Two step meso-acidophilic bioleaching of chalcopyrite containing ball mill spillage and removal of the surface passivation layer

Bioleaching of heavy metals from metal tailings utilizing bacteria and fungi: Mechanisms, strengthen measures, and development prospect

Recovering key metals from secondary sources is an indispensable strategy for preventing metal shortages and reducing the risk of toxic releases into the environment. Metal mineral resources continue to be depleted and the global supply chain will face metal scarcity. The use of microorganisms for metal transformation plays an important role in the bioremediation of secondary resources. It shows great potential for development due to its compatibility with the environment and possible cost effectiveness. The results of the study show that the influence of bioleaching processes and effects are mainly analyzed from microorganisms, mineral properties and leaching environmental conditions. In this review article, we elucidate light on the role and mechanisms of fungi and bacteria involved in extracting different metals from tailings, including acidolysis, complexolysis, redoxolysis, and bioaccumulation. Key process parameters that affect the efficiency based bioleaching are discussed, providing referenceable pathways to improve leaching efficiency. The investigation concludes that exploitation of the functional genetic role of microorganisms and their optimal growth conditions can achieve efficient leaching of metals. It was found that the improvement of microbial performance was achieved at the level of mutagenesis breeding, mixed culture microorganisms, and genetics. Moreover, control of leaching system parameters and removal of passivation films can be achieved by adding biochar and surfactants in the leaching system as an effective means to improve tailings leaching. Knowledge about cells with minerals and their detailed interactions at the molecular level is still relatively scarce and the field could be deepened and this area needs to be further explored in the future. The challenges and the key issues associated with the bioleaching technology development are elaborated as a green and effective bioremediation strategy for the environment and prospects for imminent are also highlighted.

Effects of Extracellular Polymeric Substances and Specific Compositions on Enhancement of Copper Bioleaching Efficiency from Waste Printed Circuit Boards

Bioleaching has been proven to be an efficient and environment-friendly method for processing metalliferous ore and waste printed circuit boards (PCBs), a type of urban mine waste. Extracellular polymeric substances (EPS) play a major role in the attachment of bacteria to the surface of sulfide minerals. However, there are few reports on the effects of EPS components on the bioleaching of metals from PCBs. In this study, synthetic EPS were used to investigate the effects of the composition of exo-polymers on the bioleaching of copper from waste PCBs, including the process efficiency. The copper extraction rate in bioleaching assays with synthetic EPS was 11.7% greater than in those without synthetic EPS. Moreover, the composition of EPS was proven to be a crucial factor affecting the efficiency of copper bioleaching, with EPS containing arginine yielding the highest recovery (95.2% copper). Under the condition of 0.5 g/L synthetic EPS added at the early stage of log phase, the copper leaching efficiency from waste PCBs was highly improved. This study provides important insights into how to analyze the working mechanisms of EPS for a better recovery efficiency.

Bioleaching and Electrochemical Behavior of Chalcopyrite by a Mixed Culture at Low Temperature

Low-temperature biohydrometallurgy is implicated in metal recovery in alpine mining areas, but bioleaching using microbial consortia at temperatures <10°C was scarcely discussed. To this end, a mixed culture was used for chalcopyrite bioleaching at 6°C. The mixed culture resulted in a higher copper leaching rate than the pure culture of Acidithiobacillus ferrivorans strain YL15. High-throughput sequencing technology showed that Acidithiobacillus spp. and Sulfobacillus spp. were the mixed culture's major lineages. Cyclic voltammograms, potentiodynamic polarization and electrochemical impedance spectroscopy unveiled that the mixed culture enhanced the dissolution reactions, decreased the corrosion potential and increased the corrosion current, and lowered the charge transfer resistance and passivation layer impedance of the chalcopyrite electrode compared with the pure culture. This study revealed the mechanisms via which the mixed culture promoted the chalcopyrite bioleaching.

An integrated insight into bioleaching performance of chalcopyrite mediated by microbial factors: Functional types and biodiversity

Six artificial communities with different function or biodiversity were reconstructed by six typical bioleaching species for chalcopyrite leaching. Absence of sulfur oxidizers in communities significantly reduced copper extraction rates, and low diversity communities also exhibited slightly poor bioleaching performances. The variations of pH, redox potential, ferrous and copper ions indicated that the community with both sulfur oxidizers and high diversity showed fast adaptation to the environment and rapid dissolution of chalcopyrite. Integrated analysis of mineralogical and microbial parameters demonstrated that functional types of microorganisms made more contributions in mediating chalcopyrite dissolution than microbial diversity. Further correlation analysis between microbial types and chalcopyrite dissolution performances showed that sulfur oxidizers, especially Acidithiobacillus caldus, could greatly accelerate chalcopyrite dissolution by regulating solution physicochemical factors, such as redox potential and pH. This study provided a theoretical basis for improving bioleaching efficiency by balancing microbial functional types and biodiversity.

