Recently, we reported the production of Cadmium sulfide (CdS) fluorescent semiconductor nanoparti... more Recently, we reported the production of Cadmium sulfide (CdS) fluorescent semiconductor nanoparticles (quantum dots, QDs) by acidophilic bacteria of thegenus. Here, we report that the addition of inorganic phosphate toATCC 19703 cultures favors the biosynthesis of CdS QDs at acidic conditions (pH 3.5). The effect of pH, phosphate and cadmium concentrations on QDs biosynthesis was studied by using Response Surface Methodology (RSM), a multivariate technique for analytical optimization scarcely used in microbiological studies to date. To address how phosphate affects intracellular biosynthesis of CdS QDs, the effect of inorganic phosphate on bacterial cadmium-uptake was evaluated. By measuring intracellular levels of cadmium we determined that phosphate influences the capacity of cells to incorporate this metal. A relation between cadmium tolerance and phosphate concentrations was also determined, suggesting that phosphate participates in the adaptation of bacteria to toxic levels of ...
The oxidation of ferrous iron and elemental sulfur by Thiobacillus ferrooxidans that was absorbed... more 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...
The effect of two flotation reagents: isopropyl- and ethyl-xanthates and two solvent extraction r... more The effect of two flotation reagents: isopropyl- and ethyl-xanthates and two solvent extraction reagents (SX): Lix 984 and Lix 860IC on the bioleaching of a copper concentrate with Sulfolobus metallicus was analyzed. The experiments were performed in 250 ml shake flasks with 100 ml basal medium with an initial pH of 1.6, inoculated with a pure culture of S. metallicus and 0.5 % copper concentrate (38% of Cu) at 70oC. In the bioleaching flasks 0, 50 or 500 μg/mL of flotation reagent and 0, 10 or 100μg/mL of SX reagents was added. All organic reagents caused a strong inhibition of ferrous iron oxidation and growth of planktonic cells of S. metallicus. However, bioleaching in presence of 50 μg/mL of isopropyl-xanthate or 10 μg/mL of Lix 984 reached copper dissolutions of 70% and 72% respectively after 200 hours, compared with 98% in the process without organic reagents. These results suggest that isopropyl-xanthate and Lix 984 at the lowest concentrations used in this study would not a...
The catalytic influence of Sulfolobus metallicus in the bioleaching of pure chalcopyrite at 70° C... more The catalytic influence of Sulfolobus metallicus in the bioleaching of pure chalcopyrite at 70° C and pH 1.5 was studied in shake flask experiments. In order to evaluate separately the influence of planktonic and attached cells on the catalytic process, in some experiments the microorganisms were prevented from reaching chalcopyrite surface by keeping them in a chamber separated by a 0.1 Millipore membrane. Leaching, which was conducted with a -80 # + 120# chalcopyrite sample, was characterized from monitoring Eh, pH, copper, ferrous and ferric ion concentration in solution. In addition, the concentration of different sulphur species dissolved in solution either in aerated-abiotic and aerobic - biotic conditions, was determined with HPLC. Maximum copper dissolution was reached in experiments where all the microorganisms could reach chalcopyrite. In experiments where microorganisms were maintained separated from the sulphide, the population of microorganisms still increased. However,...
World Journal of Microbiology & Biotechnology, 2002
In bioleaching processes, bacteria adhered to agglomerated ores are frequently determined in the ... more In bioleaching processes, bacteria adhered to agglomerated ores are frequently determined in the washing solution after treating the mineral with different techniques like sonification or chemical treatment with SDS, Tween 20, Tritón X-100, or only basal medium to release the adhered cells. In this work we compare the efficiency of these techniques, not only by determination of the number of
Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper diss... more Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper dissolution (52% after 550 h of leaching) was obtained with bacteria and 1 g l−1 ferric ion. In the absence of ferric ion, Sulfolobus BC catalyzes the bioleaching of enargite through a direct mechanism after adhesion onto the mineral surface. In ferric bioleaching, arsenic precipitated as ferric arsenate and
The electrokinetic and hydrophobic properties of the autotrophic bacteria Thiobacillus ferrooxida... more The electrokinetic and hydrophobic properties of the autotrophic bacteria Thiobacillus ferrooxidans as well as selected minerals have been studied by microelectrophoresis, contact angle and hexadecane/aqueous phase partition measurements. Adhesion measurements were ...
