Selective extraction of metals from zinc concentrate by association of chemolithotrophic bacteria

Ability for selective extraction of copper and zinc from zinc concentrate using association of chemolithotrophic bacteria was investigated. In the presence of bacterial association, the rate of leaching of zinc, copper, and iron was increased 3-fold, 4–5-fold, and 2-fold, respectively. The results indicate the maximum dissolution rate for zinc, then followed by copperand iron. It was revealed that addition of Fe³⁺ 2 g/l resulted in reduction of iron leaching and in 3-fold increase of leaching rate of copper at constant dissolution rate of mineral zinc. It is suggested that the intensification of copper leaching is connected with the activity of sulfur-oxidizing bacteria able to activate the mineral surface via elimination of passivation layer of elemental sulfur. It was concluded that sulfur-oxidizing bacteria play a significant role in copper leaching from zinc concentrate. A unique strain of mesophile sulfur-oxidizing bacteria was isolated from leaching pulp of zinc concentrate; in the perspective, it may serve as efficient candidate for performing of selective extraction of copper from zinc concentrate.     

Selective leaching of zinc from copper-zinc concentrate

Biooxidation of copper-zinc concentrate with the use of consortia of mesophilic and moderately thermophilic acidophilic chemolithotrophic microorganisms was studied. Pyrrhotite, sphalerite, and chalcopyrite were the main sulfide minerals of the concentrate. The possibility in principal of complete selective leaching of zinc from sulfide concentrate coupled with minimal recovery of copper (less than 20%) was demonstrated. Selective leaching of zinc could be caused by galvanic interactions between minerals of the concentrate during the biooxidation. The results can be used as the basis for the development of the technologies for production of grade copper concentrate not containing zinc from sulfide copper-zinc concentrate obtained from refractory ores.     

Chalcopyrite concentrate leaching with biologically produced ferric sulphate

Biological ferric iron production was combined with ferric sulphate leaching of chalcopyrite concentrate and the effects of pH, Fe3+, temperature and solids concentration on the leaching were studied. The copper leaching rates were similar at pH of 1.0-1.8 and in the presence of 7-90 g L-1 Fe3+ despite massive iron precipitation with 90 g L-1 Fe3+. Increase of the leaching temperature from 50 degrees C to 86 degrees C and solids concentration from 1% to 10% increased the copper leaching rate. Increase in solids concentration from 1% to 10% decreased the copper yields from 80% to 40%. Stepwise addition of ferric iron did not improve the copper yields. CuFeS2, Ag and Cu1.96S potentials indicated the formation of a passivating layer, which consisted of jarosite and sulphur precipitates and which was responsible for the decreased leaching rates.     

Biohydrometallurgical technology of a complex copper concentrate process

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

The effects of bioleaching conditions on the nonferrous metals content in copper-zinc concentrate

The effects of pH and ferrous iron concentration in cultural medium on the bioleaching of copper-zinc concentrate by mesophilic and moderately thermophilic acidophilic microorganisms were studied. It was revealed that the optimum pH for bioleaching in presence of 5 g/L of ferrous iron was 1.4–1.5. It was shown that bioleaching under optimal conditions led to an increase in the copper content in solid phase from 10.1 to 14% and a decrease in the zinc content from 7.4 to 1.4%. The results of the present work demonstrate that acidophilic microorganisms can be used for treatment of complex sulfide concentrates containing copper and zinc.     

Effect of anions on selective solubilization of zinc and copper in bacterial leaching of sulfide ores

Bacterial leaching of sulfide ores using Thiobacillus ferrooxidans, Thiobacillus thiooxidans, or a combination of the two was studied at various concentrations of specific anions. Selective zinc and copper solubilization was obtained by inhibiting iron oxidation without affecting sulfur/sulfide oxidation. Phosphate reduced iron solubilization from a pyrite (FeS(2))-sphalerite (ZnS) mixture without significantly affecting zinc solubilization. Copper leaching from a chalcopyrite (CuFeS(2))-sphalerite mixture was stimulated by phosphate, whereas chloride accelerated zinc extraction. In a complex sulfide ore containing pyrite, chalcopyrite, and sphalerite, both phosphate and chloride reduced iron solubilization and increased copper extraction, whereas only chloride stimulated zinc extraction. Maximum leaching obtained was 100% zinc and 50% copper. Time-course studies of copper and zinc solubilization suggest the possibility of selective metal recovery following treatment with specific anions.     

