Microbial extraction of nickel from Sukinda chromite overburden by Acidithiobacillus ferrooxidans and Aspergillus strains

In this study, the recovery of nickel from a low-grade chromite overburden was attempted by employing two fungal strains, Aspergillus niger and Aspergillus fumigatus, and a mixed culture of mesophilic acidophiles (predominantly Acidithiobacillus ferrooxidans). Various factors were studied for bioleaching of chromite overburden such as, temperature, pH and pulp density. It was found that the At. ferrooxidans culture solubilized nickel effectively at temperatures ranging from 30 °C to 37 °C, whereas the organism was not able to solubilize nickel at higher temperatures, such as 45 °C. The use of higher pulp density resulted in a decrease of the percent nickel recovery whereas lower pulp density resulted in higher recovery values. Besides, increased supplemental ferrous iron increased the leaching efficiency of the At. ferrooxidans culture. The maximum nickel solubilization was 40%, at 2% pulp density, and 24%, at 10% pulp density, at 30 °C after 28 days leaching at 150 rpm.In the case of fungal strains, a comparison of leach ability of chromite overburden and roasted overburden was made. The factors studied were pulp density and reaction time. The adapted fungal strain showed better leaching results as compared to the unadapted strains. The in situ nickel leaching efficiency of a laboratory stock culture of A. niger showed maximum recovery of 34% nickel with roasted chromite overburden, at 2% pulp density, while 32% nickel was solubilized by A. fumigatus, under the same conditions at 30 °C and 150 rpm, after 28 days incubation.     

Dissolution of uranium from silicate-apatite ore by Acidithiobacillus ferrooxidans

Bioleaching of a low-grade Indian silicate-apatite uranium ore containing 0.024% U₃O₈ and 10.6% iron with minor amounts of base metals has been reported. The studies involved extraction of uranium using enriched culture containing Acidithiobacillus ferrooxidans (A. ferrooxidans) derived from the source mine water employing bio-chemically generated ferric ion as an oxidant. Parameters such as particle size of the ore, pulp density, and pH of lixiviant media were optimised. Maximum uranium bio-dissolution of 98% was achieved using ore of mixed particles of < 76 μm size. Uranium bio-recovery was found to be 96% at the pulp density (PD) of 10% (w/v) and 20% (w/v) with the particles of < 76 μm size in 40 days at 2.0 pH and 35 °C temperature. At 1.7 pH and 20% (w/v) PD, 98% uranium bio-recovery was achieved with a rise in redox potential from 595 mV to 715 mV in 40 days. Uranium bio-dissolution may be correlated with the generation of ferric ions through the bio-chemical action on the ore. The work illustrated the efficacy of leaching of uranium by the involvement of bacteria by indirect mechanism.     

Silver-catalyzed bioleaching of low-grade copper ores.: Part I: Shake flasks tests

A study of the effect of different variables (inoculation, pulp density, [Ag], nutrient medium, pH and [Fe³⁺]) on the silver-catalyzed bioleaching of a low-grade copper sulfide ore has been carried out in shake flasks. Chalcopyrite was the dominant copper mineral in the ore. Preliminary tests showed that addition of other ions (Sb, Bi, Co, Mn, Ni and Sn) did not enhance the copper dissolution rate. Conversely, an inoculation with mesophilic microorganisms and the addition of silver had a markedly catalytic effect on the extraction of copper. The kinetics of the silver-catalyzed chalcopyritic ore bioleaching was greatly affected by pulp density and silver concentration. Small amounts of silver (14.7 g Ag/kg Cu) dramatically accelerated the copper dissolution process while large amounts (294.12 g Ag/kg Cu) had an inhibitory effect. The copper dissolution rate was slightly affected in the range of pH between 1.2 and 2.5 but was significantly slower at pH 3.0. The effect of [Fe³⁺] in the presence of silver was studied both in abiotic and biotic conditions. High ferric iron concentrations in abiotic tests recovered similar copper amounts (∼ 95%) to those obtained without or with low [Fe³⁺] in the presence of bacteria. The leaching of copper from the low-grade copper ore can be very effectively enhanced with silver and mesophilic microorganisms. For that system, the onset of oxidizing conditions starts at an Eh value slightly higher than 650 mV. Above that critical value of potential the copper dissolution rate slows down. This also corresponds with the completion of the leaching process. As the potential rises past 650 mV, the copper extraction reaches a plateau.     

