Bioleaching Research Articles

The main groups of microorganisms involved in the biohydrometallurgical process

Recovery of valuable components from minerals by microorganisms and their metabolic products is recognized biotechnology reception processing of sulphide ores. To date, this technology is cost-effective and environmentally friendly. The article describes the main groups of bacteria involved in the process biohydrometallurgical extraction of metals from natural sulfide ores, and recent data on the mechanism of bacterial and chemical oxidation. The main phenotypic and genotypic properties of acidophilic chemolithotrophic bacteria involved in biohydrometallurgical processes - mesophilic and moderately thermophilic chemolithotrophic members of the genera Acidithiobacillus, Leptospirillum, Sulfobacillus. Promising uses of bacterial leaching and the possible importance of this method for obtaining metals from non-traditional minerals indicated.

Bacterial leaching kinetics for copper dissolution from a lowgrade Indian chalcopyrite ore

Bio-leaching of copper (0.3%) from a low grade Indian chalcopyrite ore of Malanjkhand copper mines, using a native mesophilic isolate predominantly Acidithiobacillus ferrooxidans (A.ferrooxidans), is reported. A bio-recovery of 72% Cu was recorded in the presence of this culture (not adapted), which increased to 75% with an ore adapted culture after 35 days at 35ºC and pH 2.0 with <50fim particles. The kinetic data showed best fit for the diffusion-controlled shrinking core model, exhibiting linear plots for [1- 2/3X-(1-X)2/3] vs time (X-fraction leached). Apparently, the role of the bacteria is to convert the ferrous ion to the ferric state, which oxidizes the chalcopyrite in order to dissolve copper, while maintaining a high redox potential. The activation energy value (E) was calculated to be 96 and 108 kJ/mol for the un-adapted culture and the ore adapted culture respectively in the temperature range 25-35ºC. This leaching mechanism was corroborated by XRD phase identification and SEM studies of the leach residue.

Effect of Na-chloride on the bioleaching of a chalcopyrite concentrate in shake flasks and stirred tank bioreactors

Oxidative dissolution of chalcopyrite at ambient temperatures is generally slow and subject to passivation, posing a major challenge for developing bioleaching applications for this recalcitrant mineral. Chloride is known to enhance the chemical leaching of chalcopyrite, but much of this effect has been demonstrated at elevated temperatures. This study was undertaken to test whether 100–200mM Na-chloride enhances the chemical and bacterial leaching of chalcopyrite in shake flasks and stirred tank bioreactor conditions at mesophilic temperatures. Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and abiotic controls were employed for the leaching experiments. Addition of Na-chloride to the bioleaching suspension inhibited the formation of secondary phases from chalcopyrite and decreased the Fe(III) precipitation. Neither elemental S nor secondary Cu-sulfides were detected in solid residues by X-ray diffraction. Chalcopyrite leaching was enhanced when the solution contained bacteria, ferrous iron and Na-chloride under low redox potential (<450mV) conditions. Scanning electron micrographs and energy-dispersive analysis of X-rays revealed the presence of precipitates that were identified as brushite and jarosites in solid residues. Minor amounts of gypsum may also have been present. Electrochemical analysis of solid residues was in concurrence of the differential effects between chemical controls, chloride ions, and bacteria. Electrochemical impedance spectroscopy was used to characterize interfacial changes on chalcopyrite surface caused by different bioleaching conditions. In abiotic controls, the impedance signal stabilized after 28days, indicating the lack of changes on mineral surface thereafter, but with more resistive behavior than chalcopyrite itself. For bioleached samples, the signal suggested some capacitive response with time owing to the formation of less conductive precipitates. At Bode-phase angle plots (middle frequency), a new time constant was observed that was associated with the formation of jarosite, possibly also with minor amount or elemental S, although this intermediate could not be verified by XRD. Real impedance vs. frequency plots indicated that the bioleaching continued to modify the chalcopyrite/solution interface even after 42days.