Bioleaching of chalcopyrite concentrate by a moderately thermophilic culture in a stirred tank reactor

A mixed culture of moderately thermophilic microorganisms was enriched from acid mine drainage samples collected from several chalcopyrite mines in China. Such mixed culture can be used to effectively extract copper from chalcopyrite. Furthermore, after being adapted to gradually increased concentration of chalcopyrite concentrate, the tolerance of the mixed culture to chalcopyrite concentrate was brought up to 80 g/L. The effects of several leaching parameters on copper recovery in stirred tank reactor also had been investigated. The results of the investigation show that it was possible to achieve a copper extraction rate of 75% in 44 days at a pulp density of 8%. The leaching rate of chalcopyrite concentrate tended to increase with dissolved total iron concentration. At low pH ranges, more microscopic counts of microorganisms were found in the solution. Furthermore, the analysis of leached residues indicates that the passivation of chalcopyrite concentrate was mainly due to a mass of jarosite and PbSO(4) on the mineral surface, other than the elemental sulphur layer. The bacterial community composition was analyzed by using Amplified Ribosomal DNA Restriction Analysis. Two moderately thermophilic bacteria species were identified as Leptospirillum ferriphilum and Acidithiobacillus caldus with abundance of 67% and 33% in the bio-pulp, respectively.     

Leaching of nonferrous metals from copper converter slag with application of acidophilic microorganisms

The leaching process of copper and zinc from copper converter slag with ferric iron in sulfuric acid solutions obtained using the association of acidophilic chemolithotrophic microorganisms was investigated. The best parameters of chemical leaching (temperature 70°C, an initial concentration of ferric iron in the leaching solution of 10.1 g/L, and a solid phase content in the pulp of 10%) were selected. Carrying out the process under these parameters resulted in the recovery of 89.4% of copper and 39.3% of zinc into the solution. The possibility of the bioregeneration of ferric iron in the solution obtained after the chemical leaching of slag by iron-oxidizing acidophilic chemolithotrophic microorganisms without inhibiting their activity was demonstrated.     

Effect of Activated Carbon Addition on the Conventional and Electrochemical Bioleaching of Chalcopyrite Concentrates

The effect of activated carbon addition on the rate and efficiency of copper mobilization from Sarcheshmeh chalcopyrite concentrate was studied in the presence and absence of a mixed culture of moderately thermophilic microorganisms. Conventional leaching at a 10% (w/v) pulp density in 500-ml Erlenmeyer flasks on a rotary shaker at 150 rpm, and electrochemical bioleaching in a stirred bioreactor at an ORP (oxidation-reduction potential) range of 400 to 430 mV measured against a Ag/AgCl reference electrode. The bioreactor contained ore concentrate at a pulp density of 20%, which was stirred at 600 rpm. All experiments were conducted in the presence and absence of 3 g/L activated carbon, at initial pH 1.5, temperature 50°C, in Norris's nutrient medium with an addition of 0.02% (w/v) yeast extract. The results showed that the addition of activated carbon increased the rate and yield of copper extraction from the concentrate especially in the presence of bacteria. Final recovery after 20 days was 52% and 44% in the shake flask experiments with and without carbon addition, respectively. Enhanced rates of copper mobilization were achieved in the electrochemical bioleaching experiments in which copper was leached selectively relative to iron. Final copper recovery after 10 days was 85% and 77% in the presence and absence of activated carbon, respectively. The positive effect of activated carbon on copper extraction could be related to the galvanic interaction between the inert carbon as cathode and chalcopyrite as anode. The bacterial elimination of sulfur produced on the sulfide minerals during chemical leaching is assumed to intensify the galvanic interaction. It seems that maintaining the ORP at a low potential and efficient mixing improves the bacterial and chemical subsystems in the electro-bioreactor that accelerates the rate of copper mobilization from the concentrate.     

