minerals
Article Leaching of Chalcopyrite under Bacteria–Mineral Contact/Noncontact Leaching Model
Pengcheng Ma 1,2, Hongying Yang 2,*, Zuochun Luan 1, Qifei Sun 1, Auwalu Ali 2 and Linlin Tong 2
1 Technology Center, Shandong Zhaojin Group Co., Ltd., No.108 Shengtai Road, Zhaoyuan 265400, China; [email protected] (P.M.); [email protected] (Z.L.); [email protected] (Q.S.) 2 School of Metallurgy, Northeastern University, 3-11 Wenhua Road, Shenyang 110819, China; [email protected] (A.A.); [email protected] (L.T.) * Correspondence: [email protected]
Abstract: Bacteria–mineral contact and noncontact leaching models coexist in the bioleaching process. In the present paper, dialysis bags were used to study the bioleaching process by separating the bacteria from the mineral, and the reasons for chalcopyrite surface passivation were discussed. The results show that the copper leaching efficiency of the bacteria–mineral contact model was higher than that of the bacteria–mineral noncontact model. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) were used to discover that the leaching process led to the formation of a sulfur film to inhibit the diffusion of reactive ions. In addition, the deposited jarosite on chalcopyrite surface was crystallized by the hydrolysis of the excess Fe3+ ions. The depositions passivated the chalcopyrite leaching process. The crystallized jarosite in the bacteria EPS layer belonged to bacteria–mineral contact leaching system, while that in the sulfur films belonged to the bacteria–mineral noncontact system.
Citation: Ma, P.; Yang, H.; Luan, Z.; Keywords: chalcopyrite; bacteria leaching; passivation; jarosite Sun, Q.; Ali, A.; Tong, L. Leaching of Chalcopyrite under Bacteria–Mineral Contact/Noncontact Leaching Model. Minerals 2021, 11, 230. https:// 1. Introduction doi.org/10.3390/min11030230 Chalcopyrite (CuFeS2) is one of the most widespread and refractory copper-containing minerals [1]. The main technologies to extract copper are pyrometallurgical processes; Academic Editor: Jean-François Blais however, the byproduct, i.e., sulfur dioxide, leads to serious environmental pollution. Currently, researchers are focusing on developing new environmentally friendly metallurgy Received: 16 January 2021 technologies and, since bio-metallurgy is renowned for low cost and pollution [2,3], it has Accepted: 4 February 2021 already become a research hotspot. There are two widely received bioleaching mechanisms, Published: 24 February 2021 i.e., direct action and indirect action, providing theoretical support for research on sulfuric mineral bio-metallurgy [4]. On the other hand, further research has shown that these Publisher’s Note: MDPI stays neutral mechanisms cannot explain several complex chemical, electrochemical, and biochemical with regard to jurisdictional claims in phenomena. Tributsch found that an extracellular polymeric substance (EPS) is produced published maps and institutional affil- + iations. as the bacteria are adsorbed onto the ore surface [5]. Fe(III) and H are accumulated on the contact surface of the ore/solution by EPS to hasten ore decomposition. This conclusion was rather different from the previously characterized “direct action”. Crundwell [6] developed Tributsch’s theory and summarized other research results, eventually establishing the indirect leaching mechanism, indirect contact leaching mechanism, and direct contact Copyright: © 2021 by the authors. leaching mechanism. This mechanism has been already authorized in the bio-metallurgy Licensee MDPI, Basel, Switzerland. academic community. In recent years, bio-metallurgy technology developed rapidly and This article is an open access article was applied in the smelting process of arsenic-bearing refractory gold ore and secondary distributed under the terms and conditions of the Creative Commons copper sulfide [7]. For chalcopyrite bioleaching technology, the development is slow Attribution (CC BY) license (https:// due to the following reasons: the high lattice energy of chalcopyrite [8], its difficulty creativecommons.org/licenses/by/ to be oxidized in the bioleaching process, and the passivation layer produced by the 4.0/). insoluble substance that inhibits the further diffusion of bacteria and reactant [9–15].
Minerals 2021, 11, 230. https://doi.org/10.3390/min11030230 https://www.mdpi.com/journal/minerals Minerals 2021, 11, 230 2 of 12
Parker reported that jarosite deposition has an important role in the decrease in copper leaching efficiency [16]. Dutrizac promoted that a dense sulfur layer covered the surface of chalcopyrite which would inhibit leaching [17]. Ghahremaninez promoted that leaching of Cu1−xFe1−yS2 (x < y) was the main reason for the observation of electrochemistry [18,19]. Altogether, the widely accepted view is that jarosite deposition leads to chalcopyrite passivation [20,21]. Fe3+ ion concentration, pH, and monovalent cation concentration have an effect on the generation of the jarosite deposition. Rapid crystallization of jarosite is produced by bacteria, hastening the Fe3+ ion supply [22–27]. However, the location of crystallization and mechanism of generation remain unclear. It is very important to study the passiva- tion mechanism of chalcopyrite, especially to ascertain whether jarosite crystallizes on the ore surface or in the EPS layer of bacteria absorbed onto ore surface. In this paper, the chalcopyrite bioleaching processes are divided into two parts by bag filters so as to separate bacteria from ore. The aim was to study the leaching mechanism under different conditions including the bacterium–mineral contact and noncontact leaching models. The leaching residue was analyzed by several experimental methods, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) in order to discuss the reason for chalcopyrite surface passivation.
2. Materials and Methods 2.1. Leaching Bacteria The bioleaching bacterial strains were composed of Acidithiobacillus ferrooxidans, Acidi- thiobacillus thiooxidans, and Leptospirillum ferriphilum. They were provided by the Northeast- ern University bio-metallurgical laboratory. The strains have good antitoxic characteristic and oxidative ability of sulfur and ferrous ions, and they grow in a pH range of 1.0–2.5 and a temperature range of 25–44 ◦C[28,29].
2.2. Microorganism Culture The culture medium used for this experiment was 9 K [28,29]. The composition of the medium is as follows: 3.0 g/L (NH4)2SO4; 0.1 g/L KCl; 0.5 g/L K2HPO4; 0.5 g/L MgSO4·7H2O; 0.01 g/L Ca(NO3)2; 44.3 g/L FeSO4·7H2O. All chemical reagents used were of analytical grade.
2.3. Mineral Sample The mineral sample was obtained from a certain copper mine in Hubei province of China. The elementary composition of the sample is listed in Table1. It can be seen that the mineral sample contained Cu 13.82%, Fe 37.50%, and S 39.76%. The particle size distribution is listed in Table2. It can be seen that the proportions of particles with size >75 µm, 75–45 µm, 45–37 µm, and <37 µm were 1.12%, 9.53%, 20.16%, and 69.19%, respectively. The X-ray diffraction pattern is shown in Figure1. The main metallic minerals in the mineral sample were chalcopyrite and pyrite.
Table 1. The main element contents of mineral samples.
Element Cu Fe S SiO2 CaO Al2O3 MgO Content, % 13.82 37.50 39.76 2.72 0.79 0.40 0.15
Table 2. Particle size distribution of mineral samples.