Optimal parameters for bioleaching of realgar using Acidithiobacillus ferrooxidans under different growth conditions and mathematical analysis

Bioleaching, a long-standing technology in hydrometallurgy, has been applied to the field of pharmaceuticals. Here, the bacterial leaching of realgar as a novel preparation method was investigated using Acidithiobacillus ferrooxidans BY-3 (A. ferrooxidans BY-3). We evaluated the effects of a range of crucial operational parameters, including temperature, pH, bacterial population, ferrous iron concentration, and pulp density, on the efficiency of the bioleaching process. Moreover, a conversion algorithm based on linear regression was developed for analyzing the extraction of arsenic. The optimized bioleaching parameters obtained by mathematical analysis were in good agreement with the experimental data, indicating that the model was suitable for design of a realgar bioleaching process.

Shake flask and column bioleaching of a pyritic porphyry copper sulphide ore

The purpose of this study was to test the feasibility of using bacterial leaching to solubilize copper from a porphyry sulphide ore, a part of the Sarcheshmeh Copper Complex. The bulk ore sample contained 18% pyrite and 0.8% Cu mostly as secondary chalcocite and Cu oxides. Mineral microscopy showed that pyrite grains in this porphyry ore were coated by chalcocite. Conventional flotation could not be used for ore beneficiation because Cu-sulphide could not be selectively separated from pyrite and consequently the flotation concentrate contained too much Fe and less Cu. Hence bioleaching was tested as an alternative process for this ore. The bioleaching was tested with a consortium of mesophilic acidophiles comprising Leptospirillum and Acidithiobacillus spp., originally enriched from the Sarcheshmeh site. Several mineral salt formulations were tested in shake flask bioleaching experiments. These experiments resulted in 89–92% Cu yields with no discernible differences between the different formulations. Sterile controls representing chemical acid leaching resulted in about 60% Cu solubilization. For column bioleaching experiments, ore samples (~40kg each; 75% −12mm) were agglomerated and treated with a schedule of 4days of irrigation and 4days of rest period. The column bioleaching tests yielded Cu recoveries of about 90%. The abiotic control had 50% Cu recovery. Thus the test results were favorable for using the bioleaching approach for this Cu-ore material.

LIXIVIAÇÃO BACTERIANA DE SUCATA ELETRÔNICA: INFLUÊNCIA DOS PARÂMETROS DE PROCESSO

The application of bacterial leaching in the ore treatment is already known and also can be applied such as treatment of electronic waste to copper recovery. This paper investigates the influence of process parameters (pulp density, inoculums volume, rotation speed and initial concentration of ferrous iron) on bacterial leaching of copper from printed circuit board of computers using the bacterium Acidithiobacillus ferrooxidans–LR. Printed circuit boards from computers were comminuted using a hammer mill. The powder obtained was magnetically separated and the non-magnetic material used in this study. A shake flask study was carried out on the non-magnetic material using a shaker. The results show that Acidithiobacillus ferrooxidans–LR can leach 99% of copper from printed circuit boards (non–magnetic material) under the determined conditions through of the studies.

Extraction of metals from electronic waste by bacterial leaching

Extraction of metals from electronic waste by bacterial leaching

Improvement of copper–molybdenum ore beneficiation using a combined flotation and biohydrometallurgy method

The authors present the results of analysis of material composition and experimental investigations of acid and biohydrometallurgical leaching of middlings on grain size, pH level, leaching process duration, temperature and slurry density. The rational parameters of flotation and acid-bacterial leaching of middlings providing an efficient release of valuable components from mineral complexes and recovery to flotation concentrate and leaching solution have been determined. A combined flowsheet and a beneficiation process for bulk flotation middlings of copper–molybdenum ore have been suggested, which include middlings grinding, sulfide minerals flotation, bacterial leaching of sulfide flotation tailings, liquid-phase extraction of dissolved copper and electrolysis of re-extraction eluates. The suggested combined method of cleaning of middlings of copper–molybdenum ores beneficiation provides the total copper recovery increase by 0.8% with a reduction of the cost price of saleable material by 0.5%.

