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

Enhancing column bioleaching of chalcocite by isolated iron metabolism partners Leptospirillum ferriphilum/Acidiphilium sp. coupling with systematically utilizing cellulosic waste

The iron metabolism partners Leptospirillum ferriphilum and Acidiphilium sp. were screened from industrial bioheap site. An integrated multi-stage strategy was proposed to improve chalcolite column bioleaching coupling with synergistical utilization of cellulosic waste such as acid hydrolysate of aquatic plants. L. ferriphilum was used to accelerate the initial iron metabolism, and Acidithiobacillus caldus maintained a lower pH in the middle stage, while Acidiphilium sp. greatly inhibited jarosite passivation in the later stage. Meanwhile, L. ferriphilum (38.3 %) and Acidiphilium sp. (37.0 %) dominated the middle stage, while the abundance of Acidiphilium sp. reached 63.5 % in the later stage. The ferrous, sulfate ion and biomass were improved and the transcriptional levels of some biofilm and morphology related genes were significantly up-regulated. The final Cu2+ concentration reached 325.5 mg·L-1, improved by 43.8 %. Moreover, Canonical Correlation Analysis (CCA) analysis between bioleaching performance, iron/sulfur metabolism and community verified the important role of iron metabolism partners.

An efficient approach for enhancement of gold and silver bioleaching from spent telecommunication printed circuit boards using cyanogenic bacteria: Prevention of biofilm formation

Environmentally friendly bioleaching of gold and silver from electronic waste using cyanogenic bacteria has emerged as a promising approach. In the process of cyanide bioleaching, cyanide ions produced by cyanogenic bacteria form complexes (such as AuCN and AgCN) with metals in the waste structure and lead to their dissolution. The recovery rate of these valuable elements during bioleaching is influenced by extracellular polymeric substances (EPS). For the first time, this study presents an investigation into the role of EPS from Pseudomonas atacamensis in the bioleaching of gold and silver from spent telecommunication printed circuit boards (STPCBs). The experimental results demonstrate that, after 6 days of bioleaching, gold and silver recoveries reached 22% and 36.2%, respectively. Complementary analyses employing FE-SEM and attachment tests shed light on the interactions between EPS, bacterial attachment to particle surfaces, and biofilm development stages during gold and silver bioleaching. Notably, the most significant bacterial attachment occurred on the fourth day of bioleaching. Zeta potential tests conducted on bacteria and EPS provided insights into the potential absorption of soluble cations such as Au+ and Ag+ by EPS. Furthermore, 250 mg/L polyvinylpyrrolidone (PVP) effectively removed EPS from the particle surfaces, improving gold and silver recovery rates, reaching 26% and 43.2%, respectively. These findings highlight the importance of understanding the role of EPS in bioleaching processes and offer insights into enhancing gold and silver recovery from electronic waste.

Sulfur enhancement effects for uranium bioleaching in column reactors from a refractory uranium ore

The feasibility of sulfur enhancement for uranium bioleaching in column reactors was assessed with a designed mixed Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferriphilum from a refractory uranium ore. The uranium extraction reached 86.2% with the sulfur enhancement (1 g/kg) in 77 days leaching process, increased by 12.6% vs. the control without sulfur addition. The kinetic analysis showed that uranium bioleaching with sulfur enhancement in columns followed an internal diffusion through the product layer-controlled model. Ore residue characteristics indicated that sulfur enhancement could strengthen the porosity of passivation layer, improving the ore permeability. Notably, bacterial community analysis showed that sulfur enhancement at 1 g/kg could make the iron-oxidizing and sulfur-oxidizing bacteria on the ore surface maintain a good balance (approx. 1:1), and thus decomposing ore more effectively. Lastly, a possible mechanism model for uranium bioleaching with sulfur enhancement was proposed.

Co-inoculation with beneficial microorganisms enhances tannery sludge bioleaching with Acidithiobacillus thiooxidans

Bioleaching of tannery sludge is an efficient and environmentally friendly way for chromium (Cr) removal, which supports the sustainable development of the leather industry. Acidithiobacillus thiooxidans has been reported effective in Cr bioleaching of tannery sludge. However, little is known about whether the presence of other benefiting species could further improve the Cr leaching efficiency of A. thiooxidans. Here, we studied the enhancing roles of four species namely Acidiphilium cryptum, Sulfobacillus acidophilus, Alicyclobacillus cycloheptanicus, and Rhodotorula mucilaginosa in chromium bioleaching of tannery sludge with A. thiooxidans by batch bioleaching experiments. We found that each of the four species facilitated the quick dominance of A. thiooxidans in the bioleaching process and significantly improved the bioleaching performance including bioleaching rate and efficiency. The bioleaching efficiency of Cr in the tannery sludge could reach 100% on the sixth day by co-inoculating A. thiooxidans and four auxiliary species. The achievements shed a light on the role of the community-level interactions on bioleaching and may also serve as guidance for managing bioleaching consortiums for better outcomes.

