Bioleaching Research Articles

LOW COMPLEXITY MODELLING AND PARAMETER ESTIMATION IN COPPER BIOLEACHING PROCESSES

In heap bioleaching, metal is dissolved from ore by a percolating solution, catalysed by naturally occurring bacteria. Increased interest in the technology motivated the development of accurate models of such process in recent years. In contrast, the utilisation of such models for control has received limited attention, given their high mathematical complexity. This paper presents a low complexity model aimed as the basis for control design. The model parameters are estimated using least squares on data generated by a high complexity, experimentally validated model provided by BHP Billiton Innovation. Simulation results indicate significant potential of the approach.

Bacterial desulphurization of coal from mine CSA Most

The objective of the paper was application of bacterial leaching on 3 brown coal samples from bore S 187 (CV) from locality Mine CSA Most. Based on the results of bacterial leaching and petrologic analyses of the given samples, it is possible to state that the individual samples are very similar, they contain significant shares of clay materials and pyrite is predominantly represented in a framboidal form, which intergrowths into a massive form. Applying bacterial leaching it is possible to remove from 24 to 40% of total sulphur and from 20 to 37% of pyritic sulphur from the coals.

Recovery of copper from melting furnaces dust by microorganisms

Bacterial leaching of the copper dust emanating from smelting furnaces of Sarcheshmeh Copper Mine has been studied. The present procedure to treat the dust which consists of about 30% copper is included in its collection and sending back to the furnace. Regarding the considerable amount of copper oxide minerals in the dust, a sulphuric acid leaching process was performed prior to bacterial leaching. Shake flask experiments were run using a mixed culture of thiobacilli and the effects of some parameters such as culture medium and pulp density on copper extraction were studied. Copper recoveries in 5% pulp density of inoculated and control flasks after 22 days incubation were 87% and 38%, respectively.

A model for heap bioleaching of chalcocite with heat balance: Bacterial temperature dependence

A three-phase computational fluid dynamics model for heap bioleaching of chalcocite is investigated to identify and understand the thermodynamic processes in a heap. The study uses an existing one-dimensional model of liquid flow, bacterial transport (including attachment/detachment of bacteria to ore particles), and the depletion of a copper-sulphide, coupled with a model of heat flow in the heap, with bacterial temperature dependence. The model is used to investigate aspects of heat balance in regard to the temperature dependence of the bacterial concentration and the temperatures reached in a typical heap. The heap is found to leach in a top–down manner, due to the ability of the incoming liquid to cool the heap at the top, and to allow bacteria to grow under optimal temperature conditions. As the top leaches, the temperature there drops and progressively cools the heap as the leaching front moves down through the heap to leach the whole bed.

Comparative study on the bioleaching of zinc sulphides

Bioleaching processes of three zinc sulphides (marmatite, sphalerite and ZnS synthetically prepared) with Acidithiobacillus ferrooxidans and a moderately thermoacidophilic iron-oxidizing bacterium (MLY) were investigated by leaching experiments and electrochemical methods. Experimental results showed that marmatite had the highest dissolution rate in the presence of bacterial strains among the three zinc sulphides due to the difference of physicochemical property. Compared with synthetic ZnS, the part iron existed as pyrite contained in two concentrates and the dissolution of zinc sulphides was accelerated for galvanic cell effect. More Fe existed in the crystal lattice of marmatite solid solution were released to liquid phase and oxidized into Fe 3+ ions by bacterial strains to accelerate the dissolution of marmatite during the bioleaching process. The bacterial leaching of zinc sulphides could become diffusion controlled when insufficient bacterial oxidation of the sulphur layer occurred, especially in the more rapid marmatite leaching reaction. The zinc sulphides bioleaching was significantly affected by mineralogical properties and leach solutions, which was supported by electrochemical measurements based on the working electrode of zinc sulphides–carbon paste electrode. The marmatite concentrate was more suitable for the extraction of zinc by the microbial leaching, when compared with the sphalerite and synthetic ZnS.