Quantification of growth and colonisation of low grade sulphidic ores by acidophilic chemoautotrophs using a novel experimental system

Microbial colonisation of low grade sulphidic ores and subsequent growth in heap bioleaching systems has not been quantified rigorously. In this study, an experimental system simulating the sub-processes that occur at the agglomerate scale was used to quantify the colonisation, growth and propagation of Acidithiobacillus ferrooxidans in an unsaturated bed of crushed and agglomerated low grade chalcopyrite ore. The relative distribution of the microorganisms in the flowing leachate solution (‘PLS’), the stagnant interstitial liquid and weakly and strongly attached to the mineral surfaces was determined at various time points during the leach. There was a distinct difference in population dynamics in each of these discrete phases. The microbial cells present in the interstitial phase dominated the microbial population in the ore bed. Particularly, the microbial concentration in the free flowing PLS was found to be a poor representation of the ore-associated microbial population. The calculated growth rate of At. ferrooxidans in the PLS was unreasonably high when modelled as a continuous system, indicating that change in cell concentration in the PLS was dominated by transfer from the mineral ore associated population. However, the transfer rate was not correlated directly to changes in either the interstitial or attached population sizes. Therefore, unless transfer rates can be accounted for, PLS population dynamics do not accurately represent those in the column as a whole. Growth rates of microorganisms in the interstitial, weakly mineral-attached and strongly mineral-attached phases better predicted growth of At. ferrooxidans on the whole ore system owing to the dominance of the microbial location in these phases.

Two step meso-acidophilic bioleaching of chalcopyrite containing ball mill spillage and removal of the surface passivation layer

Meso-acidophilic bacterial leaching of ball mill spillage (containing chalcopyrite >80%) was carried out in an innovative two-step bioleaching method. The major drawback of meso-acidophilic bioleaching limiting industrial application is the passivation phenomenon over the ore surfaces in iron–sulfur rich environments. In the present study, we present a novel wash solution that efficiently removed the passivation layer. FTIR characterization of the bioleached sample indicated that the residues could be further leached to recover extra copper after wash solution application. XRD study indicated accumulation of sulfates (SO4-) of Na, K, Fe and oxy hydroxides of iron [FeO(OH)] in the form of jarosite outlining the passivation layer. SEM, FESEM-EDS studies indicated severe corrosion effects of the wash solution on the passivation layer. Two step bioleaching of the ore sample yielded 32.6% copper in 68days in the first interlude and post wash solution application yielded 10.8% additional copper.

Phase distribution identification in the column leaching of low grade ores using MRI

Heap bioleaching is gaining importance as an approach for the recovery of valuable metals (e.g. Cu2+) from low grade ores. In this process iron and/or sulfur oxidising microorganisms are used to aid the oxidation of base metal sulfides in the ore, thereby liberating the metal ions into solution. Leach performance is strongly influenced by the contacting of the leach solution and the ore particles. In order to better understand the distribution of the leaching solution on the pore scale in these heaps, Magnetic Resonance Imaging (MRI) was used to acquire images non-invasively of a section of an irrigated ore bed. This was made possible by the use of specialist MRI acquisition sequences suited to the magnetically heterogeneous environment as presented by the ore material. From the images we were able to determine the pore-occupancy of the liquid and gas phases and to provide novel measurement of the interfacial area between air, leach solution and ore.

The Possibilities of Application of Bacterial Leaching in Retrieval of Valuable Metals From Mining Waste

Abstract The paper deals with an application of bacterial leaching on two selected samples from old ecological loads situated in the Karlovy Vary Region. To be specific, they are heaps in Prebuz and Kraslice. Bacterial leaching was applied making use of Acidithiobacillus ferrooxidans bacteria and lasted 28 days. The results imply that the given method is suitable for the retrieval of valuable metals from waste and may help to deal with the issue of old heaps and dumps.

