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ABSTRACT: Degradation of dimethoate under UV irradiation using TiO(2)/polymer films prepared by the layer-by-layer (LbL) method was investigated. The thin films were fabricated on glass slides and the surface morphology and roughness of the thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of lamp intensity, catalyst loading in the layers, number of bilayers, pH and initial dimethoate concentration on the degradation of dimethoate was systematically studied. The degradation was monitored using high performance liquid chromatography (HPLC) analysis and total organic carbon (TOC) measurements as a function of irradiation time, to see the change in concentration of dimethoate and mineralization, respectively. Complete degradation of dimethoate was achieved under TiO(2) optimum loading of 4 g/L at an UV irradiation time of 180 min. Increase in the lamp intensity, catalyst loading and number of bilayers increased the rate of degradation. At a pH of 4.62, complete degradation of dimethoate was observed. The degradation efficiency decreased with increase in initial dimethoate concentration. The degradation byproducts were analyzed and confirmed by gas chromatography-mass spectra (GC-MS). Toxicity of the irradiated samples was measured using the luminescence of bacteria Vibrio fischeri after 30 min of incubation and the results showed more toxicity than the parent compound. Catalyst reusability studies revealed that the fabricated thin films could be repeatedly used for up to ten times without affecting the photocatalytic activity of the films. The findings of the present study are very useful for the treatment of wastewaters contaminated with pesticides.
Journal of hazardous materials 08/2011; 195:214-22. · 4.14 Impact Factor
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ABSTRACT: Interpenetrating polymer networks (IPNs) comprising weakly acidic and weakly basic cross-linked polymers, namely, poly(acrylic acid-co-ethyleneglycol dimethacrylate) (XPAA) and 80% ethoxylated polyethyleneimine (EPEI) cross-linked with glutaraldehyde, were prepared by the copolymerization of acrylic acid (AA) and ethyleneglycol dimethacrylate by a free-radical method, in the presence of calculated amounts of EPEI in methanol solution, followed by cross-linking with glutaraldehyde. The resulting IPNs, containing carboxylic acid groups and weakly basic tertiary amine groups in close proximity in the same resin bead, exhibited thermally regenerable desalination properties [e.g., sorption of salt at 30 °C and desorption at higher temperatures (80 °C)], simulating the behavior of the well-known Sirotherm resins. For NaCl and MgCl2, the maximum equilibrium sorption (0.5 mmol/g of dry resin in 0.1 M salt solution) was exhibited by an IPN with a carboxylic-to-amine (C/A) mole ratio in the range of 3−5. The equilibrium sorption at 30 °C for NaCl and MgCl2 on an IPN sorbent with a C/A mole ratio of 4.2 (referred to as Sirosorb) fitted well to both the Langmuir and Freundlich isotherms for single-component sorption and the Butler−Ockrent and Jain−Snoeyink models for bicomponent sorption. Containing both carboxylic and amine groups largely in a free state, Sirosorb exhibited buffer action over a wide range of feed solution pH values (3−8) to give nearly constant sorption of NaCl, although the sorption of MgCl2 increased with increasing pH because of additional sorption by ion exchange at the ionic sites formed by neutralization of the carboxylic acid groups. The sorption rate data showed characteristics of particle diffusion control with a NaCl and MgCl2 diffusivity ratio of 2:1, yielding diffusivity values of (2.5−3.9) × 10−7cm2/s for NaCl and (1.2−1.7) × 10−7cm2/s for MgCl2 in the initial period at 30 °C, with the diffusivity falling abruptly in both cases at higher conversion. Continuous column operation performed with Sirosorb showed that the quantity of potable water with a NaCl content of less than 1500 mg/L that can be produced is about 4 times the weight (dry) of the resin, when the influent brackish water has a NaCl content of 3000 mg/L. The used resin was regenerated with 1 M NaCl solution at 90 °C and used repeatedly with no apparent loss of capacity, as demonstrated in the present work for up to 10 cycles of operation.