Dissolution kinetics of spent petroleum catalyst using two different acidophiles

Leaching studies using spent petroleum catalyst containing Ni, V and Mo were carried out using two different acidophiles, iron oxidizing (IOB) and sulfur oxidizing (SOB) bacteria. XRD analysis proved the existence of V in oxide form, Ni in sulfide form, Mo both in oxide and sulfide forms, and sulfur in elemental state. Both bacteria showed similar leaching kinetics at the same leaching parameters, such as pH, nutrient concentration, pulp density, particle size and temperature. The dissolution kinetics for Ni and V was much higher than Mo. Bioleaching kinetics was observed to follow dual rates, initially faster followed by a slower rate. So, dissolution mechanism was based on surface- and pore-diffusion rate. The dissolution process was found to follow 1st order kinetics. Unified dissolution rate kinetics equations were developed using 1st order rate kinetics. Various thermodynamic parameters were also calculated. Rate determining step for both the bacteria were evaluated and the average D₁ (surface) and D₂ (pore) values were found to be around 7 × 10^− 9 and 1 × 10^− 10 cm² respectively. The lower value of D₂ suggested that the pore diffusion is the rate determining step during bioleaching process.     

The bioleaching of different sulfide concentrates using thermophilic bacteria

The bioleaching of different mineral sulfide concentrates with thermophilic bacteria (genusSulfolobus @#@) was studied. Since the use of this type of bacteria in leaching systems involves stirring and the control of temperature, the influence of the type of stirring and the pulp density on dissolution rates was studied in order to ascertain the optimum conditions for metal recovery. At low pulp densities, the dissolution kinetic was favored by pneumatic stirring, but for higher pulp densities, orbital stirring produced the best results. A comparative study of three differential concentrates, one mixed concentrate, and one global concentrate was made. Copper and iron extraction is directly influenced by bacterial activity, while zinc dissolution is basically due to an indirect mechanism that is activated in the presence of copper ions. Galvanic interactions between the different sulfides favors the selective bioleaching of some phases (sphalerite and chalcopyrite) and leads to high metal recovery rates. However, the formation of galvanic couples depends on the type of concentrate.     

Determination of the Optimum Conditions for Leaching of Zinc Cathode Melting Furnace Slag in Ammonium Chloride Media

This research is part of a continuing effort to leach zinc from zinc cathode melting furnace slags (ZCMFSs) to produce zinc oxide. The slag with an assay of 68.05 pct Zn was used in ammonium chloride leaching for zinc extraction. In this paper, the effects of influential factors on extraction efficiency of Zn from a ZCMFS were investigated. The Taguchi’s method based on orthogonal array (OA) design has been used to arrange the experimental runs in order to maximize zinc extraction from a slag. The softwares named Excel and Design-Expert 7 have been used to design experiments and subsequent analysis. OA L ₂₅ (5⁵) consisting of five parameters, each with five levels, was employed to evaluate the effects of reaction time (t = 10, 30, 50, 70, 90 minutes), reaction temperature [T = 313, 323, 333, 343, 353 (40, 50, 60, 70, 80) K (°C)], pulp density (S/L = 20, 40, 60, 80, 100 g/L), stirring speed (R = 300, 400, 500, 600, 700 rpm), and ammonium chloride concentration (C = 10, 15, 20, 25, 30 pctwt), on zinc extraction percent. Statistical analysis, ANOVA, was also employed to determine the relationship between experimental conditions and yield levels. The results showed that the significant parameters affecting leaching of slag were ammonium chloride concentration and pulp density, and increasing pulp density reduced leaching efficiency of zinc. However, increasing ammonium chloride concentration promoted the extraction of zinc. The optimum conditions for this study were found to be t ₄: 70 minutes, T ₅: 353 K (80 °C), (S/L)₂: 40 g/L, R ₃: 500 rpm, and C ₄: 25 pctwt. Under these conditions, the dissolution percentage of Zn in ammonium chloride media was 94.61 pct.     

