2.1. Effect of Bacteria on the Leaching Processof Pure Minerals

The chemical composition analysis resultsof the secondary copper sulfide sample are shown inTable1. It shows that the sample contained0.28% of Cu, 3.03% of Fe, and 3.51% of S, respectively. The sampleconsists of quartz, muscovite, pyrite, chalcocite, and a small amountof covellite, as described in the previous work.³⁵ It can be inferred that copper mainly exists in the formof chalcocite and covellite, and iron mainly exists in the form ofpyrite.

Table2 shows thechemical composition analysis results of two pure minerals separatedand enriched from the raw ore. It shows that the purity of the twopure mineral samples is greater than 92%. The content of Fe in chalcociteand Cu in pyrite is less than 3%, which means that the influence ofthe two elements on the dissolution of respective main minerals canbe neglected.

The leaching experiments of pure minerals were carriedout in conicalflasks. The effect of the inoculation ratio on the leaching efficiencyof metal ions from two pure minerals was investigated. The resultsare shown inFigure1.

As shown inFigure1, the leaching effects of metal ions from chalcocite and pyrite bybacteria are obviously different. Between 0 and 120 h, the leachingefficiency of Cu increases slowly. When the leaching time exceeded120 h, the leaching efficiency increases significantly. For pyrite,the increase of leaching efficiency of Fe is the highest from 75 to220 h. After 220 h, the leaching efficiency of Fe barely changes.At the same leaching moment, the leaching efficiency of Cu is alwayshigher than pyrite. It can be seen that the change of the inoculationratio has little effect on the leaching efficiency of metal ions fromtwo pure minerals. The results show that the leaching efficiency ofCu is higher when the inoculation ratio is 1:10.

The solutionpotential was controlled during the leaching process.The dissolution differences of the two pure minerals at solution potentialsof 640 mV and 800 mV were investigated. The results are shown inFigures2 and3.

As shown inFigures2 and3, with the changeof the solution potential,the leaching efficiencies of copper and iron ions are different obviously.Changes of potential have little effect on the dissolution of chalcocite.At 640 mV of solution potential, the leaching efficiency of Cu ismore than 75%, while the leaching efficiency of Fe is only about 5%on day 20. At 800 mV of solution potential, the leaching efficiencyof Cu is close to 90%, and the leaching efficiency of Fe increasedabove 40%. It can be inferred that the solution potential has a significanteffect on the selective leaching of chalcocite. A lower solution potentialis helpful for selective dissolution of chalcocite.

2.2. Effect of Bacteria on Leaching Process ofMixed Pure Minerals

Due to the existence of Fe³⁺/Fe²⁺ pairs, Fe³⁺ in the solution can simultaneouslypromote the oxidation of Cu⁺ in chalcocite and Fe²⁺ in pyrite, and promote the dissolution of the two minerals in theleaching system. The ratio of Fe³⁺/Fe²⁺ pairwill be affected by the release of Fe²⁺ from pyrite dissolution,and the potential of the solution will be affected. Therefore, itis helpful to understand the selective leaching mechanism of chalcociteby mixing pure minerals of pyrite and chalcocite and studying theleaching characteristics of the mixed ore.

The chalcocite/pyritemixed pure minerals with a mass ratio of 1:2 were leached at 30 °Cfor 14 days. The variation of metal ion leaching efficiency and solutionpotential with time is shown inFigures4 and5.

It can be seen fromFigure4 that the presence of bacteriahas different effects on theleaching efficiency of copper and iron from mixed pure minerals. Whenthere were no bacteria in leaching, because of the higher electrostaticpotential of pyrite, the contact between pyrite and chalcocite wouldproduce a galvanic effect, which would inhibit the dissolution processof pyrite as the cathode.²¹ The dissolutionof pyrite and chalcocite was promoted after bacterial inoculation.With the presence of bacteria, the potential of the solution increasesfrom 260 mV to about 550 mV after 14 days of bioleaching (Figure5). This indicatesthat the oxidation of Fe²⁺ in the solution and mineralsurface by bacteria increases the potential of the solution, acceleratesthe mineral dissolution rate, and then increases the difference ofleaching efficiency between two sulfide ores due to the galvanic effect.

