Copper Bioleaching Research Articles

Novel Indigenous Strains and Communities with Copper Bioleaching Potential from the Amolanas Mine, Chile

Bioleaching, a process catalyzed by acidophilic microorganisms, offers a sustainable approach to metal extraction from sulfide minerals. Chalcopyrite, the world’s most abundant copper sulfide, presents challenges due to surface passivation limiting its bioleaching efficiency. Also, indigenous species and microbial communities may present high copper extraction rates and offer new possibilities for application in bioleaching processes. This study examines the bioleaching potential of microbial isolates and communities obtained from Amolanas Mine in Chile. Samples were collected, cultivated, and identified by Sanger sequencing. The bioleaching potential and biofilm formation of isolates and enrichments were evaluated on pyrite and chalcopyrite. The results show the isolation of nine Leptospirillum and two Acidithiobacillus strains. The bioleaching experiments demonstrated good copper bioleaching potentials of the Leptospirillum I2CS27 strain and EICA consortium (composed mainly of Leptospirillum ferriphilum, Acidiphilium sp., and Sulfobacillus thermosulfidooxidans), with 11% and 25% copper recovery rates, respectively. Microbial attachment to the surface mineral was not mandatory for increasing the bioleaching rates. Our findings underscore the importance of indigenous microbial communities in enhancing copper bioleaching efficiency.

Bioleaching of sewage sludge for copper extraction using Acidithiobacillus thiooxidans: Optimization and ecological risk assessment

In this study, Acidithiobacillus thiooxidans was used for the bioleaching of copper (Cu) from sewage sludge. In order to find optimization conditions, three factors including solid-to-liquid ratio (S/L) (0.01-0.2 %(w/v)), initial element sulfur (S0) (1–10 g/L), and initial pH (1–3) have been investigated. Based on response surface methodology (RSM) determined a significant reduced quadratic model with a p-value of 0.0022 (<0.05 significant level). The maximum Cu recovery was 85.3% in the optimum condition of S/L = 0.16% (w/v), S0 = 8.2 g/L, and pH = 1.4. Furthermore, a kinetic study based on a shrinking core model was performed and the result showed that chemical reaction was rate limiting in the extraction. Toxicity Characteristic Leaching Procedure (TCLP) results after bioleaching showed the bioleaching process detoxified sludge and the bioleached sludge residue was well within the regulatory limits for disposal. The germination seed with adding bioleached and unbioleached sludge to the soil was determined. Various parameters such as Germination Index (GI), Tolerance Index (TI), Vigor Index (VI), and stem length showed that the sewage sludge indices significantly increased than the sample soil with unbioleached sludge.

Bioleaching of Chalcopyrite by a New Strain Leptospirillum ferrodiazotrophum Ksh-L Isolated from a Dump-Bioleaching System of Kashen Copper-Molybdenum Mine

A new strain of Leptospirillum sp. Ksh-L was isolated from a dump-bioleaching system of the Kashen copper-molybdenum mine (South Caucasus). Ksh-L is an obligate chemolithoautotroph, capable of oxidizing ferrous iron (Fe2+). Cells are Gram-negative and vibrio- or spirillum-shaped of a 0.5–3 µm size. The optimal conditions for the growth are 35 °C and pH 1.6–1.8. Cu2+ and Zn2+ have different effects on the oxidizing ability of the Leptospirillum sp. Ksh-L culture depending on the phase of growth and concentration of Fe2+. Under the conditions of gradually increasing the concentration of copper in the medium, during 4–5 successive subculturing experiments, it was possible to obtain an adapted culture of Leptospirillum sp. Ksh-L, capable of growing in the medium in the presence of up to 400 mM Cu2+. A bioleaching experiment indicates that Ksh-L can efficiently oxidize chalcopyrite. However, the bioleaching of copper from chalcopyrite by Leptospirillum ferrodiazotropum Ksh-L increased about 1.8 times in association with At. thiooxidans ATCC 19377. Phylogenetic analysis based on 16S rRNA gene sequences (GenBank ID ON226845) shows that strain Ksh-L forms a single cluster into Group III. The strain possesses 99.59%, 99.52%, and 96.60% sequence similarity with the strains YTW-96-06, YTW-66-06, and Leptospirillum ferrodiazotrophum 5C in Group III, respectively.

