Leaching of Pyrites of Various Reactivities by Thiobacillus ferrooxidans

Wide variations were found in the rate of chemical and microbiological leaching of iron from pyritic materials from various sources. Thiobacillus ferrooxidans accelerated leaching of iron from all of the pyritic materials tested in shake flask suspensions at loadings of 0.4% (wt/vol) pulp density. The most chemically reactive pyrites exhibited the fastest bioleaching rates. However, at 2.0% pulp density, a delay in onset of bioleaching occurred with two of the pyrites derived from coal sources. T. ferrooxidans was unable to oxidize the most chemically reactive pyrite at 2.0% pulp density. No inhibition of pyrite oxidation by T. ferrooxidans occurred with mineral pyrite at 2.0% pulp density. Experiments with the most chemically reactive pyrite indicated that the leachates from the material were not inhibitory to iron oxidation by T. ferrooxidans.     

Role of Ferrous Ions in Synthetic Cobaltous Sulfide Leaching of Thiobacillus ferrooxidans

Microbiological leaching of synthetic cobaltous sulfide (CoS) was investigated with a pure strain of Thiobacillus ferroxidans. The strain could not grow on CoS-salts medium in the absence of ferrous ions (Fe²⁺). However, in CoS-salts medium supplemented with 18 mM Fe²⁺, the strain utilized both Fe²⁺ and the sulfur moiety in CoS for growth, resulting in an enhanced solubilization of Co²⁺. Cell growth on sulfur-salts medium was strongly inhibited by Co²⁺, and this inhibition was completely protected by Fe²⁺. Cobalt-resistant cells, obtained by subculturing the strain in medium supplemented with both Fe²⁺ and Co²⁺, brought a marked decrease in the amount of Fe²⁺ absolutely required for cell growth on CoS-salts medium. As one mechanism of protection by Fe²⁺, it is proposed that the strain utilizes one part of Fe²⁺ externally added to CoS-salts medium to synthesize the cobalt-resistant system. Since a similar protective effect by Fe²⁺ was also observed for cell inhibition by stannous, nickel, zinc, silver, and mercuric ions, a new role of Fe²⁺ in bacterial leaching in T. ferrooxidans is proposed.     

Leaching Heavy Metals from Contaminated Soil by Using Thiobacillus ferrooxidans or Thiobacillus thiooxidans

Iron- and sulfur-oxidizing bacteria identified as Thiobacillus ferrooxidans and T. thiooxidans were successfully enriched from various soil samples contaminated with heavy metals and organic compounds. Depending on the growth medium, the soil sample, and the type of contaminant, the indigenous isolates solubilized > 50% of most of the heavy metals present in the solid sample (As, Cd, Co, Cr, Cu, Ni, V, Zn, B, Be). Leaching with T. ferrooxidans strains resulted in total extraction of Cd, Co, Cu, and Ni. With sulfur-oxidizing bacteria > 80% of Cd, Co, Cu, and Zn was mobilized from rainwater sludge. Pb and Ba were not detected in the leachate, given the insolubility of their sulfate compounds. An increase in pulp density up to 20%, indicating 6.6% total organic carbon in the soil and rubble leach experiment (sample 557), did not inhibit the growth of the indigenous T. ferrooxidans strain. In view of these results, bioleaching appears to have some potential for remediation of heavy metal contaminated soils.     

Sulfide oxidation by spheroplasts of Thiobacillus ferrooxidans.

Thiobacillus ferrooxidans is an acidophilic organism important to metal leaching of low-grade ores. The aforementioned importance is related to the ability of the bacterium to oxidize reduced iron and sulfur, principally found in nature as pyrite (FeS2). The present study dealt with sulfide oxidation at low pH values and the involvement of the cell envelope in the process of the inorganic oxidations. Sulfide oxidation was noted in spheroplasts of T. ferrooxidans prepared by enzymatic and chemical treatments and partially purified by differential centrifugation. No enzyme activities were noted in membrane fractions containing enrichments of lipopolysaccharide symbolic of outer membrane material or in membrane vesicles containing (or associated with) higher levels of proteins. Results to date indicate that in an acid milieu the envelope structure containing both the outer membrane and the intact inner cytoplasmic membrane is required for sulfide oxidation.     

