Article

Bacterial Leaching of Kure Copper Ore

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

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.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... The principal difference between these two species lies in that At. thiooxidans exclusively thrives on elemental sulphur and some soluble sulphur compounds but is unable to oxidize ferrous iron. In pure culture form, these microorganisms are reported to be ineffective for degradation of pyrite and chalcopyrite (Norris 1990, Akcil and Ciftci 2003a,b, Akcil et al. 2007). Another important mesophile is Leptospirillum ferrooxidans which occurs as curved (vibroidal) rods (Harrison 1984, Rawlings et al. 2003). ...
... Ferroplasma spp.) and heterotrophs (e.g. Acidiphilium spp.) can coexist in a leaching environment (Johnson and Roberto 1997, Golyshina et al. 2000, Hallberg and Johnson 2003 and mixed cultures of these microorganisms can degrade sulphide minerals such as pyrite and chalcopyrite more effectively than single culture ( Fig. 4.1) ( Norris 1983, Akcil and Ciftci 2003a,b, Qui et al. 2005, Akcil et al. 2007). However, recent investigations into the characteristics of the mixed populations used in the commercial operations demonstrated that Leptospirillum-type bacteria dominated the microbial population with At. thiooxidans to lesser extent whereas, if detectable, At. ferrooxidans was present in small numbers ( Sand et al. 1993, Dew et al. 1997, Battaglia-Brunett et al. 1998). ...
... On the other hand, those studies (Table 1) are mainly focused on the cultures consisted one specific microorganism while in the industry, mixed microorganisms are mostly used for the bioleaching process [33]. Where using a mixed culture with different microorganisms can lead to the cooperative effects and bioleaching may show a higher efficiency than pure cultures [34][35][36][37][38][39][40]. ...
Article
Full-text available
Bioleaching is an environment-friendly and low-investment process for the extraction of metals from flotation concentrate. Surfactants such as collectors and frothers are widely used in the flotation process. These chemical reagents may have inhibitory effects on the activity of microorganisms through a bioleaching process; however, there is no report indicating influences of reagents on the activity of microorganisms in the mixed culture which is mostly used in the industry. In this investigation, influences of typical flotation frothers (methyl isobutyl carbinol and pine oil) in different concentrations (0.01, 0.10, and 1.00 g/L) were examined on activates of bacteria in the mesophilic mixed culture (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, and Acidithiobacillus thiooxidans). For comparison purposes, experiments were repeated by pure cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans in the same conditions. Results indicated that increasing the dosage of frothers has a negative correlation with bacteria activities while the mixed culture showed a lower sensitivity to the toxicity of these frothers in comparison with examined pure cultures. Outcomes showed the toxicity of Pine oil is lower than methyl isobutyl carbinol (MIBC). These results can be used for designing flotation separation procedures and to produce cleaner products for bio extraction of metals.
... There are several important factors such as temperature, pH, availability of nutrients, sulphide minerals, O 2 and CO 2 , solid ratio, metal toxicity, etc., that affect the growth of bacteria and hence the dissolution process (Akcil and Ciftci, 2003;Bosecker, 1997;Deveci, 2002;Deveci et al., 2003). The presence of some ions such as K + , Na + , and SO 4 2 À in bioleaching environments could promote the formation of solid products such as ferric precipitates (e.g., K-jarosite) which is controlled by pH (Tuovinen and Bhatti, 1999). ...
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.
... There are several important factors such as temperature, pH, availability of nutrients, sulphide minerals, O 2 and CO 2 , solid ratio, metal toxicity, etc., that affect the growth of bacteria and hence the dissolution process (Akcil and Ciftci, 2003;Bosecker, 1997;Deveci, 2002;Deveci et al., 2003). The presence of some ions such as K + , Na + , and SO 4 2 À in bioleaching environments could promote the formation of solid products such as ferric precipitates (e.g., K-jarosite) which is controlled by pH (Tuovinen and Bhatti, 1999). ...
Article
This study investigates the bioleaching of the complex Pb/Zn ore/concentrate using mesophilic (at 30 jC), moderate (at 50 jC), and extreme thermophilic (at 70 jC) strains of acidophilic bacteria. The effects of bacterial strain, pH, iron precipitation, and external addition of Fe 2 + on the extraction of zinc were evaluated. The results have shown that the ore is readily amenable to the selective extraction of zinc and lead using the acidophilic strains of bacteria [i.e., majority of lead (>98%) reports to the residue]. Moderate thermophiles displayed superior kinetics of dissolution of zinc compared with the other two groups of bacteria. The pH was found to exert a profound effect on the leaching process controlling the bacterial activity and precipitation of ferric iron mainly as K-jarosite. The K + released presumably from the alteration of the silicate phases such as K-feldspar present in the ore appeared to promote the formation K-jarosite in moderately thermophilic leaching systems. The external addition of iron was shown to be required for the bacteria to efficiently drive the extraction of zinc from the bulk concentrate. These findings place the emphasis on the prime importance of ferric iron for the dissolution of zinc and of mineralogical properties (i.e., iron and silicate content) of an ore/concentrate to be treated via bioleaching processes. D 2004 Elsevier B.V. All rights reserved.
Article
A mesophilic iron oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (33 °C) from a typical, chalcopyrite concentrate of the Sarcheshmeh copper mine in the region of Kerman located in the south of Iran. In addition, a thermophilic iron oxidizing bacterium, Sulfobacillus, has been isolated (60 °C) from the sphalerite concentrate of Kooshk lead and zinc mine near the city of Yazd in the center point of Iran. Variation of pH, ferrous and ferric concentration on time and effects of some factors such as temperature, cell growth, initial ferrous concentration and pH on bioleaching of low-grade complex zinc–lead ore were investigated. The results obtained from bioleaching experiments indicate that the efficiency of zinc extraction is dependent on all of the mentioned variables; especially the temperature and initial Fe(II) concentration have more effect than other factors for these microorganisms. In addition, results show that the maximum zinc recovery was achieved using a thermophilic culture. Zinc dissolution reached 58% with Sulfobacillus while it was 51% with A. ferrooxidans at pH=1.5, initial Fe(II) concentration=7 and 9 g/L for A. ferrooxidans and Sulfobacillus, respectively, after 30 days.
