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

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

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Abstract

In this research, the bioleaching mechanism of zinc and lead from high-grade Zn-Pb ore has been investigated. It is done by using mixed culture of iron and sulfur oxidizing moderate thermophilic bacteria at 45°C. Pulp density, initial pH and ferrous concentration were studied as influential parameters in bioleaching experiments. The optimum conditions were achieved at pulp density=50 (g/L), initial pH=1 and FeSO4.7H2O concentration= 75 (g/L) with 98.5% zinc recovery after 25 days treatment. Generally, an increase in ferrous concentration caused an improve zinc recovery, and an increase in initial pH and pulp density caused reduction in zinc recovery. However, in the test with optimum condition the lead dissolution was just 0.027% due to the lower Pb solubility. Furthermore, cadmium dissolution was 98% under optimum condition and results showed the cadmium dissolution was in direct proportion with zinc dissolution. Finally, 7.82% of arsenic and 8.52% of antimony dissolved during zinc bioleaching after 25 days treatment, both under above mentioned optimum condition.

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... Moreover, several studies demonstrated that the elevated lead bioleaching/leaching efficiencies were achieved Anugrah et al., 2017 in the presence of NaCl (Warren et al., 1987;Liao and Deng, 2004;Ye et al., 2017), FeCl 3 (Dutrizac, 1986;Kim et al., 1986;Warren et al., 1987;Dutrizac and Chen, 1990;Long et al., 2009), and ferric (Fe 3+ ) ions (Pashkov et al., 2002). Hence, the present study investigated the use of a local mixotrophic bacterium (identified as Citrobacter sp.) capable of oxidizing iron and sulfur as well as producing biosurfactants, including EPS (extracellular polymeric substances) in extracting lead from galena concentrate (Bang et al., 1995;Garcia Jr. et al., 1995;Da Silva et al., 2003;Da Silva, 2004;Pacholewska, 2004;Jiang et al., 2008;Baba et al., 2011;Mejía et al., 2012;Ghassa et al., 2014), the present study is different from previous studies and more beneficial from metallurgical standpoints as follows: (1) the bacterium Citrobacter sp. employed in this study belongs to mixotrophic group capable of utilizing both organic and inorganic compounds for energy and carbon sources, thus making much easier for industrial applications since bacterial carbon sources can be derived from any organic wastes abundant in Indonesia and many other tropical countries; ...
... The mixotrophic bacterium Citrobacter sp. (as a single culture) which exhibited the excellent selectivity of lead bioleaching to copper and zinc might be more beneficial for subsequent copper and zinc leaching processes than chemolithoautotrophic bacteria used in previous studies (listed in Table 2), which were not selective to zinc (Pacholewska, 2004;Baba et al., 2011;Ghassa et al., 2014), while selectivity for copper was not determined (Jiang et al., 2008;Mejía et al., 2012). It is reported that galena (PbS) that is often associated with zinc sulfides such as sphalerite (ZnS) and copper sulfides such as chalcopyrite (CuFeS 2 ) frequently makes passivation layers that hinder Cu and Zn dissolution (Dutrizac, 1986;Dutrizac and Chen, 1990;Da Silva et al., 2003). ...
Article
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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.
... Generally, the bacterial cells during the bioleaching process obtained their energy by oxidizing ferrous iron to ferric iron and/or sulfur to sulfuric acid (Ghassa et al., 2014;Haghshenas et al., 2012;Rohwerder et al., 2003). Commonly, within the bioleaching, the ORP mainly shows the Fe +3 /Fe +2 ratio and bacterial activity (Manafi et al., 2013;Watling, 2006). ...
... The ORP variations pattern depends upon the consumption and regeneration of the ferric iron. Higher ORP reported here in this study shows the maximum efficiency of the indigenous bacterial consortia in iron oxidation compared to the ORP in pure bacterial inoculum reported by Ghassa et al. (2014). The plane ORP pattern in the control system was due to the lack of bacterial inoculum for iron oxidation, which supports the findings of Panda et al. (2017). ...
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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.
... The culturing was carried out at a shaker-incubator (Shin Saeng SKIR-601, Korea) which operated at 45°C and 130 rpm. The FeSO 4 .7H 2 O (44.2 g/l) and elemental sulfur (10 g/l) were used as nutrients (Ghassa et al., 2014). ...
... Generally tests with high concentration of Fe 2+ had low ORP because moderate thermophilic acidophilic microorganisms have low ability in Fe 2+ oxidation (Ghassa et al., 2014), in contrast to mesophilic acidophilic microorganisms. A comparison between bioleaching and control leaching tests with 22.45 g/l FeSO 4 .7H 2 O shows that bacteria increased the ORP just~60 mV. ...
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Low kinetic is one of the most important disadvantages of bioleaching. The leaching rate can be increased by employing thermophilic microorganisms. In this research, the moderate thermophilic bioleaching of waste lithium ion batteries (LIBs) at 45 °C was investigated. The effects of sulfur (S⁰) and ferrous sulfate heptahydrate (FeSO4.7H2O) were investigated on cobalt, nickel and lithium bioleaching mechanisms. The results showed that increasing sulfur concentration improves lithium recovery; while it has no effect on cobalt and nickel dissolution. On the other hand, FeSO4.7H2O increased cobalt recovery and its leaching kinetic significantly. Fe²⁺ increased cobalt recovery by acting as reducing agent. Just within 2 days of bioleaching with 24.25 g/l FeSO4.7H2O, the Co, Ni and Li recoveries reached 99.9%, 99.7% and 84%. To reduce the process cost, iron sulfate heptahydrate was replaced with iron scrap. In bioleaching process, scrap was leached and produced Fe²⁺ which in turn acted as reducing agent and increased cobalt and nickel recoveries. The results showed that the final metals recoveries for tests with scrap and chemical FeSO4.7H2O are similar. Using iron scrap increased the bioleaching time from 2 days to 6 days. The formation of a jarosite layer on the surface of scrap particles limited the releasing ferrous ions. The microorganisms prefer to oxidize iron scrap particles before waste LIBs particles. Comparing the results of bioleaching and leaching tests shows that Li was dissolved due to acid leaching, Co was dissolved due to oxidation-reduction reactions and Ni dissolved due to direct bioleaching mechanism.
... Equation (1) describes a typical reaction for the JPP where A typically stands for potassium, sodium, hydronium, or ammonium. Other ions such as Tl + , Pb 2+ , or Ag + can be situated in A-sites as well [22][23][24][25]. Additionally, Fe 3+ can be replaced by other trivalent cations such as Al 3+ , Ga 3+ , or Cr 3+ [26,27]. ...
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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.
... These models can be used to predict the Co and Li recoveries in term of four investigated parameters. The p-values for both models are lower than 0.0001 which means that there is just 0.01% chance that models occur due to the noise (Ghassa et al., 2014). In addition, high F-values and R-squares indicate that statistical models have high validity. ...
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Recycling of lithium-ion batteries (LIBs) is essential not only to protect the environment but also to recover valuable metals, such as lithium and cobalt. The effect of ferrous (Fe²⁺) has been explored on LIBs leaching, as a reducing agent. The influence of four different parameters including agitation rate, pH, ferrous concentration and temperature has been investigated on LIBs leaching to optimize the leaching process and kinetics modelling. While ferrous ions did not have significant effect on lithium recovery, the cobalt recovery was increased from 33.6% to 88.7% when ferrous concentration were increased from 0 g/L to 6 g/L. The results indicated that the highest lithium and cobalt recoveries achieved at agitation rate = 500 rpm, pH = 0.5 (∼0.57 mol/L H2SO4), ferrous concentration = 6 g/L, and temperature = 75 °C. The kinetics modelling indicated that adding ferrous ions to leaching environment decreases the ash layer formation by reducing the metals in particles surface and transfer them in liquid medium. The activation energies for cobalt and lithium dissolution were 58.71 kJ/mol and 37.45 kJ/mol, respectively. After process optimization, the chemical ferrous ions were replaced by iron scraps were obtained from 18650 LIBs shells. The results showed that 92.67% of lithium and 98.91% of cobalt are recovered by adding 6 g/L iron scrap to the leaching environment. Therefore, the iron scrap can be used as an efficient, economic and sustainable reducing agent for LIBs leaching, at low concentrations of sulfuric acid.