Particle Size >75 µm 75–45 µm 45–37 µm <37 µm Content, % 1.12 9.53 20.16 69.19 Minerals 2021, 11, x FOR PEER REVIEW 3 of 12 Minerals 2021, 11, 230 3 of 12
■ ■ FeCuS2 ● ● FeS2
● ●
● ● Intensity,a.u. ● ■ ■ ● ● ■ ● ● ●
10 20 30 40 50 60 70 80 90 2(°) FigureFigure 1. 1.X-ray X-ray diffraction diffraction (XRD) (XRD) pattern pattern of the mineral of the samples. mineral samples. 2.4. Experimental Procedure 2.4. ExperimentalThe chalcopyrite Procedure samples were divided into two groups for bioleaching. Each group consistedThe ofchalcopyrite five parallel samples,samples aswere the leachingdivided process into two needed groups to be for observed bioleaching. and Each group consistedstudied under of five different parallel periods. samples, In the firstas the group, leaching each sample process had needed 10 g of chalcopyrite to be observed and stud- wrapped with a dialysis bag, which was added to a 500 mL shaking flask containing 180 mL ied under different periods. In the first group, each sample had 10 g of chalcopyrite of 9 K culture medium. The dialysis bag was made up of polyvinylidene fluoride with a wrappedcutoff relative with molecular a dialysis mass bag, of 8000, which preventing was added bacteria to from a 500 contacting mL shaking the mineral flask but containing 180 mLallowing of 9 K ions culture to dialyze medium. and diffuse The freely.dialysis Therefore, bag wa thes made first group up of test polyvinylidene could simulate fluoride with athe cutoff leaching relative behavior molecular of the noncontact mass of bacteria–mineral 8000, preventing model, bacteria while the from second contacting group the mineral buttest couldallowing simulate ions the to leachingdialyze behaviorand diffuse of the freely contact. Therefore, bacteria–mineral the first model. group Each test could simu- sample in the second group had 10 g of chalcopyrite directly added to a 500 mL shaking lateflask the also containingleaching 180behavior mL of 9 Kof culture the noncontact medium. Then, bacteria–mineral 20 mL of bacterial solutionmodel, with while the second group3.2 × 10 test8 cells/mL couldwas simulate injected intothe eachleaching of the 10behavi flasksor mentioned of the contact above. The bacteria–mineral initial pH model. Eachwas adjusted sample to in 1.4 the with second H2SO4. Thegroup flasks had were 10 put g intoof chalcopyrite a constant-temperature directly shakeradded to a 500 mL ◦ shakingincubator andflask shaken also atcontaining 170 rpm at 44 180C. ThemL experimentof 9 K culture was supplemented medium. withThen, distilled 20 mL of bacterial water instead of volatilized water. solution with 3.2 × 108 cells/mL was injected into each of the 10 flasks mentioned above. The2.5. Measurementinitial pH was adjusted to 1.4 with H2SO4. The flasks were put into a constant-tem- peratureA PHS-25 shaker acidometer incubator made and by Shanghai shaken digitalat 170 electronics rpm at 44 holding °C. The (group) experiment co., LTD was supple- mentedwas used with to measure distilled the water solution instead pH. A platinumof volatilized plate as water. a working electrode and a saturated calomel electrode as reference were used to measure redox potential. A Leica DM2500 biological microscope and XB-K-25 hemacytometer were used to count the number 2.5.of free Measurement bacteria in pulp. The total count on the ore surface was measured by ninhydrin col- orimetryA PHS-25 [30]. The acidometer copper concentration made by was Shanghai measured usingdigital a TAS-990 electronics atomic holding absorption (group) co., LTD wasspectrophotometer, used to measure manufactured the solution by PERSEE pH. CompanyA platinum in Beijing. plate Theas a atomic working absorption electrode and a sat- method is based on the characteristic spectral line of the element to be measured emitted urated calomel electrode as reference were used to measure redox potential. A Leica by the hollow cathode lamp. The sample vapor is absorbed by the ground-state atom of DM2500the element biological to be measured microscope in the vapor, and andXB-K-25 the content hemacytometer of the element were to be measuredused to count the num- berin the of samplefree bacteria is determined in pulp. by theThe weakening total count degree on the of theore characteristic surface was spectral measured line. by ninhydrin colorimetryThe leaching residue [30]. The was copper observed concentration using an SSX-550 wa SEM/energy-dispersives measured using a spectrometer TAS-990 atomic absorp- tion(EDS) spectrophotometer, made by the Japanese manufactured Shimadzu Company. by PERSEE The phase Company of leaching in residue Beijing. was The atomic ab- analyzed using a Netherlandish D/MAX-RB X-ray diffractometer under the condition of sorptionCuKα and method 2◦/min scanningis based speed. on the IR characteristic analysis of leaching spectral residue line was of performedthe element in ato be measured emitted400–4000 cmby− the1 scanning hollow range cathode by a Vertex70 lamp. The Fourier-transform sample vapor infrared is absorbed spectrometer by the of ground-state atomthe Germany of the BRUKER element Company. to be measured Leaching residue in the was vapor, bonded and to the the metal content platform of withthe element to be measureda conductive in adhesive. the sample is determined by the weakening degree of the characteristic spec- tral line. The leaching residue was observed using an SSX-550 SEM/energy-dispersive spectrometer (EDS) made by the Japanese Shimadzu Company. The phase of leaching residue was analyzed using a Netherlandish D/MAX-RB X-ray diffractometer under the condition of CuKα and 2°/min scanning speed. IR analysis of leaching residue was per- formed in a 400–4000 cm−1 scanning range by a Vertex70 Fourier-transform infrared spec- trometer of the Germany BRUKER Company. Leaching residue was bonded to the metal platform with a conductive adhesive.
Minerals 2021, 11, 230 4 of 12
3. Results and Discussion 3.1. pH and Potential Change Figures2 and3 show the variations of pH and potential in the process of bioleaching. During the bioleaching process of sulfide minerals, these changes are caused by the transfer of hydrogen ions and electrons. It can be seen from Figure2 that pH increased at the be- ginning of the reaction, and then subsequently decreased. Furthermore, the pH remained relatively constant in a range of 1.2–1.75, which is suitable for bacterial survival. Equa- tions (1) and (2) represent the oxidation reaction of sulfide minerals in the bacteria–mineral contact leaching model. Fe3+ as an oxidant comes from two aspects; one is dissociative Fe3+ in the solution, whereas the other occurs in EPS layer of bacteria. The solution pH increases when Fe2+ is oxidized to Fe3+ by the bacteria, according to the reaction shown in Equation (3). However, the pH decreases slowly due to sulfur being oxidized by the bacteria, as shown in Equation (4), and Fe3+ being hydrolyzed, as shown in Equation (5). In the bacteria–mineral noncontact leaching model, the bacteria were isolated from the ore using a dialysis bag, preventing them from being adsorbed onto the ore surface. The chalcopyrite was oxidized only by dissociative Fe3+ in the solution. The standard electrode potential of Fe3+/Fe2+ was 0.771 V vs. SHE which is less than the 0.808 V vs. SHE necessary for the production of S6+ [31,32]. Therefore, S2− in the chalcopyrite was oxidized only to S0, as detected on the ore surface. Fe2+ oxidized to Fe3+ after passing through the dialysis bag and reacting with bacteria, leading to a pH increase. Moreover, S0 on the ore surface could not be oxidized by Fe3+. Thus, the bacteria–mineral noncontact leaching model appeared to have a higher increase in pH than the corresponding contact leaching model. On day 9 of the bioleaching process, the pH reached 1.74, before subsequently decreasing due to Fe3+ hydrolysis, as can be seen in Equation (5). Pulp potential increased rapidly, and then remained relatively constant. Moreover, the potential of the bacteria–mineral noncontact leaching system rose higher than that of the bacteria–mineral contact leaching system. This was due to the sulfur film formed in the bacteria–mineral noncontact leaching system after the ores were oxidized by Fe3+, which in turn obstructed the leaching of ores. Furthermore, the bacteria outside the dialysis bag could oxide Fe2+ into Fe3+, which led to the increase in [Fe3+]/[Fe2+] in the solution, and oxidation reduction potential rose quickly. In the bacteria–mineral contact leaching system, the sulfur film, however, obstructed the leaching of ore to lesser extent due to the existence of Acidithiobacillus thiooxidans. Thus, the sulfide ores could be oxidized continuously [33].