Effects of temperature on the rates of iron and sulfur oxidation by selected bioleaching Bacteria and Archaea: Application of the Ratkowsky equation

Bioleaching rates are affected by temperature and temperature is a major selective pressure for the organisms that will inhabit a bioleaching operation. The relationship of microbial activity to temperature is best described by the Ratkowsky equation. Ratkowsky and Arrhenius equations were applied to temperature versus sulfur or ferrous iron oxidation data for selected bioleaching microorganisms. Extrapolated cardinal temperatures for iron and sulfur oxidation, and activation energies were derived from the fitted Ratkowsky and Arrhenius equations. The data provided definition of the temperature operating windows, to a precision not previously available, for the majority of species that are frequently encountered as the biological catalysts in tank and heap bioleaching environments.

A two-dimensional CFD model for heap bioleaching of chalcocite

A 3-phase computational fluid dynamics (CFD) model for heap bioleaching of chalcocite is investigated to identify and understand the effect of oxygen flow during air sparging. The study uses an existing one-dimensional model of liquid flow, bacterial transport (including attachment/detachment of bacteria to ore particles), and the depletion of a copper-sulphide, coupled with a two-dimensional model of gas flow in the heap. The CFD model includes the effects of oxygen and ferrous ion consumption, coupled with leaching of copper-sulphide via a shrinking core model. The model is used to investigate the two-dimensional effects of air flow in heap bioleaching with regard to oxygen limitation. Under oxygen limitation, copper leaching is found to occur from the bottom up, successively leaching the oxygenated regions and moving slowly up the heap to leach the whole bed. Some experimental validation is provided.

The influence of crystal orientation on the bacterial dissolution of pyrite

In order to understand the influence of crystallographic orientation on the mechanism of pyrite bioleaching, single crystals cut to expose plane orientations of (100), (111) and (110) were used for the study. Experiments to compare the extent of dissolution of the pyrite surfaces in the presence and absence of Acidithiobacillus ferrooxidans under similar solution conditions were undertaken by matching the conditions in abiotic solutions to those in bacterial leaching solutions using an electrolysis cell. The microbial corrosion patterns generated on the surfaces were further used to study the leaching process. Differences in the reaction rates of the pyrite surface planes in both abiotic and bacterial solutions have been observed. The results for the comparison between the bacterial and abiotic leaching of pyrite samples under similar conditions indicate higher dissolution rates in the presence of bacteria. In addition, the morphologies of corrosion patterns arising from microbial leaching were distinct from those of abiotic leached samples and were found to slightly differ from one crystal plane to another, while those in abiotic leaching generally reflected the symmetrical arrangement of the crystallographic planes in the lattice on which they formed. The results show that the surface properties of mineral sulphides control the evolution of corrosion patterns and the initial oxidation kinetics in acid bacterial leaching.

Bacterial oxidation activity in heap leaching

Bioleaching of sulfide minerals by bacteria, mainly Thiobacillus ferrooxidans (T. f.) and Thiobacillus thiooxidans, plays an important role in hydrometallurgy because of its economic and environmental attractions. The surveys of production process and the bacterial oxidation activity in the heap bioleaching were investigated. The results show that pH value is high, bacteria biomass and ferric concentration are low, generation time (above 7.13 h) is long in leachate, and less bacteria are adsorbed on the ores. The bacteria in the leachate exposing on the surface and connecting with mineral, have much faster oxidation rate of Fe(II) and shorter generation time, compared with those which are in the reservoir for a long time. There is diversity for oxidation activity of Fe(II), while there is no diversity for oxidation of sulfur. So it is advisable to add sulfuric acid to degrade pH value to 2.0, add nutrients and shorten recycling time of leachate, so as to enhance bacteria concentration of leachate and the leaching efficiency.