... Recently, improving efficiency of chalcopyrite bioleaching has attracted more attentions, especially under growing environmental pressure and copper demand. Bioleaching is a complex process, involving interactions among biological, chemical and physical factors (Panda et al., 2013; Ghassa et al., 2014). Microorganism is recognized as the dominant factor dissolving mineral through a variety of biochemical reactions (Newman, 2010; Yelton et al., 2013). ...
... Among them, Acidithiobacillus ferrooxidans (A. ferrooxidans) is the most studied bacterium [6,11]. ...
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... All three suggested models are significant with p-Values lower than 0.005. The p-values indicated there are only 2.48%, 2.51%, and 1.58% chances that models for cobalt, nickel, and lithium recoveries occur due to noise (Ghassa et al., 2014). As mentioned, the test with center point conditions was repeated three times to investigate the leaching experiments repeatability (Sabzezari et al., 2019). ...
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Current paper introduces the iron scrap as a sustainable, economic and efficient reducing agent for cobalt, nickel, and lithium leaching from waste lithium ion batteries (LIBs). In this novel method, a reducing leaching environment was provided by releasing ferrous ions (Fe²⁺) from iron scrap dissolution. The effect of iron scrap concentration, solid content and reaction time were investigated in leaching process. The results showed that using iron scrap increases the cobalt and nickel dissolution significantly; while it has negligible influence on lithium recovery. The highest cobalt (99.1%), nickel (94.9%) and lithium (90.5%) recoveries were obtained at iron scrap concentration = 25 g/l, solid content = 10 g/l, leaching time = 150 min. The added iron then was removed from pregnant leach solution (PLS) by controlling the pH. The results showed that iron was removed efficiently at pH=4, without other metals co-precipitation. After iron removal, cobalt and nickel are recovered from PLS by cementation method with zinc scrap. The results showed that cobalt-nickel mixture can be produced with zinc cementation, without any manganese, lithium and iron impurities. Finally, a conceptual process flow diagram (PFD) is proposed for waste LIBs recycling. This PFD which includes grinding, physical separation, leaching and metals recovery from pregnant leach solution is a full flowsheet to recycle all valuable metals from LIBs.
... This was also due to less oxygen access to the grains, which had a negative effect on the proper activity of the bacteria. Ghassa et al. [57] confirmed the negative effect of increasing pulp density on Zn leaching. Tipre et al. [40] found that increasing the weight of the sample in solution resulted in lower bacterial activity. ...
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Nowadays, due to fast global industrial progress and near diminution of high-grade ore reserves, there has been massive call to cost-effectively process the resources of low-grade ores and industrial effluents for metal extraction. However, conventional approaches cannot be used to process such resources due to high capital cost and energy, also causing environmental pollution. Alternatively, bioleaching is highly environmental friendly and economic method to process such resources. Metal recovery from metal sulfide ore is carried out by chemolithotrophic bacteria like Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The same is done by heterotrophic microorganisms in non-sulfide ores. Additionally, for gold and copper extractions, bioleaching is used to extract cobalt, zinc, nickel, and uranium from low-grade ores and industrial effluents. In this review, the fundamental process of bioleaching from low-grade metal sulfide ores are discussed with emphasis on mechanism, types, pathways, techniques, and bioleaching development.
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AbstractSpent Zn-Mn button cells are one of the fastest-growing battery waste streams containing considerable amounts of Zn (12-28% (w/w)) and Mn (26-45% (w/w)) that could be considered as a potential industrially demanded source of Mn and Zn. However, due to the very toxic, stable, and refractory nature of the button cell batteries, applying microbial leaching for metal extraction from spent batteries is limited. In this regard, this study focused on detoxicate, enriching, and mobilizing major elements through thermal treatment assisted by acidic bioleaching. It was witnessed after thermal pretreatment of BCBs powder at 600 oC, the A. ferrooxidans could tolerate up to 20 g/L BCBs containing a high concentration of Mn and Zn by serial step-wise adaptation process. The use of thermal pretreatment increased by 76% and 75% extraction yields of Mn and Zn compared with the results obtained using un-thermally pretreated BCBs powder. The result indicated that 95% of zinc and 91% manganese were efficiently extracted from thermally pretreated BCBs. A. ferrooxidans and Fe3+ play an important role to improve Mn and Zn extraction efficiency. The structural and morphological analyses showed that the proposed approach could successfully overcome spent button cell batteries complexities and extract most of the major metals.
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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.
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More than 70% of the world's nickel reserves are found in laterite ores. In this research, a laterite ore sample, containing Ni, Co, and Fe, was employed to study the recovery of nickel and cobalt. Thus, the effect of calcination, acid concentration, percent solids, and stirring rate on nickel and cobalt recoveries from an iron‐rich laterite sample was investigated. Optimization with response surface methodology and kinetic studies were performed. The calcination of the sample prior to leaching at 500°C for 2 h provided condition for better nickel and cobalt dissolutions. At optimal conditions, the concentration of sulfuric acid, solid‐to‐liquid ratio, stirring speed, temperature, and time test were equal to 5 M, 0.1, 370 rpm, 90°C, and 2 h, respectively. The highest recoveries of nickel and cobalt were 65.9% and 63.1%, respectively. Solids content had a negative effect on Ni and Co recovery, whereas acid concentration was positively affected. Addition of 10% (w/v) NaCl in the presence of 5 M acid concentration, 60°C, 370 rpm, and leaching time of 2 h increased the nickel and cobalt recoveries, 15.3% and 21.4%, respectively. The high dependence of process on temperature indicates chemical control; the activation energies Ea = 59.54 and Ea = 45.74 kJ/mol, respectively, for nickel and cobalt, were also consistent with this conclusion.
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Biological methods for leaching of nonferrous and noble metals from its sulfide ores are widely applied at industrial enterprises of different countries. This process is based on the use of the oxidative activity of acidophilic microorganisms. Since all bio systems are quite sensitive to the temperature, bacterial leaching process also significantly effects. In the present study, the impact of temperature on bacterial leaching of Zn from its sulphide ore, sphalerite, was investigated using ore adapted iron oxidizing bacteria. The bacteria were isolated from mine drainage samples and subjected to gene sequencing. The acquired nucleotide sequence revealed that the isolate was Leptospirillum ferriphilum. The nucleotide sequence of L. ferriphilum isolate was submitted to National Center for Biotechnology Information (NCBI) and accession number KF743135 was assigned. Using the isolate, the Zn leaching data were collected in the 298–318 K temperature range. The results showed that leaching of Zn increases with temperature until optimum temperature of 313 K and achieves highest leaching efficiency of 96.96% within 20 days. Since bioleaching of minerals have become increasingly applied in different mining industries, there is immense important to analyze mechanistically-based kinetics for the design, optimization, operation, and control of biochemical processes. The kinetic study showed that the rate of Zn leaching was maximized at the optimum temperature. Further, the leaching data were analyzed using shrinking core model which revealed that the rate of leaching was inhibited by diffusion through product layer. Reaction kinetics is also to be contrasted with thermodynamics. Using Arrhenius law of thermodynamics, it was found that activation energy for Zn bioleaching reaction was 39.557 kJ mol−1. Such investigations will be necessitated for designing and implanting the ideal bioleaching system for metal bio-mining industries.