Therefore, bacteria can promote the dissolution of mixed pure minerals,and the selective dissolution of chalcocite can be achieved by controllingthe potential of the solution.

2.3. Varietiesof Microbial Community Structuresduring Selective Leaching

2.4. Semiconductor Band Theory Analysis of SelectiveLeaching of Chalcocite

Based on the density functional theory,the crystal models of chalcocite and pyrite were constructed usingthe program CASTEP. Structural optimizations and electronic propertycalculations were also performed. The crystal structures is showninFigure9. Thereare Fe–S bonds and S–S bonds in the pyrite cell, andonly Cu–S bonds and Cu–Cu bonds in the chalcocite cell.

2.4.3. Analysisof Band Theory in Selective Dissolutionof Chalcocite

Previous studies showed that at the higherFermi level than the ORP of the solution, the electrons would migratefrom the semiconductor to the solution and the electron-deficientregion would be formed on the semiconductor surface.^25,26 The Fermi levels of chalcocite and pyrite were calculated by Dmol³. The results are shown inTable5.

Table 5. Calculated Valueof Fermi Levels ofChalcocite and Pyrite.

minerals	the calculatedvalue (eV)
pyrite (ideal)	–5.690
pyrite (Fe vacancy)	–5.638
pyrite (S vacancy)	–5.621
chalcocite (ideal)	–4.555
chalcocite (Cu vacancy)	–4.539
chalcocite (S vacancy)	–4.446

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As shown inTable5, the Fermi levels of ideal chalcocite and ideal pyriteare −4.56eV and −5.69 eV, respectively. Fe, Cu, and S vacancies raisethe Fermi level of chalcocite and pyrite. The increase of the Fermilevel is beneficial to the transfer of electrons from the mineralsurface to the solution, and to the adsorption of dissolved oxygenon the surface. With the increase of the hole on the surface, S^2– and S are more easily oxidized to SO₄^2–. This causes the formation of more hydrophilic groupson the surface of the two sulfide ores and the acceleration of mineraldissolution. No matter what vacancy exists, there are significantdifferences between the Fermi levels of the two minerals. The bandgap width of pyrite is about 0.95 eV, while that of chalcocite isabout 1.1 eV.^27,28 Based on the Fermi level datainTable5, the schematicdiagrams of the energy band structure of chalcocite and pyrite aredrawn inFigure12.

Figure 12.

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In semiconductor physics,the energy level of the standard hydrogenelectrode (SHE) can be determined to be −4.5 eV. The relationshipbetween energy levelE and solution potentialE_h can be expressed byeq1.²⁹

1

In bioleaching, the solution potentialfluctuatesin the range of 250–850 mV (vs SHE). The energy level correspondingto the potential is between the Fermi level of chalcocite and pyrite.According to the Nernst equation, when the ratio of Fe³⁺/Fe²⁺ changes from 10^–3 to 10³, the corresponding energy levels of potential change from −5.45to −5.09 eV. The energy levels of the solution and Fe³⁺/Fe²⁺ pairs are also shown inFigure12.

Figure12 showsthat the Fermi level of ideal pyrite (−5.69 eV) is lower thanthe energy level of the solution (−4.75 to −5.35 eV)without adding bacteria. Electrons can migrate from the solution tothe pyrite surface and form an electron accumulation zone. At a lowersolution potential (Figure5, about 330 mV), the energy difference between the top ofthe pyrite valence band and the solution (about 1.04 eV) is greaterthan the width of the pyrite gap (0.95 eV). Therefore, it is difficultto form electron holes at the top of the valence band, and the apparentdissolution rate of pyrite is relatively low (Figure4). The Fermi level (−4.56 eV) of idealchalcocite is greater than the energy level of the solution. Electronscan easily migrate from the chalcocite surface to the solution. Theformation of more holes on the surface of chalcocite promotes thefracture of the Cu–S bond, which shows a higher apparent dissolutionrate (Figure4).