A Sustainable Bioleaching of a Low-Grade Chalcopyrite Ore

This paper reports on a study of column bioleaching of a low-grade chalcopyrite ore that is currently dump-leached under natural biological conditions without any control over microbial populations. The experimental methodology was focused on the effect of managing the bacterial populations in a raffinate solution sourced from a dump-leach operation. This study presents results from columns of two heights (0.45 and 1.0 m). We demonstrated that intermittent irrigation enhanced the chalcopyrite dissolution during column leaching, but excessively long rest periods negatively affected the chemical and bacterial activity due to the shortage of oxidizing agents and/or nutrients for microorganisms. The recovery of low-grade chalcopyrite ore was enhanced by increasing the microbial cell density. The addition of 1.5 × 108 cells/mL to the 0.45 m column and 5.0 × 107 cells/mL to the 1 m column resulted in increased extraction, with the copper dissolution increasing from 32% to 44% in the 0.45 m column and from 30% to 40% in the 1.0 m column over 70 days of leaching. Under these conditions, the pH level remained constant at ~1.8, and the redox potential was around 840 mV vs. the SHE throughout the experiment. These results provided useful insights for evaluating a sustainable controlled dump-based technology for mineral bioprocessing.

Application of double-pulse laser-induced breakdown spectroscopy (DP-LIBS), Fourier transform infrared micro-spectroscopy and Raman microscopy for the characterization of copper-sulfides

The combined application of the structure sensitive techniques Fourier transform infrared μ-spectroscopy and Raman microscopy in conjunction with different approaches of laser-induced breakdown spectroscopy (LIBS) including the two-color double pulse (DP-LIBS) have been applied towards the characterization of whole ore copper-sulfide minerals. Discrete information from the surface of the whole ore minerals that lead to the establishment of infrared marker bands and from the surface of bioleached samples that allow the monitoring of jarosite and biofilm formation are provided by FTIR mapping experiments. Raman data can provide information related to the type of the mineral and of the secondary minerals formed on the surface of the ore. Of the four different LIBS approaches applied towards the characterization of the composition of the whole ore minerals, the DP-LIBS shows the highest sensitivity with increasing signals for both the Fe and Cu metals in the whole ore samples.

A mini-review of heavy metal recycling technologies for municipal solid waste incineration fly ash

This mini-review article summarizes the available technologies for the recycling of heavy metals (HMs) in municipal solid waste incineration (MSWI) fly ash (FA). Recovery technologies included thermal separation (TS), chemical extraction (CE), bioleaching, and electrochemical processes. The reaction conditions of various methods, the efficiency of recovering HMs from MSWI FA and the difficulties and solutions in the process of technical development were studied. Evaluation of each process has also been done to determine the best HM recycling method and future challenges. Results showed that while bioleaching had minimal environmental impact, the process was time-consuming. TS and CE were the most mature technologies, but the former process was not cost-effective. Overall, it has the greatest economic potential to recover metals by CE with scrubber liquid produced by a wet air pollution control system. An electrochemical process or solvent extraction could then be applied to recover HMs from the enriched leachate. Ongoing development of TS and bioleaching technologies could reduce the treatment cost or time.

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.

Sequential Bioleaching of Pyritic Tailings and Ferric Leaching of Nonferrous Slags as a Method for Metal Recovery from Mining and Metallurgical Wastes