Effect of biogenic jarosite on the bio-immobilization of toxic elements from sulfide tailings

The discharge of toxic elements from tailings soils in the aquatic environments occurs chiefly in the presence of indigenous bacteria. The biotic components may interact in the opposite direction, leading to the formation of a passivation layer, which can inhibit the solubility of the elements. In this work, the influence of jarosite on the bio-immobilization of toxic elements was studied by native bacteria. In batch experiments, the bio-immobilization of heavy metals by an inhibitory layer was examined in the different aquatic media using pure cultures of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. A variety of analyses also investigated the mechanisms of metals bio-immobilization. Among different tests, the highest metal solubility yielded 99% Mn, 91% Cr, 95% Fe, and 78% Cu using A. ferrooxidans in 9KFe medium after ten days. After 22 days, these percentages decreased down to 30% Mn and about 20% Cr, Fe, and Cu, likely due to metal immobilization by biogenic jarosite. The formation of jarosite was confirmed by an electron probe micro-analyzer (EPMA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The mechanisms of metal bio-immobilization by biogenic jarosite from tailings soil confirmed three main steps: 1) the dissolution of metal sulfides in the presence of Acidithiobacillus bacteria; 2) the nucleation of jarosite on the surface of sulfide minerals; 3) the co-precipitation of dissolved elements with jarosite during the bio-immobilization process, demonstrated by a structural study for jarosite. Covering the surface of soils by the jarosite provided a stable compound in the acidic environment of mine-waste.

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.

Bioleaching of copper sulfide minerals assisted by microbial fuel cells

A proof-of-concept of copper sulfide mineral bioleaching assisted by microbial fuel cells (MFCs) was demonstrated in current study. Simultaneous copper extraction and electricity generation were obtained in this bioleaching process, providing a novel approach for copper sulfide mineral bioleaching. Compared with bioleaching of a mixture of chalcopyrite concentrate and porphyry molybdenite, bioleaching of chalcopyrite concentrate achieved higher coulomb production but lower copper extraction concentration. After 320 days bioleaching of chalcopyrite concentrate, the copper ion concentration in bioleaching solution was 244.2 mg/L and the average coulomb production was 4.4 ± 2.2C/d. The introduction of MFCs into bioleaching processes promoted copper extraction, mainly via the decrease of pH deriving from the anodic sulfide/sulfur oxidation.

Dissolution and Passivation of Chalcopyrite during Bioleaching by Acidithiobacillus ferrivorans at Low Temperature

Our knowledge on the dissolution and passivation mechanisms of chalcopyrite during bioleaching at low temperature has been limited to date. In this study, an Acidithiobacillus ferrivorans strain with high tolerance to heavy metals and UV radiation was used for chalcopyrite bioleaching. At 6 °C, no apparent precipitate was detected on the mineral surface after bioleaching using a scanning electron microscope (SEM). X-ray diffraction (XRD) revealed that the ore residue contained only chalcopyrite and quartz. X-ray photoelectron spectroscopy (XPS) analysis revealed that the content of S0 on the mineral surface remained low and the ratio of SO42− decreased from 46.7% to 20.9%, but the amount of Sn2− increased from 10.4% to 21.4% after bioleaching. Expression of five critical iron- and sulfur-oxidation genes during bioleaching was analyzed using quantitative real-time PCR. The gene rusA had higher expression in the mid-log phase than in the stationary phase but hdrA and cyoC1 showed an opposite trend. All genes had higher expression at 6 °C than at 28 °C, so as to compensate for the decline in the enzyme activities. The study revealed that polysulfide was the most plausible passivating substance at 6 °C, and the strain can maintain the iron- and sulfur-oxidation activities during low-temperature bioleaching.

Environmentally friendly recovery of valuable metals from spent coin cells through two-step bioleaching using Acidithiobacillus thiooxidans

The technology for recycling the spent coin cells is pressing needed due to a large amount of generated spent coin cells. However, there is little information about the recycling technology of spent coin cells. In this work, a two-step bioleaching method for recovery of metals from spent coin cells by Acidithiobacillus thiooxidans is performed for the first time. In this regard, the growth characteristics of A. thiooxidans was investigated in pure culture and during the two-step bioleaching approach. The highest recovery of Li, Co and Mn was achieved at a pulp density of 30 g L^-1, in values of 99%, 60%, and 20%, respectively. The structural analyzes confirmed the progress of bioleaching process. In addition, the kinetics models showed that the chemical reaction was the rate-controlling step of the two-step bioleaching of spent coin cells. The comparative results between bioleaching and chemical leaching showed that Acidithiobacillus thiooxidans can enhance the leaching of metals. Toxicity characteristic leaching procedure of the spent coin cells powder demonstrated that the bioleached residue met the environmental limitations for safe disposal. In fact, bioleaching is an effective and promising route to reduce the environmental hazard of spent coin cells.