Article
The column bioleaching of copper flotation tailings was comparatively investigated using layered heap construction method (LM), agglomerate heap construction method (AM), and pellets-sintering heap construction method (PM). The bacterial communities of free, attached, weakly-attached, and strongly-attached microbes in the later bioleaching stage were investigated. In AM group, the addition of lump sulphide ore resulted in the low leachate pH, high ferric iron concentration, and rapid microbial adsorption, which obtained the maximum copper extraction (60.1%) compared with LM (54.6%) and PM (43.9%) groups. The relative abundance of dominant genera and microbial communities of different microbiota underwent changes in three heap construction methods. The alpha-diversity indexes of attached, weakly-attached, and strongly-attached microbes were different, while no significant change was observed in free bacteria. The variation of whole bacterial community was significantly associated with solution pH, total iron, and ferric iron concentrations. Pearson correlation analysis and partial least square path model both indicated that attached bacteria made larger contribution to the copper extraction of tailings.
Article
The bioleaching of nickel-containing sulfide minerals from five ophiolitic ore samples was investigated in this study, using a mesophilic, acidophilic consortium that included Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans, and Leptospirillum ferrooxidans. The experiments were carried out in the presence and absence of ferrous iron and elemental sulfur as additional energy sources for the bacteria. After 30 days of contact at 5% pulp density, nickel dissolution was in the range of 15–29% in the chemical leaching and 58–83% in the bioleaching. Accessory forsterite (Mg2SiO4) in the ophiolitic ore samples increased the acid consumption, attributed to the protonation of Mg-silicate surfaces. The ore samples with low Cr2O3/MgO ratios had high acid consumption. Post-leaching examination of solid residues showed the presence of a jarosite and sulfur layers, indicating mineral surface passivation and diffusion limitation. • Research highlights • The chemical and bioleaching of five Ni-sulfide samples was investigated • Ni bioleaching from some samples responded to Fe and sulfur addition • Leaching of samples with pentlandite yielded the highest Ni recoveries • Sulfur and a jarosite-type precipitate were formed as secondary phases • Lizardite was formed as a serpentinization alteration product of Mg-silicates
Article
The study aims to evaluate bioleaching of zinc sulfide concentrate in controlled redox potential fed-batch mode to avoid passivation occurring in redox non-controlled bioleaching. The microorganisms used in the bioleaching study were a mixed culture of iron-oxidizing microorganisms dominated with Leptospirillum ferriphilum. The motivation for the study was to cut down the cost involved in oxygen consumption due to suppression of sulfur oxidation and activating iron oxidation activity. This innovative approach was possible by carrying out bioleaching on a fed-batch mode with redox potential-controlled bioleaching. The redox-controlled bioleaching was carried out by 100% (v/v) inoculum with high redox potential 650 mV in the reaction vessel with controlled addition of zinc sulfide concentrate maintaining the redox between 550 and 650 mV. The solid percentage of 1% (v/v) of feed material (ZnS concentrate) in the redox-controlled experiment was considered for a batch mode of redox non-controlled experiment for a potential comparative assessment of fed-batch and batch modes. The fed-batch experiment succeeded in restricting the sulfur passivation layer. The time taken by the fed-batch experiment was two times shorter than the batch experiment. The recovery percentage of Zn in redox-controlled batch mode experiment was 51.6%, while in redox-controlled fed-batch mode experiment was 69.4%, which resulted in 34.55% higher recovery in redox-controlled fed-batch bioleaching of ZnS concentrate. The fed-batch bioleaching using iron-oxidizing microorganisms with controlled redox potential restricted sulfur oxidation and was advantageous over the batch process.
Article
To verifying the feasibility of uranium recovery with fungal metabolic products in large-scale applications, column leaching and ion exchange of uranium was carried out. The uranium recovery reached 81.76 % in 14 days. The ion exchange curve for the leach solution obtained with the metabolic products of Aspergillus niger was in the shape of a wave. The elution curve was similar to that of leaching with H2SO4. The results indicate that leaching with the metabolic products of A. niger is a promising and environmentally friendly method for exploitation of low grade uranium ores in large-scale applications.
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The origin of a rational (scientific) approach to extraction of metal values from ores with the aid of microorganisms (bioleaching) is traced. The removal by microbiological means of ore constituents that interfere with metal extraction (biobeneficiation), an outgrowth from bioleaching, is also traced. © 2004 SDU. All rights reserved.
Article
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The purpose of this study is to test the feasibility of using mixed culture of iron and sulfur-oxidizing bacteria for the dissolution of metals from high-grade zinc and lead sulfide ore. Considering that the roll crusher could reduce the ore size to less than 2 mm, this size fraction was selected in order to study the possibility of removing mill circuit. Effects of parameters such as pulp density, initial pH, Fe2+, oxidation–reduction potential (ORP), and pH fluctuations were investigated, as well. The maximum Zn dissolution was achieved under the conditions of initial pH 2, initial 75 g/L FeSO4 · 7H2O, and pulp density of 50 g/L. The results indicated that under the optimum conditions, about 68.8% of zinc was leached during 24 days of bacterial leaching treatment. The lead recoveries were low (about 1%), because of precipitation of Pb as lead arsenate chloride. Furthermore, the surface studies by using SEM images showed that during chemical leaching the ore dissolution starts from surface discontinuities, but in bacterial leaching all surface becomes involved. In addition, in another process the ore was leached separately with sulfuric acid and sodium hydroxide, and then final results were compared to the bacterial leaching tests in order to find the optimum hydrometallurgical method to extract zinc and lead from these ores.
Article
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Biomining is currently used successfully for the commercial-scale recovery of met- als such as copper, cobalt, and gold from their ores. The mechanism of metal extraction is mainly chemistry-driven and is due to the action of a combination of ferric and hydrogen ions, depending on the type of mineral. These ions are produced by the activity of chemolithotrophic microorganisms that use either iron or sulfur as their energy source and grow in highly acidic conditions. Therefore, metal extraction is a combination of chemistry and microbiology. The mixture of organisms present may vary between processes and is highly dependent on the temperature at which mineral oxidation takes place. In general, rel- atively low-efficiency dump and heap irrigation processes are used for base metal recovery, while the biooxidation of difficult-to-treat gold-bearing arsenopyrite concentrates is carried out in highly aerated stirred-tank reactors. Bioleaching reactions, the debate as to whether the reactions are direct or indirect, the role of microorganisms, and the types of processes by which metals are extracted from their ores are described. In addition, some new processes under development and the challenges that they present are discussed.
Conference Paper
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Bioleaching/biooxidation is essentially a dissolution process with the involvement of acidophilic bacteria acting as the "catalyst" to accelerate the dissolution of metals from sulfide minerals. The contribution of bacteria to the metal dissolution is closely controlled by the growth of bacteria, which is itself affected by the physico-chemical conditions within the bioleaching environment. There are a number of operating parameters controlling bioleaching processes, which are required to be maintained within a certain range in the leaching environment whereby the activity of bacteria with the resultant oxidation of sulfide minerals can be optimized. In this regard temperature, acidity, oxidizing conditions, availability of nutrients, oxygen and carbon dioxide, surface area and presence of toxic ions are of prime importance for control and optimization of bioleaching of sulfide ores/concentrates. Bioleaching processes are temperature and pH dependent with optimum metal dissolution occurring in a particular range where the bacterial strain is most active e.g. mesophiles at 35-40°C and pH 1.6-2.0. Provision of nutrient salts is required to maintain the optimum growth and hence metal dissolution with the quantity of nutrients apparently being dependent on the availability of substrate i.e. head grade/pulp density of an ore/concentrate. Oxygen transfer is one of the most critical factors since the oxygen levels below 1-2 mg/l may adversely affect the oxidizing activity of bacteria. Bioleaching rate tends to improve with increasing the surface area at low pulp densities but, in practice, the pulp density is limited to ~20% w/v. Increasing concentrations of ions such as Cl -may also adversely affect the oxidative activity of bacteria.
