Biohydrometallurgical technology of copper recovery from a complex copper concentrate

Leaching of sulfide-oxidized copper concentrate of the Udokan deposit ore with a copper content of 37.4% was studied. In the course of treatment in a sulfuric acid solution with pH 1.2, a copper leaching rate was 6.9 g/kg h for 22 hours, which allowed extraction of 40.6% of copper. At subsequent chemical leaching at 80°C during 7 hours with a solution of ferric sulfate obtained after biooxidation by an association of micro-organisms, the rate of copper recovery was 52.7 g/kg h. The total copper recovery was 94.5% (over 29 hours). Regeneration of the Fe³⁺ ions was carried out by an association of moderately thermophilic microorganisms, including bacteria of genus Sulfobacillus and archaea Ferroplasma acidiphilum, at 1.0 g/L h at 40°C in the presence of 3% solids obtained by chemical leaching of copper concentrate. A flowsheet scheme of a complex copper concentrate process with the use of bacterial-chemical leaching is proposed.     

Restriction Profiles of the Chromosomal DNA from Acidithiobacillus ferrooxidans Strains Adapted to Different Oxidation Substrates

Restriction profiles of chromosomal DNA were studied in different Acidithiobacillus ferrooxidans strains grown on medium with Fe²⁺ and further adapted to another oxidation substrate (S⁰, FeS₂, or sulfide ore concentrates). The restriction endonuclease XbaI digested the chromosomal DNA from different strains into different numbers of fragments of various sizes. Adaptation of two strains (TFBk and TFN-d) to new oxidation substrates resulted in structural changes in XbaI-restriction patterns of their chromosomal DNA. Such changes in the DNA restriction patterns occurred in strain TFBk after the adaptation to precyanidated gravitational pyrite-arsenopyrite concentrate (no. 1) from the Nezhdaninskoe deposit or to copper-containing ore from the Udokanskoe deposit and also in strain TFN-d adapted to untreated pyrite-arsenopyrite concentrate (no. 2) from the Nezhdaninskoe deposit. No changes in the number or size of the XbaI-restriction patterns of chromosomal DNA were revealed in either strain TFBk cultivated on media with pyrite from the Angren and Tulun deposits or in strains TFN-d and TFO grown on media with S⁰ and pyrite. Neither were changes observed in the XbaI-restriction patterns of the DNA from strain TFV-1, isolated from the copper ore of the Volkovskoe deposit, when Fe²⁺ was substituted with alternative substrates—S⁰, pyrite or concentrate no. 2 from the ore of the Nezhdaninskoe deposit. In strain TFO, no differences in the XbaI-restriction patterns of the chromosomal DNA were revealed between the culture grown on medium containing concentrate no. 2 or the concentrate of surface-lying ore from the Olimpiadinskoe deposit and the culture grown on medium with Fe²⁺. When strain TFO was cultivated on the ore concentrate from deeper horizons of the Olimpiadinskoe deposit, which are characterized by lower oxidation degrees and high antimony content, mutant TFO-2 differing from the parent strain in the chromosomal DNA structure was isolated. The correlation between the lability of the chromosomal DNA structure in A. ferrooxidans strains and the physical and chemical peculiarities of the isolation substrate and habitat is discussed.     

Evaluation of the Biotechnological Potential of Pure and Mixture of Indigenous Iron-Oxidizing Bacteria to Dissolve Trace Metals from Cu Bearing Ore