Article
Bacterial leaching of minerals is a simple, effective and environmental by benign technology in the treatment of sulphidic ores. This method has been successfully applied for the recovery of copper, gold and uranium in commercial scale for the past 25 years. Efficiency and cost-effectiveness of the bacterial leaching process depend mainly on the activity of bacteria and mineralogical and chemical composition of the ores. Bacterial leaching is based on the activity of mesophilic iron- and/or sulphur-oxidizing bacteria, notably Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans. These bacteria oxidize metal compounds to water soluble metal sulphates by a series of biological and chemical oxidation reactions occurring in leaching medium. After the isolation of above bacteria from acidic mine drainage waters, two oxidation mechanisms (direct and indirect bacterial leaching) have been discussed as related to oxidation/leaching of sulphidic ores in leaching systems. Fully understanding the bacterial leaching mechanisms of sulphidic ores improves the design and operation of bacterial leaching plants. In this article, the importance of various leaching mechanisms employed for metal recovery and their application aspects are critically reviewed with emphasis on copper, lead, zinc and nickel minerals.
Article
Recently, chemical recovery of metallic values from low-grade sulphur-bearing ores or concentrates has been replaced by biological treatment; an important recovery process from the environmental and economical respects. Bioleaching has been utilized in several countries to recover metals from sulphide ores with commercial success. In Turkey, there are also some copper and gold-bearing sulphides appropriate for bioleaching process. In this study, the copper recovery from pyritic copper ores in Küre copper mine is investigated with acidophilic bacteria (Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans). As a result of laboratory tests, the highest copper recovery was obtained by Leptospirillum ferrooxidans, Approximately 54% copper recovery was determined after 24 days (576 hours) bioleaching tests.
Article
Full-text available
The Microbial hydrometallurgy and microbial mineral processing of metal sulphides is currently a well established technology. Over past years there has been a huge amount of developments with regards to the understanding of its both engineering perspective as well as fundamental approach with regards to the microorganisms. The huge diversity of the microorganisms, which has come into picture over the years of research and development have made the engineers to go beyond several limitations of working temperature to salt tolerance of the microorganisms in harsh conditions to deliver better technologies for the future operative plants. Today scientists have been able to deliver the various mechanisms involved in bioleaching but still there are facets to be really understood and more importantly on the front how lab scale research can be turned out into full scale operation by scaling up the research and optimizing the engineering aspects of the research. Most of the bioleaching operation has shown their productivity in commercial application of refractory gold concentrates using mesophilic microorganisms followed by the cyanide leaching to recover optimum amount of gold with an environment friendly method compared to the conventional method of roasting. Research in the area of chalcopyrite bioleaching is still continuing o solve the mysteries of jarosite precipitation and formation of passivation layer, which inhibits the copper recovery in a heap leaching of chalcopyrite by biological methods. Use of extreme thermophiles in chalcopyrite bioleaching is making a revolutionary movement to solve the mystery behind the scaling up the process, which could be possible to be solved in future. Bioleaching with other sulphide minerals together with Acid Mine Drainage (AMD) mitigation, which is a serious concern today, is taking is taking shape today in order to cater the needs of the mankind. However the biohydrometallurgy research seems to contribute to a greater extent in framing environmental friendly process with regards to hydrometallurgical operations in future and establish a developed technology to benefit human beings needs by its upcoming research and development. Keywords: Biomining, refractory gold, copper, chalcopyrite, bioleaching, nickel sulphide, biooxidation, acid mine drainage
Article
This study compares the capacity of pure and mixed cultures of mesophilic bacteria for bioleaching of a low grade, pyritic chalcopyrite concentrate. In pure culture form, Acidithiobacillus ferrooxidans was found to have a higher bioleaching capacity than Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans with the capability of the latter to bioleach copper being very limited. Mixed cultures, MixA (At. ferrooxidans, L. ferrooxidans and At. thiooxidans) and MixB (L. ferrooxidans and At. thiooxidans) were shown to perform better than the pure cultures with the highest extraction of copper (62.1% Cu) being achieved by MixA. Copper bioleaching performances of the cultures were observed to agree with their respective growth pattern. The results also indicated that the increase in the pulp density (1–5% wt/vol) adversely affected bioleaching process regardless of the pure and mixed cultures used having led to the decrease in the extent of final copper extraction i.e. 50.3% Cu recovery at 1% wt/vol for At. ferrooxidans compared with 38.6% Cu at 5% wt/vol. This study underlines the importance of mixed cultures and, iron and sulphur-oxidising activity of a bacterial culture to efficiently oxidise chalcopyrite.
Article
Two sphalerite samples with different iron/sulphur (Fe/S) ratios, Shuikousan ore (Fe/S 0.2) and Dachang ore (Fe/S 0.52), were processed using three microbial species, Leptospirillum ferriphilum, Acidithiobacillus ferrooxidans and Acidithiobacillus caldus. Following 20 days of bioleaching in shake flask cultures, a higher zinc (Zn) extraction (96%) was achieved with Shuikousan ore than with Dachange ore (72%). The extraction efficiency increased when elemental S was added to Dachang ore to attain the same Fe/S ratio as that for Shuikousan ore. Following the addition of S, the redox potential, pH and total dissolved Fe for Dachang ore demonstrated similar behaviors to those of Shuikousan ore. Acidithiobacillus caldus and L. ferriphilum became the dominant species during the bioleaching of sphalerite with a high Fe/S ratio. In contrast, the dominant species were A. ferrooxidans and A. caldus during the bioleaching of sphalerite with a low Fe/S ratio. These results show that the Fe/S ratio has a significant influence on the bioleaching behavior of sphalerite and the composition of the microbial community.
Article
Full-text available
The yield of bacterial leaching of copper with Ergani and Murgul samples was lower than that with Kure samples. The Ergani sample contained pyrrhotite as impurity and trace amount of silver whereas the Murgul sample contained only silver as a trace element. The highest copper extraction was obtained with the Ktire sample that contained neither silver nor pyrrhotite.
Article
Full-text available
The direct sulphation of individual and mixed sulphides of copper and iron has been studied using a steam–oxygen mixture as the oxidant. The investigation showed that copper sulphide formed copper sulphate with this gaseous mixture at 773 K, whereas iron sulphide converted mostly to hematite at this temperature. It was also observed that the mixture of copper–iron sulphides yielded a higher amount of copper sulphate (92.7%) than that obtained (40.0%) from copper sulphide alone in the presence of 10 wt.% ferric oxide. This was mainly attributed to an improved sulphatising environment during the roasting of mixed sulphides. The kinetics study of the CuS–FeS system with a steam–oxygen mixture showed that the copper sulphate formation followed the topochemical model. An activation energy value for this conversion was found to be 30.36 kJ/mol in the temperature range 673 to 773 K. The sulphides and different calcined products obtained were characterised by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and the metallographic studies to examine the path of reaction.