Microbial Dissolution of Zn-Pb Sulfide Minerals Using Mesophilic Iron and Sulfur-Oxidizing Acidophiles

The purpose of this study is to test the feasibility of using mixed culture of iron and sulfur-oxidizing bacteria for the dissolution of metals from high-grade zinc and lead sulfide ore. Considering that the roll crusher could reduce the ore size to less than 2 mm, this size fraction was selected in order to study the possibility of removing mill circuit. Effects of parameters such as pulp density, initial pH, Fe²⁺, oxidation–reduction potential (ORP), and pH fluctuations were investigated, as well. The maximum Zn dissolution was achieved under the conditions of initial pH 2, initial 75 g/L FeSO₄ · 7H₂O, and pulp density of 50 g/L. The results indicated that under the optimum conditions, about 68.8% of zinc was leached during 24 days of bacterial leaching treatment. The lead recoveries were low (about 1%), because of precipitation of Pb as lead arsenate chloride. Furthermore, the surface studies by using SEM images showed that during chemical leaching the ore dissolution starts from surface discontinuities, but in bacterial leaching all surface becomes involved. In addition, in another process the ore was leached separately with sulfuric acid and sodium hydroxide, and then final results were compared to the bacterial leaching tests in order to find the optimum hydrometallurgical method to extract zinc and lead from these ores.     

Utilisation of native microbes from a spent chalcocite test heap

A variety of acidophilic iron and/or sulphur-oxidising microbes capable of growth on several substrates (chalcopyrite, pyrite, ferrous ion, sulphur, glucose) in the range 30–60 °C were recovered from a spent chalcocite/chalcopyrite/pyrite heap. Several isolates exhibited tolerance to salt, up to 5 g/L NaCl, and to the metals nickel, cobalt, zinc and copper at up to 50 g/L.Leaching tests on chalcopyrite concentrate indicated higher copper yields when native isolates were employed, compared with the laboratory reference strains Acidithiobacillus ferrooxidans (DSM 583) and Sulfobacillus thermosulfidooxidans (DSM 9293). After 30 days, several native isolates had leached 20–30% more copper than the abiotic controls during experiments conducted at 45 °C. The results demonstrate that the native isolates are potential bioleaching candidates, adapted to diverse growth conditions.     

Oxidative Pressure Leaching of Silver from Flotation Concentrates with Ammonium Thiocyanate Solution

The thermodynamics and technologies of the selective pressure leaching of silver from flotation concentrates were investigated in an ammonium thiocyanate medium. Thermodynamic analyses, which include silver solubility in NH₄SCN solution and Eh-pH diagrams of the Me-MeS-NH₄SCN-H₂O system at 25 °C, were discussed. The effects of several factors, such as temperature, leaching time, oxidant, pH value, flotation concentrates concentration, surfactant concentration, and so on, on the extraction percentages of silver and zinc were investigated. The following optimal leaching conditions were obtained: NH₄SCN concentration 1.5 M, lignin concentration 0.5 g/L, Fe³⁺ concentration 2 g/L, flotation concentrates addition 200 g/L, and oxygen pressure 1.2 MPa at 130 °C for 3 hours. Under these optimum conditions, the average extraction percentage of silver exceeded 94 pct, whereas the average extraction percentage of zinc was less than 3 pct. Only 7 pct of ammonium thiocyanate was consumed after 4 cycles, which indicated that ammonium thiocyanate hardly was oxidized under these oxidative pressure leaching conditions.     