Abstract

This study aimed to investigate the ability of pure and consortia of indigenous iron-oxidizing bacteria to enhance the dissolution of trace metals from Cu and Zn-bearing ore. Three bacterial strains Acidithiobacillus ferrooxidans strain WG101, Leptospirillum ferriphilum strain WG102, Leptospirillum ferrooxidans strain WG103 isolated from Baiyin copper mine, China were used in this study. The biotechnological potential of these indigenous isolates was evaluated both in pure and in consortia to extract cobalt, chromium, and lead from the copper and zinc bearing ore. The sulfur and iron-oxidizing bacterial isolate Acidithiobacillus ferrooxidans strain WG101 exhibited efficient dissolution compared to sole iron-oxidizing Leptospirillum ferriphilum strain WG102, and Leptospirillum ferrooxidans strain WG103. Initial medium pH, pulp density, and temperature were studied as influential parameters in bioleaching carried out by bacterial consortia. The achieved optimum conditions were; initial pH of 1.5, 10% of pulp density, and temperature 30?°C with 68.7?±?3.9% cobalt, 56.6?±?3.9% chromium, and 36?±?3.7% lead recovery. Analytical study of oxidation-reduction potential and pH fluctuation were observed during this whole process that shows the metal dissolution efficiency of bacterial consortia. Alterations in spectral bands of processed residues were reported through FTIR analysis compared with control ore sample. Mössbauer spectroscopy analysis showed the influence of bacterial consortia on iron speciation in bioleached samples. The findings confirm that the indigenous acidophilic iron-oxidizing bacterial strains are highly effective in the dissolution of trace elements present in ore samples. This study not only supports the notion that indigenous bacterial strains are highly effectual in metal dissolution but provides the basic vital conditions to upscale the bioleaching technique for metals dissolution.     

The Effect of the Facultative Chemolithotrophic Bacterium Thiobacillus acidophilus on the Leaching of Low-Grade Cu-Ni Sulfide Ore by Thiobacillus ferrooxidans

The purpose of this investigation was to determine the effect of Thiobacillus acidophilus on the leaching of a low-grade Cu-Ni sulfide ore by Thiobacillus ferrooxidans. A sample of low-grade Cu-Ni sulfide ore containing 0.36% Cu, 0.48% Ni, and 7.87% Fe was pulverized and initially leached for a 21-day period using two different pure cultures of T. ferrooxidans, an environmental strain (F2) and a strain from the American Type Culture Collection (ATCC 23270). Samples of the ore slurries were drawn and the pH was monitored over the course of the leaching period. The concentrations of Cu and Ni leached by each strain were determined and compared. No significant differences were observed in the concentrations of Cu and Ni leached by the two pure cultures of T. ferrooxidans. Subsequently, the ore was leached with mixed cultures of T. ferrooxidans and T. acidophilus to determine the effect of the latter on the concentrations of Cu and Ni leached from the ore. The environmental strain F2 of T. ferrooxidans was used in combination with both a type strain (ATCC 27807) and an environmental strain (64) of T. acidophilus. After 21 days, the mixed cultures of T. ferrooxidans and T. acidophilus leached significantly greater amounts of copper than the pure strain alone, but no such difference was observed for the leaching of nickel.     

Microbiological leaching of a chalcopyrite concentrate by Thiobacillus ferrooxidans

The microbiological leaching of a chalcopyrite concentrate has been investigated using a pure strain of Thiobacillus ferrooxidans. The optimum leaching conditions regarding pH, temperature, and pulp density were found to be 2.3, 35°C, and 22%, respectively. The energy of activation was calculated to be 16.7 kcal/mol. During these experiments the maximum rate of copper dissolution was about 215 mg/liters/hr and the final copper concentration was as high as 55 g/liter. This latter value is in the range of copper concentrations which may be used for direct electrorecovery of copper. Jarosite formation was observed during the leaching of the chalcopyrite concentrate. When the leach residue was reground to expose new substrate surface, subsequent leaching resulted in copper extractions up to about 80%. On the basis of this experimental work, a flow sheet has been proposed for commercial scale biohydrometallurgical treatment of high-grade chalcopyrite materials.     