Conference Paper
Full-text available
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
Full-text available
Modern commercial application of biohydrometallurgy for processing ores became reality in the 1950s with the advent of copper bioleaching at the Kennecott Copper Bingham Mine. Early application entailed dump leaching of low-grade, low-value, run-of-mine material. Dump bioleaching has evolved into a commercially accepted option for bioheap copper leaching of higher-grade, higher value ores. This commercial practice is exemplified by at least 11 mining operations. Paradoxically, application of biohydrometallurgy in the pretreatment of refractory gold ores began with processing high value concentrates, using biooxidation-tank processes and was followed by extension to processing low-grade, lower value ores in heaps. Now, bioleaching has been extended to the commercial extraction and recovery of cobalt. Even with the current success of biohydrometallurgical applications in the mining industry, the real potential of biotechnology in mining remains to be realized. As confidence in commercial bioprocessing grows and experience extends the application's knowledge base, innovations and new commercial practices will emerge. Near-term future commercial applications will likely remain focused on recoveries of copper, gold and possibly nickel. Recent technical advances show that very refractory chalcopyrite can be successfully bioleached. Processes for copper recovery from this mineral will include both heap and stirred-tank reactors. Next generation technologies for pretreatment of refractory gold ores will be based on use of thermophilic bacteria for sulfide oxidation. For biohydrometallurgy to commercially advance, the microbiologist must work cooperatively with the practitioners of the technology for mutual understanding of operational limitations and practical constraints affecting the microbiological component. q 2001 Elsevier Science B.V. All rights reserved.
Article
Full-text available
The presence of some anions and cations at certain levels in the bioleaching environment may exert an inhibitory effect on the growth and hence leaching activity of a bacterial culture. In this respect, the quality of process water available with particular reference to salinity can be of prime importance for the application or development of a bioleaching process for a particular feed at an operation site. The current study investigates the extent to which salinity up to 8% Cl- (~80 g/l) affects the bioleaching activity of mesophilic, moderately and extremely thermophilic strains of bacteria during the bioleaching of a complex Zn/Pb sulphide ore. The results indicated that salinity can adversely influence the “optimum” bioleaching activity of mesophiles and moderate thermophiles; the extent being dependent upon the strain (and type) of bacteria and the concentration of chloride. The mesophilic WJM strain was found to oxidise the complex ore at concentrations of up to 0.8% Cl- (~8 g/l) without any significant effect on the extraction of zinc while the limited extraction of zinc by DSM 583 strain occurred at 0.2% Cl-. It was noted that mesophiles can be adapted to tolerate 0.8-1% Cl- (~8-10 g/l) in solution. The bioleaching ability of the strains of moderate themophiles was adversely influenced even at 0.2% Cl- (~2 g/l). On the other hand, the extreme thermophiles were shown to perform well under saline conditions up to 5% Cl- (~50 g/l). This probably indicates the halophilic peculiarity of the extreme thermophiles compared with the mesophiles and the moderate thermophiles.
Article
Full-text available
It was examined whether gas–liquid transfer of oxygen or carbon dioxide has determined the bacterial oxidation rate of sulphide minerals in the kinetic experiments reported in the literature. Correlations available in the literature were used to estimate the gas–liquid mass transfer coefficients of oxygen and carbon-dioxide, kLa (s−1), in the reported experimental equipment (e.g. shake flasks or aerated stirred tanks). The maximum oxygen and carbon dioxide transfer rates were estimated for reported kinetic experiments with pyrite and compared with estimated maximum oxygen and carbon dioxide consumption rates that occurred in those experiments. It was concluded that gas–liquid carbon dioxide transfer limitation and exhaustion of carbon dioxide in the gas-phase, often occurred. Therefore, the observed decrease of the bacterial oxidation rate constant at increasing slurry densities was probably caused by carbon dioxide limitation. Consequently, the method presented in this work needs to be applied in order to ensure that the bioleaching kinetics are properly measured in the absence of carbon dioxide and/or oxygen transfer limitation.
Article
Full-text available
The problem of the refractory nature of gold-bearing sulphide ores is described and possible pretreatments are reviewed. Among them, bioleaching is an interesting one from an environmental point of view, but up to the present the process has been too slow. The IBES (Indirect Bioleaching with Effect Separation) process improves the kinetics of the bioleaching by means of a physical separation of the chemical and biological effects involved in what we call the indirect contact mechanism. This permits the enhancement of each stage. This process, which has been developed for the treatment of high-grade sulphide flotation concentrates, is proposed for the pretreatment of gold-bearing sulphide ores.
Article
Full-text available
The book covers the general principles of solution chemistry, engineering aspects, and detailed studies of hydrometallurgical processes in 750 pages fully illustrated with drawings and photographs. It contains a selected list of over 250 review articles, proceedings volumes, and books directly related to the subject. Emphasis is laid on chemical reactions, equipment used, and flowsheets.
Article
An integrated pilot plant for the development of the S-C Copper Process was constructed at Fort Saskatchewan in 1975 and operated in 1976. The pilot plant was designed to treat 9 tonnes per day of a pyritic copper concentrate. A demonstration run conducted during the last quarter of 1976 averaged 90% on-stream time, and confirmed that the process is operable as a stable and integrated unit. Part 2 of this article describes the parameters and equipment developed for thermal activation of chalcopyrite copper concentrates to make them amenable for the dissolution of iron and zinc, and their subsequent separation and recovery. The resulting high-grade copper sulphide was leached with return electrolyte and oxygen to extract 98. 5% of the copper into solution. The copper was electrowon at 65 amps per square meter from purified solution, to produce cathodes analyzing 0. 1 ppm Se, 0. 1 ppm Bi, 4 ppm Pb and 10 ppm S.