In this work, we proposed a method for biohydrometallurgical processing of mining (old pyritic flotation tailings) and metallurgical (slag) wastes to recover gold and other nonferrous metals. Since this processing allows the removal of toxic metals or at least decreases their content in the solids, this approach may reduce the negative environmental impacts of such waste. The proposed process was based on pyritic tailings’ bioleaching to recover metals and produce leach liquor containing a strong oxidizing agent (ferric sulfate) to dissolve nonferrous metal from slag. This approach also allows us to increase concentrations of nonferrous metals in the pregnant leach solution after pyritic waste bioleaching to allow efficient extraction. The old pyritic tailings were previously leached with 0.25% sulfuric acid for 10 min to remove soluble metal sulfates. As a result, 36% of copper and 35% of zinc were extracted. After 12 days of bioleaching with a microbial consortium containing Leptospirillum spp., Sulfobacillus spp., Ferroplasma spp., and Acidithiobacillus spp. at 35 °C, the total recovery of metals from pyritic tailings reached 68% for copper and 77% for zinc; and subsequent cyanidation allowed 92% recovery of gold. Ferric leaching of two types of slag at 70 °C with the leachate obtained during bioleaching of the tailings and containing 15 g/L of Fe3+ allowed 88.9 and 43.4% recovery of copper and zinc, respectively, from copper slag within 150 min. Meanwhile, 91.5% of copper, 84.1% of nickel, and 70.2% of cobalt were extracted from copper–nickel slag within 120 min under the same conditions.

Mechanical Activation on Bioleaching of Chalcopyrite: A New Insight

Mechanical activation as a means of accelerating the mineral dissolution may play an important role in chalcopyrite bioleaching. In the present work, the mechanical activation by ball-milling with 10 min, 30 min, 60 min, 90 min, 120 min and 180 min time periods of bioleaching of chalcopyrite was studied, and then evaluated by a Density Functional Theory (DFT) calculation. The results showed that the specific surface area increased sharply in the very beginning of mechanical activation and then increased slowly until the agglomeration of the particles occurred, while the chalcopyrite lattices increased with the mechanical activation. The reaction activity analyzed by cyclic voltammetry (CV) increased slowly in 30 min, increased quickly in the following 90 min, and then decreased, while the hydrophobicity analyzed by contact angles of the chalcopyrite after activation showed less of a change. The results showed that after 15 days of bioleaching, the Cu leaching by Sulfobacillus thermosulfidooxidans (S. thermosulfidooxidans) increased from 9.39% in the 0 min of mechanical activation to 87.41% in the 120 min of mechanical activation, and the copper leaching rate increased by about 78%. The DFT results provide solid proof that the activated chalcopyrite can be adsorbed more easily by cells with higher adsorption energies and stronger bonds.

Metal recovery from incineration bottom ash: State-of-the-art and recent developments

Municipal solid waste incineration (MSWI) is one of the leading technologies for municipal solid waste (MSW) treatment in Europe. Incineration bottom ash (IBA) is the main solid residue from MSWI, and its annual European production is about 20 million tons. The composition of IBA depends on the composition of the incinerated waste; therefore, it may contain significant amounts of ferrous and non-ferrous (NFe) metals as well as glass that can be recovered. Technologies for NFe metals recovery have emerged in IBA treatment since the 1990s and became common practice in many developed countries. Although the principles and used apparatus are nearly the same in all treatment trains, the differences in technological approaches to recovery of valuable components from IBA - with a special focus on NFe metals recovery - are summarized in this paper.

A novel step-wise indirect bioleaching using biogenic ferric agent for enhancement recovery of valuable metals from waste light emitting diode (WLED)

Waste light-emitting diodes (WLED) are of major interest as they are a considered secondary source of valuable metals with a high potential for polluting the environment. To recover the valuable metals from WLEDs, various methods have been applied such as direct and indirect bioleaching. A novel step-wise indirect bioleaching process has been developed in this study for recycling valuable metals from WLEDs using adapted Acidithiobacillus ferrooxidans. The ferric ion concentration was controlled at 4-5 g/L with step-wise addition of biogenic ferric for faster bioleaching rate. The results indicated the negative effect of bacterial attachment in bioleaching of WLEDs. A direct bioleaching offers low copper, nickel, and gallium leach yields, while all metals' recovery improved with step-wise indirect bioleaching. At a pulp density of 20 g/L, the copper, nickel, and gallium recovery efficiency was 83%, 97%, 84%, respectively. In addition, leaching time was reduced to 15 days from 30 days. From a technological perspective, the study proved that step-wise indirect bioleaching by biogenic ferric resulted in maximum valuable metal recovery from WLEDs at a low cost and via a short, simple and environmentally-friendly process.

