Bioleaching of high grade Zn–Pb bearing ore by mixed moderate thermophilic microorganisms

Bioremediation of organic/heavy metal contaminants by mixed cultures of microorganisms: A review

Although microbial remediation has been widely used in the bioremediation of various contaminants, in practical applications of biological remediation, pure cultures of microorganisms are seriously limited by their adaptability, efficiency, and capacity to handle multiple contaminants. Mixed cultures of microorganisms involve the symbiosis of two or more microorganisms. Such cultures exhibit a collection of the characteristics of each microorganism species or strain, showing enormous potential in the bioremediation of organic or heavy metal pollutants. The present review focuses on the mixed cultures of microorganisms, demonstrating its importance and summarizing the advantages of mixed cultures of microorganisms in bioremediation. Furthermore, the internal and external relations of mixed culture microorganisms were analyzed with respect to their involvement in the removal process to elucidate the underlying mechanisms.

Bioleaching of Iron, Copper, Lead, and Zinc from the Sludge Mining Sediment at Different Particle Sizes, pH, and Pulp Density Using Acidithiobacillus ferrooxidans

Globally, the amounts of metal ore deposits have been declining, so the research directions investigating the extraction of metals from materials that are classified as waste are gaining more importance every year. High concentrations of Cu, Pb, Zn, and Fe were analyzed in the sludge sediment (Zlaté Hory, Czech Republic), which is a waste product of the mining industry. In the bioleaching process, bacterial cells have been established as being able to convert metals from solid to liquid phase. However, the most important parameters of bioleaching are particle size, pH, and pulp density, thus our research focused on their optimization. The acidophilic and mesophilic bacteria Acidithiobacillus ferrooxidans were applied due to the high Fe content in the sample. The recovery of metals in the leachate was determined by F-AAS and the residual metal concentrations in the waste fraction were analyzed by XRF. The grain size fractions <40 µm –200 µm were investigated. The atomic absorption spectrometry (AAS) results show that the highest Fe (76.48%), Cu (82.01%), and Pb (88.90%) recoveries were obtained at particle size of 71–100 μm. Zn was dissolved for all fractions above 90%. Experiments with different pH values were performed at a pH of 1.6–2.0. The highest dissolution rates of Zn, Fe, and Cu were achieved with a suspension pH of 1.8, where 98.73% of Zn, 85.42% of Fe, and 96.44% of Cu were recovered. Due to the high percentage dissolution of metals, experiments were performed under pilot conditions in a bioreactor at a pulp density of 2.5% and 4.2% (w/v). From an economic point of view, the leaching time of 28 days was evaluated as sufficient.

Bioleaching of Indonesian Galena Concentrate With an Iron- and Sulfur-Oxidizing Mixotrophic Bacterium at Room Temperature

Biohydrometallurgy is believed to be a promising future study field for the recovery of lead (Pb) from ores/concentrates since the pyrometallurgical/hydrometallurgical processes have been largely applied to recover Pb to date, which operates at high temperature and generates volatile Pb matters that are hazardous and carcinogenic to human health. Hence, the main purpose of this study was to investigate the biohydrometallurgical extraction of Pb from the Indonesian galena concentrate through bioleaching using an iron- and sulfur-oxidizing mixotrophic bacterium (identified as Citrobacter sp.). The bioleaching experiments were conducted in shake flasks containing the modified LB broth medium supplemented with galena concentrate with a particle size of d₈₀ = 75 μm at room temperature. Both semi-direct and direct bioleaching methods were employed in this study. The bacterium was able to extract lead (Pb) from galena concentrate with high selectivity to Cu and Zn (0.99 and 0.86, respectively). The highest extraction level of 90 g lead dissolved/kg galena concentrate was achieved using direct bioleaching method at bioleaching conditions of 2% w/v pulp density, 5 g/L FeCl₃, 50 g/L NaCl, 20 g/L molasses and a rotation speed of 180 rpm at room temperature (25°C). The addition of FeCl₃, NaCl, and molasses increased the lead leaching efficiencies, which were also evidenced by the FTIR, XRD, and SEM-EDS analyses. From industrial and commercial standpoints, the selective bioleaching represented in this study may be beneficial to the development of lead leaching from sulfide minerals, since insoluble anglesite (PbSO₄) precipitates are formed during ferric sulfate oxidation, thus making the recovery of lead through bioleaching unpractical.

Effects of Operational Parameters on the Low Contaminant Jarosite Precipitation Process-an Industrial Scale Study

Jarosite precipitation process (JPP) is the most frequently used procedure for iron removal in the hydrometallurgical zinc extraction process. However, there is a gap in the knowledge of the relationship between operational parameters and the low contaminant JPP on the industrial scale. This study will address these issues by investigating the behavior of zinc calcine (ZC) as a neutralizing agent, exploring the source of zinc and iron through leaching experiments, and simulating the Jarosite process of the Bafgh Zinc Smelting Company (BZSC). The results showed that the zinc dissolution efficiency was 90.3% at 90 °C, and 73% of the iron present in the calcine can be solubilized. The main outcome was the iron removal of about 85% by alkaline ions present in ZC without the addition of any precipitating agent. The second target was to evaluate the effect of operational parameters on jarosite precipitation. Results revealed that increasing the temperature to 90 °C and the stirring rate to 500 RPM as well as adjusting the ZC's pH during the jarosite precipitation remarkably improved iron removal. Considering all these factors in the plant could improve Fe precipitation to around 80% on average.