Leaching of marine manganese nodules by acidophilic bacteria growing on elemental sulfur

This article describes the bioleaching of manganese nodules by thermophilic and mesophilic sulfuroxidizing bacteria, in which oxidized sulfur compounds are biologically produced from elemental sulfur added to liquid medium and are simultaneously used to leach nodules. The thermophile Acidianus brierleyi solubilized the manganese nodules faster at 65 °C than did the mesophiles Thiobacillus ferrooxidans and Thiobacillus thiooxidans at 30 °C. Leaching experiments with A. brierleyi growing on elemental sulfur were used to optimize various process parameters, such as medium pH, initial sulfur-liquid loading ratio, and initial cell concentration. The observed dependencies of the leaching rates at a pH optimum on the initial amounts of elemental sulfur and A. brierleyi cells were qualitatively consistent with model simulations for microbial sulfur oxidation. Under the conditions determined as optimum, the leaching of nodule particles (−330+500 mesh) by A. brierleyi yielded 100 pct extraction of both copper and zinc within 4 days and high extractions of nickel (85 pct), cobalt (70 pct), and manganese (55 pct) for 10 days. However, the iron leaching was practically negligible.     

Effects of pH, pulp density and particle size on solubilization of metals from a Pb/Zn smelting slag using indigenous moderate thermophilic bacteria

A series of bioleaching experiments were designed to elucidate the effect of pH, pulp density and particle size on solubilization of heavy metals, such as As, Fe, Cu, Zn, Pb and Mn, from a Pb/Zn smelting slag using indigenous moderate thermophilic bacteria, and the surface morphological characteristics of the residues were observed by SEM. The results showed that the solubilization of heavy metals from the slag was significantly influenced by pH and pulp density in bioleaching, however, it was slightly influenced by particle size of the slag when the particle size is less than 0.83 mm. Under the optimum condition (pH 1.5, pulp density 10%, and particle size of the slag less than 0.83 mm, respectively), about 86%-91% of As, 90%-93% of Cu, 90%-94% of Mn and 81%-87% of Zn from the slag have been bioleached after 6 days. The surface morphological characteristics of the residues after 6 days bioleaching analyzed by SEM showed that metal solubilization can be improved by acid leaching but significantly contributed to the activities of the ingenious bacteria. Consequently, metals in the slag can be extracted by bacteria according to the corrosive holes on the surface of the bioleached residues.     

Issues in Bioleaching: To Inoculate or not to Inoculate

Abstract

Two active bioleaching microbial strains were isolated from a zinc mineral sample. These bacteria isolates were grown on media containing sulfur or iron and reintroduced, individually or in combination, to the original mineral sample in controlled shake-flask bioleaching experiments. Uninoculated controls were included but no attempt was made to sterilize the solid material. On the contrary, growth of the same indigenous microorganisms was encouraged in the control flasks. Zinc was leached from both inoculated and uninoculated mineral at the same rate. The only difference was that the lag times before onset of leaching were shorter if active bacteria were present from the very beginning. In all cases, zinc was leached preferentially over iron. This difference was even more pronounced on leaching by sulfur-grown bacteria which did not extract iron to the same degree as iron-grown bacteria. When total leaching times required for 100% zinc extraction were compared, no statistically significant difference was observed between the inoculated and uninoculated tests. This conclusion may have some bearing on experimental and process design, when decisions must be made on whether to stimulate leaching by addition of extraneous bacteria or by fostering the proliferation of indigenous microorganisms.     

Oxidative Leaching of Chalcopyrite by Cupric Ion in Chloride Media

In this study, chalcopyrite concentrate produced in Sarcheshmeh copper plant was subjected to oxidative leaching investigation by cupric ion to determine the effect of several parameters on the copper and iron dissolution, including temperature of leaching, time of holding and cupric concentration as oxidant agent in a range of 38–97 °C, 1.5–8.5 h and 0.2–0.8 M, respectively. The leaching media was chloride providing with 3 M HCl 37% and CuCl₂. The experiments were designed by central composite design method. The dissolution of copper and iron was examined. The maximum dissolution of copper 62.64%, was obtained at 85 °C, 7 h and oxidant concentration of 0.7 M. The kinetics model of chalcopyrite leaching and an optimized condition with maximum dissolution of copper and minimum dissolution of iron was obtained by Minitab^®18 software. Additionally, the thermodynamics of leaching was investigated by Pourbaix diagrams of copper and iron composition, using HSC Chemistry6 software. It was found that the oxidative leaching process is controlled by diffusion through passivation layer with an activation energy of 19.57 kJ/mol.