3+ chemical 2+ 2+ 0 CuFeS2 + 4Fe → Cu + 5Fe + 2S . (1)
3+ chemical 2+ 0 FeS2 + 2Fe → 3Fe + 2S . (2)
2+ + biological 3+ 4Fe + 4H + O2 → 4Fe + 2H2O. (3)
0 biological 2S + 3O2 + 2H2O → 2H2SO4. (4) 3+ 2− + + 3Fe + 2SO4 + 6H2O + M → MFe3(SO4)2(OH)6 + 6H . + + + (5) (M = K , NH4 ,H3O Minerals 2021, 11, x FOR PEER REVIEW 4 of 12
3. Results and Discussion 3.1. pH and Potential Change Figures 2 and 3 show the variations of pH and potential in the process of bioleaching. During the bioleaching process of sulfide minerals, these changes are caused by the trans- fer of hydrogen ions and electrons. It can be seen from Figure 2 that pH increased at the beginning of the reaction, and then subsequently decreased. Furthermore, the pH re- mained relatively constant in a range of 1.2–1.75, which is suitable for bacterial survival. Equations (1) and (2) represent the oxidation reaction of sulfide minerals in the bacteria– mineral contact leaching model. Fe3+ as an oxidant comes from two aspects; one is disso- ciative Fe3+ in the solution, whereas the other occurs in EPS layer of bacteria. The solution pH increases when Fe2+ is oxidized to Fe3+ by the bacteria, according to the reaction shown in Equation (3). However, the pH decreases slowly due to sulfur being oxidized by the bacteria, as shown in Equation (4), and Fe3+ being hydrolyzed, as shown in Equation (5). In the bacteria–mineral noncontact leaching model, the bacteria were isolated from the ore using a dialysis bag, preventing them from being adsorbed onto the ore surface. The chal- copyrite was oxidized only by dissociative Fe3+ in the solution. The standard electrode potential of Fe3+/Fe2+ was 0.771 V vs. SHE which is less than the 0.808 V vs. SHE necessary for the production of S6+ [31,32]. Therefore, S2− in the chalcopyrite was oxidized only to S0, as detected on the ore surface. Fe2+ oxidized to Fe3+ after passing through the dialysis bag and reacting with bacteria, leading to a pH increase. Moreover, S0 on the ore surface could not be oxidized by Fe3+. Thus, the bacteria–mineral noncontact leaching model appeared to have a higher increase in pH than the corresponding contact leaching model. On day 9 of the bioleaching process, the pH reached 1.74, before subsequently decreasing due to Fe3+ hydrolysis, as can be seen in Equation (5). Pulp potential increased rapidly, and then remained relatively constant. Moreover, the potential of the bacteria–mineral noncontact leaching system rose higher than that of the bacteria–mineral contact leaching system. This was due to the sulfur film formed in the bacteria–mineral noncontact leaching system after the ores were oxidized by Fe3+, which in turn obstructed the leaching of ores. Fur- thermore, the bacteria outside the dialysis bag could oxide Fe2+ into Fe3+, which led to the increase in [Fe3+]/[Fe2+] in the solution, and oxidation reduction potential rose quickly. In the bacteria–mineral contact leaching system, the sulfur film, however, obstructed the Minerals 2021, 11, 230 leaching of ore to lesser extent due to the existence of Acidithiobacillus5 ofthiooxidans 12 . Thus, the sulfide ores could be oxidized continuously [33].
2.0
1.9 microbe-mineral contact leaching model microbe-mineral uncontact leaching model 1.8
1.7
1.6
1.5
pH value value pH 1.4
1.3
1.2
1.1 0 3 6 9 12 15 18 21 24 27 30 Minerals 2021, 11, x FOR PEER REVIEW Time/d 5 of 12
FigureFigure 2.2.pH pH changes changes with with bioleaching bioleaching time. time.
750
700
650
600
550
500 (vsSCE)/mV h
E 450 microbe-mineral contact leaching model 400 microbe-mineral uncontact leaching model
350
0 3 6 9 12 15 18 21 24 27 30 Time/d Figure 3. E changes with bioleaching time. Figure 3.h Eh changes with bioleaching time. 3.2. Bacterial Concentration Change
The change in bacterial concentration during3220 thechemical process of bioleaching is shown in CuFeS 4Fe Cu 5Fe 2S (1) Figure4. In the bacteria–mineral contact2 leaching system, the bacterial concentration. is the sum of the adsorbed count and free count. According to Figure4, leaching from 3 days to 320chemical 15 days followed the bacterial growthFeS logarithmic 2Fe phase. Bacterial 3Fe concentration 2S reached (2) 6 × 108 cells/mL on the 15th day, before2 approaching the stationary phase.. During the whole bioleaching process, the bacterial concentration remained relatively stable. There bio log ical was no obvious decline phase, indicating23 that the bacteria adapted very well to the leaching 4Fe 4H O22 4Fe 2H O . (3) system, and the energy provided by the oxidation of sulfide ore could support the bacteria.