07/2010;
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ABSTRACT: Fabrication of multilayer ultrathin composite films composed of nanosized titanium dioxide particles (P25, Degussa) and polyelectrolytes (PELs), such as poly(allyl amine hydrochloride) (PAH) and poly(styrene sulfonate sodium salt) (PSS), on glass substrates using the layer-by-layer (LbL) assembly technique and its potential application for the photodegradation of rhodamine B under ultraviolet (UV) irradiation has been reported. The polyelectrolytes and TiO(2) were deposited on glass substrates at pH 2.5 and the growth of the multilayers was studied using UV/vis spectrophotometer. Thickness measurements of the films showed a linear increase in film thickness with increase in number of bilayers. The surface microstructure of the thin films was characterized by field emission scanning electron microscope. The ability of the catalysts immobilized by this technique was compared with TiO(2) films prepared by drop casting and spin coating methods. Comparison has been made in terms of film stability and photodegradation of rhodamine B. Process variables such as the effect of surface area of the multilayers, number of bilayers, and initial dye concentration on photodegradation of rhodamine B were studied. Degradation efficiency increased with increase in number of catalysts (total surface area) and bilayers. Kinetics analysis indicated that the photodegradation rates follow first order kinetics. Under maximum loading of TiO(2), with five catalyst slides having 20 bilayers of polyelectrolyte/TiO(2) on each, 100 mL of 10 mg/L dye solution could be degraded completely in 4 h. The same slides could be reused with the same efficiency for several cycles. This study demonstrates that nanoparticles can be used in wastewater treatment using a simple immobilization technique. This makes the process an attractive option for scale up.
ACS Applied Materials & Interfaces 11/2009; 1(11):2684-93. · 4.53 Impact Factor
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ABSTRACT: Crosslinked poly(acrylic acid) (XPAA) made by copolymerization of acrylic acid and ethylene glycol dimethacrylate in bulk was further reacted with 80% ethoxylated polyethyleneimine, and the latter insolubilized by treatment with glutaraldehyde. The resulting composite sorbent, XPAA(EPEI.XG), containing carboxylic acid groups and weakly basic tertiary amine groups in close proximity in the same resin bead exhibited thermally regenerable desalination property, simulating the well-known Sirotherm™ resins. For NaCl and MgCl2, the sorbent has saturation capacities of 0.796 and 0.839 meq/g (dry) sorbent, respectively, at 30°C but less than 0.1 meq/g (dry) sorbent at 80–90°C. The equilibrium sorption data at 30°C fit well to both Langmuir and Freundlich isotherms for single-component sorption and to Butler-Ockrent and Jain-Snoeyink models for bicomponent sorption. Although the sorption of NaCl exhibits a plateau in the pH range of 4–5, that of MgCl2 increases sharply above pH 4 because of additional sorption by cation exchange at the ionic sites formed at higher pH. The sorption rate data show characteristics of particle-diffusion controlled ion-exchange process, yielding diffusivity values of 1.0–1.3 × 10−6 cm2/s for NaCl and 3.0–3.5 × 10−7 cm2/s for MgCl2, in the initial period at 30°C, with the diffusivity falling abruptly in both cases at higher conversions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Journal of Applied Polymer Science 12/2008; 111(6):2741 - 2750. · 1.29 Impact Factor
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ABSTRACT: The optimal design of a multiproduct batch chemical plant is formulated as a multiobjective optimization problem, and the resulting constrained mixed-integer nonlinear program (MINLP) is solved by the nondominated sorting genetic algorithm approach (NSGA-II). By putting bounds on the objective function values, the constrained MINLP problem can be solved efficiently by NSGA-II to generate a set of feasible nondominated solutions in the range desired by the decision-maker in a single run of the algorithm. The evolution of the entire set of nondominated solutions helps the decision-maker to make a better choice of the appropriate design from among several alternatives. The large set of solutions also provides a rich source of excellent initial guesses for solution of the same problem by alternative approaches to achieve any specific target for the objective functions. Copyright © 2006 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering 11/2006; 1(1‐2):13 - 20. · 0.76 Impact Factor