Article
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A scanning electron microscope (SEM) study was performed to provide a visual insight into the oxidation patterns of sulfide minerals during chemical and bacterial leaching of a complex ore for 3 days. The mineral grains were studied under SEM before and after bacterial and chemical leaching with or without the addition of ferrous iron to generate ferric iron in situ by bacteria or chemical oxidant (MnO2). Both mesophilic and moderately thermophilic cultures of bacteria were used in bioleaching tests. A limited oxidation of sphalerite and pyrite, similar to those in acid leaching (control), was observed to occur when no ferrous iron was added. However, the initial addition of ferrous iron into bioleaching media was shown to significantly improve the oxidation of sphalerite and pyrite. Galena was readily oxidized in the presence or absence of bacteria. Sphalerite was oxidized more extensively/selectively than chalcopyrite and pyrite, consistent with their respective nobility/electrochemical activity. Provided that chemical/biological oxidation of sphalerite was intensive, a sulfur-rich layer appeared to form on mineral surface. But, no such layer on pyrite surfaces was discernable. Supplementary bioleaching data were also provided to support SEM observations and to further elucidate the bioleaching characteristics of these sulfide phases. It can be inferred from this study that the oxidation of sulfides proceeds most discernibly via “indirect mechanism” and the generation of ferric iron by bacteria in sufficient quantity is essential for the effective oxidation of sulfide minerals.
Chapter
Bacteria that bring about dissimilatory transformations of iron are important from both biogeochemical and industrial perspectives (Ehrlich and Brierley, 1990; Johnson, 1995). The oxido-reduction of iron in extremely acidic (pH > 3) environments is particularly interesting because of the greater solubility of ionic (particularly ferric) iron and the relative stability of soluble ferrous iron under these conditions. Acidophilic iron-oxidizing bacteria are generally considered the most significant microorganisms in the biological processing of sulfide ores (“biomining”) in which the accelerated oxidative dissolution of sulfidic minerals (e.g., pyrite, arsenopyrite, and chalcopyrite) solubilizes (e.g., copper) or releases (refractory gold) metals, thereby facilitating their recovery (Rawlings and Silver, 1995). Most research into bacterial iron transformations at low pH has focused on mesophilic chemolithotrophs, particularly Thiobacillus ferrooxidans, though a number of physiologically and phenotypically diverse mesophilic acidophiles, it is now known, are involved in the dissimilatory oxido-reduction of iron (Johnson, 1995; Norris and Johnson, 1997; Pronk and Johnson, 1992).
Article
The hydrometallurgical treatment of zinc sulfide concentrates involves the separation of zinc from iron, since most zinc concentrates contain 5-12% iron. Several processes, such as hematite, magnetite, goethite and jarosite, have been developed for the removal of iron from solution prior to zinc electrolysis. The precipitation of iron is controlled by a set of thermodynamic and kinetic factors operative both in iron solutions and in precipitates. Identifying these factors and their relations is important for the control of these processes. Inbrief, thermodynamic stability regions of iron compounds formed during the jarosite and goethite processes, which are commercially used in the zinc industry, are outlined in this paper.
Article
This paper is a progress report on the commercialization of using bioleaching for base-metal concentrates. The paper focuses on bioleach processes for recovering copper from chalcopyrite and nickel/cobalt from pentlandite/pyrrhotite. Data is discussed from pilot-plant trials in which an overall recovery >95% was obtained for the bioleaching of copper from chalcopyrite. The pilot plant was operated in closed circuit with solvent extraction and electrowinning circuits for final metal recovery. For the bioleaching of nickel and cobalt from pentlandite/pyrrhotite, an overall recovery of 97% was achieved. Precipitation routines were used to produce a final nickel/cobalt product. The pilot plants were capable of treating a few kilograms of concentrate per day. Prominent features in the design of a 1-t/day (1.1-stpd) copper-bioleach demonstration plant for the treatment of chalcopyrite concentrate are discussed. The plant, which is now under design, will be constructed and operated based on the results obtained from the laboratory pilot-plant campaigns. Issues of scale-up for the demonstration plant, together with integration into upstream and downstream processing, are also addressed. Independently derived capital and operating costs are presented for a possible commercial plant. These cost studies indicate the principle economic issues in considering the application of bioleaching to the extraction of base metals. The benefits of bioleaching complex concentrates that are not amenable to physical beneficiation and economic treatment by conventional smelting are highlighted. Issues, such as the environmental aspects, that illustrate the benefits of bioleach technology are given.
Chapter
The recovery of mineral and metal values by solution mining has been practiced for centuries. What appears at first glance to be a simple, empirical technique, is in actuality a very complicated process involving a large number of critical parameters that encompass several scientific and engineering disciplines. Hydrometallurgy, hydrology, geology and geochemistry, rock mechanics, chemistry, and environmental engineering and management are a few of the specialties utilized by modern operators. Solution mining is conveniently divided into three main categories: heap leaching, dump leaching, and in situ leaching. In situ leaching (ISL) involves the application of a specific lixiviant to dissolve en masse minerals within the confines of a deposit or in very close proximity to its original geologic setting. Currently there is considerable interest in applying ISL technology to recover copper. Substantial research and engineering effort is being expended to recover copper from oxide ores. However, the greatest potential for copper ISL extraction remains with the deep seated deposits that would otherwise be left unmined by conventional methods. This paper highlights some historical aspects of copper in situ leaching, and also reviews some commercial and experimental projects involving both oxide and sulfide deposits. In addition, large whole-core leaching experiments using a copper oxide ore will be described. This work has provided better understanding of the physical and chemical factors associated with the in situ leaching response.
Article
Microbiological leaching has been used as an alternative approach to conventional hydrometallurgical methods of uranium extraction. In the microbiological leaching process, iron-oxidizing bacteria oxidize pyritic phases to ferric iron and sulfuric acid, and uranium is solubilized from the ore due to sulfuric acid attack. If uranium in the ore material is in the reduced, tetravalent form (UIV), a redox reaction is involved whereby uranium is oxidized to the hexavalent form (UVI) upon dissolution. In acid-leaching systems, the primary oxidant is ferric iron, which is reduced to ferrous iron by its chemical reaction with UIV. The ferrous iron thus formed is reoxidized to ferric iron by iron-oxidizing bacteria such as Thiobacillus ferrooxidans and Leptospirillum ferrooxidans. Nutritional requirements and responses to environmental extremes of acidophilic iron-oxidizing bacteria are appraised. The S-entity in Fe-sulfides is oxidized to sulfate by bacteria similar to Thiobacillus ferrooxidans and Thiobacillus thiooxidans. Pyrite and marcasite oxidation is a sulfuric acid forming reaction. Heap, dump and in situ leach techniques are feasible as bacterial leaching systems.
Article
An experimental study of the bacterial oxidation of naturally occurring high-purity sulphide minerals (FeS//2, Fe//1// minus //xS, Cu//5FeS//4, ZnS) is presented using a mesophilic strain of T. ferrooxidans. As well as metal analyses and solution pH, partitioning of sulphide sulphur into elemental sulphur and sulphate has been monitored as a function of leach time. Partially oxidized sulphide substrates have been characterized, at regular time intervals, by X-ray diffraction methods and extracellular organic compounds reporting into leach solution have been identified by thin layer chromatography.