Controlled microbiological in-situ stope leaching of a sulphidic ore

A mixed culture of Thiobacillus ferrooxidans, T. thiooxidans, and Leptospirillum ferrooxidans was used for inoculation of a sulphidic ore body for a bacterial in-situ stope-leaching experiment in the Ilba mine in Romania. The ore body was inoculated with 10⁷ cells/g ore. Measurements at six main sites of the ore body indicated that microbial leaching was started by the inoculation. After about 8 weeks, sufficient microbial activity was measurable only in the upper third of the ore body. Due to the angle of incidence of the ore (75°), the leach liquor percolated only through the upper part leaving two-thirds humidified unsatisfactorily. The leach results, metal mobilization, indicated that by inoculation with the indigenous microorganisms efficient leaching was achieved. Metal output after 18 months of operation amounted to 10% of Cu and 78% of Zn. In the winter months energy for aeration and circulation was not available and this was reflected by reduced values for microbial activity, temperature, and daily metal output. The biological metal mobilisation after 18 months of operation was as active as at the beginning. Cu was mobilised predominantly by microbial leaching whereas Zn was leached mainly by chemical reactions. Both mechanisms contributed equally to iron output. Correspondence to: W. Sand     

Microbiological leaching of a zinc sulfide concentrate

The microbiological extraction of zinc from a high-grade zinc sulfide concentrate has been investigated, using a pure strain of Thiobacillus ferrooxidans. Conditions such as temperature, pH, pulp density, nutrient, concentration, and specific surface of solids have been studied in terms of their effects on zinc extraction rate and in some instances on final zinc concentration in solution. Where appropriate, optimum conditions for leaching have been specified.     

Industrial practice and the biology of leaching of metals from ores The 1997 Pan Labs Lecture

Biomining processes have been used successfully on a commercial scale for the recovery of metals, the most important of which are copper, uranium and gold. These processes are based on the activity of chemoautolithotrophic bacteria which are able to use either iron or sulfur as their energy source and which grow in highly acid conditions. In general, low-rate dump and heap leaching processes are used for copper recovery while the biooxidation of difficult-to-treat gold-bearing arsenopyrite ores is carried out commercially in highly aerated stirred tank reactors. Because of the high levels of bacterial activity required, limitations in the growth rate of the microorganisms which were not apparent in low-rate processes have become an important factor. A key to the commercialization of the gold-bearing arsenopyrite biooxidation process was the development of a rapidly-growing, arsenic-resistant bacterial consortium. The empirical technique of mutation and selection in a continuous-flow system was used to improve the ability of the bacteria to decompose the ore. This approach resulted in a dramatic initial enhancement in growth rate but a plateau in improvement of performance has been reached. Further advances will require a more direct approach based on an understanding of the underlying physiological mechanisms and an application of the tools of molecular biology. Considerable advances have been made in our understanding of the molecular biology of Thiobacillus ferrooxidans. However much less is known about the other biomining bacteria. Recent studies using 16S rRNA analysis techniques have indicated that T. ferrooxidans may play a smaller role in continuous flow stirred tank biomining processes than was previously thought. Received 20 November 1997/ Accepted in revised form 2 March 1998     

Effect of Cell Lysis (CLs) Products on Acidophilic Chemolithotrophic Microorganisms and the Role of Acidocella Species

Acidophilic chemolithotrophic microorganisms (CMs) are widely used for bioleaching of mineral resources. However, the growth of bacteria and their leaching activity are often inhibited (restricted) by organic components, e.g. lysates and exudates. The aims of this study were to examine the extent of cell lysis (CLs) inhibition on acidophilic microorganisms and to identify microorganisms that can utilize CLs products and eliminate their inhibition effect on acidophilic microorganisms. Specifically, it was revealed that Acidithiobacillus caldus was severely inhibited at 5% CLs products, whereas A. ferrooxidans and Leptospirillum ferriphilum are severely inhibited at 20%. It has been found that strains RBA and RBB of heterotrophic bacteria, isolated from anaerobic sludge, can biodegrade CLs products and when co-cultured with A. ferrooxidans, they can alleviate the toxic effect of CLs products under low pH (2–3). It has been shown that besides CLs, isolated strains can grow on glucose, glycerol, yeast extract, citric acid, and tryptone soya broth with an optimum temperature of 35°C and a pH of 3. The strains showed the ability to reduce ferric ions to ferrous ions when glycerol was used as a substrate after 2 days under both aerobic and anaerobic conditions. On the basis of morphophysiological and molecular biological studies, the isolated strains RBA and RBB were identified as Acidocella spp.     