Investigating the impact of inoculation on bioleaching of copper flotation concentrate using a continuous reactor at pilot scale - study case: Tizert deposit

The world is witnessing a major challenge of energy transition which involves the decline of fossil fuels specifically, but which increasingly calls on metallic resources, base metals, mainly copper. The main methods of processing copper minerals are pyrometallurgical and hydrometallurgical processes. Biohydrometallurgy appeared as a very interesting and promising alternative way. In this context, the bioleaching process was studied for the treatment and upgrading of the Tizert concentrate from the Tizert deposit, located 160 km southeast of Agadir, Morocco. Chemical, mineralogical and metagenomic characterizations were carried out on samples from the Tizert deposit. Metagenomic analysis of deposit samples revealed the abundance of genera Paenibacillus (11.38 %), followed by Phynylobacterium (7.54 %) when DSM 670 medium was used while Acidithiobacillus (41.48 %) and Pseudomonas (35.01 %) were abundant when DSM 71 medium was used, indicating the need to use selected consortium species for copper bioleaching experiments. Inoculation with the three species Acidithiobacillus ferrooxidans DSM 583, Leptospirillum ferriphilum DSM 14647 and Acidithiobacillus thiooxidans DSM 14887 was carried out. Laboratory scale leaching experiments with and without inoculation with the bacterial consortium were carried out on the copper concentrate obtained by flotation pretreatment, to compare the copper leaching behavior and yield. Inoculation with exogenous bioleaching bacteria improved the copper yield to 91 % compared to the leaching process without inoculation. These results were confirmed by a pilot-scale study with a copper yield of 95 %.

Indirect in situ bioleaching is an emerging tool for accessing deeply buried metal reserves, but can the process be managed? – A case study of copper leaching at 1 km depth

Copper is a strategic raw material widely needed for electrification. One possibility to diversify the supply to answer the market demand is to produce copper with in situ technology. In this study, feasibility of in situ bioleaching of copper was tested in a deep subsurface deposit. During in situ bioleaching of copper, copper is leached using a biologically produced ferric iron solution, which is recycled back to the in situ reactor after valuable metals are recovered, after which the solution is re-oxidized by iron-oxidizing microorganisms (IOB). A rock reactor was constructed in the Rudna Mine at ca 1 km depth and the microbiology and hydrogeochemistry of the water circulated through the reactor after blasting for fracturing the rock was monitored over time. The test site was rich in carbonates requiring large quantities of acid to remove the buffering capacity. The bacterial, archaeal and fungal communities in the rock reactor were monitored and characterized by quantitative polymerase chain reaction (qPCR) and amplicon sequencing, and acidophilic, iron oxidizing activity of the microbial communities during operation and pre- and post-operation phases was tested by cultivation. No acidophilic iron oxidizers were detected in the water samples during construction of the pilot reactor. Acidic leaching solution originating from the underground ferric iron generating bioreactor (FIGB) contained acidophilic IOB, which were also viable after the leach liquor was returned from the rock reactor. In the post-operation phase, when the rock reactor was neutralized with CaCO3/Ca(HCO3)2 solution, to inhibit the acidophilic IOB, iron oxidizing microorganisms were still present in the effluent solution one week after termination of the leaching and start of neutralization. Therefore, the post-operation phase needs further attention to completely stop the activity of added microorganisms. Copper was abundantly leached during the acid wash and leaching phases, proving the concept of deep in situ bioleaching.

Regulatory-systemic approach in Aspergillus niger for bioleaching improvement by controlling precipitation.