In the bacteria–mineral noncontact leaching0 system, the bacterialbio log ical concentration increased 8 slowly and reached 2.1 × 10 cells/mL2S on 3O the22 15th 2H day, O which was 2H one-third 24 SO . that of the (4) bacteria–mineral contact leaching system. After 15 days, bacterial growth started to decline. 7 The bacterial concentration3Fe32 decreased 2SO rapidly 6H O and Mreached MFe 8.2 × 10 SOcells/mL OH at the 6H end of the bioleaching process, which shows42 that Fe3+ had no obvious 34 effect on26 the oxidation . (5) of chalcopyrite in the bacteria–mineral(M=K+++ , NH , H noncontact O ) leaching system. It was so hard for chalcopyrite to decompose persistently43 that some bacteria struggled to survive. This led to the occurrence of a decline phase and the decrease in bacterial concentration. 3.2. Bacterial Concentration Change The change in bacterial concentration during the process of bioleaching is shown in Figure 4. In the bacteria–mineral contact leaching system, the bacterial concentration is the sum of the adsorbed count and free count. According to Figure 4, leaching from 3 days to 15 days followed the bacterial growth logarithmic phase. Bacterial concentration reached 6 × 108 cells/mL on the 15th day, before approaching the stationary phase. During the whole bioleaching process, the bacterial concentration remained relatively stable. There was no obvious decline phase, indicating that the bacteria adapted very well to the leaching system, and the energy provided by the oxidation of sulfide ore could support the bacteria. In the bacteria–mineral noncontact leaching system, the bacterial concentra- tion increased slowly and reached 2.1 × 108 cells/mL on the 15th day, which was one-third that of the bacteria–mineral contact leaching system. After 15 days, bacterial growth started to decline. The bacterial concentration decreased rapidly and reached 8.2 × 107 cells/mL at the end of the bioleaching process, which shows that Fe3+ had no obvious effect on the oxidation of chalcopyrite in the bacteria–mineral noncontact leaching system. It was so hard for chalcopyrite to decompose persistently that some bacteria struggled to survive. This led to the occurrence of a decline phase and the decrease in bacterial concen- tration.
Minerals 2021, 11, x FOR PEER REVIEW 6 of 12
Minerals 2021, 11, x FOR PEER REVIEW 6 of 12 Minerals 2021, 11, 230 6 of 12 9.0
8.8
8.6
9.0] 8.4 8.8 8.2 8.6
cells/mL 8.0 [ ] 8.4lg 7.8 microbe-mineral contact leaching model
8.27.6 microbe-mineral uncontact leaching model
cells/mL 8.0 [ 7.4
lg 036912151821242730 7.8 Time/d microbe-mineral contact leaching model 7.6 microbe-mineral uncontact leaching model
Figure7.4 4. Bacterial concentration changes with bioleaching time. 036912151821242730 Time/d 3.3. Copper Leaching Efficiency Figure 4. Bacterial concentration changes with bioleaching time. FigureThe 4. Bacterial copper concentration leaching efficiency changes duringwith bioleaching the bioleaching time. process is shown in Figure 5. As3.3. seen Copper from Leaching Figure Efficiency 5, the percentage of leached copper reached 61.67% on the 30th day 3.3.during CopperThe copperthe Leaching bacteria–mineral leaching Efficiency efficiency contact during the leaching bioleaching system, process iswhile shown that in Figure of the5. Asbacteria–mineral seenThe from copper Figure5, theleaching percentage efficiency of leached during copper reachedthe bioleaching 61.67% on theprocess 30th day is during shown in Figure 5. noncontactthe bacteria–mineral leaching contact system leaching reached system, whileonly that 21.86%. of the bacteria–mineral In the bacteria–mineral noncontact noncontact- Asleaching seen from system system, Figure reached both 5, only the 21.86%. copperpercentage In leaching the bacteria–mineralof leached rate and copper the noncontact-leaching efficiency reached 61.67%were system, very on lowthe 30thas a func-day duringtionboth theof the the copper bacteria–mineraloxidation leaching rateof dissociative and thecontact efficiency leachingFe3+ were. In verythe system, lowbacteria–mineral as awhile function that of the ofcontact oxidationthe bacteria–mineral leaching system, noncontacttheof dissociative bacteria–EPS–ore leaching Fe3+. In the system system bacteria–mineral reached was formed contactonly when21.86%. leaching bacteria system,In the were the bacteria–mineral bacteria–EPS–ore adsorbed on thenoncontact- chalcopy- 3+ leachingritesystem surface. was system, formed Fe3+ both was when theaccumulated bacteria copper were leaching adsorbed in the rateEPS on theand layer, chalcopyrite the subsequently efficiency surface. were Feoxidizing verywas low the as ore.a func- The accumulated in the EPS layer, subsequently oxidizing the ore. The efficiency was higher tion of the oxidation of dissociative Fe3+. In the bacteria–mineral contact leaching system, efficiencythan that of was the bacteria–mineral higher than that noncontact of the leachingbacteria–mineral system. This noncontact shows that bacterialleaching system. This theshowsadsorption bacteria–EPS–ore that has bacterial an important adsorptionsystem influence was has onformed chalcopyrite an important when bioleaching. bacteria influence were on adsorbed chalcopyrite on the bioleaching. chalcopy- rite surface. Fe3+ was accumulated in the EPS layer, subsequently oxidizing the ore. The efficiency80 was higher than that of the bacteria–mineral noncontact leaching system. This microbe-mineral contact leaching model shows70 that bacterialmicrobe-mineral adsorption uncontact leaching model has an important influence on chalcopyrite bioleaching. 60 80 50 microbe-mineral contact leaching model 70 40 microbe-mineral uncontact leaching model 60 30 50 20
40 efficiency/% Copper Leaching 10 30 0 0 3 6 9 12 15 18 21 24 27 30 20 Time/d
Copper Leaching efficiency/% Copper Leaching 10 Figure 5. Copper leaching efficiency with bioleaching time. Figure0 5. Copper leaching efficiency with bioleaching time. 3.4.0 Discussion 3 6 9 12 15 18 21 24 27 30 Time/d 3.4.3.4.1. Discussion XRD Analysis of Leaching Residue FigureFigure 5. Copper6 presents leaching the XRD efficiency spectrum with of several bioleaching bioleaching time. residues after chalcopyrite 3.4.1.was bioleached XRD Analysis for 30 days of underLeaching two different Residue leaching conditions. As shown in Figure6, the residueFigure composition 6 presents of the bacteria–mineral XRD spectrum contact of seve leachingral bioleaching system was essentiallyresidues theafter chalcopyrite 3.4. Discussion wassame bioleached as that of the for bacteria–mineral 30 days under noncontact two differen leachingt system,leaching including conditions. chalcopyrite, As shown in Figure 3.4.1.pyrite, XRD elementary Analysis sulfur, of Leaching and jarosite. Residue There were two kinds of leaching mode in the 6,bacteria–mineral the residue composition contact leaching of system.the bacteria–mineral According to the contact first mode, leaching an EPS layersystem was was essentially theformed Figuresame on chalcopyriteas 6 thatpresents of the surface the bacteria–mineral XRD by bacteria, spectrum and of oreno sevencontact wasral oxidized bioleaching leaching by Fe3+ system,enriched residues inincluding after EPS. chalcopyrite chalcopy- wasrite,In the bioleached pyrite, second elementary mode, for bacteria,30 days sulfur, suchunder and as Thiobacillustwo jarosite. differen ferrooxidansThtere leaching were, were two conditions. adsorbed kinds of onto Asleaching shown the mode in Figure in the − 0 2− 6,bacteria–mineralore the surface residue and composition supported contact