Chapter
GENCOR S.A. Ltd. has pioneered the commercialization of biooxidation of refractory gold ores. Development of the BIOX® process started in the late 197os at GENCOR Process Research, in Johannesburg, South Africa. The early work was championed by Eric Livesey-Goldblatt, the manager of GENCOR Process Research who directed pioneering and innovative research into bacterial oxidation of refractory gold ores prior to cyanidation. This work was driven by the need to replace Fairview’s outmoded Edward’s roasters, which at the time were seriously contributing to pollution in the Barberton area.
Article
This research aimed at finding the factors with more impact on the bioleaching of a spent hydrocracking catalyst by thermophilic acidophilic archaea called Acidianus brierleyi and determining the optimal condition in order to reach the maximum metals recovery. Initially, four more significant factors affecting the bioleaching efficiency including pH, pulp density, inoculation and elemental sulfur concentration, were screened and identified among ten key factors using Plackett-Burman factorial design. Next, a central composite design was applied to obtain the optimum conditions for achieving the maximum efficiency of the bioleaching process. pH 1.6, pulp density 0.6% (w/v), inoculation 4% (v/v) and elemental sulfur concentration 4 g/L were determined as the best conditions to reach the maximum recovery of the process. The experimental recoveries in optimal conditions were 35%, 83% and 69% for Al, Mo and Ni, respectively. To better understanding the mechanism of the leaching reaction, the rate limiting step of the process was determined under the optimum conditions and it revealed that diffusion through product layer is the rate controlling step.
Article
The leachability tests for manufacturing scrap TV boards (STVB) have indicated the release of metals beyond the limit levels with potential problems for environmental pollution. Treatment of STVB is therefore requisite for its safe disposal in landfills. The nitric acid leaching of STVB for the removal/recovery of valuable metals (Cu and Ag) was studied by adopting the Box–Behnken design. Statistical analysis of data has revealed that the concentration of nitric acid is the most influential parameter affecting the leaching process. Effects of solids ratio and temperature on the rate and extent of the extraction of copper were also proved to be statistically significant. However, the interaction effects of these parameters were found to be insignificant. The leaching kinetics were consistent with the shrinking particle model under chemical control with an activation energy of 38.6 kJ/mol. High concentrations of nitric acid (2–5 M HNO3) were required to achieve high copper extractions (88.5–99.9%) at a pulp density of 6% w/v. The extraction of silver was enhanced from 14% to 68% with increasing the concentration of nitric acid from 1 to 5 M. These findings also demonstrate that copper may well be selectively extracted from STVB by adjusting the concentration of nitric acid.
Article
In this research, the bioleaching mechanism of zinc and lead from high-grade Zn–Pb ore has been investigated. It is done by using mixed culture of iron and sulfur oxidizing moderate thermophilic bacteria at 45 C. Pulp density, initial pH and ferrous concentration were studied as influential parameters in bioleaching experiments. The optimum conditions were achieved at pulp density = 50 (g/L), initial pH = 1 and FeSO4.7H2O concentration = 75 (g/L) with 98.5% zinc recovery after 25 days treatment. Generally, an increase in ferrous concentration caused an improve zinc recovery, and an increase in initial pH and pulp density caused reduction in zinc recovery. However, in the test with optimum condition the lead dissolution was just 0.027% due to the lower Pb solubility. Furthermore, cadmium dissolution was 98% under optimum condition and results showed the cadmium dissolution was in direct proportion with zinc dissolution. Finally, 7.82% of arsenic and 8.52% of antimony dissolved during zinc bioleaching after 25 days treatment, both under above mentioned optimum condition.
Article
Mixed mesophilic and extreme thermophilic bioleaching were evaluated to remove copper from the molybdenite concentrate. Bioleaching tests were carried out in shake flasks and in a 50-L bioreactor. The shake flask tests were performed with different inoculum size, solids density, pH, and temperature in order to identify optimum conditions. The highest amount of copper elimination, 75% was obtained with extreme thermophilic microorganisms (at 12% inoculation, 10% solids, 65 °C and a pH of 1.5). The highest copper elimination by mesophilic microorganisms was 55% (at 12% inoculation, 5% solids, 30 °C at pH 2). The optimum conditions in shake flask tests were applied to 7 days batch tests in a 50-L bioreactor. Extreme thermophilic experiment gave the best copper elimination of 60% (at 12% inoculation, 10% solids, 65 °C and pH 1.5). Mesophilic test removed 50% of the copper (at 12% inoculation, 10% solids, 35 °C at pH 2).
Article
Focusing bands, as “hot spots”, severely influence the clean-up verification of contaminated soil remediation projects using electrokinetic remediation (EKR) technology. In this experiment, artificial high conductance bands (HCB) were created in the Cr(VI)-contaminated kaolin–gypsum soil to imitate the conductance heterogeneity of nature soils. Potential gradient monitoring was used to trace the behavior of HCBs. Visual observation and X-ray fluorescence analysis were used to trace the generation and moving patterns of the focusing bands caused by HCBs. Results show that the HCBs caused focusing bands in the soil by ion-induced potential gradient trapping effect (IIPGWTE), not chemical precipitation or isoelectric effect, and the heavier the HCB, the heavier the focusing phenomenon. The HCBs gradually disappeared due to the ionic diffusion increase caused by temperature increase during EKR, whereas the focusing bands remained and moved toward the anodes. In addition to causing focusing bands, some HCBs also could prolong the EKR duration resulting in higher energy consumption. In this case, the HCB’s location plays more significant role than its magnitude. Only the HCB that is caught up with by the tail of chromium (VI) plug-flow can slow down the EKR process resulting in lower energy efficiency.
Article
In this study the performance of Fe(III) formed in situ, generated by oxidizing Fe(II) with H2O2 or KMnO4 (denoted as H2O2–Fe(II) or KMnO4–Fe(II) process), for As(V) removal was compared with FeCl3 coagulation and the mechanisms were explored. The optimum oxidant/Fe(II) molar ratios for the H2O2–Fe(II) and KMnO4–Fe(II) processes were 1:2 and 1:3, respectively. The advantage of Fe(III) formed in situ over pre-formed Fe(III) for As(V) removal was strongly dependent on the Fe/As ratio and the advantage became less significant at high Fe/As ratio. The hydrolysis of Fe(III) formed in situ generated much more Feb species than the pre-formed Fe(III) did. Moreover, Fe(III) formed in situ hydrolyzed more slowly and generated flocs with smaller size compared to the pre-formed Fe(III) did over the pH range of 6.0–8.0. An introduction of high shear force for 1 min in the flocculation stage to break the aggregates into small particles enhanced the uptake of As(V) by pre-formed Fe(III) to a larger extent than that by Fe(III) formed in situ. The good performance of Fe(III) formed in situ for As(V) removal should be ascribed primarily to slow floc aggregation rate and small floc size and secondly to the formation of large amount of polymeric hydrolysis species.
Article
The leaching kinetics of zinc residue, having total Zn content of 12.31%, along with other metallic components such as Fe and Pb, is leached using sulfuric acid as solvent, augmented with ultrasound is presented. The effects of variables such as the leaching temperature, sulfuric acid concentration, particle size, liquid/solid ratio and the ultrasound power have been assessed. The results show the maximum recovery of zinc to be 80% at an ultrasound power of 160 W, leaching temperature of 65 °C, sulfuric acid concentration of 1.4 mol/L, particle size range of 74–89 μm and liquid/solid ratio of 4. The kinetics of leaching is modeled using shrinking core model and the rate controlling step is identified to be the diffusion through the product layer. The raw and the leached residue are characterized using XRD and SEM/EDX analysis. The activation energy is estimated to be 6.57 KJ/mol, while the order of reaction with respect to sulfuric acid concentration is 0.94 and particle size is 0.12 respectively.