Biohydrometallurgical technology of a complex copper concentrate process

Leaching of sulfide-oxidized copper concentrate of the Udokan deposit ore with a copper content of 37.4% was studied. In the course of treatment in a sulfuric acid solution with pH 1.2, a copper leaching rate was 6.9 g/kg h for 22 h, which allowed extraction of 40.6% of copper. As a result of subsequent chemical leaching at 80 degrees C during 7 h with a solution of sulphate ferric iron obtained after bio-oxidation by an association of microorganisms, the rate of copper recovery was 52.7 g/kg h. The total copper recovery was 94.5% (over 29 h). Regeneration of the Fe3+ ions was carried out by an association of moderately thermophilic microorganisms, including bacteria of genus Sulfobacillus and archaea of genus Ferroplasma acidiphilum, at 1.0 g/l h at 40 degrees C in the presence of 3% solids obtained by chemical leaching of copper concentrate. A technological scheme of a complex copper concentrate process with the use of bacterial-chemical leaching is proposed.     

Leaching of copper ores by chemoorganotrophic microorganisms

Summary Some copper-leaching microorganisms were isolated from weathered rock material of old copper deposits. Among these the strain Bacillus sp. L 1 was able to solubilize completely the copper contained in low-grade ore material under optimal conditions. The most suitable leaching solution was sulphite waste liquor from the paper industry. Decreasing effectiveness of metal recovery was observed with increasing particle size and increasing solid-liquid ratio. In silver leaching, a maximum was measured after 3 days followed by a rapid decrease. Possible technical uses of leaching processes are discussed. Offprint requests to: G. Straube     

Bioleaching of copper- and zinc-bearing ore using consortia of indigenous iron-oxidizing bacteria

Indigenous iron-oxidizing bacteria were isolated on modified selective 9KFe²⁺ medium from Baiyin copper mine stope, China. Three distinct acidophilic bacteria were isolated and identified by analyzing the sequences of 16S rRNA gene. Based on published sequences of 16S rRNA gene in the GenBank, a phylogenetic tree was constructed. The sequence of isolate WG101 showed 99% homology with Acidithiobacillus ferrooxidans strain AS2. Isolate WG102 exhibited 98% similarity with Leptospirillum ferriphilum strain YSK. Similarly, isolate WG103 showed 98% similarity with Leptospirillum ferrooxidans strain L15. Furthermore, the biotechnological potential of these isolates in consortia form was evaluated to recover copper and zinc from their ore. Under optimized conditions, 77.68 ± 3.55% of copper and 70.58 ± 3.77% of zinc were dissolved. During the bioleaching process, analytical study of pH and oxidation–reduction potential fluctuations were monitored that reflected efficient activity of the bacterial consortia. The FTIR analysis confirmed the variation in bands after treatment with consortia. The impact of consortia on iron speciation within bioleached ore was analyzed using Mössbauer spectroscopy and clear changes in iron speciation was reported. The use of indigenous bacterial consortia is more efficient compared to pure inoculum. This study provided the basic essential conditions for further upscaling bioleaching application for metal extraction.

     

Biological Oxidation of Sulfide Raw Material Using a Culture of Thiobacillus ferrooxidans under Various Conditions of Leaching

Major parameters of the first stage of leaching of a copper–zinc sulfide product (raw material) by a culture of Thiobacillus ferrooxidans have been studied, including the effects of solid-phase concentration, Fe²⁺ and Fe³⁺ ions, pH, and the intensity of mixing. The first stage of leaching of the sulfide raw material is optimum under the following conditions: pH of the original leaching solution equal to 1.6; Fe³⁺ concentration of the order of 10 g/l; and vigorous mixing of the suspension at solid-phase concentrations of 30–35%. A theoretical substantiation of the observed dependences is proposed.     