Article
Thermal analysis (TA) studies have been made to understand changes in mineralogy that occur when pure sulphide minerals, single concentrates and different Cu-Zn-Pb sulphide concentrates are heated in air. The observed sequential oxidation behaviour of bath the synthetic and natural sulphide minerals is characterised by TA traces that are reasonably reproducible. It is shown that oxidation mechanisms of synthetic analogues during roasting are similar to those of bulk concentrates. The oxidation data thus obtained on sulphide roast products are also found to be useful to characterise some partial leach residues. During ammonia leaching of bulk concentrates, the pyrite grains are practically inert and remain in the leach residue along with oxidated lead compounds and goethite. The TA data for roasting of partially leached samples are compared with those for roasting of untreated feed concentrates. The oxidation behaviour of copper, zinc and lead mineral phases of leach residues is then characterised. The observations are corroborated by chemical phase analysis, X-ray diffraction (XRD) and optical microscopy.
Article
Oxidation in an autoclave with sulfuric acid has been shown to extract 95 to 99 pct of the zinc present, produce a quantitative amount of elemental sulfur, and avoid loss of zinc due to ferrite formation.
Article
The first ammonia leaching plants, applied to copper carbonate and native copper tailings in 1915, were followed more recently by research and development of flowsheets for ammonia leaching of sulfide concentrates. These were applied to two commercial plants. Anaconda's Arbiter Plant started up in 1974 with a design capacity of 36,000 tons/year of cathodes, to be produced by ammonia leaching with oxygen, followed by solvent extraction and electrowinning. The plant shutdown in late 1977 as a result of high maintenance and operating costs, partly due to harsh winters; to complications associated with sulfate disposal; and to changes in mineralogy. BHP's Coloso plant in Chile was designed to produce 80,000 tons/year of cathodes by leaching part of Escondida's concentrate production. Using a similar flowsheet but with air and low temperatures to avoid sulfate production, it started up in late 1994 and shutdown in mid-1998, after failing to reach cathode design capacity, and experiencing problems with its technology. The paper reviews the technologies and also alternative methods for overcoming the problems.
Article
First developed in the 1950s for treating base metal sulfides and refractory gold ores, pressure leaching technology underwent rapid commercial expansion during the 1980s. Initially used to treat nickel concentrates and mattes, pressure leaching has since been extended to the processing of zinc sulfide concentrates and sulfide-containing refractory gold ores. The adoption of pressure leaching in the zinc industry and of pressure oxidation in the gold industry is expected to continue throughout this decade.
Chapter
The bioleaching process has been restricted to copper and uranium extraction using heap, dump and in situ leaching technologies from mining wastes and low grade mineral resources. In these, the contribution of microorganisms was not appreciated. Thiobacillus ferrooxidans, the most studied microorganism, has been found responsible for the oxidation of metal sulphides. Later, the discovery of new microorganisms, as moderately, extremely thermophilic bacteria and heterotropic microorganisms and the understanding of the mechanism of leaching extended the possibilities of the bioleaching process. Moreover, progress in reactor design and kinetics of the process made the adoption of biooxidation, as a pretreatment to cyanidation, in the extraction of gold from refractory sulphide-bearing ores and concentrates. The existence of biooxidation plants in different parts of the world is showing the economical viability of the process. The success in biooxidation at extreme temperatures and biodegradation of highly refractory base metal sulphide mineral promises that this technology will be commercially used in the next years. Bacterial leaching is presented as an environmentally and economically alternative technology for the mineral industry.
Article
The electrochemical behaviour of chalcopyrite has been studied in sulphuric acid solutions with the carbon paste electrode technique. Cyclic voltammetry were performed and the effect of cathodic scan limit, Fe2+ and Cu2+ ion concentrations were followed. The presence of Cu2+ ions in solutions leads to an increase in both the oxidation and the reduction currents, but in either case further increases in currents were observed when Fe2+ ion was added in admixture to the electrolyte. Chalcocite was identified as a product of reactions at extremely high cathodic potentials. The morphology and structure of the produced products after anodic or cathodic treatments of chalcopyrite were examined by the scanning electron microscopy.
Article
Recovery of copper, lead and zinc from complex sulphide concentrates with hydrometallurgical processes has been used as an alternative due to the technological and environmental impacts. In laboratory evaluation of the selective leaching, the metal values in the flotation concentrates were selectively recovered by sulphuric acid (H2SO4) and ferric sulphate (Fe2SO4)3. The experimental parameters studied were pulp density, temperature and time for leaching. From the experimental results, it is concluded that recovery of Cu and Zn from sulphide concentrates can be as high as 89% and 97%, respectively under laboratory conditions.
Article
Chalcopyrite leaching in sulfuric acid solutions depends on the redox potential determined by the concentration ratio of ferric to ferrous ions, and the leaching rate is higher at redox potentials below a critical value. Previously, the authors have proposed a reaction model to interpret this phenomenon. The present study applied the model to interpret the catalytic effect of silver ions on chalcopyrite leaching.The model assumes that at lower potentials, chalcopyrite leaching proceeds in two steps: first, chalcopyrite is reduced by ferrous ions to form Cu2S that is more rapidly leached; next, the intermediate Cu2S is oxidized by ferric and/or dissolved oxygen to release cupric ions. During the chalcopyrite reduction, hydrogen sulfide is released to the liquid phase. Silver ions react with the hydrogen sulfide to form silver sulfide precipitate and decrease the concentration of hydrogen sulfide in the liquid phase, causing a rise in the critical potential of Cu2S formation and broadening of the potential range where rapid copper extraction takes place.To confirm the model, the redox potential dependence of chalcopyrite leaching was investigated in the presence of various concentrations of silver ions with 0.1 kmol m−3 sulfuric acid containing known concentrations of ferrous and ferric ions at 298 K in air. The critical potential increased with increasing concentrations of silver ions. This agrees with the model proposed here but cannot be explained by the conventional model proposed by Miller et al.
Conclusion Examination of calcine from a multihearth roaster and a 4 in diam fluid bed roaster suggest that part of the concentrate feed remains unreacted while the remainder reacts to completion forming magnetite. No systematic difference is observed between samples from the fluid bed roaster and the multihearth roaster. An empirical equation is proposed (Eq. [6]) for estimating magnetite content for different level of sulfur removal. The work described here was carried out during a vacation school at Mount Isa Mines, Limited, Mount Isa. The author wishes to thank the management of the company for providing facilities for this work and for permission to publish this paper; the students Messrs. Bruce, Fisher, Hanrahan, Ho, Hoa, Hutton, Koh, McPherson, Moretto and Schache who carried out the experiments; and to the laboratory staff at Mount Isa Mines for carrying out the numerous analyses.