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.

Biohydrometallurgy as an environmentally friendly approach in metals recovery from electrical waste: A review

Nowadays, large amount of municipal solid waste is because of electrical scraps (i.e. waste electrical and electronic equipment) that contain large quantities of electrical conductive metals like copper and gold. Recovery of these metals decreases the environmental effects of waste electrical and electronic equipment (also called E-waste) disposal, and as a result, the extracted metals can be used for future industrial purposes. Several studies reported in this review, demonstrated that the biohydrometallurgical processes were successful in efficient extraction of metals from electrical and electronic wastes. The main advantages of biohydrometallurgy are lower operation cost, less energy input, skilled labour, and also less environmental effect in comparison with pyro-metallurgical and hydrometallurgical processes. This study concentrated on fundamentals and technical aspects of biohydrometallurgy. Some points of drawbacks and research directions to develop the process in the future are highlighted in brief.

Removal of metals from lead-zinc mine tailings using bioleaching and followed by sulfide precipitation

Mine tailings often contain significant amounts of metals and sulfide, many traditional operations used to minerals was not as good as those currently available. This study investigated metals removal from lead-zinc mine tailings using bioleaching and followed by sulfide precipitation. Metals were dissolved from the tailings by the bacteria in a bioleaching reactor. During a 10% pulp density bioleaching experiment, approximately 0.82% Pb, 97.38% Zn, and 71.37% Fe were extracted after 50 days. With the pulp density of 10% and 20%, the dissolution of metals followed shrinking core kinetic model. Metals (Pb, Zn, and Fe) present in the pregnant bioleaching leachate. Metals were next precipitated as a sulfide phase using sodium sulfide (Na₂S). Metal precipitations were selectively and quantitatively produced from the bioleaching leachate by adding Na₂S. More than 99% of the zinc and 75% of the iron was precipitated using 25 g/L Na₂S in the bioleaching leachate. The results in the study were to provide useful information for recovering or removing metals from lead-zinc mine tailings.

Bioleaching combined brine leaching of heavy metals from lead-zinc mine tailings: Transformations during the leaching process

During the process of bioleaching, lead (Pb) recovery is low. This low recovery is caused by a problem with the bioleaching technique. This research investigated the bioleaching combination of bioleaching with brine leaching to remove heavy metals from lead-zinc mine tailings. The impact of different parameters were studied, including the effects of initial pH (1.5-3.0) and solid concentration (5-20%) for bioleaching, and the effects of sodium chloride (NaCl) concentration (10-200 g/L) and temperature (25 and 50 °C) for brine leaching. Complementary characterization experiments (Sequential extraction, X-ray diffractometer (XRD), scanning electronic microscope (SEM)) were also conducted to explore the transformation of tailings during the leaching process. The results showed that bioleaching efficiency was significantly influenced by initial pH and solid concentration. Approximately 85.45% of iron (Fe), 4.12% of Pb, and 97.85% of zinc (Zn) were recovered through bioleaching in optimum conditions. Increasing the brine concentration and temperature promoted lead recovery. Lead was recovered from the bioleaching residues at a rate of 94.70% at 25 °C and at a rate of 99.46% at 50 °C when the NaCl concentration was 150 g/L. The study showed that bioleaching significantly changed the speciation of heavy metals and the formation and surface morphology of tailings. The metals were mainly bound in stable fractions after bioleaching.

Integrated bioleaching of copper metal from waste printed circuit board-a comprehensive review of approaches and challenges

Waste electrical and electronic equipment (e-waste) is the most rapidly growing waste stream in the world, and the majority of the residues are openly disposed of in developing countries. Waste printed circuit boards (WPCBs) make up the major portion of e-waste, and their informal recycling can cause environmental pollution and health risks. Furthermore, the conventional disposal and recycling techniques-mechanical treatments used to recover valuable metals, including copper-are not sustainable in the long term. Chemical leaching is rapid and efficient but causes secondary pollution. Bioleaching is a promising approach, eco-friendly and economically feasible, but it is slower process. This review considers the recycling potential of microbes and suggests an integrated bioleaching approach for Cu extraction and recovery from WPCBs. The proposed recycling system should be more effective, efficient and both technically and economically feasible.

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.

Insights into the enhancement mechanism coupled with adapted adsorption behavior from mineralogical aspects in bioleaching of copper-bearing sulfide ore by Acidithiobacillus sp

In this study, two typical bioleaching strains (A. ferrooxidansandA. thiooxidans) were employed for exploring the enhancement mechanism of the adapted adsorption behavior in the bioleaching of copper-bearing sulfide ore.