Bioactive glasses (SiO 2-P 2 O 5-CaO) having tailored concentrations of different biocide metal i... more Bioactive glasses (SiO 2-P 2 O 5-CaO) having tailored concentrations of different biocide metal ions (copper or silver) were produced by the sol-gel method. All the particles release phosphorous ions when immersed in water and simulated body fluid (SBF). Moreover, a surface layer of polycrystalline hydroxy-carbonate apatite was formed on the particle surfaces after 10 day immersion in SBF as confirmed by X-ray diffraction and scanning electron microscopy (SEM) showing the bioactive materials. Samples with embedded either copper or silver ions were able to further release the biocide ions with a release rate that depends on the metal embedded and the dissolution medium: water or SBF. This biocide ion release from the samples explains the antimicrobial effect of our active particles against Escherichia coli DH5α ampicillin-resistant (Gram-negative) and Streptococcus mutans (Gram-positive) as determined by the Minimum Bactericidal Concentration (MBC) method. The antimicrobial behavior of the particles depends on the bacteria and the biocide ion used. Noteworthy, although samples with copper are able to release more metal ion than samples with silver, they present higher MBC showing the high effect of silver against these bacteria.
The catalytic influence of Sulfolobus metallicus in the bioleaching of chalcopyrite at 70°C and p... more The catalytic influence of Sulfolobus metallicus in the bioleaching of chalcopyrite at 70°C and pH 1.5 was studied in shake flask experiments. Leaching was conducted in an iron-free basal medium with a −80 # + 120 # chalcopyrite sample, and was characterized from monitoring in solution the pH, Eh, copper and iron concentration, and cell population. In order to evaluate separately the influence of planktonic and attached cells on the catalytic process, in some experiments the microorganisms were prevented from reaching the chalcopyrite surface by keeping them in a chamber separated by a 0.1 Millipore membrane. In a complementary experimental series, the concentration of different sulfur species dissolved in the solution was determined with HPLC at different conditions, under nitrogen or air, abiotic or inoculated with S. metallicus. Maximum copper dissolution was reached when at least one fraction of the inoculated microorganisms were able to approach chalcopyrite surface. In this case, notably, the fraction of the population of microorganisms that were prevented from reaching chalcopyrite was still observed to increase. In experiments where all the inoculated microorganisms were prevented from reaching chalcopyrite, the cell population did not grow. In this case copper dissolution was only 50% of the amount reached when full bacterial contact was allowed, and was similar to the amount of copper dissolved at aerated-abiotic conditions. HPLC results on the analysis of dissolved sulfur species showed that when microorganisms were able to reach chalcopyrite there was accumulation in solution of thiosulfate (S 2 O 3) − 2 and sulfite (SO 3) − 2 , in addition to the formation of bisulfite (HSO 3) − , bisulfate (HSO 4) − and sulfate (SO 4) − 2 which was also observed in aerobic-abiotic conditions. It could be concluded that in bioleaching of chalcopyrite in the presence of S. metallicus there is a cooperative action between attached cells which can oxidize sulfur-containing surface layers on chalcopyrite, forming thiosulfate, sulfite and bisulfite, and planktonic cells which further oxidize these intermediate compound to bisulfate and sulfate. Removal of surface passivating layers under the catalytic action of attached microorganisms is a key catalytic factor as it greatly enhances the oxidative action of ferric iron on chalcopyrite.
Arsenic, present as impurity in many sulfide ores, dissolves during the bioleaching process and t... more Arsenic, present as impurity in many sulfide ores, dissolves during the bioleaching process and the resulting high As(III) concentration can inhibit bacterial activity, compromising the whole process. Oxidation of As(III) to As(V) and its further precipitation as ferric arsenate is probably the most accurate way to face the problem. Thermodynamically, As(III) should be easily oxidized by Fe(III), but the reaction
A method for evaluating the proportion of bacteria attached to mineral sulfides is presented. The... more A method for evaluating the proportion of bacteria attached to mineral sulfides is presented. The method is based on the determination of the rate of ferrous iron oxidation by attached bacteria on the mineral surfaces. The values obtained with this procedure are in agreement with measurements of attached bacteria using bacteria grown with radioactive (C14) NaHCO3. The methodology was used to evaluate the fraction of bacteria attached to chalcopyrite during bioleaching of this sulfide. It was observed that a significant fraction of the bacteria grow attached to the mineral.