Fermi levels of pyrite and chalcocite increase with the presenceof vacancies in both crystals. For pyrite, it is easier to form holeson the Fe–S bond and the dissolution rate of pyrite increases.For chalcocite, the rate of electron migration from the Cu–Sbond to the solution accelerates. Chalcocite tends to further transforminto covellite and dissolve.

With the presence of bacteria,Acidithiobacillus andSulfobacillus oxidizelow-valent sulfur toS⁰, S₂O₃^2–, andSO₄^2– and assist the oxidation of Fe²⁺, which increases the ratio of Fe³⁺/Fe²⁺ and the solution potential. When the energy level of the solutioncrosses the bottom energy level of the ideal pyrite conduction band(−4.92 eV) and approaches the top energy level of the valenceband (−5.87 eV), the electron holes at the top of the valenceband increase, and the dissolution rate of pyrite also increases.At the same time, the loss of electrons at the top of the ideal chalcocitevalence band brings a large number of holes. Cu⁺, whichmoves to the solid–liquid interface continuously is oxidizedto Cu²⁺ by dissolved oxygen and Fe³⁺ of thesolution. When the potential is not controlled, the concentrationof Fe³⁺ and the potential of the solution will continueto increase. Above 800 mV,Leptospirillum becomesa dominant group, rapidly oxidizing Fe²⁺ and leads to theincrease of the Fe³⁺/Fe²⁺ ratio continuously.It is difficult to inhibit the dissolution of pyrite.

If vacanciesexist in pyrite and chalcocite crystals,Leptospirillum will replaceAcidithiobacillus andSulfobacillus as the dominant group earlier because of the higher Fe²⁺ concentration in the solution.

If the potential of the solutionis controlled at a lower level(<700 mV or −5.2 eV), the oxidation extent of Fe²⁺ byLeptospirillum is limited, and the concentrationof Fe³⁺ in the solution is relatively low. Chalcocite isselectively dissolved by oxygen and a small amount of Fe³⁺ in the solution. Because of the presence of Fe, Cu, and S vacancies,the Fermi level of real minerals is higher than ideal. Therefore,the solution potential should be controlled at 600 mV or less to ensurethe selective dissolution of chalcocite.

Accordingly, we canconsider the feasibility of treating the secondarysulfide ore by two-stage bioleaching. In the first stage of bioleaching,ORP is maintained below 600 mV, so that chalcocite is completely convertedto covellite and some copper ions, and the iron leaching amount iscontrolled at a low level. In the second stage, the separation ofcovellite and pyrite is considered to realize the effective controlof the iron ion concentration in the leaching solution. The kineticinvestigation of the two-stage dissolution process of chalcocite alsosupports this view indirectly.³⁰

4.1. Samples

The secondary copper sulfidesample was obtained from the Zijinshan Copper Mine of Fujian Provinceof China. The particle size of the sample was less than 2 mm. Pureminerals of pyrite and chalcocite were obtained by separating andenriching from raw ore through hand sorting, gravity separation, andflotation. Pure minerals were all ground and sieved to minus 0.074mm.

The bacteria used in the experiment were collected fromthe sump pit of ore heap of Zijinshan Copper Mine. After 4 to 5 days’breeding and domestication in the laboratory, the bacteria with goodtolerance on copper and iron ions were obtained. Bacteria were culturedon 9 K medium. The optimum growth temperature of the bacteria is 30–45°C, and the optimum pH value is about 1.2–2.5.

4.2. Leaching Experiments

The copper sulfidesample and pure minerals were ground and sieved to minus 0.074 mm,respectively. The leaching experiments of pure minerals were carriedout in conical flasks. A certain amount of samples and 9 K mediumwere added into the conical flask. The pH of the solution was adjustedto a certain value between 1.8 and 2.0 with 20% (v/v) sulfuric acidand ensured that the initial pH of the solution in the conical flaskswas the same so that the initial solution potential was roughly thesame. The initial inoculated cell density was 2 × 10⁷ cells/mL. The inoculation ratio (volume ratio of bacterial liquidto pulp) in conical flasks were 1:20, 1:10, and 1:5, respectively.In the process of leaching, the pH and potential of the solution weremeasured every day, and the concentration of copper and iron ionsin the supernatant were measured every 3 days. After leaching, residueswere filtered and dried. The leaching experiments of copper sulfidesamples were carried out in a stirred tank reactor, as shown inFigure13. The reactor coulddetect the solution pH value and ORP online and control the potentialby filling different gases during the leaching process. Before everyleaching, the pulp concentration was adjusted to 5%. In the leachingprocess, the stirring speed was 120 rpm, and the temperature was controlledin the range of 30–35 °C. The pH range of the solutionwas the same as that of pure mineral leaching experiment. After leaching,residues were filtered and dried.