Article
Cyanide leaching is the traditional process for the extraction of gold from primary raw materials. When the gold host rock contains high concentrations of sulphides, an oxidative thermal or a chemical pretreatment is often needed to access precious metal particles. Biooxidative leaching may be an interesting alternative, if compared with the environmental effects and costs of the conventional pretreatment processes, to liberate gold from the sulphide matrix and then to make it amenable to cyanidation. In this work, bioleaching with Thiobacillus ferrooxidans and Thiobacillus thiooxidans has been investigated at a bench scale on a refractory gold-bearing arsenopyrite (2 g/t Au) ore coming from the Gölcück mine (Turkey). The factors influencing the biooxidative pretreatment, in order to enhance the gold recovery in a conventional cyanidation process, were tested using a factorial plan of experiments. Direct cyanide leaching of the arsenopyrite ground to −74 μm showed no gold dissolution at all, but with fine grinding to −30 μm, gold recovery reached about 55.3% after 48 h of cyanidation. On the contrary, cyanidation accomplished on a 72 h bioleached arsenopyrite has allowed 84.3% of gold to be solubilized in 2 h, using the following bioleaching conditions: 20% pulp density, pH 2, stirring conditions 200 rpm, temperature 30°C, time 3 days. Under these conditions, the preliminary tests in a semi-continuous lab-scale microfermentor have been performed to evaluate the scale-up of the biooxidative process. It was possible to solubilise 95.2% Au after 48 h cyanidation for the samples bioleached during 3 days, and 96.8% Au when the time of bioleaching was 7 days.
Article
The effects of lignite type and lignite particle size on the rate of sulphur removal were studied. Biodesulphurization experiments were carried out with Mengen, Elbistan, Tunçbilek and Gediz lignites at the optimum growth conditions of Rhodococcus rhodochrous. The highest decreases in the total (25.3%) and organic sulphur contents (21.4%) were obtained with Gediz and Mengen lignites, respectively. Furthermore, increased desulphurization rates have been observed with smaller particle sizes. Reduction in particle size from 390 to 63 μm resulted in an increase in total sulphur and organic sulphur removal rates by factors of 2.8 and 19, respectively.
Article
The purpose of this paper is to review the leaching of base metal sulfides and of uranium oxides by acidic ferric ion media. A description is also given of the preparation, regeneration, and properties of such leaching media. From the discussion of the kinetics of reaction of various minerals with ferric ion, it emerges that, for many minerals, the reaction rates are sufficiently rapid to be of commercial interest for recovering the sought-after metal. A brief discussion of actual and proposed commercial processes using ferric ion leaching is also given.
Article
A critical appraisal has been made of methods that have been proposed for the hydro metallurgical treatment of chalcopyrite concentrates. Those methods in which the primary breakdown of chalcopyrite is effected by leachants are discussed. Methods in which leaching is preceded by pyrometal-lurgical decomposition of the mineral include selective sulphation and nonoxidizing treatments in which the ratios of copper, iron and sulphur are changed. No process has yet been found that can replace conventional pyrometallurgical processing, although several have reached the pilot plant stage. The incentives for devising an economic hydrometallurgical process for extracting copper from sulphide ores are the avoidance of air pollution and the possibility of recovering iron, elemental sulphur and other nonferrous metals. Résumé Une appréciation critique a été faite des méthodes proposees pour le traitement hydrométallurgique des concentrés de chalcopyrite. Les méthodes par lesquelles la deécomposition originale de la chalcopyrite est affectée par les lixiviants, sont décrites. Les méthodes selon lesquelles la lixiviation est précédée par la décomposition pyrométa1lurgique du minerai comprennent la sulphatation sélective et les traitements non-oxydants dans lesquels les concentrations relatives de cuivre, fer et souffre sont changées. Aucun procédé pouvant remplacer les procédés pyrométallurgiques conventionnels n'a encore été trouvé, bien que plusieurs soient parvenus au stade de l'exploitation sur pilote. L'intérêt d'un procédé hydrométallurgique économique, pour l'extraction du cuivre, à partir des minerais de souffre, serait la non-pollution de l'air et la possibilité de récupération du fer, du souffre élémentaire et des autres métaux non-ferreux.
Article
This chapter discusses the microbial formation and degradation of minerals in detail. It has been characteristic of microbiology and other disciplines that the tempo of man's research activities has been in direct proportion to his needs and his welfare. Thus, the diseases of man received early are stressed by microbiologists. Man's dependence upon agriculture for his food supply gave impetus to soil microbiology with special emphasis on plant diseases and soil fertility, and resulted in establishing the importance of microorganisms in the cycles of carbon, nitrogen, phosphorus, and sulfur in nature. Much less attention was paid to other natural activities of microorganisms, except where such obvious occurrences as the evolution of H2S, H2, and CH4, from stagnant bodies of water or the deposition of iron oxides in swamps and bogs demanded attention. By and large, microbiologists concerned themselves with the metabolism of organic matter and virtually ignored the inorganic environment.
Many industrially important metallurgical processes are accompanied by the emission of light, the analysis of which often supplies useful information concerning the current state of the process while also providing insight into the details of specific process mechanisms. Optical diagnostic techniques are finding an increasingly wide range of application throughout the metallurgical community. This paper discusses the application of emission spectroscopy and imaging techniques to the analysis of such diverse processes as vacuum arc remelting, laser welding, and arc welding. A discussion of these techniques will be presented addressing such subjects as instrumentation, data analysis, the kind of information available and its potential impact on the selection of process parameters. Special attention will be given to discussing the difficulties encountered in applying these diagnostic technologies to “real life” processes in non-laboratory environments.
Article
Earlier work on the roasting of precipitated copper sulphide has been extended to comprise a study of the roasting of covellite and chalcopyrite concentrates. It is found that the mechanism of roasting of covellite does not differ from that of precipitated sulphide proposed earlier. In case of chalcopyrite, sulphatation of iron takes place more readily than that of copper, but above 450° interaction between the formed ferric sulphate and copper oxide leads to the production of copper sulphate in increasing quantities. Above 600° both sulphates decompose to yield the corresponding oxides which react together at 900° to form cupric ferrite.