El tratamiento de aguas residuales mediante de lodos activados es un sistema biológico complejo, ... more El tratamiento de aguas residuales mediante de lodos activados es un sistema biológico complejo, dinámico, no homogéneo, cuyo desconocimiento de su biología se debe principalmente a la dificultad de cultivo de los microorganismos mediante metodologías convencionales. ...
Copper sulphide ore bioleaching processes are currently under full development in Chile and world... more Copper sulphide ore bioleaching processes are currently under full development in Chile and worldwide, for treatment of: secondary sulphide in heaps [1], low-grade ores in dumps, and concentrates in reactors at high temperatures [2]. Abundant knowledge is available in the literature and great experience has been gathered about the behavior of mesophilic microorganisms and their application in bioleaching of sulfides in heaps and dumps [, as well as, about the behavior of extreme thermophilic microorganisms in reactors [. However, there is little information about the behavior of some moderately thermophilic microorganisms in the dissolution of chalcopyrite and pyrite at 45oC [. This is the case of S. acidophilus, a gram-positive rod shaped that often forms endospores and grow at temperature optima, generally between 45 and 55°C. It has been characterized as a chemolithoheterotrophic bacteria that obtains energy from the oxidation of ferrous iron or from reduced sulfur compounds and ...
In the bioleaching of mineral sulphides under the catalytic action ofAt. ferrooxidans,ferrous ion... more In the bioleaching of mineral sulphides under the catalytic action ofAt. ferrooxidans,ferrous ion oxidation and sulfides/sulfur solubilization uses oxygen as the final electron acceptor. Also, under anaerobic conditions,At. ferrooxidanscan alternatively catalize the oxidation of sulfur or reduced inorganic sulfur compounds (RISC) using ferric iron as electron acceptor [1]. The formation of Fe (II) from pyrite and covellite in the ferric anaerobic bioleaching withA. ferrooxidans,has been studied and well documented [2,3]. The requirements of ferric iron as electron acceptor for the anaerobic growth ofAt. ferrooxidanson elemental sulfur has been demonstrated and a linear relationship was obtained between the concentration of ferrous iron accumulated in the cultures and the increase in cell density [4]. It has been suggested a possible role in the solubilization of metals from sulfide ores involving the participation of the enzyme sulfur (sulfide): Fe (III) oxidoreductase [5]. Bacteria...
Enargite (Cu 3 AsS 4 ) was leached faster by bacteria in sulfuric acid medium (pH 1.6) with added... more Enargite (Cu 3 AsS 4 ) was leached faster by bacteria in sulfuric acid medium (pH 1.6) with added ferric sulfate than by chemical leaching at the same or higher iron concentration. During chemical leaching with ferric iron, the copper dissolution rate decreased from an initial value of 0.03% per hour to a value of 0.002% per hour. Enargite is
Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans are two of the most important bact... more Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans are two of the most important bacteria in heap bioleaching processes of copper sulphide at common operating temperatures (18-24°C). In this paper, both microorganisms were detected in solutions and ores coming from processes in 2 days, using specific amplification of 16S rDNA sequences by PCR. The technique was first validated using template DNA from pure cultures of the microorganisms. Then it was applied to samples of solutions and ores from bioleaching processes. Results were confirmed using tRFLP (terminal Restriction Fragment Length Polymorphism) with universal primers and by identification of isolated bacteria by means of culture. This methodology is more rapid and specific than the identification by tRFLP or by culture, which require from 1 to three weeks to positively detect the bacteria. The detection limit of this technique is 10 5 cells per ml.