4.3. Model of Crystal Structures of Minerals

Based on the density functional theory, the calculations were performedusing the programs CASTEP and DMol³. Structural optimizationsand electronic property calculations were performed using CASTEP andGGA-PW91.^16,17 The valence electrons (Fe 3d⁶4s², S 3s²3p⁴, and Cu 3d¹⁰4s²) were considered using ultra-soft pseudopotentials.¹⁸ A plane wave basis set with an energy cutoffof 270 eV was employed for the geometry optimization. A Monkhorst–Packk-point sampling density of 2 × 2 × 2 mesh was used.^19,20 The convergence tolerances forgeometry optimization calculations were set to the maximum displacementof 0.002 Å, the maximum force of 0.08 eV Å^–1, the maximum energy change of 2.0 × 10^–5 eV/atomand the maximum stress of 0.1 GPa, and the self-consistent field (SCF)convergence tolerance was set to 2.0 × 10^–6 eV/atom. The spin-polarization was used for all calculations. Propertieswere calculated with the same parameters as geometry optimization.The Fermi levels of crystals were calculated by Dmol³,with the GGA-PW91 method, DNP basis set, effective core potentials,a fine quality, and SCF convergence threshold of 1.0 × 10^–6 eV/atom.

4.4. Analytical Techniques

The chemicalcompositions were confirmed by X-ray fluorescence spectroscopy (XRF,XRF-1700, Shimadzu, Kyoto, Japan) using a standardless quantitativeanalysis method and chemical analyses. Microscopic observation andanalysis of element distribution in leaching residues were conductedusing a mineral liberation analyzer, which included a scanning electronmicroscope (JSM-7001F, Japan Electron Optics Laboratory, Tokyo, Japan)and an energy-dispersive X-ray fluorescence spectrometer (INCA X-Max,Oxford Instruments, Oxford, U.K.). Potential and pH of the leachingsolution were determined by the pH/ORP meter (Seven Excellence S400,Mettler Toledo, Zurich, Switzerland) and a Pt electrode with referenceto a Ag/AgCl electrode. All of the potential values mentioned werenormalized to the hydrogen scale in this work. The concentrationsof Cu²⁺ and total iron were determined by inductively coupledplasma optical emission spectrometry (725-Agilent Technologies, California).

The leaching efficiencyE of metal ions were calculatedbyeq2. In the equation,C is the concentration of metal ions,V is the volume of the solution, α is the grade of the metal,m is the mass of ore samples, andM isthe molecular weight

2

Microorganisms were harvestedfrom 5.0 mL representative leachingsolutions. The cells were centrifuged at 12000g for10 min for cell collection. Total DNA was extracted using the PowerWaterDNA Isolation Kit (QIAGEN China Co. Ltd., Beijing, China). DNA qualityassessment and quantification were conducted using a NanoDrop ND-1000Spectrophotometer (NanoDrop Technologies Inc., Wilmington, DE). PCRwas conducted on Applied Biosystems (ABI) Veriti 96-well Fast ThermalCyclers with bacterial primer pair (341 F of the forward primer and805 R of the reverse primer) for the V3-V4 region of the 16 S rRNAgene.^31,32 Each sample was amplified under the followingconditions: 94 °C for 5 min, 28 cycles at 94 °C for 45 s,62 °C for 45 s, and 72 °C for 1 min, then 10 min at 72 °C.PCR products were purified using the EZNA Gel Extraction Kit (OmegaBio-tek). The library quality was assessed on the QuantiFluor-ST (Promega).Then, the library was sequenced on an Illumina Miseq platform (Majorbio,Shanghai) with the sequencing strategy PE300. The sequencing datasetsof bacteria and fungi have been deposited in the National Center forBiotechnology Information (NCBI) Sequence Read Archive (SRA) (accessionNo. PRJNA555796).