The detoxification potential of ferric ions for bioleaching of the chalcopyrite associated with fluoride-bearing gangue mineral

Fluoride toxicity to microorganisms was a predominant factor contributing to the failure of a commercial scale bioleach heap. An integrated control strategy for fluoride complexation without jarosite generation by stepwise adding ferric ions was first proposed to enable the bioleaching of the chalcopyrite associated with fluoride-bearing gangue mineral by Acidithiobacillus ferrooxidans. Chemical speciation calculation revealed that with the presence of Fe³⁺, the concentration of the main lethal fluoride to microorganism, HF, decreased dramatically. The pure culture study showed that the detrimental effect of fluoride on microorganism was eliminated by increasing the molar ratio of Fe³⁺/F^- to 3:1. Furthermore, chalcopyrite bioleaching experiment revealed the minimum Fe³⁺/F^- molar ratio that enabled the bioleaching was 6:1. Stepwise addition was an effective way to promote a balanced system and avoid the formation of jarosite caused by the excessive Fe³⁺. Above all, the introduction of Fe³⁺ is a feasible method for reducing the fluoride toxicity during the bioleaching of chalcopyrite, shedding light on the industrial applications.

Intensified bioleaching of chalcopyrite by communities with enriched ferrous or sulfur oxidizers

The chalcopyrite bioleaching by enriched ferrous or sulfur oxidizers was investigated. The bioleaching was also intensified three times by the enriched communities. The results indicated that copper recoveries extracted by the enriched ferrous and sulfur oxidizers (Fe-O and S-O) were 38.87% and 43.13%, compared with that by the original community (35.35%). The positive effects of re-introducing S-enriched community to Fe-O and S-O groups were observed with copper extraction rates up to 41.67% and 46.45%. CCA indicated that the community dynamics intensified by S-enriched community was closer to that of the no re-inoculated one, but the Fe-enriched community drove a great fluctuation. A mechanism model for S-enriched community intensifying chalcopyrite bioleaching was proposed. More sulfur oxidizers in community slowed down jarosite formation and maintained lower ORP, which was propitious to chalcopyrite dissolution. Meanwhile, they accelerated S⁰ decomposition and decreased pH, which promoted acid leaching of chalcopyrite at a low cost.

Recovery of Al, Cr and V from steel slag by bioleaching: Batch and column experiments

Steel slag is a major by-product of the steel industry and a potential resource of technology critical elements. For this study, a basic oxygen furnace (BOF) steel slag was tested for bacterial leaching and recovery of aluminium (Al), chromium (Cr), and vanadium (V). Mixed acidophilic bacteria were adapted to the steel slag up to 5% (w/v). In the batch tests, Al, Cr, and V were bioleached significantly more from steel slag than in control treatments. No statistical difference was observed arising from the duration of the leaching (3 vs 6 d) in the batch tests. Al and Cr concentrations in the leachate were higher for the smaller particle size of the steel slag (<75 μm), but no difference was observed for V. In the column tests, no statistical difference was found for pH, Al, Cr and V between the live culture (one-step bioleaching) and the supernatant (two-step bioleaching). The results show that the culture supernatant can be effectively used in an upscaled industrial application for metal recovery. If bioleaching is used in the 170-250 million tonnes of steel slag produced per year globally, significant recoveries of metals (100% of Al, 84% of Cr and 8% of V) can be achieved, depending on the slag composition. The removal and recovery percentages of metals from the leachate with Amberlite^®IRA-400 are relatively modest (<67% and <5%, respectively), due to the high concentration of competing ions (SO₄^2-, PO₄^3-) in the culture medium. Other ion exchange resins can be better suited for the leachate or methods such as selective precipitation could improve the performance of the resin. Further research is needed to minimise interference and maximise metal recovery.