     

Electrochemical study of enargite bioleaching by mesophilic and thermophilic microorganisms

The bioleaching effects of two microorganisms on two different enargite (Cu₃AsS₄) minerals have been followed by solution titration and rest potential measurements and studied by cyclic voltammetry. The investigation focused on the superficial modifications produced in the minerals by the activity of the mesophilic bacterium Acidithiobacillus ferrooxidans at 35 °C and the thermophilic archaeon Sulfolobus sp. at 68 °C after 3 and 12 days of attack, comparing the modified surfaces with that of untreated samples. The electrochemical characterization of all the electrodes was done by means of potentiometric assays performed under the same conditions: acidulated deionized water as electrolyte (pH 2.0), and temperature of 26 ± 2 °C. Additionally, a comparative SEM and EDX study of untreated and biotreated samples was carried out.     

Copper recovery from chalcopyrite concentrate by acidophilic thermophile Acidianus brierleyi in batch and continuous-flow stirred tank reactors

The mechanism and kinetics of bioleaching of chalcopyrite concentrate by the thermophilic archaea Acidianus brierleyi was studied in batch and continuous-flow stirred tank reactors (CSTR). In the batch reactor, the thermophile A. brierleyi solubilized chalcopyrite much faster at 65°C than did the mesophile, Thiobacillus ferrooxidans at 30°C. The chalcopyrite leaching with A. brierleyi was found to take place with a direct attack by adsorbed cells on the mineral surface, the chemical leaching with ferric iron being insignificant. Rate data collected in the batch reactor were analyzed to estimate kinetic and stoichiometric parameters for the growth of A. brierleyi on chalcopyrite. The batch model and the estimated parameter values were used to find optimum levels of initial cell concentration and initial mineral/liquid loading ratio. Simulations based on continuous reactor model and the parameter values were used to predict the leaching fraction as a function of the number of reactors connected in series.     

Column bioleaching of a low grade nickel-bearing sulfide ore containing high magnesium as olivine,chlorite and antigorite

This work investigates the bioleaching of Jinchuan low grade nickel-bearing sulfide ore containing rather high levels of olivine, chlorite and antigorite (MgO 30–35%) present in the main gangue minerals using a mixed mesophiles which are composed of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. It aims to test the technical feasibility to recover valuable metals from Jinchuan low-grade nickel-bearing sulfide ore by bioleaching process. The tolerance of the mixed bacteria to Mg²⁺ could be improved markedly from 10 g/L to 25 g/L after nearly 2 years adaptation. A nickel recovery of 91% and a cobalt recovery of 81% were achieved in 312 days column leaching process including 60 days acid pre-leaching stage and 252 days bioleaching stage.     

Copper recovery from chalcopyrite concentrates by the BRISA process

The technical viability of the BRISA process (Biolixiviación Rápida Indirecta con Separación de Acciones: Fast Indirect Bioleaching with Actions Separation) for the copper recovery from chalcopyrite concentrates has been proved. Two copper concentrates (with a copper content of 8.9 and 9.9 wt.%) with chalcopyrite as the dominant copper mineral have been leached with ferric sulphate at 12 g/L of ferric iron and pH 1.25 in agitated reactors using silver as a catalyst. Effects of temperature, amount of catalyst and catalyst addition time have been investigated. Small amounts of catalyst (from 0.5 to 2 mg Ag/g concentrate) were required to achieve high copper extractions (>95%) from concentrates at 70 °C and 8–10 h leaching. Liquors generated in the chemical leaching were biooxidized for ferrous iron oxidation and ferric regeneration with a mixed culture of ferrooxidant bacteria. No inhibition effect inherent in the liquor composition was detected. The silver added as a catalyst remained in the solid residue, and it was never detected in solution. The recovery of silver may be achieved by leaching the leach residue in an acid-brine medium with 200 g/L of NaCl and either hydrochloric or sulphuric acid, provided that elemental sulphur has been previously removed by steam hot filtration. The effect of variables such as temperature, NaCl concentration, type of acid and acidity–pulp density relationship on the silver extraction from an elemental sulphur-free residue has been examined. It is possible to obtain total recovery of the silver added as a catalyst plus 75% of the silver originally present in concentrate B (44 mg/kg) by leaching a leach residue with a 200 g/L NaCl–0.5 M H₂SO₄ medium at 90 °C and 10 wt.% of pulp density in two stages of 2 h each. The incorporation of silver catalysis to the BRISA process allows a technology based on bioleaching capable of processing chalcopyrite concentrates with rapid kinetics.     