This work presents preliminary results of a study to determine the technical feasibility of heap ... more This work presents preliminary results of a study to determine the technical feasibility of heap bioleaching of copper sulfides in a mixed ore that had previously undergone a chemical leach to recover the copper from the copper oxides in the ore. The recovery of the copper sulfides is economically and environmentally important. The first step in this study was to determine the presence of bacteria in samples of both the agglomerated ores taken from the heaps and the samples from the irrigation solution used in the leaching process. No bacteria were detected in either sample, probably because of the very low pH, the high concentration of sulfate (200 g/l), and the presence of other ions in the irrigation solution. On the other hand, the cultivation of bacteria from recently crushed, fresh mixed ore (oxide-sulfide), and from cured, agglomerated ore, showed the presence of a small bacterial population, with ferrous iron-oxidizing activity. This indicates that the ore initially contained viable bacteria that were inhibited in the heap. Based on these results, a glass laboratory column containing 700 g of agglomerated ore from a partially, chemically leached heap was set up. The ore in the column was irrigated in a closed circuit with nutrient medium containing 2 g of ferrous sulfate per liter. Bacteria were detected, and the redox potential in the leaching solution began to increase on day 20 of the bioleaching experiment, indicating the beginning of the bioleaching stage of the sulfide mineral. The data indicate that the bacteria initially present on the ore can be recovered after acid curing, and also after prolonged contact with a solution containing a high concentration of sulfate. These results indicate that it is technically possible to induce a change from a chemical leaching process with high ionic strength to a bacterial leaching process, by dilution of the irrigation solution.
Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper diss... more Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper dissolution (52% after 550 h of leaching) was obtained with bacteria and 1 g l−1 ferric ion. In the absence of ferric ion, Sulfolobus BC catalyzes the bioleaching of enargite through a direct mechanism after adhesion onto the mineral surface. In ferric bioleaching, arsenic precipitated as ferric arsenate and arsenic remained associated to the solid residues, preventing the presence of a high dissolved arsenic concentration in the leaching solution. About 90% inhibition of bacterial growth rate and activity was observed for dissolved arsenic concentrations above 600 mg l−1 for As(III) and above 1000 mg l−1 for As(V). Arsenic-bearing copper ores and concentrates could be leached by Sulfolobus BC in the presence of ferric iron due to the favourable precipitation of arsenic ion as ferric arsenate, avoiding significant bacterial inhibition.
Recently, we reported the production of Cadmium sulfide (CdS) fluorescent semiconductor nanoparti... more Recently, we reported the production of Cadmium sulfide (CdS) fluorescent semiconductor nanoparticles (quantum dots, QDs) by acidophilic bacteria of thegenus. Here, we report that the addition of inorganic phosphate toATCC 19703 cultures favors the biosynthesis of CdS QDs at acidic conditions (pH 3.5). The effect of pH, phosphate and cadmium concentrations on QDs biosynthesis was studied by using Response Surface Methodology (RSM), a multivariate technique for analytical optimization scarcely used in microbiological studies to date. To address how phosphate affects intracellular biosynthesis of CdS QDs, the effect of inorganic phosphate on bacterial cadmium-uptake was evaluated. By measuring intracellular levels of cadmium we determined that phosphate influences the capacity of cells to incorporate this metal. A relation between cadmium tolerance and phosphate concentrations was also determined, suggesting that phosphate participates in the adaptation of bacteria to toxic levels of ...
The oxidation of ferrous iron and elemental sulfur by Thiobacillus ferrooxidans that was absorbed... more 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...
The effect of two flotation reagents: isopropyl- and ethyl-xanthates and two solvent extraction r... more The effect of two flotation reagents: isopropyl- and ethyl-xanthates and two solvent extraction reagents (SX): Lix 984 and Lix 860IC on the bioleaching of a copper concentrate with Sulfolobus metallicus was analyzed. The experiments were performed in 250 ml shake flasks with 100 ml basal medium with an initial pH of 1.6, inoculated with a pure culture of S. metallicus and 0.5 % copper concentrate (38% of Cu) at 70oC. In the bioleaching flasks 0, 50 or 500 μg/mL of flotation reagent and 0, 10 or 100μg/mL of SX reagents was added. All organic reagents caused a strong inhibition of ferrous iron oxidation and growth of planktonic cells of S. metallicus. However, bioleaching in presence of 50 μg/mL of isopropyl-xanthate or 10 μg/mL of Lix 984 reached copper dissolutions of 70% and 72% respectively after 200 hours, compared with 98% in the process without organic reagents. These results suggest that isopropyl-xanthate and Lix 984 at the lowest concentrations used in this study would not a...