Oxidation of stibnite byThiobacillus ferrooxidans

Optimum pH, temperature and pulp density for microbiological leaching of museum-grade stibnite mineral has been investigated using a stibnite-adapted strain ofThiobacillus ferrooxidans. Optimum conditions were found to be pH 1.75, 35 C and 12 g solid substrate per 100 ml of basal salts medium as the initial dose. The energy of activation was determined to be 16.8 kcal per mole, and the temperature coefficient 2.2. The highest total dissolved-antimony concentration, [Sb_t] = [Sb⁺³] + [Sb⁺⁵] + [SbO⁺] + [SbO₂ ⁺], was about 1400 mg/litre, due to relatively low solubility of (SbO)₂SO₄ and (SbO₂)₂SO₄.     

Role of cell attachment in leaching of chalcopyrite mineral by Thiobacillus ferrooxidans

Summary Experiments on the leaching of copper from chalcopyrite mineral by the bacterium Thiobacillus ferrooxidans show that, in the presence of adequate amounts of sulphide, iron-grown bacteria preferentially oxidise sulphur in the ore (through direct attachment) rather than ferrous sulphate in solution. At 20% pulp density, the leaching initially takes place by a predominantly direct mechanism. The cell density in the liquid phase increases, but the Fe²⁺ is not oxidised. However, in the later stages when less solid substrate is available and the cell density becomes very high, the bacteria start oxidising Fe²⁺ in the liquid phase, thus contributing to the indirect mechanism of leaching. Contrary to expectations, the rate of leaching increased with increasing particle size in spite of the decreasing specific surface area. This has been found to be due to increasing attachment efficiency with increase in particle size. Offprint requests to: R. Kumar     

Copper removal from an industrial waste by bioleaching

Summary Copper contained in a solid industrial waste produced in a silicone manufacturing process was leached with spent iron medium from aThiobacillus ferrooxidans culture. Most effective leaching was observed in a continuously fed, dual reactor system. Spent iron medium was generated by growingT. ferrooxidans in 0.9 K iron medium at pH 1.5 in the first reactor, and was transferred to a second reactor in which it leached the copper from the waste. Leaching was effective at a pulp density of the waste material as high as 20%. In experiments run at a pulp density of 2.5%, the spent iron medium was most efficient in leaching copper when it was first diluted 100-fold with a mineral salts solution at pH 1.5. Removal of the copper from the waste appeared to involve its displacement by acid, dissolved mineral salts, and ferric iron. Potentials for practical application of this process are discussed.     

Autotrophic,sulfur-oxidizing actinobacteria in acidic environments

Some novel actinobacteria from geothermal environments were shown to grow autotrophically with sulfur as an energy source. These bacteria have not been formally named and are referred to here as “Acidithiomicrobium” species, as the first of the acidophilic actinobacteria observed to grow on sulfur. They are related to Acidimicrobium ferrooxidans with which they share a capacity for ferrous iron oxidation. Ribulose bisphosphate carboxylase/oxygenase (RuBisCO) is active in CO₂ fixation by Acidimicrobium ferrooxidans, which appears to have acquired its RuBisCO-encoding genes from the proteobacterium Acidithiobacillus ferrooxidans or its ancestor. This lateral transfer of RuBisCO genes between a proteobacterium and an actinobacterium would add to those noted previously among proteobacteria, between proteobacteria and cyanobacteria and between proteobacteria and plastids. “Acidithiomicrobium” has RuBisCO-encoding genes which are most closely related to those of Acidimicrobium ferrooxidans and Acidithiobacillus ferrooxidans, and has additional RuBisCO genes of a different lineage. 16S rRNA gene sequences from “Acidithiomicrobium” species dominated clone banks of the genes extracted from mixed cultures of moderate thermophiles growing on copper sulfide and polymetallic sulfide ores in ore leaching columns.     

