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.     

Microbiological leaching of a zinc sulfide concentrate

The microbiological extraction of zinc from a high-grade zinc sulfide concentrate has been investigated, using a pure strain of Thiobacillus ferrooxidans. Conditions such as temperature, pH, pulp density, nutrient, concentration, and specific surface of solids have been studied in terms of their effects on zinc extraction rate and in some instances on final zinc concentration in solution. Where appropriate, optimum conditions for leaching have been specified.     

The removal of pyritic sulphur from coal by Leptospirillum-like bacteria

Summary The microbial oxidation of pyritic sulphur was studied in a 4.5-l airlift fermentor at pH 1.5 and 100 g/l pulp density. By microbial leaching with Leptospirillum-like bacteria 85% of the pyritic sulphur was removed within 40 days; 30% of the removed pyrite was oxidized to elemental sulphur, the rest being transformed to soluble sulphate. Accumulation of elemental sulphur could be avoided by using a mixed culture of Leptospirillum-like bacteria and Thiobacillus ferrooxidans. Apart from oxidation of elemental sulphur neither the pure nor the mixed culture showed a significant difference as to removal of pyrite.     

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.     

A dynamic mathematical model for microbial removal of pyritic sulfur from coal

A dynamic mathematical model has been developed to describe microbial desulfurization of coal by Thiobacillus ferrooxidans. The model considers adsorption and desorption of cells on coal particles and microbial oxidation of pyritic sulfur on particle surfaces. The influence of certain parameters, such as microbial growth rate constants, adsorption-descrption constants, pulp density, coal particle size, initial cell and solid phase substrate concentration on the maximum rate of pyritic sulfur removal, have been elucidated. The maximum rate of pyritic sulfur removal was strongly dependent upon the number of attached cells per coal particle. At sufficiently high initial cell concentrations, the surfaces of coal particles are nearly saturated by the cells and the maximum leaching rate is limited either by total external surface area of coal particles or by the concentration of pyritic sulfur in the coal phase. The maximum volumetric rate of pyritic sulfur removal (mg S/h cm(3) mixture) increases with the pulp density of coal and reaches a saturation level at high pulp densities (e.g. 45%). The maximum rate also increases with decreasing particle diameter in a hyperbolic form. Increases in adsorption coefficient or decreases in the desorption coefficient also result in considerable improvements in this rate. The model can be applied to other systems consisting of suspended solid substrate particles in liquid medium with microbial oxidation occurring on the particle surfaces (e.g., bacterial ore leaching). The results obtained from this model are in good agreement with published experimental data on microbial desulfurization of coal and bacterial ore leaching.     

A growth model for the continuous microbiological leaching of a zinc sulfide concentrate by Thiobacillus ferrooxidans

The leaching of a zinc sulfide concentrate by Thiobacillus ferrooxidans was investigated in continuous stirred tank reactors. A mathematical model for the growth of T. ferrooxidans on this solid substrate is presented and tested. Experimental leaching studies were done using two reactors in series with and without recycle of solids from the outlet of the first reactor back to its inlet. The proposed model fits the authors' experimental data well. However, comparison of the parameters calculated with those calculated from the data of others showed that a wide variation can exist; thus, the parameters seem to depend on the nature of the substrate. The area occupied on the sulfide surface by a bacterium was found to be 5.4 mum(2). The calculated maximum specific growth rates ranged from 0.20 to 0.31 h(-1), and these values were dependent on whether they were observed in the first or second of the two reactors in series.     

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.     

Chemical leaching of copper-zinc concentrate with ferric iron biosolution

The process of leaching of copper-zinc concentrate with a solution containing biogenic iron, which is a product of the metabolism of iron-oxidizing microorganisms, was studied. The dependence of leaching rate of metals on temperature and pH was determined. It was shown that up to 98% of zinc and 70% of iron could be removed from the concentrate, while up to 7 and 4 g/L of zinc and copper, respectively, were accumulated in the liquid phase, which was sufficient for metal recovery. It was established that a copper concentrate with copper content up to 16% and only 0.5% of zinc could be obtained after chemical leaching for 340 min at 80°C.     

Hydroxyapatite adherence as a means to concentrate bacteria.