矿石粒度和矿浆浓度对原生硫化铜矿细菌浸出的影响

通过摇瓶试验研究矿石粒度和矿浆浓度对原生硫化铜矿石中细菌浸出的影响,并初步探讨了浸矿过程中细菌的氧化活性及其对浸矿的影响。研究结果表明:在原生硫化铜矿石细菌浸出过程中,有利于铜浸出的矿石粒度和矿浆浓度分别是5 mm和20%~25%;溶液中三价铁含量过高或产生的铁沉淀都会直接影响细菌的氧化活性和浸矿效果。     

Separation of zinc from spent zinc-carbon batteries by selective leaching with sodium hydroxide

Physical methods such as crushing and sieving followed by magnetic separation steps were applied to separate non-magnetic material (88.4 wt.%) from zinc-carbon spent batteries. The oversize material was processed by eddy current separation to recover zinc sheet, carbon rods, and plastics. The undersize fraction (− 2.36 mm) with a metal composition of 15.5% Zn, 17.5% Mn, and 1.4% Fe was used for the leaching experiments under different conditions such as concentration of sodium hydroxide, temperature, agitation speed, and pulp density. Selective leaching using 4 mol dm^− 3 NaOH at 100 g dm^− 3 solid/liquid ratio, 80 °C and 200 rpm gave a zinc extraction of 82% and a manganese extraction of less than 0.1%. An overall zinc recovery was about 88.5% by the processes described in this study.     

Silver-catalyzed bioleaching of low-grade copper ores. Part II: Stirred tank tests

A study of the effect of different variables (inoculation, aeration, silver complexants, [Ag], [Fe³⁺], temperature and chemical activation stage) on the silver-catalyzed bioleaching of two different low-grade copper ores has been carried out in stirred tanks. The catalyzed bioleaching process was greatly affected by bacterial activity. Aeration and the use of different complexing agents (thiosulfate and thiosulfate plus cupric ions) did not enhance but also did not inhibit the copper kinetics in the silver-catalyzed process. On the contrary, the presence of 5 g/L Cl⁻ inhibited the catalytic effect of silver. The effect of silver concentration was tested on two different low-grade copper ores in the range between 10 and 500 mg Ag/kg for the lower K-ore and between 1.4 and 35.7 g Ag/kg Cu for the PVD ore, the former with a higher content of copper. Silver catalysis was effective for both ores but the PVD ore was basically unaffected by silver concentration in the range studied. Maximum copper extractions and copper dissolution rates were obtained with a very small amount of silver (3.6 g Ag/kg Cu). In all cases, the copper recovery was at least twice that in the absence of silver (∼ 30%). High ferric concentrations have been tested in the absence and in the presence of silver. The presence of silver was essential to improve the copper extraction from chalcopyrite in acidic ferric sulfate solutions. However, bioleaching experiments conducted with silver and 1 g/L Fe³⁺ produced lower copper extractions (20%) compared to experiments where ferric iron was absent (55%). The copper dissolution in the silver-catalyzed lower K-ore bioleaching is temperature dependent, with an optimum temperature around 35 °C. The activation energies of the copper dissolution process were 109.7 and 20 kJ/mol in the ranges of temperature between 15 and 28 °C and 28 and 45 °C respectively. The chemical activation stage establishes optimum conditions that promote higher copper extractions in the presence of silver.