Article
A study was carried out to examine the possibility for Aspergillus niger strain KBS4 to bioleach metals from sulphide ore with low concentration of arsenic and to optimize the parameters that affect this process by orthogonal array optimization. Fungal sample was collected, purified and sequenced. The bioleaching process was optimized with L25 Taguchi orthogonal experimental array design. Five factors were investigated and 25 batch bioleaching tests were run at five levels for each factor. The parameters were initial pH, particle size, pulp density, initial inoculums and residence time for bioleaching. The experimental results showed that under optimized leaching conditions: pH 5.5, particle size 180 μm, initial inoculums size 3×107 spores per ml, pulp density 15% and residence time of 20 days, the bioleach ability of metals were 63% Fe, 68% Zn, 60% As, 79% Cu and 54% Al. The biosorption of metal ions by fungal biomass might occur during the bioleaching process but it did not hinder the removal of metal ions by bioleaching.
Article
The application of the response surface methodology and the central composite design (CCD) technique for modeling and optimization of the influence of some operating variables on copper, molybdenum and rhenium recoveries in a bioleaching process was investigated. Three main bioleaching parameters, namely pH, solid concentration and inoculum percent, were changed during the bioleaching tests based on CCD. The ranges of the bioleaching process variables used in the design were as follows: pH 1.46–2.14, solid concentration 0.95%–11.05%, and inoculum percent 1.59%–18.41%. A total of 20 bioleaching tests were carried out by the CCD method according to software-based designed matrix. Empirical model equations were developed according to the copper, molybdenum and rhenium recoveries obtained with these three parameters. Model equations of responses at the base of parameters were achieved by using statistical software. The model equations were then individually optimized by using quadratic programming to maximize copper, molybdenum and rhenium recoveries individually within the experimental range. The optimum conditions for copper recovery were pH 1.68, solid concentration 0.95% and the inoculum 18.41% (v/v), while molybdenum and rhenium recoveries were 2.18% and 24.41%, respectively. The predicted values for copper, molybdenum and rhenium recoveries were found to be in good agreement with the experimental values. Also jarosite formation during bioleaching tests was also investigated.
Article
A study of the effect of different variables (inoculation, pulp density, [Ag], nutrient medium, pH and [Fe3+]) on the silver-catalyzed bioleaching of a low-grade copper sulfide ore has been carried out in shake flasks. Chalcopyrite was the dominant copper mineral in the ore. Preliminary tests showed that addition of other ions (Sb, Bi, Co, Mn, Ni and Sn) did not enhance the copper dissolution rate. Conversely, an inoculation with mesophilic microorganisms and the addition of silver had a markedly catalytic effect on the extraction of copper. The kinetics of the silver-catalyzed chalcopyritic ore bioleaching was greatly affected by pulp density and silver concentration. Small amounts of silver (14.7 g Ag/kg Cu) dramatically accelerated the copper dissolution process while large amounts (294.12 g Ag/kg Cu) had an inhibitory effect. The copper dissolution rate was slightly affected in the range of pH between 1.2 and 2.5 but was significantly slower at pH 3.0. The effect of [Fe3+] in the presence of silver was studied both in abiotic and biotic conditions. High ferric iron concentrations in abiotic tests recovered similar copper amounts (∼ 95%) to those obtained without or with low [Fe3+] in the presence of bacteria. The leaching of copper from the low-grade copper ore can be very effectively enhanced with silver and mesophilic microorganisms. For that system, the onset of oxidizing conditions starts at an Eh value slightly higher than 650 mV. Above that critical value of potential the copper dissolution rate slows down. This also corresponds with the completion of the leaching process. As the potential rises past 650 mV, the copper extraction reaches a plateau.
Article
In this study, we have investigated the bioleaching potential of a native strain of Acidithiobacillus ferrooxidans isolated from zinc and lead sulfide mines under varied ambient conditions of growth and substrate consumption. The effects of intermittent irrigation, type of agglomeration, feed formulation in terms of acid, enriched salt solution, initial number of microorganism, and their interactions on the bioleaching of low-grade zinc sulfide ores (containing 5.78% zinc) on growth and biooxidation efficiency of the bacteria have been evaluated. Bioleaching capacities of the isolate were optimized by the utilization the Taguchi method (e-qualitic-4) for design of experiments. As a result, eight column bioreactors with 5.7kg ore (100%
Article
Both Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans attached to pyrite rapidly, reaching the adsorption equilibrium in 20–25min. Furthermore, the adsorption content of substrate-grown bacteria was larger than that of solution-grown ones. Zeta potential studies revealed that isoelectric points (IEP) of pyrite shifted to lower pH after interacting with bacteria.Iron solubilisation by the mixed culture was faster than that for the A. ferrooxidans. There was no close relation between iron recovery and fineness. Circular, square and elongated etch pits were visible by scanning electron microscopy (SEM). Moreover, jarosite in the leaching of 3%(w/v) pulp density was detected by Fourier transform infrared spectroscopy(FTIR) and X-ray diffraction(XRD), though the pH of the solutions declined to below 1.00. S was not detected in the leaching residues. Furthermore, the contact angles showed there was no S produced. These results point to a thiosulfate mechanism in pyrite bioleaching, where the thiosulfate leads to sulphate without S formation.
Article
Bioleaching processes for extraction of zinc from sphalerite are more environmentally friendly and consume less energy than conventional technologies but are as yet less economic. One necessary step towards arriving at a cost-effective sphalerite bioleaching process is the use of appropriate methodology for the optimization of pertinent factors in such processes. Previous studies on Zn bioleaching systems have reported a fairly wide range of values as the optimum level of relevant physicochemical parameters for Zn bioleaching processes. This is partly due to the different strains and Zn source type employed but another reason could be that important parameters in this process interact with each other. In order to shed more light on this matter, in the present work Response Surface Methodology was employed for the study and optimization of important factors in a sphalerite bioleaching process by Acidithiobacillus ferrooxidans using shaking bioreactors. The effect of change in the levels of temperature, pH, initial Fe(II) concentration and pulp density – in the range 30–36°C, 1.4–2.0, 3–11gL−1 and 4–6% wt/vol respectively – on the rate Zn bioleaching was studied using a Central Composite Design. The results showed a statistically significant effect of pH and pulp density – and to a lesser extent temperature and initial Fe(II) concentration – on the rate of bioleaching of Zn. A statistically significant interaction was found between pH and temperature, which means that the optimum values of these two parameters can only be correctly obtained through the use of factorial design of experiments. Additionally, the optimum level of temperature and pH was found to depend on the level of pulp density. This means that when employing shaking bioreactors for optimization of these parameters the level of pulp density should be carefully chosen. However, there was no statistically significant interaction between initial Fe(II) concentration and the other three factors studied.
Article
Acid mine drainage (AMD) represents a serious environmental problem related to sulfide minerals and coal mining. High content of toxic metals and high acidity in AMD adversely affects surface water, groundwater and soil. The abandoned mine of the Smolník deposit in Slovakia is a typical example in this respect. The quality of AMD needs to be monitored and suitable treatment methods need to be developed.The aim of this paper was to demonstrate the technical feasibility of heavy metals removal from AMD using physical–chemical and biological–chemical methods. The base of the physical–chemical method was electrowinning. The principle of the biological–chemical method was the selective sequential precipitation (SSP) of metals with the application of hydrogen sulfide produced by sulfate-reducing bacteria and sodium hydroxide solution. Both the electrowinning and SSP processes decrease the content of heavy metals in AMD. The pre-treatment of AMD by chemical iron–aluminum precipitation (in the case of electrowinning tests) and chemical iron precipitation (in the case of SSP tests) improved the selectivity of the processes. A further aim of the work was the improvement of the SSP.During the electrochemical experiments, 99% Zn removal – under metallic form – and 94% Mn removal – under MnO2 form – both with a high degree of purity, were achieved. The SSP process reached the selective precipitation of chosen metals with 99% efficiency – Fe, Al and Mn in the form of metal hydroxides, Cu and Zn as metal sulfides. The results achieved may be used for designing a process appropriate for the selective recovery of metals from the AMD discharged from the Smolník deposit.