4.5. Data Analysis

All sequence processingand diversity estimates were performed using the QIIME. To obtainclean tags, low-quality sequences and chimeras were filtered, trimmed,and removed.³³ Most of the sequence lengthsafter quality control were between 450 bp and 460 bp. High-qualitynonchimeric sequences were clustered into operational taxonomic units(OTUs) using a 97% similarity threshold and the uclust algorithm withoptimal uclust settings. The taxonomy of OTU representative sequenceswas phylogenetically assigned to taxonomic classifications by theRDP Classifier with a confidence threshold of 0.8.³⁴ All experiments were performed at least three times. Eachdata point and error bar represented the mean and standard deviation,respectively.

1. Schippers A.; Sand W.Bacterial leachingof metal sulfide proceeds by two indirect mechanismsvia thiosulfate or via polysulfides and sulfur. Appl.Environ. Microbiol.1999, 65, 319–321. [DOI] [PMC free article] [PubMed] [Google Scholar]
2. Jia Y.; Tan Q. Y.; Sun H. Y.; Zhang Y. P.; Gao H. S.; Ruan R. M.Sulfidemineral dissolution microbes: Community structureand function in industrial bioleaching heaps. Green Energy Environ.2019, 4, 29–37. 10.1016/j.gee.2018.04.001. [DOI] [Google Scholar]
3. Fowler T. A.; Holmes P. R.; Crundwell F. K.Mechanism of pyrite dissolution inthe presence ofThiobacillus ferrooxidans. Appl. Environ. Microbiol.1999, 65, 2987–2993. [DOI] [PMC free article] [PubMed] [Google Scholar]
4. Lee J.; Acar S.; Doerr D. L.; Brierley J. A.Comparative bioleachingand mineralogy of composited sulfide ores containing enargite, covelliteand chalcocite by mesophilic and thermophilic microorganisms. Hydrometallurgy2011, 105, 213–221. 10.1016/j.hydromet.2010.10.001. [DOI] [Google Scholar]
5. Liu H. C.; Xia J. L.; Nie Z. Y.; Wen W.; Yang Y.; Ma C. Y.; Zheng L.; Zhao Y. D.Formationand evolutionof secondary minerals during bioleaching of chalcopyrite by thermoacidophilicArchaea acidianus manzaensis. Trans. Nonferrous Met. Soc. China2016, 26, 2485–2494. 10.1016/S1003-6326(16)64369-8. [DOI] [Google Scholar]
6. Bouffard S. C.; Rivera-Vasquez B. F.; Dixon D. G.Leaching kineticsand stoichiometryof pyrite oxidation from a pyrite-marcasite concentrate in acid ferricsulfate media. Hydrometallurgy2006, 84, 225–238. 10.1016/j.hydromet.2006.05.008. [DOI] [Google Scholar]
7. Holmes P. R.; Crundwell F. K.The kineticsof the oxidation of pyrite by ferric ionsand dissolved oxygen: An electrochemical study. Geochim. Cosmochim. Acta2000, 64, 263–274. 10.1016/S0016-7037(99)00296-3. [DOI] [Google Scholar]
8. Chandra A. P.; Gerson A. R.The mechanisms ofpyrite oxidation and leaching: Afundamental perspective. Surf. Sci. Rep.2010, 65, 293–315. 10.1016/j.surfrep.2010.08.003. [DOI] [Google Scholar]
9. Mikkelsen D.; Kappler U.; Webb R. I.; Rasch R.; McEwan A. G.; Sly L. I.Visualisation ofpyrite leaching by selected thermophilicarchaea: Nature of microorganism-ore interactions during bioleaching. Hydrometallurgy2007, 88, 143–153. 10.1016/j.hydromet.2007.02.013. [DOI] [Google Scholar]