In the context of e-waste recycling by fungal bioleaching, nickel and cobalt precipitate as toxic metals by oxalic acid, whereas organic acids, such as citric, act as a high-performance chelating agent in dissolving these metals. Oxalic acid elimination requires an excess and uneconomical carbon source concentration in culture media. To resolve this issue, a novel and straightforward systems metabolic engineering method was devised to switch metabolic flux from oxalic acid to citric acid. In this technique, the genome-scale metabolic model of Aspergillus niger was applied to predicting flux variability and key reactions through the calculation of multiple optimal solutions for cellular regulation. Accordingly, BRENDA regulators and a novel molecular docking-oriented approach were defined a regulatory medium for this end. Then, ligands were evaluated in fungal culture to assess their impact on organic acid production for bioleaching of copper and nickel from waste telecommunication printed circuit boards. The protein structure of oxaloacetate hydrolase was modeled based on homology modeling for molecular docking. Metformin, glutathione, and sodium fluoride were found to be effective as inhibitors of oxalic acid production, enabling the production of 8100 ppm citric acid by controlling cellular metabolism. Indirect bioleaching demonstrated that nickel did not precipitate, and the bioleaching efficiency of copper and nickel increased from 40% and 24% to 61% and 100%, respectively. Bioleaching efficiency was evaluated qualitatively by FE-SEM, EDX, mapping, and XRD analysis. KEY POINTS: • A regulatory-systemic procedure for controlling cellular metabolism was introduced • Metformin inhibited oxalic acid, leading to 8100 ppm citric acid production • Bioleaching of copper and nickel in TPCBs improved by 21% and 76.

Bioleaching of chalcopyrite using native Acidithiobacillus ferrooxidans isolated in a mining area in Kitwe Zambia

This study aimed to assess the influence of the physical-chemical factors (particle size, shake flask speed, starting pH, and pulp density) in bioleaching of Zambian chalcopyrite using a novel native isolated Acidithiobacillus ferrooxidans strain DJN1 2021 from samples collected within mining area at Copper Nkana slag dump also known as the Black Mountain in Kitwe, Copperbelt Province in Zambia. The bacterium isolation was done using the modified 9 K selective media and was identified as A. ferrooxidans by using conventional procedures and 16S rRNA gene sequencing. The resulting sequences were analyzed by trimming and generating consensus sequences using Bio-edit software. Blasting results produced a significant alignment of 99.6% similarity with the corresponding sequences of A. ferrooxidans in GenBank. The phylogenetic analysis entails that the isolated strain was identified as A. ferrooxidans and named A. ferrooxidans strain DJN1 2021 with accession number MZ713091. Bioleaching of chalcopyrite (CuFeS2) by A. ferrooxidans (DJN1 2021) was conducted in shake flasks (100 ml) with a 9 K medium. The experiments were tested to optimize the initial pH, particle size, pulp density, and shake flask speed in the recovery of copper from its ore. The results revealed that all of the factors significantly influence the bioleaching process. When the initial pH was 1.8, copper was extracted at the rate of 30.6% within 30 bioleaching days. This was the maximum dissolution observed. The effect of revolution speed in the three different shake flask speeds (i.e. 50 rpm, 90 rpm, and 150 rpm) showed a significant difference in the rate of copper dissolution. A marked difference was observed between shake flask speeds of 50 rpm and 90 rpm with dissolutions of 29.4% and 30.0% respectively. In experiments to look into the effect of particle size, two size fractions were subjected to bioleaching on a shake flask, i.e. (<45 and 45-<63) µm. Results showed that the (45-<63) µm size fraction gave the highest copper extraction of 29.2%. A pulp density of 6% produced the highest extraction of 32.6%. These findings reveal that this novel native A. ferrooxidans strain DJN1 2021 has the potential to bioleaching of copper from chalcopyrite upon optimization in a bioreactor.

IRON REMOVAL FROM LADEN BIOLEACHING SOLUTION BY PROCESSES OF SOLVENT EXTRACTION AND MAGNETITE SYNTHESIS

Laden leach solution, generated from bioleaching of pyrometallurgical copper slags with a mixed culture of moderately thermophilic bacteria in a bioreactor, contains several base metals (Cu, Co, Zn) and a very high concentration of iron (33,9 g/ L). Further processing of cobalt and zinc to the respective final products requires preparatory iron removal from the laden leach solution. The direct iron removal from that solution as goethite was unacceptable because of the significant co-precipitation of copper and cobalt from the solution. The main aim of this paper is to study magnetite (Fe3O4) synthesis as an approach for iron removal to a value-added product as a step of the processing of a laden solution generated due to the bioleaching of non-ferrous metals in a bioreactor. Ferrous iron oxidation to ferric state was efficient when the addition of H2O2 (30 %) was combined with maintaining the pH 3,1-3,3 with NaOH and air purging. Solvent extraction with 25 % D2EHPA and 7,5 % TBP dissolved in kerosene efficiently separated the dissolved iron and the base metals from the processed solution. However, in the presence of H2, the iron was stripped from the organic solvent with low acid consumption. The applied precise control of the chemical precipitation and oxidation processes at 50 degrees Celsius allowed the iron content (11,7 g/ L) in the stripping solution to be removed efficiently as magnetite (Fe3O4). Based on the chemical content of iron, copper and sulphur, the synthesised nanoparticles of magnetite could be applicable in many sectors (steel, chemical, and electronics).