Metal biorecovery and bioremediation: Whether or not thermophilic are better than mesophilic microorganisms

Metal mobilization and immobilization catalyzed by microbial action are key processes in environmental biotechnology. Metal mobilization from ores, mining wastes, or solid residues can be used for recovering metals and/or remediating polluted environments; furthermore, immobilization reduces the migration of metals; cleans up effluents plus ground- and surface water; and, moreover, can help to concentrate and recover metals. Usually these processes provide certain advantages over traditional technologies such as more efficient economical and environmentally sustainable results. Since elevated temperatures typically increase chemical kinetics, it could be expected that bioprocesses should also be enhanced by replacing mesophiles with thermophiles or hyperthermophiles. Nevertheless, other issues like process stability, flexibility, and thermophile-versus-mesophile resistance to acidity and/or metal toxicity should be carefully considered. This review critically analyzes and compares thermophilic and mesophilic microbial performances in recent and selected representative examples of metal bioremediation and biorecovery.

Chalcopyrite bioleaching of an in situ leaching system by introducing different functional oxidizers

Introducing exogenous species to an indigenous microbial community is an effective way to reveal the connections between metabolic processes, ecological function and microbial community structure. Herein, three different functional consortia (ferrous oxidizers, sulfur oxidizers and ferrous/sulfur oxidizers) were added to a natural leaching solution system derived from Zijin copper mine, China. The leaching experiment showed that the copper extraction rate of the community invaded by a sulfur-oxidizing consortium was 50.40% higher than that of the indigenous leachate at the endpoint of bioleaching. The variations of ferrous content, total iron, pH and redox potential in leachates also provided evidence that the community with exogenous sulfur oxidizers was more efficient. XRD analysis demonstrated that a proper addition of the sulfur-oxidizing consortium could eliminate sulfur passivation, promote production of chalcocite and enhance leaching. Furthermore, an exogenous ferrous-oxidizing consortium and a sulfur-oxidizing consortium greatly changed the community structure and microbial succession and promoted the cell growth rate during the bioleaching process, while ferrous/sulfur oxidizers showed no obvious effects on the indigenous community. Exogenous ferrous oxidizers, mainly L. ferriphilum, and sulfur oxidizers, mainly A. thiooxidans, successfully established and colonized in the indigenous community. However, only colonized A. thiooxidans, rather than L. ferriphilum, showed advantageous enhancement in the dissolution of chalcopyrite. Results indicated that exogenous sulfur oxidizer A. thiooxidans, which was scarce in the indigenous community, could easily colonize in the indigenous community, significantly change the community structure, sufficiently execute its function, and greatly enhance copper dissolution.

Introducing different functional consortia into a native system revealed that complementary sulfur invaders greatly enhanced the community function.

Evolution of copper arsenate resistance for enhanced enargite bioleaching using the extreme thermoacidophile Metallosphaera sedula

Adaptive laboratory evolution (ALE) was employed to isolate arsenate and copper cross-resistant strains, from the copper-resistant M. sedula CuR1. The evolved strains, M. sedula ARS50-1 and M. sedula ARS50-2, contained 12 and 13 additional mutations, respectively, relative to M. sedula CuR1. Bioleaching capacity of a defined consortium (consisting of a naturally occurring strain and a genetically engineered copper sensitive strain) was increased by introduction of M. sedula ARS50-2, with 5.31 and 26.29% more copper recovered from enargite at a pulp density (PD) of 1 and 3% (w/v), respectively. M. sedula ARS50-2 arose as the predominant species and modulated the proportions of the other two strains after it had been introduced. Collectively, the higher Cu2+ resistance trait of M. sedula ARS50-2 resulted in a modulated microbial community structure, and consolidating enargite bioleaching especially at elevated PD.

Catalytic potential of selected metal ions for bioleaching, and potential techno-economic and environmental issues: A critical review

Bioleaching is considered to be a low-cost, eco-friendly technique for leaching valuable metals from a variety of matrixes. However, the inherent slow dissolution kinetics and low metal leaching yields have restricted its wider commercial applicability. Recent advancements in bio-hydrometallurgy have suggested that these critical issues can be successfully alleviated through the addition of a catalyst. The catalyzing properties of a variety of metals ions (Ag⁺, Hg⁺⁺, Bi⁺⁺⁺, Cu⁺⁺, Co⁺⁺ etc.) during bioleaching have been successfully demonstrated. In this article, the role and mechanisms of these metal species in catalyzing bioleaching from different minerals (chalcopyrite, complex sulfides, etc.) and waste materials (spent batteries) are reviewed, techno-economic and environmental challenges associated with the use of metals ions as catalysts are identified, and future prospectives are discussed. Based on the analysis, it is suggested that metal ion-catalyzed bioleaching will play a key role in the development of future industrial bio-hydrometallurgical processes.