Study on Comprehensive Utilization of Arsenic from High Arsenic-Bearing Copper Sulphide Concentrate

In this paper a new technology for comprehensive utilization of arsenic in high-arsenic copper sulfide concentrate has been studied out. Firstly,the concentrate was bioleached by moderate thermophile Sulfobacillus thermosulfidooxidans, under the suitable leaching conditions, the experiments results show that the concentrate is bioleached 82% of Cu,78% of As and 40% of Fe. Secondly, removal of Fe3+ by solvent extraction with P204 from bacterial leaching solution are presented, and Fe3+ is extracted up to 93％, and the content of Fe3+ in raffinate is under 9 mg/L. The comprehensive utilizations of most of arsenic from leaching liquor after removal Fe3+ has been carried out. When the temperature is 80 to 90°C, pH at 4.0~5.0 and ammonia as a neutralizer, the results of XRD analysis show that the forming process of copper arsenate is complicated, and the formed molecular formulas are in different types, and they are CuAs2O4, Cu5As2O10•5H2O, C4H6As6Cu4O16, Cu5As4O15•9H2O and Cu2AsO4OH•3H2O. The comprehensive utilizations of most of arsenic are in the form of copper arsenate, and the content of arsenic is 9.11~35.82mg/L in solution after its precipitated. This study provides a new treatments and process for the utilization of arsenic in the high-arsenic copper sulfide concentrate.

Microbial colonisation in heaps for mineral bioleaching and the influence of irrigation rate

Microbial colonisation is important for mineral dissolution in heap bioleaching of low grade ore. Colonisation studies to date have focused on the microbial attachment of single species to mineral concentrates in batch and flow systems. Hydrology and soil engineering studies suggest interaction between microbial colonisation and fluid flow in porous systems that result from solution-ore and microbe-mineral contacting (Wan et al., 1994; Yarwood et al., 2006).The effect of the irrigation rate on microbial colonisation was assessed using columns packed with acid agglomerated low grade copper-containing ore. Continuous flow, unsaturated, aerated bed reactors were inoculated by pulse irrigation with iron and sulphur oxidising mesophilic microorganisms (1012cells/ton ore), followed by operation at irrigation rates of 2, 6 and 18l/m2/h. A novel in-bed sampling technique allowed the extraction of ore samples from the bed during the leaching process. Novel insights regarding microbial growth, interstitial and weakly and strongly attached microbial populations were obtained.Bacterial adherence and cell number retained in the ore bed increased over the 32day leaching period. Average specific growth rates of ore-associated micro-organisms of 0.161±0.0045, 0.155±0.026 and 0.120 (± 0.00)1/h were obtained at 2, 6 and 18L/m2/h respectively. Faster colonisation occurred at lower irrigation rates. At higher irrigation rates, higher detachment and cell removal were apparent, based on PLS cell numbers. The interstitial cells from the stagnant fluid in the ore bed formed the dominant contribution to the microbial population within all the heap systems.

Mechanism of nonoxidizing and oxidative pyrrhotite leaching

Pyrrhotite is one of the main components of sulfide ores. As a result, its behavior has a significant influence on the course of metallurgical processes and on the extraction of nonferrous metals. There is no definitive description of the mechanism of the chemical reactions that occur during nonstoichiometric iron sulfide dissolution. In some studies on pyrrhotite dissolution, pyrite formation is assumed; in others, elemental sulfur is assumed to form. The aim of this study is to clarify the mechanism of the chemical reactions of pyrrhotite dissolution in nonoxidizing acids during oxidative bacterial leaching. In this work, different methods of analysis have been used: scanning electron microscopy, micro X-ray spectral, X-ray diffraction, Mossbauer and IR-spectroscopy analysis. It has been established that acid pyrrhotite dissolution in nonoxidative conditions proceeds in stages, beginning with low-sulfur pyrrhotite dissolution. This occurs with the transition of iron ions to solution and to hydrogen sulfide, with the simultaneous formation of sulfur-rich iron sulfide in the residue from the leaching. Pyrrhotite oxidative bacterial leaching proceeds in two stages. In the first stage, the pyrrhotites are enriched with iron and then, in the second stage, the low-sulfur sulfides dissolve with the formation of iron sulfate (Fe2+). This study proposes a mechanism for sulfide oxidative bacterial leaching that can predict the parameters and the results of the process.