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ABSTRACT: A commercial acrylic fiber with 92% (w/w) acrylonitrile content was partially hydrolyzed converting a fraction of the nitrile (CN) groups to carboxylic acid (COOH) groups, to coat the fiber with polyethylenimine (PEI) resin, which was then crosslinked with glutaraldehyde and further quaternized with ethyl chloroacetate to produce a novel strong-base anionic exchanger in the form of fiber. Designated as PAN(QPEI.XG)(Cl−), the fibrous sorbent was compared with a commercial bead-form resin Amberlite IRA-458(Cl−) in respect of sorption capacity, selectivity, and kinetics for removal of silver thiosulfate complexes from aqueous solutions. Though the saturation level of [Ag(S2O3)2]3− on PAN(QPEI.XG)(Cl−) is considerably less than that on IRA-458(Cl−), the gel-coated fibrous sorbent exhibits, as compared to the bead-form sorbent, a significantly higher sorption selectivity for the silver thiosulfate complex in the presence of excess of other anions such as S2O32−, SO42−, and Cl−, and a remarkably faster rate of both sorption and stripping. The initial uptake of the sorbate by the fibrous sorbent is nearly instantaneous, reaching up to ∼80% of the saturation capacity within 10 s, as compared to only ∼12% on the bead-form sorbent. The high initial rate of uptake fits a shell-core kinetic model for sorption on fiber of cylindrical geometry. With 4M HCl, the stripping of the sorbed silver complex from the fibrous sorbent is clean and nearly instantaneous, while, in contrast, a much slower rate of stripping on the bead-form sorbent leads to its fouling due to a slow decomposition of the silver thiosulfate complex in the acidic medium. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2604–2613, 2006
Journal of Applied Polymer Science 02/2006; 100(4):2604 - 2613. · 1.29 Impact Factor
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ABSTRACT: In this work the effect of organic reducing reagents, namely, ascorbic acid, oxalic acid and L-cysteine on dissolution of commercial TiO(2) has been investigated. Kinetic studies showed that a maximum of about 45% of TiO(2) was dissolved by ascorbic acid in 4h when oxide:acid molar ratio was kept at 1:2. The dissolution of TiO(2) increased with increase in ascorbic acid and oxalic acid concentration up to 0.15M in 4h (corresponding to molar ratio of oxide to acid of 1:3) and further addition did not affect the dissolution. Nearly 45% TiO(2) dissolution was obtained with ascorbic acid alone while oxalic acid yielded 40% dissolution. When oxalic acid was added along with ascorbic acid in equi-molar concentrations, dissolution of TiO(2) was enhanced to 60% in 2.5h but when cysteine was added to ascorbic acid the dissolution was about 50% in just 1h.
Chemosphere 11/2005; 61(4):585-8. · 3.21 Impact Factor
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ABSTRACT: Polymetallic ocean nodules offer an alternative source for extracting valuable strategic metals like Cu, Co and Ni. A novel biodissolution process was carried out, employing the cell-free spent growth medium from a marine organism ( Bacillus M1) isolated from nodules; and Cu, Co and Ni solubilization from the nodules was observed to be beyond the theoretical solubility limits at near neutral pH. Different characterization techniques revealed the presence of phenolic substances in the spent growth medium, which might have formed soluble complexes with the transition metals. The low prevailing E(h) redox value in the medium suggested a strong reducing environment, favoring the reductive dissolution of the oxides. A correlation study of dissolution of Cu, Co and Ni with that of Mn and Fe in the nodules was made to investigate the mechanisms of metal solubilization by the marine isolate. Under the influence of a strong reducing environment coupled with complexation by a phenolic substance present in the spent growth medium, Mn and Fe oxides were solubilized from the nodules, resulting in concomitant dissolution of Cu, Co and Ni associated with them in the nodules.