Microbiological leaching of a chalcopyrite concentrate by Thiobacillus ferrooxidans

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

Microbial leaching of zinc concentrate in fresh‐water microcosms: Comparison between aerobic and oxygen‐limited conditions

Microbially mediated leaching and solubilization of zinc ore concentrate by native aquatic microbial communities incubated under aerobic and oxygen‐limited conditions were examined in static microcosms consisting of stream sediment and water. Sterile controls provided information on abiotic sulfide oxidation and leaching of zinc, lead, cadmium, and copper. The flux of these heavy metals from the sediments to the water column was greatest under biotic oxygen‐limited conditions. When calculated as the percentage of total metal available in zinc concentrate‐amended microcosms, the order of metal solubilization under oxygen‐limited conditions was lead, copper, zinc, and cadmium. Under biotic aerobic conditions, the order of solubilization was zinc, lead, cadmium, and copper. This study indicates that aquatic heterotrophs are capable of leaching and solubilizing metallic sulfides under conditions of neutral to slightly acidic pH and are effective in releasing heavy metals to the water column under oxygen‐limited conditions.     

Kinetics improvement of high-grade sulphides bioleaching by effects separation

Abstract: The kinetics of bioleaching of sulphide concentrates by Thiobacillus ferrooxidans can be improved by performing separately the two operations relating the two effects involved in the indirect contact mechanism, (1) chemical leaching and (2) biological oxidation of the Fe2+ produced in the chemical stage (IBES: Indirect Bioleaching with Effects Separation). This scheme permits the separate enhancement of each stage. On the one hand, the chemical attack of the ferric iron to sulphides can be performed at a higher temperature. On the other hand, the biological oxidation stage is more effective when biofilm models are applied. At the same time, inhibitory phenomena produced as a result of the bacterial breaking caused by the abrasion of the solid particles on microorganisms are prevented. In this work the 1BES process has been applied to a Spanish copper-zinc and a copper sulphide concentrate. The objective has been to selectively dissolve zinc, which may be recovered by solvent exraction, the remaining residue being a copper concentrate suitable for pyrometallurgical treatment. The attributes of moderate temperature, atmospheric pressure, low cost of the leaching agent, flexibility and effectiveness make the process very attractive from an economic point of view.     

Trace element uptake by L-cells as a function of trace elements in a synthetic growth medium

The concentration of trace elements in L-cells has been studied as a function of the trace metal content of the growth medium. Cells were cultured in synthetic media which contained varying trace amounts of the elements manganese, iron, cobalt, copper, zinc and molybdenum. The cellular concentration of the elements potassium, iron, copper and zinc were then determined. It was found that the cell accumulates trace metals at a different rate than they are made available. Deficiencies in zinc could be “induced” in the cell by increasing the concentration of iron, manganese and cobalt; cellular iron deficiencies were observed at larger medium concentrations of zinc, manganese, copper and cobalt. Trace metal uptake by the cell was seen to parallel the utilization by multicellular organisms.     

Biohydrometallurgical technology of copper recovery from a complex copper concentrate

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

Trace metals in edible marine molluscs and crustaceans from Lebanon

Samples of the edible tissue of cephalopod molluscs (cuttlefish, squid, octopus) and crustaceans (lobster, shrimp) collected off the coast of Lebanon were found to concentrate similar levels of cadmium, copper, nickel, and chromium. Lead and zinc were highest in the cephalopods and iron was highest in the crustaceans.The molluscs collected from Beirut had higher levels of many metals than those taken from the other locations. The Beirut octopus had higher lead, cadmium, copper, iron, and chromium. Lead, cadmium, and copper were also highest in the Beirut cuttlefish while iron and zinc were elevated. The crustaceans from Beirut showed no strong tendency to concentrate higher metal levels, except for the Beirut lobster which had higher copper than the other samples.In the cuttlefish, the analysis of bone showed generally higher cadmium, zinc, nickel, and chromium but lower copper and iron than the muscle. However, at Beirut, the bone samples had much higher iron. Levels of most metals in the exoskeletons of the lobster and shrimp were quite similar to those in the muscle tissue with the exception of iron in the lobster which was highest in the exoskeleton, and zinc in both crustaceans, which was more highly concentrated in the muscle.     