A novel bioreactor system for simultaneous mutli-metal leaching from industrial pyrite ash: Effect of agitation and sulphur dosage

Simultaneous multi-metal leaching from industrial pyrite ash is reported for the first time using a novel bioreactor system that allows natural diffusion of atmospheric O₂ and CO₂ along with the required temperature maintenance. The waste containing economically important metals (Cu, Co, Zn & As) was leached using an adapted consortium of meso-acidophilic Fe²⁺ and S oxidising bacteria. The unique property of the sample supported adequate growth and activity of the acidophiles, thereby, driving the (bio) chemical reactions. Oxido-reductive potentials were seen to improve with time and the system's pH lowered as a result of active S oxidation. Increase in sulphur dosage (>1g/L) and agitation speed (>150rpm) did not bear any significant effect on metal dissolution. The consortium was able to leach 94.01% Cu (11.75% dissolution/d), 98.54% Co (12.3% dissolution/d), 75.95% Zn (9.49% dissolution/d) and 60.80% As (7.6% dissolution/d) at 150rpm, 1g/L sulphur, 30°C in 8days.

Synergistic effect of biogenic Fe3+ coupled to S° oxidation on simultaneous bioleaching of Cu, Co, Zn and As from hazardous Pyrite Ash Waste

Pyrite ash, a waste by-product formed during roasting of pyrite ores, is a good source of valuable metals. The waste is associated with several environmental issues due to its dumping in sea and/or land filling. Although several other management practices are available for its utilization, the waste still awaits and calls for an eco-friendly biotechnological application for metal recovery. In the present study, chemolithotrophic meso-acidophilic iron and sulphur oxidisers were evaluated for the first time towards simultaneous mutli-metal recovery from pyrite ash. XRD and XRF analysis indicated higher amount of Hematite (Fe₂O₃) in the sample. ICP-OES analysis indicated concentrations of Cu>Zn>Co>As that were considered for bioleaching. Optimization studies indicated Cu - 95%, Co - 97%, Zn - 78% and As - 60% recovery within 8days at 10% pulp density, pH - 1.75, 10% (v/v) inoculum and 9g/L Fe²⁺. The productivity of the bioleaching system was found to be Cu - 1696ppm/d (12% dissolution/d), Co - 338ppm/d (12.2% dissolution/d), Zn k 576ppm/d (9.8% dissolution/d) and As - 75ppm/d (7.5% dissolution/d). Synergistic actions for Fe²⁺ - S° oxidation by iron and sulphur oxidisers were identified as the key drivers for enhanced metal dissolution from pyrite ash sample.

Co-culture microorganisms with different initial proportions reveal the mechanism of chalcopyrite bioleaching coupling with microbial community succession

The effect of co-culture microorganisms with different initial proportions on chalcopyrite bioleaching was investigated. Communities were rebuilt by six typical strains isolated from the same habitat. The results indicated, by community with more sulfur oxidizers at both 30 and 40°C, the final copper extraction rate was 19.8% and 6.5% higher, respectively, than that with more ferrous oxidizers. The variations of pH, redox potential, ferrous and copper ions in leachate also provided evidences that community with more sulfur oxidizers was more efficient. Community succession of free and attached cells revealed that initial proportions played decisive roles on community dynamics at 30°C, while communities shared similar structures, not relevant to initial proportions at 40°C. X-ray diffraction analysis confirmed different microbial functions on mineral surface. A mechanism model for chalcopyrite bioleaching was established coupling with community succession. This will provide theoretical basis for reconstructing an efficient community in industrial application.

Insights to the effects of free cells on community structure of attached cells and chalcopyrite bioleaching during different stages

The effects of free cells on community structure of attached cells and chalcopyrite bioleaching by Acidithiobacillus sp. during different stages were investigated. The attached cells of Acidithiobacillus thiooxidans owned the community advantage from 14thd to the end of bioprocess in the normal system. The community structure of attached cells was greatly influenced in the free cells-deficient systems. Compared to A. thiooxidans, the attached cells community of Acidithiobacillus ferrooxidans had a higher dependence on its free cells. Meanwhile, the analysis of key biochemical parameters revealed that the effects of free cells on chalcopyrite bioleaching in different stages were diverse, ranging from 32.8% to 64.3%. The bioleaching contribution of free cells of A. ferrooxidans in the stationary stage (8-14thd) was higher than those of A. thiooxidans, while the situation was gradually reversed in the jarosite passivation inhibited stage (26-40thd). These results may be useful in guiding chalcopyrite bioleaching.