Sulfide oxidation by spheroplasts of Thiobacillus ferrooxidans.

Thiobacillus ferrooxidans is an acidophilic organism important to metal leaching of low-grade ores. The aforementioned importance is related to the ability of the bacterium to oxidize reduced iron and sulfur, principally found in nature as pyrite (FeS2). The present study dealt with sulfide oxidation at low pH values and the involvement of the cell envelope in the process of the inorganic oxidations. Sulfide oxidation was noted in spheroplasts of T. ferrooxidans prepared by enzymatic and chemical treatments and partially purified by differential centrifugation. No enzyme activities were noted in membrane fractions containing enrichments of lipopolysaccharide symbolic of outer membrane material or in membrane vesicles containing (or associated with) higher levels of proteins. Results to date indicate that in an acid milieu the envelope structure containing both the outer membrane and the intact inner cytoplasmic membrane is required for sulfide oxidation.     

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.     

Kinetics of Iron Oxidation by Thiobacillus ferrooxidans

A statistical relationship between the rate of ferric ion production by a strain of Thiobacillus ferrooxidans and various levels of cell concentration, Fe²⁺ concentration, Na⁺ concentration, and temperature was studied by a direct colorimetric method at 304 nm. The relationship was linear (90 to 93%), cross-product (3 to 4%), and quadratic (1 to 2%). The levels of cell concentration and Fe²⁺ concentration and their respective interactions with one another and the other factors had the most significant effects on the regression models. The solution of the quadratic response surface for optimum oxidation was a saddle point, and the predicted critical levels of temperature, cell concentration, Fe²⁺ concentration, and Na⁺ concentration ranged between −6 and 2°C, 0.43 and 0.62 mg/ml, 72 and 233 mM, and 29.6 mM, respectively.     

氧化亚铁硫杆菌的形态及对Fe2+的氧化研究

在纯培养的条件下,对江西德兴铜矿酸性矿坑水中分离出的一株氧化亚铁硫杆菌(Thiobacillus ferrooxidans)的细胞形态、生长条件以及对Fe2 的氧化进行了初步研究。透射电子显微镜检查的结果表明,其成熟菌体大小均一,有较好的运动性;采用光学显微镜对微生物进行菌群观测和利用血小板计数器法对细菌计数的结果表明,在摇床转速为160r/min的条件下,T.f.菌在9K液体培养基中最适生长条件为温度30℃左右,最佳初始pH 2.0;用重铬酸钾滴定法测定铁的结果表明,在摇床转速为160r/min的条件下,pH值1.7,温度30℃时T.f.菌对Fe2 的氧化速率最大,约为0.58g/L·h。     

Leaching of Zinc Sulfide by Thiobacillus ferrooxidans: Experiments with a Controlled Redox Potential Indicate No Direct Bacterial Mechanism

The role of Thiobacillus ferrooxidans in bacterial leaching of mineral sulfides is controversial. Much of the controversy is due to the fact that the solution conditions, especially the concentrations of ferric and ferrous ions, change during experiments. The role of the bacteria would be more easily discernible if the concentrations of ferric and ferrous ions were maintained at set values throughout the experimental period. In this paper we report results obtained by using the constant redox potential apparatus described previously (P. I. Harvey and F. K. Crundwell, Appl. Environ. Microbiol. 63:2586–2592, 1997). This apparatus is designed to control the redox potential in the leaching compartment of an electrolytic cell by reduction or oxidation of dissolved iron. By controlling the redox potential the apparatus maintains the concentrations of ferrous and ferric ions at their initial values. Experiments were conducted in the presence of T. ferrooxidans and under sterile conditions. Analysis of the conversion of zinc sulfide in the absence of the bacteria and analysis of the conversion of zinc sulfate in the presence of the bacteria produced the same results. This indicates that the only role of the bacteria under the conditions used is regeneration of ferric ions in solution. In this work we found no evidence that there is a direct mechanism for bacterial leaching.     