Testing the ability of a low grade sphalerite concentrate to achieve autothermality during biooxidation heap leaching

GeoBiotics, LLC has developed a proprietary heap bioleaching technology for the processing of sulphide base metal and gold concentrates. In this process, known as GEOCOAT ®, thickened flotation concentrate is contacted during heap stacking with gravel-sized support rock, forming a thin adherent concentrate coating on the support rock particles. The stacked heap has an open structure and is highly permeable to the flows of solution and air. Acid solution, which contains acidophilic bacteria, is circulated through the heap to biooxidise and leach the contained metals. The heat produced by the exothermic oxidation reactions causes the internal temperature of the heap to rise. Heat is transferred to the percolating solution and to the air blown up through the heap. Rates of solution application and aeration can be varied to control the heap temperature and maintain it within the optimum range for bacterial activity. GeoBiotics and Kumba Resources have investigated the feasibility of applying the GEOCOAT ® process to the leaching and recovery of zinc from a low-grade sphalerite concentrate produced from accumulated flotation tailings at Kumba’s Rosh Pinah zinc mine in Namibia. The concentrate contained 18% Zn, 4.5% Fe, 12.8% S 2−, 0.2% Cu, and the D 80 particle size was 53 μm. To confirm that a GEOCOAT ® heap to bioleach this concentrate would operate autothermally, a large engineering column test was conducted. The insulated stainless steel column, 6.5 m high and 1.2 m in diameter, was equipped with sample ports, airflow measurement, oxygen analysis and thermocouples to monitor temperatures during the test. The large column was designed to simulate a unit cell from a commercial heap and similar operating parameters where applied to its operation. The column was filled to a 6 m height with concentrate coated support rock which was produced using a batch coating method. After acid stabilization to reduce the solution pH to 1.5–1.8, the column was inoculated with an adapted mixed mesophilic bacterial culture. Through control of the exothermic biooxidation reactions and the solution and aeration rates, the temperature in the column was increased from ambient to a maximum of 49 °C. The solution application rate and the aeration rate adjusted to control the temperature and prevent it from rising beyond the maximum tolerable by mesophiles. The column was operated for a total of 90 days. Final zinc dissolution after 90 days was 91% with a corresponding sulphide sulphur oxidation of 89%. Concentrations of in excess of 90 g/l Zn in the column effluent did not appear to inhibit the microbial oxidation. The comparison of the zinc dissolution kinetics between the large diameter autothermal column and that exhibited by previous heated small diameter columns (6.5 m high × 0.15 m diameter) showed excellent correlation. The small diameter column test produced a zinc dissolution of 92% in 63 days compared to 91% after 60 days in the large column. The operation of the large diameter column was successful in demonstrating that the GEOCOAT ® process can be operated autothermally at mesophilic temperatures treating a low-grade sphalerite concentrate. Zinc dissolution in excess of 90% can be achieved in a leach time of 60 days, while results of small diameter column testing indicate zinc dissolutions in excess of 95% in 60–100 days.

Bacterial leaching

Bacterial leaching is the extraction of metals from their ores using microorganisms. Microbial technology offers an economic alternative for the mining industry, at a time when high-grade mineral resources are being depleted.

INNOVATIVE HYDROMETALLURGICAL PROCESSES FOR THE PRIMARY PROCESSING OF ZINC

The zinc industry has been in the forefront of hydrometallurgical developments for almost a century. The development of pressure leaching in the 1980s and the development of atmospheric direct leaching in the 1990s for treating zinc-sulphide concentrates have resulted in a number of zinc-refinery expansions without an increase in roasting capacity. Likewise, solvent extraction techniques are now used for the hydrometallurgical treatment of zinc-oxide ores on an industrial scale. The treatment of poor and complex zinc-sulphide resources has been extensively studied using processes as diverse as pyrolusite leaching and heap bioleaching. Finally, the precipitation of relatively pure zinc oxide at the mine site, a process that has been proven to be technically feasible very recently, may significantly change the paradigm of primary zinc production.