Current scenario of chalcopyrite bioleaching: a review on the recent advances to its heap-leach technology

Chalcopyrite is the primary copper mineral used for production of copper metal. Today, as a result of rapid industrialization, there has been enormous demand to profitably process the low grade chalcopyrite and "dirty" concentrates through bioleaching. In the current scenario, heap bioleaching is the most advanced and preferred eco-friendly technology for processing of low grade, uneconomic/difficult-to-enrich ores for copper extraction. This paper reviews the current status of chalcopyrite bioleaching. Advanced information with the attempts made for understanding the diversity of bioleaching microorganisms; role of OMICs based research for future applications to industrial sectors and chemical/microbial aspects of chalcopyrite bioleaching is discussed. Additionally, the current progress made to overcome the problems of passivation as seen in chalcopyrite bioleaching systems have been conversed. Furthermore, advances in the designing of heap bioleaching plant along with microbial and environmental factors of importance have been reviewed with conclusions into the future prospects of chalcopyrite bioleaching.

Improved chalcopyrite bioleaching by Acidithiobacillus sp. via direct step-wise regulation of microbial community structure

A direct step-wise regulation strategy of microbial community structure was developed for improving chalcopyrite bioleaching by Acidithiobacillus sp. Specially, the initial microbial proportion between Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was controlled at 3:1 with additional 2 g/L Fe(2+) for faster initiating iron metabolism. A. thiooxidans biomass was fed via a step-wise strategy (8-12th d) with the microbial proportion 1:1 for balancing community structure and promoting sulfur metabolism in the stationary phase. A. thiooxidans proportion was further improved via another step-wise feeding strategy (14-18th d) with the microbial proportion 1:2 for enhancing sulfur metabolism and weakening jarosite passivation in the later phase. With the community structure-shift control strategy, biochemical reaction was directly regulated for creating a better balance in different phases. Moreover, the final copper ion was increased from 57.1 to 93.2 mg/L, with the productivity 2.33 mg/(Ld). The novel strategy may be valuable in optimization of similar bioleaching process.

Microbial community succession mechanism coupling with adaptive evolution of adsorption performance in chalcopyrite bioleaching

The community succession mechanism of Acidithiobacillus sp. coupling with adaptive evolution of adsorption performance were systematically investigated. Specifically, the μmax of attached and free cells was increased and peak time was moved ahead, indicating both cell growth of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was promoted. In the mixed strains system, the domination courses of A. thiooxidans was dramatically shortened from 22th day to 15th day, although community structure finally approached to the normal system. Compared to A. ferrooxidans, more positive effects of adaptive evolution on cell growth of A. thiooxidans were shown in either single or mixed strains system. Moreover, higher concentrations of sulfate and ferric ions indicated that both sulfur and iron metabolism was enhanced, especially of A. thiooxidans. Consistently, copper ion production was improved from 65.5 to 88.5 mg/L. This new adaptive evolution and community succession mechanism may be useful for guiding similar bioleaching processes.

Catalytic effect of light illumination on bioleaching of chalcopyrite

The influence of visible light exposure on chalcopyrite bioleaching was investigated using Acidithiobacillus ferrooxidans. The results indicated, in both shake-flasks and aerated reactors with 8500-lux light, the dissolved Cu was 91.80% and 23.71% higher, respectively, than that in the controls without light. The catalytic effect was found to increase bioleaching to a certain limit, then plateaued as the initial chalcopyrite concentration increased from 2% to 4.5%. Thus a balanced mineral concentration is highly amenable to bioleaching via offering increased available active sites for light adsorption while eschewing mineral aggregation and screening effects. Using semiconducting chalcopyrite, the light facilitated the reduction of Fe(3+) to Fe(2+) as metabolic substrates for A.ferrooxidans, leading to better biomass, lower pH and redox potential, which are conducive to chalcopyrite leaching. The light exposure on iron redox cycling was further confirmed by chemical leaching tests using Fe(3+), which exhibited higher Fe(2+) levels in the light-induced system.

Effect of dissimilatory Fe(III) reducers on bio-reduction and nickel-cobalt recovery from Sukinda chromite-overburden

The effect of an adapted dissimilatory iron reducing bacterial consortium (DIRB) towards bio-reduction of Sukinda chromite overburden (COB) with enhanced recovery of nickel and cobalt is being reported for the first time. The remarkable ability of DIRB to utilize Fe(III) as terminal electron acceptor reducing it to Fe(II) proved beneficial for treatment of COB as compared to previous reports for nickel leaching. XRD studies showed goethite as the major iron-bearing phase in COB. Under facultative anaerobic conditions, goethite was reduced to hematite and magnetite with the exposure of nickel oxide. FESEM studies showed DIRB to be associated with COB through biofilm formation with secondary mineral precipitates of magnetite deposited as tiny globular clusters on the extra polymeric substances. The morphological and mineralogical changes in COB, post DIRB application, yielded a maximum of 68.5% nickel and 80.98% cobalt in 10 days using 8M H2SO4.