Article
Billiton Process Research has carried out extensive research over the past four years to develop new process technology using bioleaching for extraction of copper and nickel from their sulphide concentrates. Continuous pilot scale and laboratory batch testwork has been carried out with adapted mesophile bacterial cultures at 40°C - 45°C, moderate thermophile cultures at 50°C - 55°C and thermophile cultures at 65°C - 85°C. Pilot scale work has demonstrated the commercial viability of mesophile cultures for bioleaching of secondary copper sulphide and nickel sulphide concentrates. Moderate thermophiles offer benefits in terms of reduced cooling requirements for commercial reactors and, in the case of bioleaching of nickel concentrates, some selectivity over bioleaching of pyrite. Continuous pilot scale testwork has shown that thermophiles achieve efficient bioleaching of primary copper sulphide and nickel sulphide concentrates, giving much higher recoveries than achieved by bioleaching with a mesophile or moderate thermophile culture.
Article
Previous studies identifying Fe3+ as the main oxidizing agent in CuFeS2 bioleaching suggests that if the precipitation of additional Fe3+ could be prevented, the Cu extraction yields should be enhanced. In this respect, the acid-generating nature of the biologically mediated oxidation of additional S0 to H2SO4 should theoretically serve as a pH regulator as well as biomass generator. This should prevent the precipitation of Fe3+ and attenuate the biomass reduction caused by the inhibitory effect of high Fe3+ concentrations. To prove the former hypothesis, three thermophile strains were employed for bioleaching of chalcopyrite under various additional S0 and Fe3+ concentrations. The hypotheses about additional S0 application were fully confirmed; the addition of S0 alone enhanced the leaching rates with A. brierleyi and M. sedula in media at initial pH 2. Although higher initial leaching rates were obtained with additional Fe3+, its role as the main leaching factor is questioned; leaching with thermophiles appears to depend on the availability of protons and ORP rather than on the prevention of Fe3+ precipitation. Additional S0 in media with high Fe3+ concentrations has shown the best improvements in the case of bioleaching with A. brierleyi, whereas improvements in bioleaching with M. sedula and S. metallicus were less notable.
Article
Bioleaching, also referred to as minerals biooxidation, and bioremediation have been widely employed commercially for heap and dump bioleaching of secondary copper sulfide ores, sulfidic-refractory gold concentrates and treatment of acid rock drainage. Technical and commercial challenges, identified in this paper, remain for bioleaching of primary sulfides and complex ores. New frontiers for the technology exist in processing massive sulfides, silicate-locked minerals and in the more distant future in-situ leaching. Decommissioning of cyanide heap leach operations and stabilizing mine wastes using biotechnology are opportunities requiring intensive and focused research, development and engineering efforts.
Article
The purpose of this study was to test the feasibility of using iron and sulphur oxidizing bacteria for the acid leaching of a high grade Pb–Zn ore material. Three strains (ATCC 13661, NCIMB 13537 and C2-TF) of Acidithiobacillus ferrooxidans and two strains (MT-TH1 and MT-13) of Sulfobacillus thermosulfidooxidans were tested in this study. The bioleaching was monitored by measuring the dissolved metals and by X-ray diffraction analysis of leach residues. The bioleaching efficiency varied between 0.014 and 0.35. The maximum dissolution of lead was achieved with the mesophilic At. ferrooxidans (NCIMB 13537) at 30 °C. The maximum recovery of zinc was achieved with moderately thermopilic S. thermosulfidooxidans (MT-TH1) at 45 °C.
Article
The electrochemical response of massive chalcopyrite electrodes bioleached with mesophile microorganisms in both presence and absence of Ag(I) ions was studied using linear and cyclic voltammetry. The electrolyte employed for the electrochemical tests was the medium used to bioleaching the electrodes (3.0 g/L (NH4)2·SO4, 0.5 g/L K2HPO4, 0.5 g/L MgSO4·7H2O and 0.1 g/L Ca(NO3)2).The results showed small differences in voltagramms carried out in presence and absence of Ag(I): In bioleached electrodes tested in presence of Ag(I) ions, the anodic and cathodic current signals were bigger than when Ag(I) ions were not present. Moreover, the passivation of chalcopyrite occurred at two different times: First, the passivation was observed in the bioleached electrodes in absence of Ag(I) and after in the bioleached electrodes in presence of Ag(I). The pre-wave observed in the anodic dissolution of the chalcopyrite was not seen in the bioleached electrodes in absence of Ag(I) ions, but in the electrode treated with bacteria in presence of Ag(I) ions an increase in current signals was observed.
Article
The technical viability of the BRISA process (Biolixiviación Rápida Indirecta con Separación de Acciones: Fast Indirect Bioleaching with Actions Separation) for the copper recovery from chalcopyrite concentrates has been proved. Two copper concentrates (with a copper content of 8.9 and 9.9 wt.%) with chalcopyrite as the dominant copper mineral have been leached with ferric sulphate at 12 g/L of ferric iron and pH 1.25 in agitated reactors using silver as a catalyst. Effects of temperature, amount of catalyst and catalyst addition time have been investigated. Small amounts of catalyst (from 0.5 to 2 mg Ag/g concentrate) were required to achieve high copper extractions (>95%) from concentrates at 70 °C and 8–10 h leaching. Liquors generated in the chemical leaching were biooxidized for ferrous iron oxidation and ferric regeneration with a mixed culture of ferrooxidant bacteria. No inhibition effect inherent in the liquor composition was detected. The silver added as a catalyst remained in the solid residue, and it was never detected in solution. The recovery of silver may be achieved by leaching the leach residue in an acid-brine medium with 200 g/L of NaCl and either hydrochloric or sulphuric acid, provided that elemental sulphur has been previously removed by steam hot filtration. The effect of variables such as temperature, NaCl concentration, type of acid and acidity–pulp density relationship on the silver extraction from an elemental sulphur-free residue has been examined. It is possible to obtain total recovery of the silver added as a catalyst plus 75% of the silver originally present in concentrate B (44 mg/kg) by leaching a leach residue with a 200 g/L NaCl–0.5 M H2SO4 medium at 90 °C and 10 wt.% of pulp density in two stages of 2 h each. The incorporation of silver catalysis to the BRISA process allows a technology based on bioleaching capable of processing chalcopyrite concentrates with rapid kinetics.
Article
Affecting factors, such as ore size, leaching temperature, holding time, alkaline concentration and liquid: solid ratio (volume/weight) (L/S), were studied to leach refractory hemimorphite [Zn4(Si2O7)(OH)·H2O] zinc oxide ores with NaOH solution in this paper. The impact of leaching recovery of Zn and its concomitant metals was checked through experiments. Results showed that when the ores of 65–76 µm size were leached for 2 h at 358 K in the presence of 5 mol/L sodium hydroxide and liquid:solid ratio of 10:1, the leaching rate of Zn, Al, Pb and Cd were about 73%, 45%, 11% and 5%, respectively, but that of Fe was less than 1‰. Moreover, the leaching experiments were repetitive and reliable. And the kinetic study indicates that the calculated activation energy is 45.7 kJ/mol, which illuminates that alkaline leaching the refractory hemimorphite [Zn4(Si2O7)(OH)⁎H2O] zinc oxide ores is controlled by the chemical process of the reaction of leach liquor and ores in the whole leach process.