The catalytic influence of Sulfolobus metallicus in the bioleaching of pure chalcopyrite at 70° C... more The catalytic influence of Sulfolobus metallicus in the bioleaching of pure chalcopyrite at 70° C and pH 1.5 was studied in shake flask experiments. In order to evaluate separately the influence of planktonic and attached cells on the catalytic process, in some experiments the microorganisms were prevented from reaching chalcopyrite surface by keeping them in a chamber separated by a 0.1 Millipore membrane. Leaching, which was conducted with a -80 # + 120# chalcopyrite sample, was characterized from monitoring Eh, pH, copper, ferrous and ferric ion concentration in solution. In addition, the concentration of different sulphur species dissolved in solution either in aerated-abiotic and aerobic - biotic conditions, was determined with HPLC. Maximum copper dissolution was reached in experiments where all the microorganisms could reach chalcopyrite. In experiments where microorganisms were maintained separated from the sulphide, the population of microorganisms still increased. However,...
World Journal of Microbiology & Biotechnology, 2002
In bioleaching processes, bacteria adhered to agglomerated ores are frequently determined in the ... more In bioleaching processes, bacteria adhered to agglomerated ores are frequently determined in the washing solution after treating the mineral with different techniques like sonification or chemical treatment with SDS, Tween 20, Tritón X-100, or only basal medium to release the adhered cells. In this work we compare the efficiency of these techniques, not only by determination of the number of
Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper diss... more Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper dissolution (52% after 550 h of leaching) was obtained with bacteria and 1 g l−1 ferric ion. In the absence of ferric ion, Sulfolobus BC catalyzes the bioleaching of enargite through a direct mechanism after adhesion onto the mineral surface. In ferric bioleaching, arsenic precipitated as ferric arsenate and
The electrokinetic and hydrophobic properties of the autotrophic bacteria Thiobacillus ferrooxida... more The electrokinetic and hydrophobic properties of the autotrophic bacteria Thiobacillus ferrooxidans as well as selected minerals have been studied by microelectrophoresis, contact angle and hexadecane/aqueous phase partition measurements. Adhesion measurements were ...
Bioactive glasses (SiO 2-P 2 O 5-CaO) having tailored concentrations of different biocide metal i... more Bioactive glasses (SiO 2-P 2 O 5-CaO) having tailored concentrations of different biocide metal ions (copper or silver) were produced by the sol-gel method. All the particles release phosphorous ions when immersed in water and simulated body fluid (SBF). Moreover, a surface layer of polycrystalline hydroxy-carbonate apatite was formed on the particle surfaces after 10 day immersion in SBF as confirmed by X-ray diffraction and scanning electron microscopy (SEM) showing the bioactive materials. Samples with embedded either copper or silver ions were able to further release the biocide ions with a release rate that depends on the metal embedded and the dissolution medium: water or SBF. This biocide ion release from the samples explains the antimicrobial effect of our active particles against Escherichia coli DH5α ampicillin-resistant (Gram-negative) and Streptococcus mutans (Gram-positive) as determined by the Minimum Bactericidal Concentration (MBC) method. The antimicrobial behavior of the particles depends on the bacteria and the biocide ion used. Noteworthy, although samples with copper are able to release more metal ion than samples with silver, they present higher MBC showing the high effect of silver against these bacteria.