Sessile Lifestyle Offers Protection against Copper Stress in Saccharolobus solfataricus.

Some archaea from the genus Sulfolobus are important for bioleaching of copper, where metal resistant microorganisms are required. Biofilm generation is one of the ways microorganisms cope with some stimuli in nature, including heavy metals. The response to external factors, particularly in the biofilm form of life, is still underexplored in archaea. To explore how model thermoacidophilic archaeon Saccharolobus solfataricus faces copper stress during this lifestyle, changes in biofilms were studied using crystal violet staining, confocal fluorescence microscopy, and qPCR approaches. It was found that biofilm formation reached a maximum at 0.5 mM Cu, before starting to decrease at higher metal concentrations. The morphology of biofilms at 0.5 mM Cu was observed to be different, displaying lower thickness, different sugar patterns, and higher amounts of cells compared to standard growing conditions. Furthermore, copA, which is responsive to intracellular Cu concentration, was downregulated in biofilm cells when compared with planktonic cells exposed to the same metal concentration. The latest results suggests that cells in biofilms are less exposed to Cu than those in planktonic culture. In a PolyP-deficient strain, Cu was not able to induce biofilm formation at 0.5 mM. In summary, the findings reported here suggest that the biofilm form of life confers S. solfataricus advantages to face stress caused by Cu.Biofilm formation remains a relatively unexplored topic in archaeal research. Therefore, this knowledge in model organisms such as S. solfataricus, and how they use it to face stress, could be of great importance to engineer organisms with improved capabilities to be applied in biotechnological processes, such as bioleaching of metals.

Multi-Objective Optimization of Copper Bioleaching: Comparative Study of Pure and Co-Cultured Cultivation.

Bioleaching is a practical method to recover metals from low-grade mineral sulfides. The most frequent bacteria involved in the bioleaching of metals from ores are Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Experimental design is a method through which the optimum activity condition will be obtained, avoiding numerous trials and errors. This study aimed to optimize the bioleaching condition of two indigenous iron- and sulfur-oxidizing bacteria from the Meydouk mine, Iran, and evaluate their function in a semi-pilot operation in pure and mixed cultures. After treatment with sulfuric acid, the bacterial DNA was extracted, and further 16S rRNA was sequenced to characterize the bacterial species. The cultivation condition of these bacteria was optimized using Design-expert (6.1.1 version) software. The copper recovery rate and the differentiation in the ORP rate in the percolation columns were also investigated. These strains were isolated from the Meydouk mine for the first time. 16S rRNA analysis revealed that both bacteria belong to the Acidithiobacillus genus. The factors with the most significant impact on Acidithiobacillus ferrooxidans with their optimum level were temperature=35 °C, pH=2.5, and initial FeSO4 concentration=25 g.L-1. Also, initial sulfur concentration had the most significant impact on Acidithiobacillus thiooxidans with the optimum level of 35 g.L-1. Moreover, the mixed culture determined higher bioleaching efficiency compared with the case of employing the pure cultures. Utilizing a mixture of both bacteria, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans elevated the Cu recovery rate due to the synergetic function of the strains. Also, introducing an initial dosage of sulfur and pre-acidification could elevate metal recovery efficiency.

Understanding the mechanism of microcrack-enhanced bioleaching of copper

Investigations on the microcrack distribution characteristics and bioleaching behaviors of particles were conducted to obtain better bioleaching efficiency and deepen the mechanism understanding. Results indicate that comminution by high-pressure grinding roll (HPGR) is the desirable method for obtaining particles with more abundant and wider microcracks. Fixing the HPGR pressure at 4 MPa results in the highest bioleaching efficiency for copper extraction, namely 86% for the shaking flask bioleaching (particle size: <1.7 mm) and 52% for the column bioleaching of particles (particle size: 3.35–6.7 mm). The suggested model for reaction kinetics of microcrack-containing particles implies that more abundant and wider microcracks can promote the exposure of both Cu-containing phases and ferrous iron as well as solution infiltration, as evidenced by the COMSOL simulation results and bacteria proliferation analysis. The results highlight the importance of microcracks for enhancing the bioleaching process and provide insights for the mechanism understanding.