by leaching HSof the,S bacteria–mineral, and system. S2O3 Accordingreleased contact by oreto decompositiontheleaching first mode, system [5, 34an was]. EPS essentially layer was In the earlier stage of chalcopyrite bioleaching, the oxidation rate of ore was faster than theformed same onas chalcopyritethat of the bacteria–mineral surface by bacteria, noncontact and ore leaching was oxidized system, by including Fe3+ enriched chalcopy- in EPS. that of sulfur by Thiobacillus thiooxidans. Therefore, elementary sulfur accumulated on the rite,In the pyrite, second elementary mode, bacteria, sulfur, andsuch jarosite. as Thiobacillus There were ferrooxidans two kinds, were of leachingadsorbed mode onto thein the ore bacteria–mineralsurface and supported contact by leaching HS−, S0 system., and S2O According32− released to by the ore first decomposition mode, an EPS [5,34]. layer In was the formedearlier onstage chalcopyrite of chalcopyrite surface bioleaching, by bacteria, the and ox oreidation was oxidizedrate of ore by was Fe3+ faster enriched than in that EPS. of Insulfur the second by Thiobacillus mode, bacteria, thiooxidans such. Therefore, as Thiobacillus elementary ferrooxidans sulfur, were accumulated adsorbed on onto the the chalco- ore surfacepyrite surface.and supported In the bacteria–mineral by HS−, S0, and S nonc2O32− ontactreleased leaching by ore systemdecomposition, chalcopyrite [5,34]. was In theoxi- earlierdized stageonly byof dissociativechalcopyrite Fe bioleaching,3+ in the leaching the ox solution,idation rate as shown of ore inwas Equations faster than (1) thatand (2),of sulfur by Thiobacillus thiooxidans. Therefore, elementary sulfur accumulated on the chalco- pyrite surface. In the bacteria–mineral noncontact leaching system, chalcopyrite was oxi- dized only by dissociative Fe3+ in the leaching solution, as shown in Equations (1) and (2),
Minerals 2021, 11, 230 7 of 12
Minerals 2021, 11, x FOR PEER REVIEW 7 of 12
chalcopyrite surface. In the bacteria–mineral noncontact leaching system, chalcopyrite was oxidized only by dissociative Fe3+ in the leaching solution, as shown in Equations (1) andsuch (2), that such the sulfur that the formed sulfur could formed not couldbe oxidized not be and oxidized accumulate and accumulate on the ore surface. on the ore As surface.bioleaching As bioleachingproceeded in proceeded the bacteria–mineral in the bacteria–mineral contact leaching contact system, leaching the further system, oxida- the furthertion of oxidationore by Acidithiobacillus of ore by Acidithiobacillus ferrooxidans ferrooxidans was inhibitedwas inhibited by sulfu byr accumulated sulfur accumulated on the onchalcopyrite the chalcopyrite surface, surface, resulting resulting in a rise in in a risepH inin pHthe inEPS the layer EPS and layer the and hydrolysis the hydrolysis of re- ofdundant redundant Fe3+. FeIn 3+addition,. In addition, the jarosite the jarositecrystal was crystal separated was separated out from out the fromactive the matter active in matterthe EPS in layer the EPS as a layer nucleation as a nucleation center. In center. the bacteria–mineral In the bacteria–mineral noncontact noncontact leaching leaching system, system,the chalcopyrite the chalcopyrite surface surfacewas passivated was passivated due to duethe toformation the formation of elementary of elementary sulfur; sulfur; thus, thus,chalcopyrite chalcopyrite could couldnot effectively not effectively be further be further oxidized oxidized by Fe3+ by. As Fe redundant3+. As redundant Fe3+ content Fe3+ contentincreased, increased, Fe3+ was Fe hydrolyzed,3+ was hydrolyzed, and the andjarosite the jarositecrystal was crystal separated was separated out on the out chalco- on the chalcopyritepyrite surface. surface. Thus, Thus, there there was wasno further no further increase increase in inthe the leaching leaching efficiency. efficiency. Figure3 3 showsshows thethe XRDXRD spectraspectra ofof bioleachingbioleaching residueresidue afterafter bioleaching.bioleaching.
FigureFigure 6.6. XRDXRD spectraspectra ofof thethe leachingleaching residueresidue afterafter 3030 days.days.
3.4.2.3.4.2. SEM AnalysisAnalysis ofof LeachingLeaching ResidueResidue SEMSEM micrographs micrographs of of leaching leaching residue residue at different at different leaching leaching times timesare shown are shownin Figures in Figures7 and 8.7 Asand shown8 . As in shown Figure in 7a, Figure most7a, of most the ofelliptic the elliptic eroded eroded pits and pits cracks and cracks can be can found be foundon the onsurface the surface of several of several residues residues after leachi afterng leaching for 10 fordays 10 due days to due bacterial to bacterial adsorption adsorp- in tionthe bacteria–mineral in the bacteria–mineral contact contactleaching leaching system. system.Passivation Passivation did not occur did not due occur to a dueslippery to a slipperyore surface, ore but surface, fine butjarosite fine crystals jarosite crystalsexisted in existed the pits. in theAfter pits. leaching After leaching for 20 days, for 20 the days, pits theincreased, pits increased, and the andcracks the started cracks to started broaden to broaden and deepen, and deepen, which clearly which indicates clearly indicates that the thatores thewere ores severely were severely corroded. corroded. The ore The surface ore surface remained remained sleek, sleek, and no and jarosite no jarosite crystal crystal was wasfound found on the on theouter outer surface surface of ofthe the ore. ore. The The ja jarositerosite was was produced produced only only in the pits.pits. TheThe jarosite appeared only in the eroded area of the ore surface, as shown in Figure7b. At jarosite appeared only in the eroded area of the ore surface, as shown in Figure 7b. At 20 20 days through 30 days, since bacteria constantly produced Fe3+, jarosite crystal in the days through 30 days, since bacteria constantly produced Fe3+, jarosite crystal in the cor- corrosion pits grew, eventually covering the whole chalcopyrite surface, especially where rosion pits grew, eventually covering the whole chalcopyrite surface, especially where there was no reaction. This led to the thorough passivation of the chalcopyrite surface, as there was no reaction. This led to the thorough passivation of the chalcopyrite surface, as seen in Figure7a . Figure8 shows that bacteria were not adsorbed onto the chalcopyrite seen in Figure 7a. Figure 8 shows that bacteria were not adsorbed onto the chalcopyrite surface because of the isolation of the bag filter. Chalcopyrite was oxidized by dissociative surface because of the isolation of the bag filter. Chalcopyrite was oxidized by dissociative Fe3+. Elementary sulfur occurred on the chalcopyrite surface after leaching for 10 days. The Fe3+. Elementary sulfur occurred on the chalcopyrite surface after leaching for 10 days. energy spectrum shows that the crystal floc around sulfur is jarosite, as seen in Figure8a . The energy spectrum shows that the crystal floc around sulfur is jarosite, as seen in Figure Along with the steady oxidation by bacteria, both the Fe3+ concentration and its redox 8a. Along with the steady oxidation by bacteria, both the Fe3+ concentration and its redox potential increased, resulting in the chemical deposition of jarosite and severe passivation onpotential the chalcopyrite increased, resulting surface. Finally,in the chemical the copper deposition bioleaching of jarosite process and stopped, severe passivation as shown inon Figure the chalcopyrite8b,c. surface. Finally, the copper bioleaching process stopped, as shown in Figure 8b,c.