Leaching of Zinc Sulfide by Thiobacillus ferrooxidans: Bacterial Oxidation of the Sulfur Product Layer Increases the Rate of Zinc Sulfide Dissolution at High Concentrations of Ferrous Ions

This paper reports the results of leaching experiments conducted with and without Thiobacillus ferrooxidans at the same conditions in solution. The extent of leaching of ZnS with bacteria is significantly higher than that without bacteria at high concentrations of ferrous ions. A porous layer of elemental sulfur is present on the surfaces of the chemically leached particles, while no sulfur is present on the surfaces of the bacterially leached particles. The analysis of the data using the shrinking-core model shows that the chemical leaching of ZnS is limited by the diffusion of ferrous ions through the sulfur product layer at high concentrations of ferrous ions. The analysis of the data shows that diffusion through the product layer does not limit the rate of dissolution when bacteria are present. This suggests that the action of T. ferrooxidans in oxidizing the sulfur formed on the particle surface is to remove the barrier to diffusion by ferrous ions.     

Oxidation of gallium sulfides by Thiobacillus ferrooxidans.

The bacterial oxidation of naturally occurring gallium-bearing chalcopyrite concentrate and a pure synthetic gallium (III) sulfide has been investigated at pH 1.8 and 35 degree C, using an active culture of Thiobacillus ferrooxidans. This oxidation process may proceed by direct or by indirect bacterial action. The highest dissolved gallium and copper concentrations were about 2.2 and 40.2 g/l, respectively. The order of the specific rate of oxygen uptake by T. ferrooxidans in approximately CuFES2 greater than or equal to gallium-bearing CuFeS2 greater than FeS2 greater than Cu2S greater than Cu2S greater than Ga2S3.     

Corrosion and Electrochemical Oxidation of a Pyrite by Thiobacillus ferrooxidans

The oxidation of a pure pyrite by Thiobacillus ferrooxidans is not really a constant phenomenon; it must be considered to be more like a succession of different steps which need characterization. Electrochemical studies using a combination of a platinum electrode and a specific pyrite electrode (packed-ground-pyrite electrode) revealed four steps in the bioleaching process. Each step can be identified by the electrochemical behavior (redox potentials) of pyrite, which in turn can be related to chemical (leachate content), bacterial (growth), and physical (corrosion patterns) parameters of the leaching process. A comparison of the oxidation rates of iron and sulfur indicated the nonstoichiometric bacterial oxidation of a pure pyrite in which superficial phenomena, aqueous oxidation, and deep crystal dissolution are successively involved.     

Mineral Products of Pyrrhotite Oxidation by Thiobacillus ferrooxidans

The biological leaching of pyrrhotite (Fe_1-xS) by Thiobacillus ferrooxidans was studied to characterize the oxidation process and to identify the mineral weathering products. The process was biphasic in that an initial phase of acid consumption and decrease in redox potential was followed by an acid-producing phase and an increase in redox potential. Elemental S was one of the first products of pyrrhotite degradation detected by X-ray diffraction. Pyrrhotite oxidation also yielded K-jarosite [KFe₃(SO₄)₂(OH)₆], goethite (α-FeOOH), and schwertmannite [Fe₈O₈(OH)₆SO₄] as solid-phase products. Pyrrhotite was mostly depleted after 14 days, whereas impurities in the form of pyrite (cubic FeS₂) and marcasite (orthorhombic FeS₂) accumulated in the leach residue.     

Oxidation of arsenopyrite by Thiobacillus ferrooxidans detected by a mineral electrode

Summary A new electrochemical study of arsenopyrite biooxidation was based on process detection by arsenopyrite electrode. The rate of reaction was evaluated as the exchange current density calculated from polarization curves. Obtained data were used for determination of released electrons from mineral and for evaluation of reaction mechanism of its oxidation.     