Journal of Industrial Microbiology and Biotechnology 12/2004; 31(10):462-8. · 2.73 Impact Factor
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ABSTRACT: When using a genetic algorithm (GA) to solve optimal control problems that can arise in a fed-batch bioreactor, the most obvious direct approach is to rely on a finite dimensional discretization of the optimal control problem into a nonlinear programming problem. Usually only the control function is discretized, and the continuous control function is approximated by a series of piecewise constant functions. Even though the piecewise discretized controls that the GA produces for the optimal control problem may give good performances, the control policies often show very high activity and differ considerably from those obtained using a continuous optimization strategy. The present study introduces a few filters into a real-coded genetic algorithm as additional operators and investigates the smoothing capabilities of the filters employed. It is observed that inclusion of a filter significantly smoothens the optimal control profile and often encourages the convergence of the algorithm. The applicability of the technique is illustrated by solving two previously reported optimal control problems in fed-batch bioreactors that are known to have singular arcs.
Bioprocess and Biosystems Engineering 11/2004; 26(5):295-306. · 1.81 Impact Factor
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ABSTRACT: Selective separation of pyrite from other associated ferrous sulphides at acidic and neutral pH has been a challenging problem. This paper discusses the utility of Acidithiobacillus ferrooxidans for the selective flotation of chalcopyrite from pyrite. Consequent to interaction with bacterial cells, pyrite remained depressed even in the presence of potassium isopropyl xanthate collector while chalcopyrite exhibited significant flotability. However, when the minerals were conditioned together, the selectivity achieved was poor due to the activation of pyrite surface by the copper ions in solution. The selectivity was improved when the sequence of conditioning with bacterial cells and collector was reversed, since the bacterial cells were able to depress collector interacted pyrite effectively, while having negligible effect on chalcopyrite. The observed behaviour is analysed and discussed in detail. The separation obtained was significant both at acidic and alkaline pH. This selectivity achieved was retained when the minerals were interacted with both bacterial cells and collector simultaneously.
Colloids and Surfaces B Biointerfaces 10/2004; 37(3-4):93-100. · 3.46 Impact Factor
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ABSTRACT: A commercial acrylic fiber containing 92 wt % acrylonitrile was hydrolyzed to convert a part of its nitrile (CN) groups to carboxylic acid (COOH) groups and then was coated chemically with 80% ethoxylated polyethylenimine (EPEI) resin, followed by crosslinking with glutaraldehyde. The resulting sorbent, PAN(CO2H)(EPEI.XG), containing carboxylic acid groups and weakly basic tertiary amine groups in close proximity on the same fiber is found to simulate the well-known Sirotherm™ resins used for partial desalination of brine solution by adsorbing the salt at ambient temperature and desorbing it at an elevated temperature in the same solution. The sorption behavior of the new sorbent was evaluated for solutes NaCl and MgCl2, showing saturation capacities of 0.797 and 0.877 meq/g (dry) sorbent fiber, respectively, at 30°C. The equilibrium sorption data show good agreement with both Langmuir and Freundlich isotherms for sorption from single-component solutions and with Butler–Ockrent and LeVan–Vermeulen models for bicomponent sorption. Although the equilibrium uptake of NaCl reaches maximum in neutral solutions (pH ∼ 6.5), falling at both lower and higher pH, that of MgCl2 is augmented in alkaline pH due to additional sorption by cation exchange at the ionic sites formed at higher pH. The initial uptake of the salt, which is nearly instantaneous, exceeds the sorption value attainable at equilibrium. The high initial rate of salt uptake fits a shell-core kinetic model for sorption on fiber of cylindrical geometry. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 883–893, 2004
Journal of Applied Polymer Science 07/2004; 93(2):883 - 893. · 1.29 Impact Factor