Bioleaching of Sulfide Minerals by Leptospirillum ferriphilum CC from Polymetallic Mine (Armenia)

A strain of Leptospirillum sp. CC previously isolated from Akhtala polymetallic ore (Armenia) was studied. The main morphological and physiological characteristics of CC were revealed. The optimal growth temperature was 40 °C and optimal pH 1.5. A phylogenetic analysis based on 16S rRNA gene sequences (GenBank ID OM272948) showed that isolate CC was clustered with L. ferriphilum and possessed 99.8% sequence similarity with the strain L. ferriphilum OL12-2 (KF356024). The molar fraction of DNA (G + C) of the isolate was 58.5%. Bioleaching experiment indicates that L. ferriphilum CC can oxidize Fe(II) efficiently, and after 17 days, 44.1% of copper and 91.4% of iron are extracted from chalcopyrite and pyrite, respectively. The efficiency of L. ferriphilum CC in pyrite oxidation increases 1.7 times when co-cultivated with At. ferrooxidans ZnC. However, the highest activity in pyrite oxidation shows the association of L.ferriphilum CC with heterotrophic Acidocella sp. RBA bacteria. It was shown that bioleaching of copper and iron from chalcopyrite by association of L. ferriphilum CC, At. ferrooxidans ZnC, and At. albertensis SO-2 in comparison with pure culture L. ferriphilum CC for 21 days increased about 1.2 and 1.4–1.6 times, respectively.

Continuous Bioleaching of Arsenic-Containing Copper-Zinc Concentrate and Shift of Microbial Population under Various Conditions

The goal of this work was to study the bioleaching of arsenic-containing polymetallic concentrate that contained 6.2% Cu, 7.3% Zn and 1.7% As, depending on different temperatures and in the presence of CO2 and molasses in the medium, as well as the difference in the composition of microbial population formed under various conditions. A mixed population of moderately thermophilic and thermotolerant acidophilic microorganisms formed during the continuous bioleaching of copper concentrate was used as an inoculum. The experiments were carried out in a continuous mode in laboratory scale reactors, with a temperature range of 40 °C to 60 °C. To assess the effect of CO2 and molasses on metal leaching and microbial population composition, the experiments were carried out in three reactors: CO2 (~0.01 L/min) was supplied into the first reactor; 0.02% molasses were added to the pulp of the second reactor; and no additional carbon sources were supplied into the control reactor. The highest copper recovery (27%) was achieved at 50°C in the experiment with molasses, while the highest zinc recovery (82.1%) was reached at 45°C in the control experiment. Additional carbon sources affected the extraction of non-ferrous metals only at 60 °C and increased the extraction of copper and zinc by 12.6% and 24.2%, respectively. Both the temperature and carbon source used affected the microbial population composition. The main microbial genera revealed in the populations by next generation sequencing (NGS) were bacteria of the genera Sulfobacillus and Acidithiobacillus, as well as archaea of the genera Ferroplasma, Acidiplasma, and Cuniculiplasma. At low temperatures (40 and 45 °C), Acidithiobacillus, Sulfobacillus, and Ferroplasma predominated, while at temperatures 50–55 °C, the decrease in relative abundance of these genera occurred, and the predominance of Acidiplasma archaea was observed. The usage of both CO2 and molasses led to the increase in Sulfobacillus and Acidiplasma in relative abundance.

Stirred-tank bioleaching of copper and cobalt from mine tailings in Chile

Metals from low-grade sulfide ores, electronic waste and mine tailings can be recovered using biohydrometallurgy. In this study, acidophilic microbial consortia of mesophiles and moderate thermophiles were applied in shake flasks as well as in stirred tank reactors (STR) to bioleach cobalt and copper from mine tailings in Chile. The mine tailings near Taltal contained considerable amounts of copper (∼5000 ppm) and cobalt (∼115 ppm). After adaptation of the mesophilic consortium, 38% of Co and 86% of Cu were recovered in 2-L STR at 10% solid load after 12 days bioleaching at 30 °C. In a mini-pilot test in 20-L STR at 15% solid load, Co and Cu extraction reached 49% and 83%, respectively. Improved metal recovery was obtained by using a moderate thermophilic microbial consortium at 42 °C, reaching 74% of Co and almost 100 % Cu in 2-L STR at 10% solid load. Low Fe dissolution below 14% for all tests was observed which may favor the downstream processing of Cu and Co. Together with the results from chemical leaching, the data indicated that Cu was mainly leached by sulfuric acid (acid leaching) while a high Co extraction required Fe(II)-oxidizing microbial activity (bioleaching).