The catalytic influence of Sulfolobus metallicus in the bioleaching of chalcopyrite at 70°C and p... more The catalytic influence of Sulfolobus metallicus in the bioleaching of chalcopyrite at 70°C and pH 1.5 was studied in shake flask experiments. Leaching was conducted in an iron-free basal medium with a −80 # + 120 # chalcopyrite sample, and was characterized from monitoring in solution the pH, Eh, copper and iron concentration, and cell population. In order to evaluate separately the influence of planktonic and attached cells on the catalytic process, in some experiments the microorganisms were prevented from reaching the chalcopyrite surface by keeping them in a chamber separated by a 0.1 Millipore membrane. In a complementary experimental series, the concentration of different sulfur species dissolved in the solution was determined with HPLC at different conditions, under nitrogen or air, abiotic or inoculated with S. metallicus. Maximum copper dissolution was reached when at least one fraction of the inoculated microorganisms were able to approach chalcopyrite surface. In this case, notably, the fraction of the population of microorganisms that were prevented from reaching chalcopyrite was still observed to increase. In experiments where all the inoculated microorganisms were prevented from reaching chalcopyrite, the cell population did not grow. In this case copper dissolution was only 50% of the amount reached when full bacterial contact was allowed, and was similar to the amount of copper dissolved at aerated-abiotic conditions. HPLC results on the analysis of dissolved sulfur species showed that when microorganisms were able to reach chalcopyrite there was accumulation in solution of thiosulfate (S 2 O 3) − 2 and sulfite (SO 3) − 2 , in addition to the formation of bisulfite (HSO 3) − , bisulfate (HSO 4) − and sulfate (SO 4) − 2 which was also observed in aerobic-abiotic conditions. It could be concluded that in bioleaching of chalcopyrite in the presence of S. metallicus there is a cooperative action between attached cells which can oxidize sulfur-containing surface layers on chalcopyrite, forming thiosulfate, sulfite and bisulfite, and planktonic cells which further oxidize these intermediate compound to bisulfate and sulfate. Removal of surface passivating layers under the catalytic action of attached microorganisms is a key catalytic factor as it greatly enhances the oxidative action of ferric iron on chalcopyrite.
Arsenic, present as impurity in many sulfide ores, dissolves during the bioleaching process and t... more Arsenic, present as impurity in many sulfide ores, dissolves during the bioleaching process and the resulting high As(III) concentration can inhibit bacterial activity, compromising the whole process. Oxidation of As(III) to As(V) and its further precipitation as ferric arsenate is probably the most accurate way to face the problem. Thermodynamically, As(III) should be easily oxidized by Fe(III), but the reaction
A method for evaluating the proportion of bacteria attached to mineral sulfides is presented. The... more A method for evaluating the proportion of bacteria attached to mineral sulfides is presented. The method is based on the determination of the rate of ferrous iron oxidation by attached bacteria on the mineral surfaces. The values obtained with this procedure are in agreement with measurements of attached bacteria using bacteria grown with radioactive (C14) NaHCO3. The methodology was used to evaluate the fraction of bacteria attached to chalcopyrite during bioleaching of this sulfide. It was observed that a significant fraction of the bacteria grow attached to the mineral.
El tratamiento de aguas residuales mediante de lodos activados es un sistema biológico complejo, ... more El tratamiento de aguas residuales mediante de lodos activados es un sistema biológico complejo, dinámico, no homogéneo, cuyo desconocimiento de su biología se debe principalmente a la dificultad de cultivo de los microorganismos mediante metodologías convencionales. ...
Copper sulphide ore bioleaching processes are currently under full development in Chile and world... more Copper sulphide ore bioleaching processes are currently under full development in Chile and worldwide, for treatment of: secondary sulphide in heaps [1], low-grade ores in dumps, and concentrates in reactors at high temperatures [2]. Abundant knowledge is available in the literature and great experience has been gathered about the behavior of mesophilic microorganisms and their application in bioleaching of sulfides in heaps and dumps [, as well as, about the behavior of extreme thermophilic microorganisms in reactors [. However, there is little information about the behavior of some moderately thermophilic microorganisms in the dissolution of chalcopyrite and pyrite at 45oC [. This is the case of S. acidophilus, a gram-positive rod shaped that often forms endospores and grow at temperature optima, generally between 45 and 55°C. It has been characterized as a chemolithoheterotrophic bacteria that obtains energy from the oxidation of ferrous iron or from reduced sulfur compounds and ...
In the bioleaching of mineral sulphides under the catalytic action ofAt. ferrooxidans,ferrous ion... more In the bioleaching of mineral sulphides under the catalytic action ofAt. ferrooxidans,ferrous ion oxidation and sulfides/sulfur solubilization uses oxygen as the final electron acceptor. Also, under anaerobic conditions,At. ferrooxidanscan alternatively catalize the oxidation of sulfur or reduced inorganic sulfur compounds (RISC) using ferric iron as electron acceptor [1]. The formation of Fe (II) from pyrite and covellite in the ferric anaerobic bioleaching withA. ferrooxidans,has been studied and well documented [2,3]. The requirements of ferric iron as electron acceptor for the anaerobic growth ofAt. ferrooxidanson elemental sulfur has been demonstrated and a linear relationship was obtained between the concentration of ferrous iron accumulated in the cultures and the increase in cell density [4]. It has been suggested a possible role in the solubilization of metals from sulfide ores involving the participation of the enzyme sulfur (sulfide): Fe (III) oxidoreductase [5]. Bacteria...