Article
A thermophilic culture specific to bioleaching chalcopyritic materials has been obtained from a typical chalcopyritic copper concentrate of the Spanish Pyritic Belt. This paper shows the effect of pulp density (w/v) on bioleaching culture capacity with respect to this copper concentrate. The results of the batch tests show that it is possible, operating at 10% of pulp density to attain copper extraction of 94% in 10 days and, at higher pulp densities (20%), to attain good copper extraction (80%) in only 14 days. In the same way, the culture has been amply tested with different chalcopyritic ores and copper concentrates. The results obtained with four of these materials, two refractory gold ores and two copper concentrates are also presented. These results show a varying and versatile bioleaching capacity of this bacterial culture. A model of bacterial attack of this culture to leach chalcopyrite is postulated.
Article
Biological solubilization and subsequent gasification of lignite samples from three of the largest reserves in this country, which are also characterized by high sulphur contents and low calorific values, were investigated in this project. Several white-rot fungi were screened for their ability to solubilize lignites and Phanerochaete chrysosporium was found to depolymerize Elbistan lignites with 60% efficiency. Acetate served perfectly as the primary carbon source. Whereas, Çan lignites could be depolymerized only after lengthy pre-treatment with 8N HNO3 while Beypazari lignites were completely inert to biological attack. Gasification tests with the solubilize material revealed 21% energy recovery through gaseous methane product.
Article
In the Artvin-Kafkasör ore deposit gold and silver are the main precious metals and are associated with quartz and limonite. In the present investigation, a fungal culture isolated from a mine water was tested under laboratory conditions for its bioleaching potential for enhancing silver recovery prior to cyanidation. The silver recovery was expressed as both the silver dissolved after biotreatment and that recovered after cyanidation following biotreatment. Silver recovery increased as a function of fungal pretreatment time. After 40 days, silver recovery was about 83 % (of which 15% was due to direct microbial action). The recovery by cyanidation alone, on the other hand (as observed with the uninoculated control), was 53%. These results suggest that the microbial action favours a more effective cyanidation by changing the physical properties of the ore.
Article
The effect of solids (up to 30% w/w) on the viability of a mesophilic culture of acidophilic bacteria was investigated in stirred tank reactors (STRs) using the Rushton turbine (RT) and the pitched blade turbine impellers in a speed range of 2.01–3.35 m/s. The results showed that hydrodynamic shear alone as a characteristic function of impeller type and speed has a very limited effect on the bacterial cells during mixing in STRs, but mechanical damage to bacterial cells occurs, to a most significant extent, via the attrition by solid particles promoted by the intensity of agitation. Extent of the adverse effect on the bacterial cells was found to depend on impeller design/speed and solids density. The loss in the viability of bacterial population with a tendency to increase with agitation rate and solids density was more extensive with the RT than the PBT impellers under the same experimental conditions e.g. 72% loss in the viability c.f. 40% over 4 h of mixing at 20% w/w solids and 3.35 m/s impeller speed. The kinetic analysis of the experimental data suggest that the rate and extent of oxidation of a substrate in a given process would be controlled by the inoculum size and by the difference between the ''normal'' growth rate and the deactivation rate of bacterial cells incurred at a particular mixing condition (impeller type/speed and solids density) i.e. by the ''actual'' growth rate.
Article
The effect of solid loading (mineral pulp density) on thermophilic bioleaching of pyrite by Sulfolobus metallicus (BC) was investigated in a batch reactor. Different mineral pulp densities in the range 3–18% (w/v) were tested. With mineral pulp densities ranging from 3 to 9% the bioleaching proceeded in a single stage with a relatively constant rate. The bioleaching rates calculated for pulp densities of 3, 6 and 9% were 0.10, 0.11 and 0.09 kg iron m−3 h−1 respectively. By contrast the bioleaching of pyrite at pulp densities of 12 and 15% proceeded in two distinct stages. During the exponential phase of microbial growth a sharp and linear increase in concentration of released iron was achieved. This increasing trend levelled off in the presence of non-growing cells and the second stage of bioleaching continued with a slower rate. For the pulp density of 12% the bioleaching rates of the first and the second stages were 0.09 and 0.02 kg iron m−3 h−1 respectively, whereas the calculated rates in the presence of 15% mineral were 0.07 and 0.017 kg iron m−3 h−1 for the first and the second stages. Application of 18% mineral adversely influenced the activity of the cells and the extent of bioleaching in this case was insignificant.© 2000 Society of Chemical Industry
Article
This study evaluates different bioleaching treatments of a molybdenite concentrate using mesophilic and thermophilic bacterial cultures. Further studies on the chemical leaching and the electrochemical behavior of the MoS2 concentrate were carried out. Bioleaching tests showed a progressive removal of chalcopyrite from the molybdenite concentrate with an increase in temperature. Chemical leaching tests support the idea of an indirect attack of the concentrate. Electrochemical tests indicate that chalcopyrite dissolution is favored when molybdenite is present. Therefore, this type of bioleaching treatment could be applied to purify molybdenite flotation concentrates by selectively dissolving chalcopyrite.
Article
The kinetics and rate limiting sub-processes in the bacterial oxidation of zinc sulphide with Thiobacillus ferrooxidans were examined. The oxidation rate of synthetic ZnS in the presence and absence of bacteria at equal ferrous and ferric iron concentration and pH, was measured in parallel batch experiments. Bacteria oxidize Fe2+ produced in the chemical oxidation of ZnS with Fe3+. In the fermenter without bacteria hydrogen peroxide was added to regenerate ferric iron and maintain the Fe2+ concentration equal to that in the fermenter with bacteria. No significant differences in the oxidation rates of zinc sulphide were found between the slurry with and without bacteria at equal Fe2+ and Fe3+ concentrations. Consequently, an indirect mechanism (i.e. chemical oxidation of ZnS with Fe3+ to Zn2+, S0 and Fe2+, and bacterial oxidation of S0 to SO42− and Fe2+ to Fe3+) determines the oxidation rate of ZnS in the bacterial oxidation process. From the experiments it was shown that T. ferrooxidans prefers S0 as a substrate and the regeneration of Fe3+ can even become terminated. From the experimental data several suggestions for improved process design and experimental research are given.