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.

Bioelectrochemical-assisted bioleaching of chalcopyrite: Effect of pulp density, anode material, and sliver ion

Chalcopyrite bioleaching has developed rapidly because of the advantages such as environmental protection, low capital investment and simple operation, but its application has been limited by the slow reaction rate and other problems. Bioelectrochemical system (BES) as a promising wastewater treatment technology could solve the problem of reaction abort due to insufficient electron acceptors inside the mineral heap. In this study, the effect of pulp density, anode material and silver ion on the copper bioleaching were carried out. Experimental results showed that the maximum bioleaching efficiency (1.70 ± 0.18%) in 11 d was achieved at a pulp density of 1% with the application of titanium-silver anode and the assistance of BES. BES promoted the bioleaching of Cu mainly by promoting the bacterial reproduction and the Fe2+ production from the chalcopyrite. Moreover, the introduction of BES promoted the release of Ag+, further enhancing the bioleaching of Cu by 1.5 times (187.7 ± 18.1 mg/L vs. 120.9 ± 22.2 mg/L). In addition, the inhibition of conductive silver glue on the copper bioleaching and bacteria was alleviated by the BES. As an anode material, carbon cloth couldn't improve the leaching of Cu as compared to titanium foam, but it could increase the electron transfer efficiency.

Bioleaching Process for Copper Extraction from Waste in Alkaline and Acid Medium

Flotation wastes are becoming a valuable secondary raw material and source of many metals and semimetals worldwide with the possibilities of industrial recycling. The flotation tailings contain oxide and sulfide minerals that have not been sufficiently stabilized and form acidic mine waters, which in turn contaminate groundwater, rivers, and reservoi6sediments. An effective way to recycle these mine wastes is to recover the metals through leaching. While the focus is on acid bioleaching by iron- and sulfur-oxidizing bacteria, alkaline leaching, and the removal of iron-containing surface coatings on sulfide minerals contribute significantly to the overall environmental efficiency of leaching. For this study, static and percolate bioleaching of copper from flotation waste at the Bor copper mine in Serbia was investigated in alkaline and then acidic environments. The aim of the study was to verify the effect of alkaline pH and nutrient stimulation on the bioleaching process and element extraction. A sample was taken from a mine waste site, which was characterized by XRF analyses. The concentration of leached copper was increased when copper oxide minerals dissolved during alkaline bioleaching. The highest copper yield during alkaline bioleaching was achieved after 9 days and reached 67%. The addition of nutrients in acidic medium enhanced the degradation of sulfide minerals and increased Cu recovery to 74%, while Fe and Ag recoveries were not significantly affected. Combined bioleaching with alkaline media and iron- and sulfur-oxidizing bacteria in acidic media should be a good reference for ecological Cu recovery from copper oxide and sulfide wastes.

Biosorption and Bioleaching of Heavy Metals from Electronic Waste Varied with Microbial Genera