10. Cabral T.; Ignatiadis I.Mechanisticstudy of the pyrite–solution interfaceduring the oxidative bacterial dissolution of pyrite (FeS₂) by using electrochemical. Int. J. Miner.Process.2001, 62, 41–64. 10.1016/S0301-7516(00)00044-2. [DOI] [Google Scholar]
11. Gu G. H.; Sun X. J.; Hu K. T.; Li J. H.; Qiu G. Z.Electrochemicaloxidation behavior of pyrite bioleaching byAcidthiobacillusferrooxidans. Trans. NonferrousMet. Soc. China2012, 22, 1250–1254. 10.1016/S1003-6326(11)61312-5. [DOI] [Google Scholar]
12. Angeles C.Kinetics of Leachingof Covellite in Ferric-Sulfate-Sulfuric Acid Media. University of British Columbia: Vancouver, BC, 2015. [Google Scholar]
13. Ruan R. M.; Zhou E.; Liu X. Y.; Wu B.; Zhou G. Y.; Wen J. K.Comparison on the leaching kineticsof chalcocite andpyrite with or without bacteria. Rare Met.2010, 29, 552–556. 10.1007/s12598-010-0167-3. [DOI] [Google Scholar]
14. Echeverría-Vega A.; Demergasso C.Copper resistance,motility and the mineral dissolutionbehavior were assessed as novel factors involved in bacterial adhesionin bioleaching. Hydrometallurgy2015, 157, 107–115. 10.1016/j.hydromet.2015.07.018. [DOI] [Google Scholar]
15. Estrada-delos Santos F.; Rivera-Santillán R. E.; Talavera-Ortega M.; Bautista F.Catalytic and galvanic effects of pyrite on ferricleaching of sphalerite. Hydrometallurgy2016, 163, 167–175. 10.1016/j.hydromet.2016.04.003. [DOI] [Google Scholar]
16. Segall M. D.; Lindan P. J. D.; Probert M. J.; Pickard C. J.; Hasnip P. J.; Clark S. J.; Payne M. C.First-principlessimulation: ideas,illustrated and the CASTEP code. J. Phys.: Condens.Matter2002, 14, 2717–2744. 10.1088/0953-8984/14/11/301. [DOI] [Google Scholar]
17. Perdew J. P.; Chevary J. A.; Vosko S. H.; Jackson K. A.; Pederson M. R.; Singh D. J.; Fiolhais C.Atoms, molecules,solids, and surfaces:Applications of the generalized gradient approximation for exchangeand correlation. Phys. Rev. B1992, 46, 6671–6687. 10.1103/PhysRevB.46.6671. [DOI] [PubMed] [Google Scholar]
18. Xi P.; Shi C. X.; Yan P. K.; Liu W. L.; Tang L. G.DFT studyon the influence of sulfur on the hydrophobicity of pyrite surfacesin the process of oxidation. Appl. Surf. Sci.2019, 466, 964–969. 10.1016/j.apsusc.2018.09.197. [DOI] [Google Scholar]
19. Ahlberg E.; Broo A. E.Oxygen reductionat sulphide minerals. 2. A rotatingring disc electrode (RRDE) study at galena and pyrite in the presenceof xanthate. Int. J. Miner. Process.1996, 47, 33–47. 10.1016/0301-7516(95)00099-2. [DOI] [Google Scholar]
20. Yakovkin I. N.; Petrova N. V.Influence of thethickness and surface compositionon the electronic structure of FeS₂ layers. Appl. Surf. Sci.2016, 377, 184–190. 10.1016/j.apsusc.2018.09.197. [DOI] [Google Scholar]
21. Wang X. X.; Liao R.; Zhao H. B.; Hong M. X.; et al. Synergeticeffect of pyrite on strengthening bornite bioleaching byLeptospirillum ferriphilum. Hydrometallurgy2018, 176, 9–16. 10.1016/j.hydromet.2017.12.003. [DOI] [Google Scholar]
22. Rawlings D. E.; Coram N. J.; Gardner M. N.; Deane S. M.Thiobacilluscaldus andLeptospirillum ferrooxidans are widely distributed in continuous-flow biooxidation tanks usedto treat a variety of metal-containing ores and concentrates. Process Metall.1999, 9, 777–786. 10.1016/S1572-4409(99)80080-7. [DOI] [Google Scholar]