Bioleaching of low grade uranium ore containing pyrite using A. ferrooxidans and A. thiooxidans

A process of uranium extraction from ore containing 3.1 % pyrite by bacterial leaching was investigated in shaken flasks during 90 days. The highest uranium recovery amounting to 85.1 % was obtained using binary mixture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans that was exceeding results obtained by traditional acid leaching technique up to 27 %. High uranium recovery was founded to be due to the high degree of pyrite dissolution that can be readily achieved by bacterial leaching (up to 98.0 %).

Insights into heap bioleaching of low grade chalcopyrite ores — A pilot scale study

Heap bioleaching of low grade chalcopyrite (CuFeS2) was carried out in 1000tons scale over a time period of 383days. Bacterial solution was prepared and re‐circulated in specially designed BACFOX (BACterial Film OXidation) tank. The micro‐organisms used in the pilot scale were a mixed culture of acidophilic bacteria predominantly of the Acidithiobacillus ferrooxidans strain. Effect of rest period, solution recirculation, acid concentration, frequency of solution transfers and seasonal effects on copper recovery were monitored. The leaching studies showed a cumulative copper dissolution rate of 0.14% per day (2.37kgd−1). The overall recovery of the heap was 30%. Variation in leaching efficiency and some of the precautionary measures to improve performance of heap bioleaching are also discussed.

Modification of the ferric chloride assay for the spectrophotometric determination of ferric and total iron in acidic solutions containing high concentrations of copper

During heap bioleaching for copper recovery, solution containing high concentrations of copper is recycled to the heaps. The commonly used 1,10-phenanthroline assay is not suitable in such situations; the presence of 6gL−1 copper in a solution containing 50mgL−1 ferrous iron resulted in the complete loss of the absorbance band associated with the tris(1,10-phenanthroline)iron(II) complex. The colorimetric determination of soluble ferric iron concentration using the ferric chloride assay is simple and rapid. However, it offers relatively low resolution and cannot be used to determine total iron concentrations. The detection wavelength was changed to improve resolution and the assay further modified to include an oxidation step using potassium persulfate. Therefore, both ferric and total iron concentrations can be determined rapidly using the same aliquot. There was minimal interference of copper (<5% deviation) on the modified assay with copper concentrations of 10gL−1 and below. At greater copper concentrations the deviation increased. However, a linear relationship between absorbance and ferric iron concentration was maintained for all the solutions tested allowing correction through appropriate calibration.

Surface alteration of realgar (As4S4) by Acidithiobacillus ferrooxidans

The chemical and physical characteristics of realgar (an arsenic sulfide mineral that occurs in several crystalline forms) in the presence of Acidithiobacillus ferrooxidans BY-3 were investigated in this work. Grains of the mineral were incubated for 10, 20, and 30 days with A. ferrooxidans cultured in 9K medium at 30 °C and at 150 rpm agitation. Abiotic control experiments were conducted in identical solutions. The effect of bioleaching on the surface properties of realgar was characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), inductively coupled plasma atomic emission spectroscope (ICP-AES), X-ray diffraction (XRD), and Raman spectroscopy. SEM and EDS analyses confirmed the ability of A. ferrooxidans to modify surfaces of realgar and to efficiently enhance its dissolution. ICP-AES showed the dissolution and precipitation of realgar during bioleaching. Based on the XRD pattern and the Raman spectra, the decrease in arsenic in the liquid phase was due to co-precipitation of the mineral with Fe(III) or Fe(III) compounds (e.g., jarosite or goethite). Thus, not only did Fe(III) alter the surface of realgar, but it also promoted its dissolution during bioleaching.

Recovery Uranium from Uranium-Bearing Waste Ore Using Heap Bioleaching

The feasibility of heap bioleaching recovery of uranium from the one Uranium Mine deposit uranium-bearing waste ore, located in south of China, were investigated. A 4500 ton industrial heap was constructed in the waste ore dump site. The waste ore sample was crushed to -25 mm, the ore uranium grade is 0.0211%. After 146 days of performance, the slag uranium leaching rate was 55.92% that calculated by its residue has been recovered, content of uranium in residue was 0.0093%, the acid consumption rate was 2.69% by ore weight. The study has proven that recovery uranium from uranium-bearing waste ore using heap bioleaching is feasible.