Industrialization and technological advancements have led to the exploitation of natural resources and the production of hazardous wastes, including electronic waste (E-waste). The traditional physical and chemical techniques used to combat E-waste accumulation have inherent drawbacks, such as the production of harmful gases and toxic by-products. These limitations may be prudently addressed by employing green biological methods, such as biosorption and bioleaching. Therefore, this study was aimed at evaluating the biosorption and bioleaching potential of seven microbial cultures using E-waste (printed circuit board (PCB)) as a substrate under submerged culture conditions. The cut pieces of PCB were incubated with seven microbial cultures in liquid broth conditions in three replicates. Atomic absorption spectroscopy (AAS) analysis of the culture biomass and culture filtrates was performed to evaluate and screen the better-performing microbial cultures for biosorption and bioleaching potentials. The best four cultures were further evaluated through SEM, energy-dispersive X-ray spectroscopy (EDX), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) studies to identify the possible culture that can be utilized for the biological decontamination of E-waste. The study revealed the highest and differential ability of Pleurotus florida and Pseudomonas spp. for biosorption and bioleaching of copper and iron. This can be attributed to bio-catalysis by the laccase enzyme. For both P. florida and Pseudomonas spp. on the 20th day of incubation, laccase exhibited higher specific activity (6.98 U/mg and 5.98 U/mg, respectively) than other microbial cultures. The biomass loaded with Cu2+ and Fe2+ ions after biosorption was used for the desorption process for recovery. The test cultures exhibited variable copper recovery efficiencies varying between 10.5 and 18.0%. Protein characterization through SDS-PAGE of four promising microbial cultures exhibited a higher number of bands in E-waste as compared with microbial cultures without E-waste. The surface topography studies of the E-waste substrate showed etching, as well as deposition of vegetative and spore cells on the surfaces of PCB cards. The EDX studies of the E-waste showed decreases in metal element content (% wt/% atom basis) on microbial treatment from the respective initial concentrations present in non-treated samples, which established the bioleaching phenomenon. Therefore, these microbial cultures can be utilized to develop a biological remediation method to manage E-waste.

Co-occurrence Interaction Networks of Extremophile Species Living in a Copper Mining Tailing.

Copper mining tailings are characterized by high concentrations of heavy metals and an acidic pH, conditions that require an extreme adaptation for any organism. Currently, several bacterial species have been isolated and characterized from mining environments; however, very little is known about the structure of microbial communities and how their members interact with each other under the extreme conditions where they live. This work generates a co-occurrence network, representing the bacterial soil community from the Cauquenes copper tailing, which is the largest copper waste deposit worldwide. A representative sampling of six zones from the Cauquenes tailing was carried out to determine pH, heavy metal concentration, total DNA extraction, and subsequent assignment of Operational Taxonomic Units (OTUs). According to the elemental concentrations and pH, the six zones could be grouped into two sectors: (1) the “new tailing,” characterized by neutral pH and low concentration of elements, and (2) the “old tailing,” having extremely low pH (~3.5) and a high concentration of heavy metals (mainly copper). Even though the abundance and diversity of species were low in both sectors, the Pseudomonadaceae and Flavobacteriaceae families were over-represented. Additionally, the OTU identifications allowed us to identify a series of bacterial species with diverse biotechnological potentials, such as copper bioleaching and drought stress alleviation in plants. Using the OTU information as a template, we generated co-occurrence networks for the old and new tailings. The resulting models revealed a rearrangement between the interactions of members living in the old and new tailings, and highlighted conserved bacterial drivers as key nodes, with positive interactions in the network of the old tailings, compared to the new tailings. These results provide insights into the structure of the soil bacterial communities growing under extreme environmental conditions in mines.

Bioleaching of copper from chalcopyrite ore at higher NaCl concentrations

The formation of hydrolyzed ferric iron (Fe (III)) as jarosite could limit the bioleaching of copper and significantly lower the dissolution rate of low-grade chalcopyrite ore. Thus, to improve the rate through overcoming the hindered dissolution of chalcopyrite, this study investigated the influence of chloride addition into leaching lixiviant. As a microbial source, mixed mesophiles, moderately thermophilic, and thermophilic microorganisms were adapted to about 120 mM NaCl solution. After optimization of the ore bioleaching in 64 controlled mini-columns, the scaled tests in 2-m tall columns were conducted to study the overall leaching procedure and precipitation of the jarosite. Under normal aeration conditions (0.05 Nm3/m2/h) with hybrid irrigation (120 mM NaCl in H2SO4 solution at pH = 1.5), copper recovery reached 80% after 120 days while it was approximately 50% with limited one (0.003 Nm3/m2/h). The limited aeration column had a moderate oxidation–reduction potential (ORP) with values < 450 mV. This significant improvement in dissolution is explained by the reduced precipitation of passivating layer (mainly jarosite). These conclusions were also confirmed by the estimation of pyrite and natrojarosite with a modified ASTM D-2492 (MASTM D-2492). Moreover, to identify the microbial communities in the columns, DNA extraction and 16Sr RNA gene PCR amplification and sequencing were done.