23. Mutch L. A.; Watling H. R.; Watkin E. L. J.Microbialpopulation dynamics ofinoculated low-grade chalcopyrite bioleaching columns. Hydrometallurgy2010, 104, 391–398. 10.1016/j.hydromet.2010.02.022. [DOI] [Google Scholar]
24. Liu H.; Gu G. H.; Xu Y. B.Surfaceproperties of pyrite in thecourse of bioleaching by pure culture ofAcidithiobacillusferrooxidans and a mixed culture ofAcidithiobacillus ferrooxidans andAcidithiobacillus thiooxidans. Hydrometallurgy2011, 108, 143–148. 10.1016/j.hydromet.2011.03.010. [DOI] [Google Scholar]
25. Bott A. W.Electrochemistryof semiconductors. Curr. Sep.1998, 17, 87–91. [Google Scholar]
26. Licht S.SemiconductorElectrodes and Photoelectrochemistry. In Encyclopediaof Electrochemistry; Bard A. J., Stratmann M., Eds.; Wiley-VCH: Weinheim, 2002; Vol. 6, pp 3–47. [Google Scholar]
27. Boldish S. I.; White W. B.Optical band gaps of selected ternary sulfide minerals. Am. Mineral.1998, 83, 865–871. 10.2138/am-1998-7-818. [DOI] [Google Scholar]
28. Wei D. W.; Osseo-Asare K.Semiconductorelectrochemistry of particulate pyrite:mechanisms and products of dissolution. J. Electrochem.Soc.1997, 144, 546–553. 10.1149/1.1837446. [DOI] [Google Scholar]
29. Mcmillan R. S.; MacKinnon D. J.; Dutrizac J. E.Anodic dissolution of n-type andp-type chalcopyrite. J. Appl. Electrochem.1982, 12, 743–757. 10.1007/BF00617495. [DOI] [Google Scholar]
30. Niu X. P.; Ruan R. M.; Tan Q. Y.; Jia Y.; Sun H. Y.Study onthe second stage of chalcocite leaching in column with redox potentialcontrol and its implications. Hydrometallurgy2015, 155, 141–152. 10.1016/j.hydromet.2015.04.022. [DOI] [Google Scholar]
31. Zhang L.; Su F.; Wang N.; Liu S.; Yang M.; Wang Y. Z.; Huo D. Q.; Zhao T. T.Biodegradabilityenhancement of hydrolyzedpolyacrylamide wastewater by a combined Fenton-SBR treatment process. Bioresour. Technol.2019, 278, 99–107. 10.1016/j.biortech.2019.01.074. [DOI] [PubMed] [Google Scholar]
32. Peiffer J. A.; Spor A.; Koren O.; Zhao J.; Tringe S. G.; Dangl J. L.; Buckler E. S.; Ley R. E.Diversity and heritabilityof the maize rhizosphere microbiome under field conditions. Proc. Natl. Acad. Sci. U.S.A.2013, 110, 6548–6553. 10.1073/pnas.1302837110. [DOI] [PMC free article] [PubMed] [Google Scholar]
33. Edgar R. C.; Haas B. J.; Clemente J. C.; Quince C.; Knight R.UCHIME improvessensitivity and speed of chimera detection. Bioinformatics2011, 27, 2194–2200. 10.1093/bioinformatics/btr381. [DOI] [PMC free article] [PubMed] [Google Scholar]
34. Wang Q.; Garrity G. M.; Tiedje J. M.; Cole J. R.Naïve Bayesianclassifier for rapid assignment of rRNA sequences into the new bacterialtaxonomy. Appl. Environ. Microbiol.2007, 73, 5261–5267. 10.1128/AEM.00062-07. [DOI] [PMC free article] [PubMed] [Google Scholar]
35. Wu B.; Wen J. K.; Chen B. W.; Yao G. C.; Wang D. Z.Controlof redox potential by oxygen limitation in selective bioleaching ofchalcocite and pyrite. Rare Met.2014, 33, 622–627. 10.1007/s12598-014-0364-6. [DOI] [Google Scholar]