Proteomic insights into cold adaptation of psychrotrophic and mesophilic <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> strains

Cold tolerant strains of Acidithiobacillus ferrooxidans play a role in metal leaching and acid mine drainage (AMD) production in northern latitude/boreal mining environments. In this study we used a proteomics and bioinformatics approach to decipher the proteome changes related to sustained growth at low temperatures to increase our understanding of cold adaptation mechanisms in A. ferrooxidans strains. Changes in protein abundance in response to low temperatures (5 and 15°C) were monitored and protein analyses of a psychrotrophic strain (D6) versus a mesophilic strain (F1) showed that both strains increased levels of 11 stress-related and metabolic proteins including survival protein SurA, trigger factor Tig, and AhpC-Tsa antioxidant proteins. However, a unique set of changes in the proteome of psychrotrophic strain D6 were observed. In particular, the importance of protein fate, membrane transport and structure for psychrotrophic growth were evident with increases in numerous chaperone and transport proteins including GroEL, SecB, ABC transporters and a capsule polysaccharide export protein. We also observed that low temperature iron oxidation coincides with a relative increase in the key iron metabolism protein rusticyanin, which was more highly expressed in strain D6 than in strain F1 at colder growth temperatures. We demonstrate that the psychrotrophic strain uses a global stress response and cold-active metabolism which permit growth of A. ferrooxidans in the extreme AMD environment in colder climates.     

Bacterial leaching of metals from sewage sludge

Summary Thiobacillus thiooxidans is capable of oxidizing sulfur in digested sludge, while decreasing the pH value from about 5.5 to, say, 1.0 to 1.5. Insoluble metal sulfides can be solubilized through this acidification. Thiobacillus ferrooxidans oxidises pyritic ore in the presence of 6% centrifuged sludge if the pH value is adjusted to about 2.5. When mixing T. thiooxidans and T. ferrooxidans with sludge and 1% sulfur, the former acidifies the sludge and the latter oxidizes metal sulfides; together they solubilize more metal than T. thiooxidans alone. The following metals solubilized from their sulfides have been investigated so far: iron, copper, zinc, nickel, and cadmium. The possibility of recycling metals from sewage sludge with this method is discussed.     

Isolation and Characterization of Iron and Sulfur-Oxidizing Bacteria from Maiduk Copper Mine at Shahrbabk Province in Iran

Microbial oxidation of iron and sulfur are important steps in biogeochemical cycles in mining environments. The aim of this study was the enrichment and identification of two important groups of bacteria that are involved in bioleaching of copper ores. Some soil samples were collected from the Maiduk copper mine. Iron-oxidizing bacteria were enriched in 9K medium containing ferrous sulfate, and sulfur oxidizers were enriched in 9K medium containing powdered sulfur instead of ferrous sulfate as energy source. After three subcultures, autotrophic bacteria were isolated on 9K agarose medium with appropriate energy sources. The autotrophic bacteria from the enrichments were identified by amplification of 16S rRNA gene and sequencing. Bioleaching experiments were performed in 100 ml of 9K medium containing 5 g of low-grade copper ore instead of ferrous sulfate. Twelve different iron and sulfur-oxidizing bacteria were isolated from the collected soil samples of Maiduk copper mine. Molecular identification indicated that two prevalent strains in the ore enrichments could be assigned to the Acidithiobacillus ferooxidans strain HGM and the Thiobacillus thioparus strain HGE. These two strains reached their logarithmic phase of growth after 8 days of incubation in their respective media at 30°C. Of these two cultures, strain HGM leached more copper ore (300 ppm) from the Maiduk copper ore than did strain HGE (200 ppm). Application of these two strains to the Maiduk copper ore in situ and to ore heaps should improve the leaching process.