Role of a Ferric Ion-Reducing System in Sulfur Oxidation of Thiobacillus ferrooxidans

The properties of a ferric ion-reducing system which catalyzes the reduction of ferric ion with elemental sulfur was investigated with a pure strain of Thiobacillus ferrooxidans. In anaerobic conditions, washed intact cells of the strain reduced 6 mol of Fe³⁺ with 1 mol of elemental sulfur to give 6 mol of Fe²⁺, 1 mol of sulfate, and a small amount of sulfite. In aerobic conditions, the 6 mol of Fe²⁺ produced was immediately reoxidized by the iron oxidase of the cell, with a consumption of 1.5 mol of oxygen. As a result, Fe²⁺ production was never observed under aerobic conditions. However, in the presence of 5 mM cyanide, which completely inhibits the iron oxidase of the cell, an amount of Fe²⁺ production comparable to that formed under anaerobic conditions was observed under aerobic conditions. The ferric ion-reducing system had a pH optimum between 2.0 and 3.8, and the activity was completely destroyed by 10 min of incubation at 60°C. A short treatment of the strain with 0.5% phenol completely destroyed the ferric ion-reducing system of the cell. However, this treatment did not affect the iron oxidase of the cell. Since a concomitant complete loss of the activity of sulfur oxidation by molecular oxygen was observed in 0.5% phenol-treated cells, it was concluded that the ferric ion-reducing system plays an important role in the sulfur oxidation activity of this strain, and a new sulfur-oxidizing route is proposed for T. ferrooxidans.     

Oxidation of Ferrous Iron and Elemental Sulfur by Thiobacillus ferrooxidans

The oxidation of ferrous iron and elemental sulfur by Thiobacillus ferrooxidans that was absorbed and unabsorbed onto the surface of sulfur prills was studied. Unadsorbed sulfur-grown cells oxidized ferrous iron at a rate that was 3 to 7 times slower than that of ferrous iron-grown cells, but sulfur-grown cells were able to reach the oxidation rate of the ferrous iron-adapted cells after only 1.5 generations in a medium containing ferrous iron. Bacteria that were adsorbed to sulfur prills oxidized ferrous iron at a rate similar to that of unadsorbed sulfur-grown bacteria. They also showed the enhancement of ferrous iron oxidation activity in the presence of ferrous iron, even though sulfur continued to be available to the bacteria in this case. An increase in the level of rusticyanin together with the enhancement of the ferrous iron oxidation rate were observed in both sulfur-adsorbed and unadsorbed cells. On the other hand, sulfur oxidation by the adsorbed bacteria was not affected by the presence of ferrous iron in the medium. When bacteria that were adsorbed to sulfur prills were grown at a higher pH (ca. 2.5) in the presence of ferrous iron, they rapidly lost both ferrous iron and sulfur oxidation capacities and became inactive, apparently because of the deposition of a jarosite-like precipitate onto the surface to which they were attached.     

氧化亚铁硫杆菌培养过程中沉淀的研究

为了减少氧化亚铁硫杆菌培养过程中产生的沉淀,对氧化亚铁硫杆菌培养过程中产生的沉淀物进行了研究,确定了在pH为1．5,K2HPO4用量为0．25g/l,KH2PO4为0．195g/l时菌体可以保持其最高氧化活性,同时产生最少量沉淀物的培养条件,并发现沉淀物对菌体的生长和氧化Fe^2 没有影响。利用饥饿状态的氧化亚铁硫杆菌证明了菌体在一定条件下可以利用黄铁钒沉淀中的部分离子进行生长繁殖。     

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 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 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.     

Leaching of Chalcopyrite with Thiobacillus ferrooxidans: Effect of Surfactants and Shaking

The rate of leaching of chalcopyrite by Thiobacillus ferrooxidans has been greatly accelerated by using shaken flasks in place of stationary bottles or percolators. A further increase in rate and extent of leaching was obtained by the use of Tween 20, 40, 60, and 80, Triton X-100, Quaker TT 5386, and Hyamine 2389. Tween 20 was the most effective surfactant. No individual component of the Tween molecule was responsible for the improved leaching. The Tween-to-chalcopyrite ratio is more important than the Tween-to-medium ratio. The effect of the surfactants is probably due to increased contact between the mineral surface and the organism, and shaking provides the necessary oxygen. Rates and yields obtained by use of surfactants and shaking as aids to microbiological leaching approach those obtained with acidified erric sulfate leaching.