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ABSTRACT: Polymetallic Indian Ocean nodules offer a lucrative resource for valuable strategic metals such as Cu, Co and Ni. A novel bioleaching process using cell-free spent growth medium from a fully-grown culture of a marine organism isolated from the nodules (Bacillus M1) dissolved about 45% Co, and 25% Cu and Ni at a the pH of 8.2 in 4 h. To enhance metal dissolution, different modifications in the bioleaching process, such as increasing the pH of the spent growth medium, carrying out leaching in multiple steps, and introducing organic reductant in the leach pulp, were investigated in this study. Increasing the initial pH of the spent growth medium to above 12 resulted in a 25–30% increase in dissolution of Cu, Co and Ni. The pKa value for the spent growth medium was observed to be in the range of 11.5–12.5. UV-visible spectroscopy of the growth medium at pH values above 10.0 suggested a change in the structure of complexing phenolic substances present therein. A four-step leaching process using the spent growth medium, each step lasting for about 4 h, was able to bring around 60% Cu and Ni and 85% Co in solution. About 85% Co, 90% Cu and 60% Ni were dissolved in two-stage leaching, in which the bioleached residue was treated with the spent growth medium from Acidithiobacillus thiooxidans in the second cycle. The effects of concentration of starch (0.1–10%) as an organic reductant to the spent growth medium were also studied. The dissolution of Cu, Co and Ni stabilized at about 80–85% at a starch concentration of 3% and did not increase much thereafter. Copyright © 2004 Society of Chemical Industry
Journal of Chemical Technology & Biotechnology 04/2004; 79(5):512 - 517. · 2.17 Impact Factor
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ABSTRACT: A marine organism ( Bacillus M1) isolated from Indian Ocean manganese nodules was characterized. The organism grew well in artificial seawater medium, at near neutral pH, 30 degrees C and 0.25 M NaCl, and showed MnO(2)-reducing activity. Growing cultures of Bacillus M1 as well as cell-free spent liquor from fully-grown cultures were employed to extract metals from the nodules. The spent liquor of cultures of the organism could dissolve around 45% cobalt (Co) at a pH of 8.2 in 2 h. Co recovery by this treatment was comparable to that in acidic leaching with 2.5 M hydrochloric acid solutions, and was independent of pulp density (w/v ratio). The amount of Co dissolved was beyond the thermodynamic solubility limit in aqueous solution at a pH of 8.2. It is inferred that the metabolites present in the spent liquor played a pivotal role in complexing the Fe (III) phase, solubilizing Co in the process. Partial characterization of spent liquor by spot tests, UV visible spectroscopy and FTIR spectroscopy, showed the presence of siderophore-like phenolic compound(s) with an attached carboxyl group that might form soluble organic complexes with Fe (III).
Journal of Industrial Microbiology and Biotechnology 11/2003; 30(10):606-12. · 2.73 Impact Factor
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ABSTRACT: A strain of Thiobacillus ferrooxidans was adapted to grow at higher concentrations of copper by single step culturing in the presence of 20 g/L (0.314 mol/L) cupric ions added to 9K medium. Exposure to copper results in change in the surface chemistry of the microorganism. The isoelectric point of the adapted strain (pI=4.7) was observed to be at a higher pH than that of the wild unadapted strain(pI=2.0). Compared to the wild strain, the copper adapted strain was found to be more hydrophobic and showed enhanced attachment efficiency to the pyrite mineral. The copper adsorption ability of the adapted strain was also found to be higher than that of the wild strain. Fourier transform infrared spectroscopy of adapted cells suggested that a proteinaceous new cell surface component is synthesized by the adapted strain. Treatment of adapted cells with proteinase-K, resulted in complete loss of tolerance to copper, reduction in copper adsorption and hydrophobicity of the adapted cells. These observations strongly suggest a role played by cell surface modifications of Thiobacillus ferrooxidans in imparting the copper tolerance to the cells and bioleaching of sulphide minerals.