Minerals 2021, 11, x FOR PEER REVIEW 8 of 12
Minerals 2021, 11, x FOR PEER REVIEW 8 of 12 Minerals 2021, 11, 230 8 of 12
Figure 7. The morphologies of leaching residue after (a) 10 days, (b) 20 days, and (c) 30 days in the Figure 7. The morphologies of leaching residue after (a) 10 days, (b) 20 days, and (c) 30 days in the bacteria–mineralFigurebacteria–mineral 7. The morphologies contact contact leaching leaching of system leaching system (SE). residue (SE). after (a) 10 days, (b) 20 days, and (c) 30 days in the bacteria–mineral contact leaching system (SE).
Figure 8. The morphologies of leaching residue after (a) 10 days, (b) 20 days, and (c) 30 days in the Figure 8. The morphologies of leaching residue after (a) 10 days, (b) 20 days, and (c) 30 days in the bacteria–mineral noncontact leaching system (SE). bacteria–mineralFigure 8. The morphologies noncontact ofleaching leaching system residue (SE). after (a) 10 days, (b) 20 days, and (c) 30 days in the bacteria–mineral noncontact leaching system (SE). 3.4.3. FTIR Analysis of Leaching Residue 3.4.3.Figure FTIR Analysis 9 shows ofthe Leaching FTIR spectra Residue of both kinds of leaching residue after leaching for 30 days.Figure The 9 adsorption shows the peaksFTIR spectra at 515 and of both 474 cmkinds−1 were of leaching attributed residue to the after stretching leaching vibra- for −1 tion30 days. of the The FeO adsorption6 octahedron peaks [35], at that515 andat 630 474 cm cm−1 was were attributed attributed to theto the υ4 stretching vibra- −1 tion of SOthe4 2FeO−, that6 octahedron at 1020 cm [35],−1 was that attributed at 630 cm to the was γ 1attributed bending vibration to the υ4 ofstretching SO42−, those vibra- at 2− −1 2− 1090tion ofand SO 11934 , that cm at−1 were1020 cmattributed was attributed to the γ3 tobending the γ1 bendingvibration vibration of SO42− [36],of SO that4 , thoseat 1663 at 1090 and 1193 cm−1 were attributed to the γ3 bending vibration of SO42− [36], that at 1663
Minerals 2021, 11, 230 9 of 12
Minerals 2021, 11, x FOR PEER REVIEW3.4.3. FTIR Analysis of Leaching Residue 9 of 12
Figure9 shows the FTIR spectra of both kinds of leaching residue after leaching for 30 days. The adsorption peaks at 515 and 474 cm−1 were attributed to the stretching −1 vibration of the FeO6 octahedron [35], that at 630 cm was attributed to the υ4 stretching −1 2− −1 2− −1 cmvibration was attributed of SO4 , that to at the 1020 δ cmdeformationwas attributed vibration to the γ 1ofbending HOH vibrationin jarosite, of SO that4 , at 3394 cm −1 2− −1 −1 wasthose attributed at 1090 and to 1193the υ cm stretchingwere attributed vibration to the ofγ OH3 bending [27], those vibration at of2958 SO 4cm[36 and], 2924 cm −1 δ werethat attributed at 1663 cm towas the attributed asymmetric to the stretchingdeformation vibration vibration of of CH HOH2, and in jarosite, that at that 2853 cm−1 was at 3394 cm−1 was attributed to the υ stretching vibration of OH [27], those at 2958 cm−1 attributed to− the1 symmetrical stretching vibration of CH2 [23,37]. The figure shows that and 2924 cm were attributed to the asymmetric stretching vibration of CH2, and that at −1 the2853 bacteria–mineral cm was attributed contact to the symmetrical leaching system stretching possessed vibration of the CH 2same[23,37 ].structure The figure of jarosite as theshows bacteria–mineral that the bacteria–mineral noncontact contact leaching leaching system. system possessed Organic thematter same structureabsorbed of in the bacte- ria–mineraljarosite as the contact bacteria–mineral leaching noncontact system leachingwas der system.ived from Organic the matter deposition absorbed of in thebiomass on the chalcopyritebacteria–mineral surface. contact The leaching biomass system deposition was derived fromhastened the deposition the nucleation of biomass and on the crystallization chalcopyrite surface. The biomass deposition hastened the nucleation and crystallization of ofjarosite. jarosite.
FigureFigure 9. 9. Fourier-transformFourier-transform infrared infrared (FTIR) (FTIR) spectra spectra of leaching of leaching residue. residue. 3.4.4. Model of Bioleaching Process 3.4.4. ModelAlthough of bacteria–mineralBioleaching Process contact and noncontact leaching coexist in chalcopyrite bioleaching,Although bacteria–mineral bacteria–mineral contact contact leaching and represents noncontact the main leaching mode. Incoexist Figure 10in, chalcopyrite a mechanism model is presented for the chalcopyrite bioleaching process and jarosite bioleaching,production. Inbacteria–mineral the initial phase, bacteria contact are leaching adsorbed represents onto the mineral the main surface mode. owing toIn Figure 10, a mechanismits chemotaxis, model as shown is presented in Figure for10a. the A substantialchalcopyrite amount bioleaching of Fe3+ exists proc iness the and EPS jarosite pro- duction.layer, which In the is reduced initial tophase, Fe2+ due bacteria to the oxidationare adsorbed of ore. Then,onto Fethe2+ ismineral oxidized surface to Fe3+, owing to its + chemotaxis,which is accompanied as shown extensive in Figure H 10a.consumption, A substantial as seen amount in Figure of10 b,c.Fe3+ Chalcopyrite exists in the EPS layer, is oxidized, and Fe and Cu are liberated. The sulfur in the reduced state is oxidized to S0, which is reduced to Fe2+ due to the oxidation of ore. Then, Fe2+ is oxidized to Fe3+, which and a sulfur film is formed on the chalcopyrite surface, thereby inhibiting the leaching of + is chalcopyrite.accompanied The extensive copper leaching H consumption, rate decreases and as pHseen increases in Figu inre the 10b,c. EPS layer. Chalcopyrite The is oxi- dized,remaining and Fe 3+ andhydrolyzes Cu are andliberated. forms jarosite, The sulf asur shown in the in Figurereduced 10d. state In the is EPS oxidized layer, to S0, and a sulfuractive film matter is isformed used as on the the nucleation chalcopyrite center of surf jarosite.ace, Fethereby2+ is oxidized inhibiting by free the bacteria, leaching of chal- 3+ copyrite.thereby increasingThe copper the Feleachingconcentration rate decreases and redox and potential. pH increases During the in anaphase, the EPS the layer. The re- jarosite sediment is increased, thereby inhibiting the copper leaching process with the rise 3+ mainingin Fe3+ concentration. Fe hydrolyzes Thus, and passivation forms jarosite, of the bacteria–mineral as shown in contactFigure and 10d. noncontact In the EPS layer, ac- tiveleaching matter systems is used depends as the on nucl the accumulationeation center of sulfurof jarosite. on the chalcopyriteFe2+ is oxidized surface. by In free bacteria, therebythe passivation increasing process, the the Fe formation3+ concentration of a sulfur and film redox has a inhibitory potentia effectl. During on the the rapid anaphase, the jarositediffusion sediment of reaction is increased, ions, thus decreasing thereby inhibi the leachingting the rate copper of chalcopyrite. leachingHowever, process with the rise jarosite is the main reason for chalcopyrite passivation. in Fe3+ concentration. Thus, passivation of the bacteria–mineral contact and noncontact leaching systems depends on the accumulation of sulfur on the chalcopyrite surface. In the passivation process, the formation of a sulfur film has a inhibitory effect on the rapid diffusion of reaction ions, thus decreasing the leaching rate of chalcopyrite. However, jar- osite is the main reason for chalcopyrite passivation.