Article
Batch biooxidation data were obtained for a gold-bearing arsenopyrite-pyrite concentrate at 12% solids, pH of 1.6 and temperature of 40°C. The specific rates of biooxidation of arsenopyrite and pyrite were found to be very similar at 0,15 d−1 or as mass rates, for arsenopyrite 2,1 kg m−3 d−1 and pyrite 6,5 kg m−3 d−1. However, it was found that the biooxidation of arsenopyrite preceded that of pyrite and was almost complete before the oxidation of pyrite commenced.Data were also obtained for four narrow size fractions prepared from the bulk concentrate. Sequential oxidation of arsenopyrite and pyrite was observed for all size fractions. The oxidation rate obtained from the linear portion of the curve was found to have a linear dependence on surface area concentration suggesting that area-based rates are more appropriate for characterizing biooxidation kinetics.The logistic equation was found to be a good fit to all the data obtained. It was found that gold liberation was linearly dependent upon the extent of arsenic oxidation. However, sulphide oxidation appeared to be preferential in the gold-rich regions, leading to a non-linear dependence of gold liberation on extent of sulphide oxidation.
Article
The aim of the present investigation was to study the biooxidation of a refractory gold-bearing pyrrhotite, in order to increase the gold recovery during the subsequent conventional cyanidation.Bacterial cultures utilised in the biological test consisted predominantly of Thiobacillus genus. Tests were conducted at laboratory scale. The gold content of the ore sample, coming from Bolivia, was of 10 g t−1 Au.After 24 h leaching time by direct cyanidation, low gold recovery was obtained (<20% Au), with a high reagent consumption. On the other hand, a high gold recovery was achieved for the biooxidated samples: after 24 h cyanidation gold dissolution reached about 91% Au.Experimental results have shown the technical feasibility of the biooxidative pretreatment prior to conventional leaching and a complete circuit of treatment, on laboratory scale, has been developed considering also the subsequent gold recovery by carbon adsorption/desorption and electrowinning.A gold extraction yield of about 86% was determined in the whole process for gold extraction from pyrrhotite (biooxidation, solid–liquid separation, cyanidation, adsorption, desorption, electrowinning).
Article
Bacterial leaching of zinc from chat (chert) pile rock and copper from tailings pond sediment was studied in shake flask experiments. Thiobacillus ferrooxidans at 26°C leached 38% of zinc from pulverized rock in 15 days and extracted copper completely from native sediment in 24 h. Experiments omitting single medium constituents for the bacterial leaching of both zinc and copper indicated that the primary mechanism of bacterial leaching is very likely by the indirect route, in which the bacteria catalyze the ferric-ferrous redox cycle. The small particle size of the native tailings pond sediment (particles of ∼ 5 μm in size contributed almost all of the surface area) is a probable reason for the relatively short amount of time required for the copper leaching. Because of the rapidity of the extraction of copper with T. ferrooxidans, larger scale tests were carried out in a bioreactor with mechanical agitation and aeration. Complete extraction of copper was obtained in 12 h. A separate fluidization experiment showed that the tailings pond sediment could be kept suspended with a low fluid bulk velocity (0.3 cm/s). Two possible routes to scale up the bacterial leaching of copper from tailings pond sediment are discussed.
Article
A laboratory-scale method for treating a bulk concentrate (CuFeS2–PbS–ZnS) for metals recovery was developed utilising a combination of thermal process (roasting) and pressure leaching as an alternative to conventional pyrometallurgical processing. Pyrometallurgy is becoming less acceptable from environmental standpoints for the treatment of bulk concentrates. Additionally, high capital costs make modern facilities cost prohibitive. The leaching agents employed, namely, sulphuric acid (lixivant) and ferric sulphate, are selective for metal sulphides, this coupled with the fact that they create fewer environmental problems and are economical makes this new process highly favourable. In the laboratory evaluation of this process, the metal values in the flotation concentrates were selectively recovered by combining roasting and pressure leaching. The experimental parameters studied included roasting temperature, and pressure leaching pulp density, temperature, and retention time. Laboratory results indicate that roasting followed by pressure leaching is an efficient and cost effective method of treating base metal sulphide concentrates.
Article
Natural monoclinic pyrrhotite particles (Fe1−xS) were subjected to pressure leaching by oxygen in sulphuric acid solutions at temperatures ranging between 353 and 453 K (80–180°C). For temperatures below the melting point of sulphur (392 K), the rate of pyrrhotite oxidation shows a moderate dependence on temperature, while it is totally independent of sulphuric acid concentration. Nonetheless, in the absence of oxygen, as much as 30% of the mineral can be dissolved in 0.5 mol/l H2SO4. The conversion data were found to fit well to a shrinking-core model with mixed control by half-order surface reaction and oxidant diffusion though a product layer. Despite the high initial reactivity of pyrrhotite, complete oxidation of the mineral was never achieved at temperatures below 393 K, apparently due to an impervious sulphur product layer covering the particles. Complete pyrrhotite oxidation was achieved at temperatures above the melting point of sulphur and only with the use of lignin sulphonate as dispersant of molten sulphur. By analysing the conversion data with the shinking-core model, pyrrhotite oxidation in the high temperature range (403–453 K) was found to be surface-reaction controlled and of first order with respect to oxygen pressure.
Article
In the present work the applicability of bioleaching using a mixed culture of mesophilic microorganisms (Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirilum ferrooxidans) on a bulk concentrate of a Spanish complex sulphide ore was studied. The bulk concentrate mainly consisted of by chalcopyrite, sphalerite and pyrite. Effects of nutrient medium, stirring, pulp density, temperature and the addition of CO2 (1% v/v) to the air flow were also studied. The highest leaching rates and recoveries were obtained with mechanically stirred reactors at 5% pulp density and 9K medium. However, by using 9K medium higher jarosite precipitation was observed. Results showed that the optimum temperature for copper bioleaching was 30°C, whereas zinc dissolution increased with a rise in the temperature.