Leaching of iron and toxic heavy metals from anaerobically-digested sewage sludge

Summary Heavy metal-loaded sewage sludge was leached abiotically using FeCl₂ and FeCl₃ which are applied in waste water treatment plants to eliminate phosphate and for coagulation. Due to the hydrolyzing nature of ferric iron, ferric chloride (100 mmll L^–1) was able to solubilize more than 90% of copper and zinc and more than 80% of cadmium, with an optimal pulp density of 3% (w/v), after 10 h of exposition at 25°C. Chromium, lead and nickel were solubilized to an extent of 40–70%. With the exception of copper (redoxolysis), all heavy metals monitored were leached following the principle of acidolysis. Chemical leaching with iron resulted in a secondary contamination of sewage sludge (96 g iron per kg dry weight). The insoluble iron compounds which were precipitated for adsorbed to sludge flocks could be resolubilized with oxalic acid (100 mM, pH<3.3) up to an extent of 90%. Iron was leached by acidolysis and held in solution by complexation with oxalic acid. The pH optimum for the treatment of sewage sludge with 100 mmol L^–1 oxalic acid was pH 3.3. At this pH an excessive solubilization of nutrient elements and compounds (phosphorus, nitrogen, alkali and alkali earth elements) could be avoided concomitantly leaching 75% iron. Furthermore the hydrophobicity of the sewage sludge was significantly reduced as a result of treatment with iron chloride.Thiobacillus ferrooxidans (isolated from arsenopyrite and adapted on sewage sludge) utilized ferrous iron as an energy source in the presence of chloride ions (FeCl₂) as efficiently as ferrous sulphate. No toxic effects of oxalic acid onT. ferrooxidans were observed at the prevailing concentration.     

Bioleaching of zinc sulfide concentrate by Thiobacillus ferrooxidans

The kinetics of the bioleaching of ZnS concentrate by Thiobacillus ferrooxidans was studied in a well-mixed batch reactor. Experimental studies were made at 30 degrees C and pH 2.2 on adsorption of the bacteria to the mineral, ferric iron leaching, and bacterial leaching. The adsorption rate of the bacteria was fairly rapid in comparison with the bioleaching rate, indicating that the bacterial adsorption is at equilibrium during the leaching process. The adsorption equilibrium data were correlated by the Langmuir isotherm, which is a useful means for predicting the number of bacteria adsorbed on the mineral surface. The rate of chemical leaching varied with the concentration of ferric iron, and the first-order reaction rate constant was determined. Bioleaching in an iron-containing medium was found to take place by both direct bacterial attack on the sulfide mineral and indirect attack via ferric iron. In this case, the ferric iron was formed from the reaction product (ferrous iron) through the biological oxidation reaction. To develop rate expressions for the kinetics of bacterial growth and zinc leaching, the two bacterial actions were considered. The key parameters appearing in the rate equations, the growth yield and specific growth rate of adsorbed bacteria, were evaluated by curve fitting using the experimental data. This kinetic model allowed us to predict the liquid-phase concentrations of the leached zinc and free cells during the batch bioleaching process.     

Continuous microbial leaching of a pyritic concentrate by Leptospirillum-like bacteria

Summary Continuous leaching of a pyritic flotation concentrate by mixed cultures of acidophilic bacteria was studied in a laboratory scale airlift reactor. Enrichment cultures adapted to the flotation concentrate contained Thiobacillus ferrooxidans and Thiobacillus thiooxidans. During the late stationary growth phase of these thiobacilli growth of Leptospirillum-like bacteria was observed, too. In discontinuous cultivation no significant influence of Leptospirillum-like bacteria on leaching rates could be detected. During continuous leaching at pH 1.5 Leptospirillum-like bacteria displaced Thiobacillus ferrooxidans. The iron leaching rate achieved by Leptospirillum-rich cultures was found to be up to 3.9 times higher than that by Leptospirillum-free cultures.     

Biooxidation of High-Sulfur Products of Ferric Leaching of a Zinc Concentrate

Microbiology - We have previously proposed a highly efficient technology for metal recovery from low-grade zinc sulfide concentrate by two-step treatment including ferric iron leaching and...     

Bioregeneration of the pregnant leach solutions obtained during the leaching of nonferrous metals from slag waste by acidophilic microorganisms

The bioregeneration of the solutions obtained after the leaching of copper and zinc from slag waste by sulfuric acid solutions containing ferric iron was examined. For bioregeneration, associations of mesophilic and moderately thermqophilic acidophilic chemolithotrophic microorganisms were made. It has been shown that the complete oxidation of iron ions in solutions is possible at a dilution of the pregnant leach solution with a nutrient medium. It has been found that the maximal rate of oxidation of iron ions is observed at the use of a mesophilic association of microorganisms at a threefold dilution of the pregnant leach solution with a nutrient medium. The application of bioregeneration during the production of nonferrous metals from both copper converter slag and its waste would make it possible to approach the technology of their processing using the closed cycle of workflows.