Antonie van Leeuwenhoek 03/1998; 73(3):215-222. · 2.09 Impact Factor
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Chemical Engineering Communications 01/1996; 143(1):99-116. · 0.95 Impact Factor
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ABSTRACT: This article reviews the state of the art in processing and extracting ocean manganese nodules. It briefly reviews the mining sites where abundant rich nodules occur and also describes the metal distribution in nodules. The physicochemical characteristics of the nodules, touching upon different facets such as mineralogy, geochemistry, moisture content, and textural properties of the nodules, are discussed in detail. In the extraction aspects of the nodules, is article reviews two different extraction routes often mentioned in the literature during the last two decades, namely hydrometallurgical and biohydrometallurgical treatments. The hydrometallurgical techniques include leaching by mineral acids, ammoniacal leaching, leaching at high temperature, and pressure and leaching with reducing agents. Reduction of manganese dioxide by organics and its probable application in leaching of nodules is described in a detailed manner. The biohydrometallurgy section extensively reviews the bioreduction phenomenon for manganese dioxide and suggests possible application in leaching of nodules. Projected future developments in the field, with an eye on commercialization, are also discussed.
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ABSTRACT: On-line reoptimisation of a bioprocess is a difficult task due to its complex, time-varying, nonlinear nature. The task is further complicated by the lack of suitable on-line sensors. Frequently, model errors due to the complex nature of bioprocesses require that kinetic model used in optimisation be reparameterised or updated on-line for effective control of fermentation processes. An on-line reoptimisation procedure based on an improved genetic algorithm approach in combination with state and parameter estimation is developed for the determination of substrate feed profiles for the optimal operation of fed-batch bioreactors. The problem specific knowledge generated through the rigorous application of the optimal control theory is used to formulate the set of decision variables representing the qualitative and quantitative aspects of the feed rate profile. An Extended Kalman Filter (EKF) is used to provide optimal estimates of the relevant state variables from readily available on-line process measurements and the model parameters are dynamically adjusted using a nonlinear programming approach over a moving window. The EKF also keeps track of the specific growth parameter to detect any change in the process. The efficiency of the proposed algorithm is demonstrated on a cell mass production problem under fed-batch operation.
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ABSTRACT: The determination of optimal feed rate profiles for fed-batch bioreactors with two feed rates is a numerically difficult problem involving two singular control variables. A solution strategy based on genetic algorithm approach for the determination of optimal substrate feeding policies for fed-batch bioreactors with two control variables is proposed. The efficiency of the algorithm is demonstrated for a fed-batch bioreactor for the production of foreign protein production by recombinant bacteria. The control policies obtained retain the characteristics of the profiles generated through the application of control theory
Computer Aided Chemical Engineering 14:1127-1132.
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ABSTRACT: A bacterium Bacillus polymyxa was found to be capable of selective removal of calcium and iron from bauxite. The bioleached residue was found to be enriched in its alumina content with insignificant amounts of iron and calcium as impurities. The developed bio- process was found to be capable of producing a bauxite product which meets the specifica- tions as a raw material for the manufacture of alumina based ceramics and refractories. The role of bacterial cells and metabolic products in the selective dissolution of calcium (present as calcite) and iron (present as hematite and goethite) from bauxite was assessed and possi- ble mechanisms illustrated. The effect of different parameters such as sucrose concentra- tion, pH, pulp density and time on selective biodissolution was studied. It was observed that periodic decantation and replenishment of the leach medium was beneficial in improving the dissolution kinetics. Calcium removal involves chelation with bacterial exopolysaccha- tides and acidolysis by organic acid generation. Hematite could be solubilized through a reductive dissolution mechanism.
Process Metallurgy 9:463-472.
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ABSTRACT: An isolate of Thiobacillus ferrooxidans derived from gold mine water samples was repeatedly subcultured at increasing temperatures (from 30° to 42°C) in 9K medium. The temperature-adapted strain was found to be more efficient in the bioleaching of pyrite mineral than the wild type. When temperature-tolerant strains were cultured repeatedly in 9K medium at 30°C, the temperature tolerance was completely lost. These results indicate that the temperature tolerance was stress-dependent and not a permanent trait of the adapted strain. The potential utility of such temperature-tolerant strains of Thiobacillus ferrooxidans in sulphide mineral dissolution is demonstrated.
Hydrometallurgy.