Enargite (Cu 3 AsS 4 ) was leached faster by bacteria in sulfuric acid medium (pH 1.6) with added... more Enargite (Cu 3 AsS 4 ) was leached faster by bacteria in sulfuric acid medium (pH 1.6) with added ferric sulfate than by chemical leaching at the same or higher iron concentration. During chemical leaching with ferric iron, the copper dissolution rate decreased from an initial value of 0.03% per hour to a value of 0.002% per hour. Enargite is
Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans are two of the most important bact... more Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans are two of the most important bacteria in heap bioleaching processes of copper sulphide at common operating temperatures (18-24°C). In this paper, both microorganisms were detected in solutions and ores coming from processes in 2 days, using specific amplification of 16S rDNA sequences by PCR. The technique was first validated using template DNA from pure cultures of the microorganisms. Then it was applied to samples of solutions and ores from bioleaching processes. Results were confirmed using tRFLP (terminal Restriction Fragment Length Polymorphism) with universal primers and by identification of isolated bacteria by means of culture. This methodology is more rapid and specific than the identification by tRFLP or by culture, which require from 1 to three weeks to positively detect the bacteria. The detection limit of this technique is 10 5 cells per ml.
This work presents preliminary results of a study to determine the technical feasibility of heap ... more This work presents preliminary results of a study to determine the technical feasibility of heap bioleaching of copper sulfides in a mixed ore that had previously undergone a chemical leach to recover the copper from the copper oxides in the ore. The recovery of the copper sulfides is economically and environmentally important. The first step in this study was to determine the presence of bacteria in samples of both the agglomerated ores taken from the heaps and the samples from the irrigation solution used in the leaching process. No bacteria were detected in either sample, probably because of the very low pH, the high concentration of sulfate (200 g/l), and the presence of other ions in the irrigation solution. On the other hand, the cultivation of bacteria from recently crushed, fresh mixed ore (oxide-sulfide), and from cured, agglomerated ore, showed the presence of a small bacterial population, with ferrous iron-oxidizing activity. This indicates that the ore initially contained viable bacteria that were inhibited in the heap. Based on these results, a glass laboratory column containing 700 g of agglomerated ore from a partially, chemically leached heap was set up. The ore in the column was irrigated in a closed circuit with nutrient medium containing 2 g of ferrous sulfate per liter. Bacteria were detected, and the redox potential in the leaching solution began to increase on day 20 of the bioleaching experiment, indicating the beginning of the bioleaching stage of the sulfide mineral. The data indicate that the bacteria initially present on the ore can be recovered after acid curing, and also after prolonged contact with a solution containing a high concentration of sulfate. These results indicate that it is technically possible to induce a change from a chemical leaching process with high ionic strength to a bacterial leaching process, by dilution of the irrigation solution.
Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper diss... more Enargite (Cu3AsS4) was leached at 70 °C by Sulfolobus BC in shake-flasks. The highest copper dissolution (52% after 550 h of leaching) was obtained with bacteria and 1 g l−1 ferric ion. In the absence of ferric ion, Sulfolobus BC catalyzes the bioleaching of enargite through a direct mechanism after adhesion onto the mineral surface. In ferric bioleaching, arsenic precipitated as ferric arsenate and arsenic remained associated to the solid residues, preventing the presence of a high dissolved arsenic concentration in the leaching solution. About 90% inhibition of bacterial growth rate and activity was observed for dissolved arsenic concentrations above 600 mg l−1 for As(III) and above 1000 mg l−1 for As(V). Arsenic-bearing copper ores and concentrates could be leached by Sulfolobus BC in the presence of ferric iron due to the favourable precipitation of arsenic ion as ferric arsenate, avoiding significant bacterial inhibition.
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