Article
Multi-mineral complex sulphide ores would, typically, not respond well to conventional single mineral flotation due to their fine grained nature. Thus, many complex ore deposits remain undeveloped due to a lack of alternative economic treatment scenarios. The selective leaching process that has been explored is capable of selectively extracting zinc from concentrates containing both sphalerite and chalcopyrite. Unfortunately, many complex sulphide concentrates may also contain appreciable levels of pyrite and galena. Understanding the influence of these mineral on the leaching system is critical to developing a selective leaching process that is easily adapted to a wide variety of concentrate materials.Based on these considerations the selective extraction of zinc using pressure oxidation from multi-mineral concentrates was investigated. Concentrates were artificially produced from pure minerals and ranged in composition of: 25–100% by weight sphalerite, 5–75% chalcopyrite, 0–75% pyrite and 0–75% galena. Zinc was selectively extracted from several Cu/Zn concentrates by utilizing various combinations of temperature and oxygen concentration in the pressure leaching process and the influence of the additions of pyrite and galena was defined. It was discovered that addition of only 5% by weight galena to the selective leaching system retarded the dissolution of sphalerite by up to 13%. Alternatively, a 10% pyrite addition increased zinc extractions while simultaneously decreasing the copper extractions, however, increased concentrations resulted in increased copper extraction and thus, decreased zinc selectivity.
Article
In the history of Turkey the first use of cyanide for gold recovery has been at the Ovacik Gold Mine. During one-year test period, this mine has successfully been mining and processing after a complicated and extensive environmental impact procedure. In Turkey about 2500 ton of sodium cyanide are used with about 240 ton of sodium cyanide being used at this mine annually. During the test period, it has been shown that an effluent quality (CNWAD) between 0.06 ppm (min) and 1 ppm (max) was achievable after cyanide destruction with the Inco Process. It was also found that treated effluent values (CNWAD) of process water (decant) were between 0.04 ppm (min) and 0.59 ppm (max). This paper presents a review of the cyanidation and cyanide destruction processes at the Ovacik Gold Mine.
Article
Biooxidation of a fine-grained, complex zinc and gold-containing sulphide ore has been performed in a series of experiments at bench scale with 201 leaching volume in a series of three continuously stirred reactors. A mixed culture of moderate thermophilic bacteria was used for bioleaching at 45°C and a mixed culture of extreme thermophilic archea were used for bioleaching at 65°C.The leaching yields for zinc were in the range 80–87% with the moderate thermophilic bacteria and 96–98% with the extremely thermophilic microorganisms. It was found that, to obtain a high zinc recovery with a low degree of pyrite oxidation, a fine particle size was essential. Changes in retention time did not influence zinc solubilisation to any greater extent. Due to a high limestone content in the ore, the bioleaching was acid consuming. The acid consumption was strongly dependent on the throughput of ore in the leaching system. Recoveries of gold and silver, of ∼90% and 60–80%, respectively, after cyanidation of the bioleaching residue were obtained, irrespective of experimental conditions.
Article
The effects of substrate type in the growth medium, mixing time of lignite into the growth medium and the biodesulfurization time on sulfur removal were studied. Biodesulfurization experiments were carried out with Mengen lignite under optimum growth conditions of Rhodococcus rhodochrous. The highest reduction of organic sulfur forms was 27.1% when sodium acetate was the substrate. Sulfate sulfur could be totally reduced when lignite was added to the culture medium 24 h after incubation. Compared with sodium acetate, glycerol yielded higher sulfate sulfur reduction rates when lignite was added at the time of incubation. The highest organic sulfur removal rates were found when sodium acetate was the substrate.
Article
This paper reports a 57Fe Mössbauer spectroscopic study of the kinetics of roasting process of chalcopyrite at two different temperatures and for different time intervals. Iron compounds formed at different stages of roasting have been identified and a possible scheme of transformations has been suggested to explain the observed kinetics.
Article
The kinetics of leaching of sphalerite by the thermophilic Acidianus brierleyi were studied in a batch stirred reactor. Experiments were done at 65°C and pH 2.0 on the adsorption of A. brierleyi onto sphalerite and the bioleaching of sphalerite particles. The distribution of A. brierleyi cells between the mineral and solution was attained within the first 30 min of exposure to sphalerite, and the equilibrium distribution data were correlated with the Langmuir isotherm. The addition of 0.3 and 1.4 kg/m3 ferric iron to the A. brierleyi culture resulted in a significant decline in the leaching rates, probably because of the formation of iron precipitates such as jarosite. Rate data collected in iron-free leach solutions were analyzed to determine microbial kinetic and stoichiometric parameters for the growth of A. brierleyi on sphalerite. These growth parameters demonstrated that the rate of bioleaching with the thermophilic A. brierleyi is about seven times that with the common leaching mesophile, Thiobacillus ferrooxidans.
Article
Microorganisms are important in metal recovery from ores, particularly sulfide ores. Copper, zinc, gold, etc. can be recovered from sulfide ores by microbial leaching. Mineral solubilization is achieved both by ‘direct (contact) leaching’ by bacteria and by ‘indirect leaching’ by ferric iron (Fe3+) that is regenerated from ferrous iron (Fe2+) by bacterial oxidation. Thiobacillus ferrooxidans is the most studied organism in microbial leaching, but other iron- or sulfide/sulfur-oxidizing bacteria as well as archaea are potential microbial agents for metal leaching at high temperature or low pH environment. Oxidation of iron or sulfur can be selectively controlled leading to solubilization of desired metals leaving undesired metals (e.g., Fe) behind. Microbial contribution is obvious even in electrochemistry of galvanic interactions between minerals.
Article
The oxidation by Ferrobacillus ferrooxidans of untreated pyrite (FeS(2)) as well as HCl-pretreated pyrite (from which most of the acid-soluble iron species were removed) was studied manometrically. Oxygen uptake was linear during bacterial oxidation of untreated pyrite, whereas with HCl-pretreated pyrite both a decrease in oxygen uptake at 2 hr and nonlinear oxygen consumption were observed. Ferric sulfate added to HCl-pretreated pyrite restored approximately two-thirds of the decrease in total bacterial oxygen uptake and caused oxygen uptake to revert to nearly linear kinetics. Ferric sulfate also oxidized pyrite in the absence of bacteria and O(2); recovery of ferric and ferrous ions was in excellent agreement with the reaction Fe(2)(SO(4))(3) + FeS(2) = 3FeSO(4) + 2S, but the elemental sulfur produced was negligible. Neither H(2)S nor S(2)O(3) (2-) was a product of the reaction. It is probable that two mechanisms of bacterial pyrite oxidation operate concurrently: the direct contact mechanism which requires physical contact between bacteria and pyrite particles for biological pyrite oxidation, and the indirect contact mechanism according to which the bacteria oxidize ferrous ions to the ferric state, thereby regenerating the ferric ions required for chemical oxidation of pyrite.