Article
The development of molecular tools for the detection and quantification of both species as well as functional traits, aids in a better understanding and control of microbial processes. Presently, these methods can also be used to assess the activity of these organisms or functions, even in complex ecosystems and difficult matrices such as ores and low pH samples. In this paper we present the versatility of one of these tools, Q-PCR, to allow accurate and fast insight in changes in two types of microbial processes representing two ways in which microbes can interact with metals, bioleaching and bioprecipitation. Using the Q-PCR technique it was possible to identify and quantify the thermoacidophilic archaeon Acidianus sp. to be the main microbial strain responsible for biooxidation of arsenite in a low pH reactor. The method was also used to study the dynamics between the iron oxidizing and sulfur oxidizing acidophiles during bioleaching of a zinc concentrate in a batch reactor system and showed that the iron oxidizer Leptospirillum ferriphilum that dominated the starting culture disappeared upon addition of the concentrate. Gradually, bacterial activity was regained starting with growth of sulfur oxidizers and at later stage iron oxidizers started to grow. Molecular analysis can be used to direct research to the relevant organisms involved and concentrate on improving their application (in the arsenite case Acidianus sp.) or in understanding appearances and disappearances of microorganisms (during leaching of zinc concentrate the disappearance of Leptospirillum after high inoculation levels) in order to allow optimization of leaching efficiencies at the lowest (oxygen) costs.
Article
Currently, low-grade and complex ores and mining wastes can be processed economically by using bacteria in heap and agitation leaching processes. Bacterial leaching tests are performed on the run-of-mine ore which is a mixture of two different massive and dissemine copper ores, fed to Küre Copper Plant. In this leaching process, using "Acidithiobacillus ferrooxidans" culture, bacteria count, pH, copper and iron recoveries are monitored during the 576 hours of test period. By increasing the solid ratio (1 %→5 %) the oxidation ability of bacteria decreases, thus the leaching rate. Therefore copper and iron recoveries decreased from 68 %, 35 % and 45 %, 20 %, respectively. As a result of laboratory tests, it is found that as the pulp density increased, the efficiency of copper recovery decreased using this bacterial culture.
Article
The extraction of molybdenum and cobalt from spent petroleum catalyst (Co–Mo/Al2O3) was investigated using sulphuric and nitric acid solution. Direct leaching of spent catalyst with sulphuric acid was not effective, whereas the combination of sulphuric and nitric acid was significant for the recovery of both molybdenum and cobalt. The effect of experimental factors such as reaction time, acid concentration, temperature, solid–liquid ratio and particle size were studied to determine the best conditions for the solubilisation of metal values. The parameters, temperature and nitric acid concentration are found to be critical factors especially on leaching of molybdenum from the spent catalyst. Under optimum conditions (pulp density 10% (w/v), [H2SO4] 0.5 M, [HNO3] 4.0 M, particle size 51–70 μm, temperature 50 °C and time 5 h), about 99.7% of molybdenum and 99.6% of cobalt could be extracted with 14.9% extraction of aluminium.
Article
Statistically based experimental designs were applied to screen and optimize the bioleaching of spent hydrocracking catalyst by Penicillium simplicissimum. Eleven factors were examined for their significance on bioleaching using a Plackett-Burman factorial design. Four significant variables (pulp density, sucrose, NaNO(3), and yeast extract concentrations) were selected for the optimization studies. The combined effect of these variables on metal bioleaching was studied using a central composite design (CCD). Second-order polynomials were established to identify the relationship between the recovery percent of the metals and the four significant variables. The optimal values of the variables for maximum metals bioleaching were as follows: pulp density (4.0%, w/v), sucrose (90 g/L), NaNO(3) (2 g/L) and yeast extract (0.36 g/L). The maximum metals recovery percentages from the predicted models were 97.6% Mo, 45.7% Ni, and 14.3% Al. These values were in perfect agreement with the actual experimental values, which were (98.8 +/- 0.9)% Mo, (46.5 +/- 0.6)% Ni, and (13.7 +/- 0.4)% Al. The growth kinetics of the fungus in the presence of the spent catalyst at various pulp densities (2-11%) and optimal condition was modeled using the modified Gompertz model. The kinetic parameters in the system were estimated using MATLAB R2008a. Results showed that the modified Gompertz model fit the experimental data well. The relationship between the specific growth rate and pulp density was found by modifying the Luong inhibition model which gave maximum specific growth rate of 0.034 day(-1), optimal pulp density of 3.95% w/v and critical inhibitor concentration of 10.9% w/v.
Article
Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to follow the surface changes occurring in galena when the bioleaching medium contained Ag(I), Hg(II) and Bi(III) ions. The results showed that the catalyst ions Ag(I), Hg(II) and Bi(III) are incorporated into the surface irrespectively of the presence of bacteria, and different reactions take place on the surface of galena depending on the cation added to the leaching medium. When the bioleaching process takes place without catalyst or with Bi(III) the galena is transformed into PbSO4 and the growth of oxidation products is characterized by needles. Ag(I) and Hg(II) ions form a layer on the galena surface, which prevents the transformation of such surface into PbSO4. The layer formed in this process can be like a silver sulphide and a mercury sulphide depending on the ion species. Microorganisms oxidize the surface sulphur of this layer and thus decrease the S/Ag and S/HG ratios at the surface.
Article
In this research, the role of zinc ferrite in the hydrometallurgical recovery of zinc in both primary zinc production and zinc-containing waste treatment processes is discussed. In the present work, experiments were performed on the caustic leaching of pure zinc ferrite. The effects of leaching time, caustic concentration and temperature were investigated in the deceleratory period. Atomic Absorption Spectroscopy (AAS) and X-Ray Diffraction (XRD) analyses were employed to analyze both the leach solutions and the residues. It was found that the percentage of decomposed zinc ferrite increased linearly with increasing leaching time. Although the decomposition rate increased with the caustic concentration, it was limited by the high viscosity of the concentrated leach solutions. The maximum percentage of decomposed zinc ferrite was only about 9% under the experimental conditions. Based on the experimental results, it was postulated that the dissolution rate of zinc ferrite in the deceleratory period, was controlled by the diffusion of zinc ions in the imperfect zinc ferrite lattice. The dissolution reaction could be represented as follows:
Article
Zn(II) and Pb(II) from Nigerian sphalerite and galena ores were bioleached by a mixed culture of acidophilic bacteria. The influences of pH and ferric ion on the bioleaching rates of sphalerite and galena were examined. The result shows that pH 2.1 and 2.7 are favourable for the leaching of Zn(II) and Pb(II) from sphalerite and galena, respectively. It was observed that the use of agarose-simulated media caused cells to excrete exopolymers containing ferric ions which enhanced oxidation. The oxidation equilibrium for sphalerite and galena took 3 and 4 d, respectively. About 38.3% sphalerite and 34.2% galena were leached within 1 d and approximately 92.0% Zn(II) and 89.0% Pb(II) were recovered in 5 d, respectively. The unleached residual products were examined by X-ray diffraction for sphalerite, revealing the presence of elemental sulphur(S), zinc sulphate (ZnSO4) and few traces of calcium aluminate (Ca3Al2O6). The XRD pattern also indicates the presence of elemental sulphur (S), lead sulphate (PbSO4) and few traces of itoite [Pb(S,Ge)(O,OH)4] and cobalt lead silicate [Pb8Co(Si2O7)3] in the unleached galena ore.