Minerals 20212021,, 11,, x 230 FOR PEER REVIEW 1010 of of 12 12
FigureFigure 10. 10. SchematicSchematic diagram diagram of of chalcopyrite chalcopyrite bioleaching bioleaching and and jarosite jarosite formation. formation. (a) (Adsorptiona) Adsorption bacteriabacteria on on chalcopyrite chalcopyrite surface, ( b) Microenvironment betweenbetween bacteria,bacteria, EPSEPS andand minerals,minerals, ((cc)) FeFe2+2 +was was oxidized oxidized to to Fe Fe3+3 +on on the the cell cell wall wall of of bacteria, bacteria, and and consuming consuming H +H,( +,d )(d Jarosite) Jarosite crystal crystal precipitation. precipita- tion. 4. Conclusions 4. Conclusions(1) The bacteria–mineral contact and noncontact leaching systems coexisted in the chalcopyrite(1) The bacteria–mineral bioleaching process. contact In and the bacteria–mineralnoncontact leaching contact systems leaching coexisted system, in the chalcopyritebacteria oxidized bioleaching elemental process. sulfur In on the the bact surfaceeria–mineral of chalcopyrite contact leaching and enriched system, Fe 3+thein bac- the teriaEPS layer,oxidized which elemental hastened sulfur copper on the leaching. surface Inof thechalcopyrite bacteria–mineral and enriched noncontact Fe3+ inleaching the EPS 3+ layer,system, which dissociative hastened Fe copperoxidized leaching. chalcopyrite, In the bacteria–mineral and it was regenerated noncontact by the leaching bacteria. sys- tem, dissociative(2) In the chalcopyrite Fe3+ oxidized bioleaching chalcopyrite, process, andthe it was formation regenerated of sulfur by the was bacteria. found in both the bacteria–mineral(2) In the chalcopyrite contact bioleaching and the bacteria–mineral process, the formation noncontact of sulfur leaching was systems. found in In both the thebacteria–mineral bacteria–mineral contact contact leaching and the system, bacteria–m the oxidationineral noncontact rate of ore leaching was faster systems. than thatIn the of bacteria–mineralsulfur by Thiobacillus contact thiooxidans leaching. Sulfursystem, was the deposited oxidation onrate the of chalcopyrite ore was faster surface. than that In the of 2− 1− 0 sulfurbacteria–mineral by Thiobacillus noncontact thiooxidans leaching. Sulfur system, was deposited the oxidation on the of chalcopyrite S and S surface.to S induced In the 3+ 4+ 6+ bacteria–mineralby Fe could not noncontact generate S leachingand S system,with a higherthe oxidation valence of state, S2-and consequently S1- to S0 induced inhibiting by Fefurther3+ could copper not generate leaching. S4+ and S6+ with a higher valence state, consequently inhibiting further(3) copper A layer leaching. of sulfur was produced and consequently inhibited the rapid diffusion of 3+ reaction(3) A ions. layer The of sulfur redundant was produced Fe was and hydrolyzed consequently and formed inhibited jarosite. the rapid In the diffusion bacteria– of reactionmineral contactions. The leaching redundant system, Fe3+jarosite was hydrolyzed was separated and formed out from jarosite. the active In the matter bacteria– in the mineralEPS layer contact as a nucleation leaching system, center. Injarosite the bacteria–mineral was separated out noncontact from the leachingactive matter system, in the jarosite crystallized on the sulfur layer of the chalcopyrite surface. EPS layer as a nucleation center. In the bacteria–mineral noncontact leaching system, the jarosite crystallized on the sulfur layer of the chalcopyrite surface. Author Contributions: Conceptualization, P.M.; methodology, P.M. and H.Y.; validation, H.Y.; formal analysis, P.M.; investigation, P.M. and Z.L.; data curation, P.M.; writing—original draft preparation, Author Contributions: Conceptualization, P.M.; methodology, P.M. and H.Y.; validation, H.Y.; for- P.M.; writing—review and editing, P.M., Q.S., A.A. and L.T.; funding acquisition, Z.L. All authors mal analysis, P.M.; investigation, P.M. and Z.L.; data curation, P.M.; writing—original draft prepa- have read and agreed to the published version of the manuscript. ration, P.M.; writing—review and editing, P.M., Q.S., A.A. and L.T.; funding acquisition, Z.L. All authorsFunding: haveThis read research and agreed was funded to the bypublished the National version Key of R&D the manuscript. Program of China (2018YFC1902003). Funding:Institutional This Review research Board was funded Statement: by theNot Nation applicable.al Key R&D Program of China (2018YFC1902003). InstitutionalInformed Consent Review Statement: Board Statement:Not applicable. Not applicable. InformedData Availability ConsentStatement: Statement:The Not studyapplicable. did not report any data. DataAcknowledgments: Availability Statement:We greatly The thank study all did anonymous not report any reviewers data. for their constructive comments, which improved the manuscript. Acknowledgments: We greatly thank all anonymous reviewers for their constructive comments, whichConflicts improved of Interest: the manuscript.The authors declare no conflict of interest. Conflicts of Interest: The authors declare no conflicts of interest.