Adherence to hydroxyapatite (HA) was examined as a method to concentrate bacteria from foods. Using HA at a level of 10% and suspensions of an Escherichia coli strain containing 10(9), 10(6), and 10(3) cells per ml, kinetic studies revealed that maximum adherence was attained within 5 min for all cell concentrations and that comparable log reductions (1.0 to 1.5) of cells in suspension were seen regardless of initial cell concentration. Eleven species of spoilage and pathogenic bacteria were found to adhere to HA, with seven species adhering at proportions of greater than 95%. Fluorescent viability staining revealed that cells bound to HA remained viable. There was greater than 92% adherence of indigenous bacteria to HA from three of five 1:10 dilutions of ground beef, indicating promise for the use of HA for concentrating bacteria from meat and other food samples.     

Continuous culture of Thiobacillus ferrooxidans on a zinc sulfide concentrate

A zinc sulfide concentrate was leached microbiologically by Thiobacillus ferrooxidans in a continuous stirred tank reactor. A model was developed to predict, the leaching kinetics when the bacterial growth rate was not limited by any substrate other than the zinc concentrate, and it was modified to explain the observed results. Stable steady sates were obtained over a range of dilution rates from 0.0171 to 0.1038 hr^?1. Because a solid substrate was used, the specific growth rate of the bacaeria was not a unique function of the subastrate concentration, and conventional contnuous culture theory based on the Monod equation did not apply to this system. The leaching rates and bacterial growth rates were first order in mineral surface area cocentration.     

Reduction of pollutant parameters of leaf protein concentrate by-product by microbial fermentation

Deproteinised juice (DLJ) is left as a waste of a leaf protein concentrate (LPC) production plant. As it contains carbohydrates, nitrogenous compounds, lipids, minerals, and vitamins, its values of chemical oxygen demand (COD) and biological oxygen demand (BOD) are high enough to pose a serious disposal problem. But this waste, due to its nutrient content, is suitable for microbial growth. The growth of a number of filamentous fungi such as Rhizopus arrhizus, Aspergillus japonicus, and Trichoderma viride have been studied in different DLJ samples from different plants, such as cowpea, winged bean, radish, and turnip. The biomasses of fungi have been harvested and found to contain a large amount of protein. The fungi were found to reduce the high COD and BOD values of the DLJ samples, indicating the possibility of large scale use of this liquid waste as a fermentation medium.     

Cyanide detoxification by microbial consortia of natural-industrial complexes of gold heap leaching

Microorganisms that have adapted not only to high concentrations of pollutants but also to environmental conditions develop in autochthonous microbial communities of natural-industrial complexes of gold heap leaching. The biotechnological potential and diversity of autochthonous microbial communities involved in cyanide detoxification was evaluated by the example of a deposit situated in the Sakha (Yakutia) Republic. Under the zoning conditions of the ore heap, the biological component had a greater impact on cyanide destruction than chemical transformation. Metabolically active representatives of a microbial consortium are capable of surviving developed under these conditions. Phylotypes of the genus Serratia and family Alcaligenaceae that are capable of cyanide destruction and are potentially promising for the detoxification of wastes of gold heap leaching were revealed.     

Thermoacidophilic microbial community oxidizing the gold-bearing flotation concentrate of a pyrite-arsenopyrite ore

An aboriginal community of thermophilic acidophilic chemolithotrophic microorganisms (ACM) was isolated from a sample of pyrite gold-bearing flotation concentrate at 45–47°C and pH 1.8–2.0. Compared to an experimental thermoacidophilic microbial consortium formed in the course of cultivation in parallel bioreactors, it had lower rates of iron leaching and oxidation, while its rate of sulfur oxidation was higher. A new thermophilic acidophilic microbial community was obtained by mutual enrichment with the microorganisms from the experimental and aboriginal communities during the oxidation of sulfide ore flotation concentrate at 47°C. The dominant bacteria of this new ACM community were Acidithiobacillus caldus (the most active sulfur oxidize) and Sulfobacillus thermotolerans (active oxidizer of both iron and sulfur), while iron-oxidizing archaea of the family Ferroplasmaceae and heterotrophic bacteria Alicyclobacillus tolerans were the minor components. The new ACM community showed promise for leaching/oxidation of sulfides from flotation concentrate at high pulp density (S : L = 1 : 4).     

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.