Synergistic catalytic effects of visible light and graphene on bioleaching of chalcopyrite

Graphene and visible light could significantly accelerate chalcopyrite dissolution by A. ferrooxidans. Furthermore, the enhancing effect of the synergy catalysis was much more significant than that when only using a single catalytic method.

The bioleaching potential of a bacterial consortium

This work presents the molecular foundation of a consortium of five efficient bacteria strains isolated from copper mines currently used in state of the art industrial-scale biotechnology. The strains Acidithiobacillus thiooxidans Licanantay, Acidiphilium multivorum Yenapatur, Leptospirillum ferriphilum Pañiwe, Acidithiobacillus ferrooxidans Wenelen and Sulfobacillus thermosulfidooxidans Cutipay were selected for genome sequencing based on metal tolerance, oxidation activity and bioleaching of copper efficiency. An integrated model of metabolic pathways representing the bioleaching capability of this consortium was generated. Results revealed that greater efficiency in copper recovery may be explained by the higher functional potential of L. ferriphilum Pañiwe and At. thiooxidans Licanantay to oxidize iron and reduced inorganic sulfur compounds. The consortium had a greater capacity to resist copper, arsenic and chloride ion compared to previously described biomining strains. Specialization and particular components in these bacteria provided the consortium a greater ability to bioleach copper sulfide ores.

Probing the whole ore chalcopyrite-bacteria interactions and jarosite biosynthesis by Raman and FTIR microspectroscopies

The whole ore chalcopyrite-bacteria interaction and the formation of the extracellular polymeric substances (EPS) during the bioleaching process by microorganisms found in the mine of Hellenic Copper Mines in Cyprus were investigated. Raman and FTIR microspectroscopies have been applied towards establishing a direct method for monitoring the formation of secondary minerals and the newly found vibrational marker bands were used to monitor the time evolution of the formation of covellite, and the K(+) and NH4(+)-jarosites from the chalcopyrite surfaces. The Raman data indicate that the formation of K(+)-jarosite is followed by the formation of NH4(+)-jarosite. The variation in color in the FTIR imaging data and the observation of the amide I vibration at 1637cm(-1) indicate that the microorganisms are attached on the mineral surface and the changes in the frequency/intensity of the biofilm marker bands in the 900-1140cm(-1) frequency range with time demonstrate the existence of biofilm conformations.

Global transcriptional responses of Acidithiobacillus ferrooxidans Wenelen under different sulfide minerals

In order to provide new information about the adaptation of Acidithiobacillus ferrooxidans during the bioleaching process, the current analysis presents the first report of the global transcriptional response of the native copper mine strain Wenelen (DSM 16786) oxidized under different sulfide minerals. Microarrays were used to measure the response of At. ferrooxidans Wenelen to shifts from iron supplemented liquid cultures (reference state) to the addition of solid substrates enriched in pyrite or chalcopyrite. Genes encoding for energy metabolism showed a similar transcriptional profile for the two sulfide minerals. Interestingly, four operons related to sulfur metabolism were over-expressed during growth on a reduced sulfur source. Genes associated with metal tolerance (RND and ATPases type P) were up-regulated in the presence of pyrite or chalcopyrite. These results suggest that At. ferrooxidans Wenelen presents an efficient transcriptional system developed to respond to environmental conditions, namely the ability to withstand high copper concentrations.

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.

Immobilization of Acidithiobacillus ferrooxidans on cotton gauze for biological oxidation of ferrous ions in a batch bioreactor

The ability of Acidithiobacillus ferrooxidans to oxidize ferrous iron has been extensively studied in bioleaching to recover metal resources. Although immobilization of A. ferrooxidans is of great importance to achieve high bioleaching performance in practical application, the reported approaches of immobilization of A. ferrooxidans are still limited. This paper is attempting to develop a novel method to immobilize A. ferrooxidans by a less-costly effective carrier from zeolite, activated carbon, and cotton gauze. The results showed that cotton gauze was the most suitable carrier to immobilize A. ferrooxidans cells in comparison with zeolite and activated carbon. Acidithiobacillus ferrooxidans immobilized on the cotton gauze by gravity dehydration could achieve an average ferrous iron oxidation rate of 0.73 g/(L·h). Furthermore, the ferrous iron oxidation ratio attained in the bioreactor under batch operation was maintained above 97.83%. All results indicated that cotton gauze could be an efficient carrier for immobilizing A. ferrooxidans cells for the biooxidation of ferrous ions.

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.