Minerals 2021, 11, 230 11 of 12
References 1. Brierley, J.A. Acdidophilic thermophilic archaebacteria: Potential application for metals recovery. FEMS Microbiol. Lett. 1990, 75, 287–291. [CrossRef] 2. Petersen, J.; Dixon, D.G. Competitive bioleaching of pyrite and chalcopyrite. Hydrometallurgy 2006, 83, 40–49. [CrossRef] 3. Brierley, J.A.; Brierley, C.L. Present and future commercial applications of biohydrometallurgy. Hydrometallurgy 2001, 59, 233–239. [CrossRef] 4. Silverman, M.P.; Ehrlich, H.L. Microbial formation and degradation of minerals. Adv. Appl. Microbiol. 1964, 6, 153–206. 5. Tributsch, H. Direct versus indirect bioleaching. Hydrometallurgy 2001, 59, 177–185. [CrossRef] 6. Crundwell, F.K. How do bacteria interact with minerals? Hydrometallurgy 2003, 71, 75–81. [CrossRef] 7. Brierley, C.L. Biohydrometallurgical prospects. Hydrometallurgy 2010, 104, 324–328. [CrossRef] 8. Hiroyoshi, N.; Kitagawa, H.; Tsunekawa, M. Effect of solution composition on the optimum redox potential for chalcopyrite leaching in sulfuric acid solutions. Hydrometallurgy 2008, 91, 144–149. [CrossRef] 9. Klauber, C. A critical review of the surface chemistry of acidic ferric sulphate dissolution of chalcopyrite with regards to hindered dissolution. Int. J. Miner. Process. 2008, 86, 1–17. [CrossRef] 10. Kinnunen, H.M.; Heimala, S.; Riekkola-Vanhanen, M.L.; Puhakka, J.A. Chalcopyrite concentrate leaching with biologically produced ferric sulphate. Bioresour. Technol. 2006, 97, 1727–1734. [CrossRef] 11. Rawlings, D.E.; Johnson, B.D. Biomining; Springer: Berlin/Heidelberg, Germany, 2007; pp. 287–301. 12. Yohana, R.; Ballester, A.; María, L.B.; Felisa, G.; Jesús, A.M. Study of bacterial attachment during the bioleaching of pyrite, chalcopyrite, and sphalerite. Geomicrobiology 2003, 20, 131–141. 13. Yang, Y.; Harmer, S.; Chen, M. Synchrotron X-ray photoelectron spectroscopic study of the chalcopyrite leached by moderate thermophiles and mesophiles. Miner. Eng. 2014, 69, 185–195. [CrossRef] 14. Akcil, A.; Ciftci, H.; Deveci, H. Role and contribution of pure and mixed cultures of mesophiles in bioleaching of a pyritic chalcopyrite concentrate. Miner. Eng. 2007, 20, 310–318. [CrossRef] 15. Ahmadi, A.; Schaffie, M.; Manafi, Z.; Ranjbar, M. Electrochemical bioleaching of high grade chalcopyrite flotation concentrates in a stirred bioreactor. Hydrometallurgy 2010, 104, 99–105. [CrossRef] 16. Parker, A.; Klauber, C.; Kougianos, A.; Watling, H.R.; Van-Bronswijk, W. An X-ray photoelectron spectroscopy study of the mechanism of oxidative dissolution of chalcopyrite. Hydrometallurgy 2003, 71, 265–276. [CrossRef] 17. Dutrizac, J.E. Elemental sulphur formation during the ferric chloride leaching of chalcopyrite. Hydrometallurgy 1990, 23, 153–176. [CrossRef] 18. Ghahremaninezhad, A.; Dixon, D.G.; Asselin, E. Kinetics of the ferric–ferrous couple on anodically passivated chalcopyrite (CuFeS2) electrodes. Hydrometallurgy 2012, 125–126, 42–44. [CrossRef] 19. Yao, G.; Wen, J.; Gao, H.; Wang, D. Chalcopyrite bioleaching by moderate thermophilic bacteria and surface passivation. J. Cent. South Univ. (Sci. Technol.) 2010, 41, 1234–1236. (In Chinese) 20. Pan, H.; Yang, H.; Tong, L.; Zhong, C.; Zhao, Y. Control method of chalcopyrite passivation in bioleaching. Trans. Nonferrous Met. Soc. China 2012, 22, 2255–2260. (In Chinese) [CrossRef] 21. Yang, H.; Pan, H.; Tong, L.; Liu, Y. Formation process of biological oxide film on chalcopyrite crystal surface. Acta Metall. Sin. 2012, 48, 1145–1152. (In Chinese) [CrossRef] 22. Lu, X.; Lu, J.; Zhu, C.; Liu, X.; Wang, R.; Li, Q.; Xu, Z. Preliminary study on surface properties of iron sulfate formed by microbially Induced mineralization. Geol. J. China Univ. 2005, 2, 194–198. (In Chinese) 23. Henao, D.M.O.; Godoy, M.A.M. Jarosite pseudomorph formation from arsenopyrite oxidation using Acidithiobacillus ferrooxidans. Hydrometallurgy 2010, 104, 162–168. [CrossRef] 24. Zhu, C.; Lu, J.; Lu, X.; Wang, R.; Li, Q. SEM study on jarosite mediated by thiobacillus ferrooxidans. Geol. J. China Univ. 2005, 11, 234–238. (In Chinese) 25. Bai, S.; Liang, J.; Wang, M.; Zhou, L. Effect of Fe(III) supply rate on the formation of amorphous schwertmannite. Acta Mineral. Sin. 2011, 2, 256–262. (In Chinese) 26. Daoud, J.; Karamanev, D. Formation of jarosite during Fe2+ oxidation by Acidithiobacillus ferrooxidans. Miner. Eng. 2006, 19, 960–967. [CrossRef] 27. Sasaki, K.; Konno, H. Morphology of jarosite-group compounds precipitated from biologically and chemically oxidized Fe ions. Can. Mineral. 2000, 38, 45–56. [CrossRef] 28. Fang, D.; Zhou, L.X. Effect of sludge dissolved organic matter on oxidation of ferrous iron and sulfur by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Water Air Soil Pollut. 2006, 171, 81–94. [CrossRef] 29. Li, J.; Tong, L.; Xia, Y.; Yang, H.; Auwalu, A. Microbial synergy and stoichiometry in heap biooxidation of low-grade porphyry arsenic-bearing gold ore. Extremophiles 2020, 24, 355–364. [CrossRef] 30. Pan, H.; Yang, H.; Chen, S. Conditions for biosorption measuring on chalcopyrite surface. J. Northeast. Univ. (Nat. Sci.) 2010, 31, 999–1002. (In Chinese) 31. Bevilaqua, D.; Lette, A.L.L.C.; Garcia, J.O.; Tuovinen, O.H. Oxidation of chalcopyrite by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans in shake flasks. Process Biochem. 2002, 38, 587–592. [CrossRef] 32. Ghahremaninezhad, A.; Asselin, E.; Dixon, D.G. Electrochemical evaluation of the surface of chalcopyrite during dissolution in sulfuric acid solution. Electrochim. Acta 2010, 55, 5041–5056. [CrossRef] Minerals 2021, 11, 230 12 of 12
33. Klauber, C.; Parker, A.; Van-Bronswijk, W.; Watling, H. Sulphur speciation of leached chalcopyrite surfaces as determined by X-ray photoelectron spectroscopy. Int. J. Miner. Process. 2001, 62, 65–94. [CrossRef] 34. Sand, W.; Gehrke, T. Extracellular polymeric substances mediate bioleaching/biocorrosion via interfacial processes involving iron(III) ions and acidophilic bacteria. Res. Microbiol. 2006, 157, 49–56. [CrossRef] 35. Powers, D.A.; Rossman, G.R.; Schugar, H.J.; Gray, H.B. Magnetic behavior and infrared spectra of jarosite, basic iron sulfate, and their chromate analogs. J. Solid State Chem. 1975, 13, 1–13. [CrossRef] 36. Lazaroff, N.; Sigal, W.; Wasserman, A. Iron oxidation and precipitation of ferric hydroxysulfates by resting Thiobacillus ferrooxidans cells. Appl. Environ. Microbiol. 1982, 43, 924–938. [CrossRef][PubMed] 37. Marel, H.W.; Beutelspacher, H. Atlas of Infrared Spectroscopy of Clay Minerals and Their Admixtures; Elsevier Publishing Company: Amsterdam, The Netherlands, 1976; p. 396.