inhibiting chalcopyrite biodissolution using biochar was proposed and verified. The effects of biochar pyrolysis temperature and biochar concentration on the inhibition of chalcopyrite biodissolution in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans) were studied. The results indicate that biochar significantly inhibited chalcopyrite biodissolution, thus reducing the number of copper and iron ions and quantity of acid released. In turn, this suggests that AMD generation was suppressed under these conditions. Biochar pyrolyzed at 300 °C (Biochar-300 °C) was the most effective at inhibiting chalcopyrite biodissolution and reduced its biodissolution rate by 17.7%. A suitable concentration of biochar-300 °C enhanced its inhibition of chalcopyrite biodissolution. The optimal concentration of biochar-300 °C for inhibiting chalcopyrite biodissolution was 3 g/L. Biodissolution results, cyclic voltammetry, mineral surface morphology, mineralogical phase, and elemental composition analyses reveal that biochar inhibited the biodissolution of chalcopyrite by promoting the formation of passivation layer (jarosite and S_n^2-/S⁰) and adsorbing bacteria.

Catalytic effect of silver on copper release from chalcopyrite mediated by Acidithiobacillus ferrooxidans

Although silver ion in the solution is an important factor affecting the biodissolution of chalcopyrite, the effect of silver ion on the release of copper ion from chalcopyrite to the environment has not been explored until now. In order to fill this knowledge gap, the effect of silver ion on copper release from chalcopyrite in the presence of Acidithiobacillus ferrooxidans was investigated. The results indicate that silver ion significantly enhanced chalcopyrite biodissolution, thereby releasing more copper ion. In turn, this indicates that the release of copper ion from chalcopyrite to the environment was increased under these conditions. Biodissolution results, bacterial adsorption experiments, elemental composition analysis, and electrochemical analysis reveal that the enhancement of silver ion on copper ion release from chalcopyrite was mainly attributed to the improvement of electrochemical activity of chalcopyrite and the inhibition of the formation of passivation layer (S_n^2-/S⁰) on the chalcopyrite surface. This study provides a better understanding of the effect of silver ion on the release of copper ion from chalcopyrite to the environment. In the future, the influence of silver ion on chalcopyrite biodissolution should be considered in the evaluation of copper ion pollution to ensure reliability.

Dissolution of Cu and Zn-bearing ore by indigenous iron-oxidizing bacterial consortia supplemented with dried bamboo sawdust and variations in bacterial structural dynamics: A new concept in bioleaching

Disposing of low-grade ores involves numerous environmental issues. Bioleaching with acidophilic bacteria is the preferred solution to process these ores for metals recovery. In this study, indigenous iron-oxidizing bacteria Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum, and Leptospirillum ferrooxidans were used in consortia supplemented with acid-treated bamboo sawdust (BSD) for copper and zinc recovery. Findings showed the extreme catalytic response of BSD with the best recovery of metals. Maximum of 92.2 ± 4.0% copper (0.35%) and 90.0 ± 5.4% zinc (0.33%) were recovered after 8 days of processing in the presence of 2 g/L BSD. Significant variations were reported in physicochemical parameters during bioleaching in the presence of a different concentration of BSD. Fourier Transform Infrared spectroscopy results of bioleached residues showed significant variations in spectral pattern and maximum variations were reported in 2.0 g/L BSD, which indicates maximum metals dissolutions. The impact of bacterial consortia and BSD on iron speciation of bioleached ores was analyzed by using Mössbauer spectroscopy and clear variations in iron speciation were reported. Furthermore, the bacterial community structure dynamics revealed significant variations in the individual bacterial proportion in each experiment. This finding shows that the dosage concentration of BSD influenced the microenvironment, which effect the bacterial abundance and these variations in the bacterial structural communities were not associated with the initial proportion of bacterial cells inoculated in the bioleaching process. Moreover, the mechanism of chemical reactions was proposed by explaining the possible role of BSD as a reductant under micro-aerophilic conditions that facilitates the bacterial reduction of ferric iron. This type of bioleaching process with indigenous iron-oxidizing bacteria and BSD has significant potential to further upscale the bioleaching process for recalcitrant ore bodies in an environment friendly and cost-effective way.

Combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans

Although jarosite and visible light are important factors for the formation of acid mine drainage (AMD), the effects of combined jarosite and visible light on chalcopyrite biodissolution have not been explored until now. In order to fill this knowledge gap, the combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans were investigated. The results indicated that jarosite and visible light could significantly accelerate chalcopyrite biodissolution, thus releasing more copper ions, iron ions and producing more acid. This in turn suggests enhanced generation of AMD under these conditions. Biodissolution results, mineral surface morphology, mineralogical phase and elemental composition analyses revealed that the promotion of chalcopyrite dissolution by additional jarosite and visible light was mainly attributed to the acceleration of ferric iron/ferrous iron cycling and the inhibition of the formation of a passivation layer (jarosite and S_n^2-/S⁰) on the surface of chalcopyrite. This study provides a better understanding of the effects of jarosite and visible light on chalcopyrite biodissolution. In the future, the influences of jarosite and visible light on chalcopyrite dissolution should be considered in AMD evaluation to ensure reliability.

Interactions between marmatite and bornite during the oxidative dissolution process in abiotic and biotic systems

Marmatite and bornite are commonly associated together in nature, and their interactions in an acidic environment are vital for both (bio)hydrometallurgy and acid mine drainage (AMD) production. In this work, dissolution experiments (marmatite : bornite = 2 : 0, 3 : 1, 1 : 1, 1 : 3 and 0 : 2) accompanied by analytic techniques such as electrochemical methods, Raman spectroscopy and synchrotron radiation-XRD (SR-XRD) were utilized to interpret the interactions between marmatite and bornite in acidic abiotic and biotic systems. The dissolution experiments showed that marmatite can significantly accelerate the oxidative dissolution of bornite, especially in the abiotic system. On the contrary, bornite inhibited the oxidative dissolution of marmatite when the percentage of bornite was high. Electrochemical measurements proved that the galvanic interactions between marmatite and bornite were slight and should not be the main cause for the interactions. Combined with the dissolution experiments, analytic techniques and previous references, it could be speculated that marmatite accelerated bornite dissolution mainly by providing an iron source, which acted as the energy source for microorganisms and oxidants. Bornite affected the dissolution of marmatite mainly by Cu²⁺ ions dissolving from bornite. Bornite inhibited the oxidative dissolution of marmatite mainly because a high Cu²⁺ concentration could significantly hinder marmatite dissolution. In addition, the formation of elemental sulfur or jarosite was also one important cause. Bornite intensified marmatite dissolution when the percentage of bornite or the Cu²⁺ concentration was extremely low and then, a synergic dissolution process occurred.

Interactions between marmatite and bornite during the oxidative dissolution process in abiotic and biotic systems.