Kinetic modeling for the bacterial leaching of chalcopyrite catalyzed by silver ions

The mechanism of bacterial leaching of chalcopyrite catalyzed by silver ions is studied in this paper. The copper and iron ions in the chalcopyrite crystal lattice are replaced by the silver ions, the silver ions then combining with the sulfur to form silver sulfide. The ferrous ions are oxidized to ferric ions by the thiobacillus ferrooxidans. The ferric ions can convert the silver sulfide into silver ions. Using this mechanism, a new kinetic model of bacterial leaching of chalcopyrite in the presence of silver ions was established. The model accurately predicts the copper recovery rate in the bacterial leaching of chalcopyrite in the presence of silver ions.

Relative importance of diffusion and reaction control during the bacterial and ferric sulphate leaching of zinc sulphide

A study has been undertaken on the bacterial and ferric sulphate leaching of sphalerite, with the aim of observing the relative importance of both diffusion and reaction control, across a range of operating conditions. To facilitate this kinetic analysis a mixed-control rate equation was developed based upon the shrinking particle and shrinking core models, featuring both an intrinsic rate of zinc extraction and a product layer diffusion coefficient. The ferric sulphate oxidation of a pure sphalerite sample was first studied, and the process was found to be mainly controlled by surface diffusion, thought to be due to formation of the elemental sulphur product layer. The mesophilic bacterial oxidation of a high-grade zinc ore was studied at 35 °C, and the process was observed to be controlled by both chemical reaction and diffusion. However, during the mesophilic bacterial oxidation of a low-grade zinc ore at 25 °C, diffusion was found to be rate limiting. It was proposed that this diffusion resistance arises from an unreacted layer of gangue material.

Zinc and lead extraction from complex raw sulfides by sequential bioleaching and acidic brine leach

This research was designed to investigate zinc and lead extraction by combined sequential biooxidation and acidic brine leaching from a raw complex sulfide ores containing sphalerite, pyrite, and galena. For the biooxidation, the zinc dissolution from the sulfide ores by the adapted bacteria was examined. The effects on ore particle size, pH, pulp density, and temperature on bacterial leaching was studied systematically. From the experiments it was shown that about 95% of zinc was extracted after 20 days of bioleaching at 30 °C. Subsequently, 98% of the lead was extracted from the bioleached residues using an acidic sodium chloride solution as the lead lixiviant at a temperature of 60 °C for 90 min leach. Leaching kinetics indicated that diffusion through the product layer was the rate controlling process during zinc bioleaching, and that the overall rate of chemical reaction at the surface was the rate controlling process during lead brine leaching. The relative activation energies of the overall rate during the two different leaching stages were calculated to be 32.09 and 44.35 kJ/mol, respectively.

Activation of bacteria in agglomerated ores by changing the composition of the leaching solution

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.

Mechanical activation in hydrometallurgy

The review paper deals with the results of the utilization of mechanical activation in hydrometallurgy. The definition of mechanochemistry is given as well as physicochemical changes in mechanically activated minerals are described. The enhancement of the leaching processes in hydrometallurgy is illustrated. The chemical and bacterial leaching of sulphide minerals are given as examples. A brief description of the established technologies (LURGI-MITTERBERG, ACTIVOX™, MELT) applying mechanical activation for metals extraction is given. In these processes, the introduction of mechanical activation step into technological cycle significantly modifies the subsequent processing steps.

Correlations between reaction rates and evolution of corrosion pits in bacterial leaching of pyrite

In order to understand the influence of crystallographic orientation on the mechanism of pyrite bioleaching, single crystals of pyrite cut to expose plane orientations of {100}, {111} and {110} were studied. Differences in the reaction rates of the pyrite surfaces in the presence of Thiobacillus ferrooxidans have been observed. The microbial corrosion patterns generated on the surfaces were further used to study the leaching process. Surfaces with high sulphur/iron atomic ratios were observed to develop surface films and to generate elongated pits similar in shape to bacteria, but much larger than the bacteria cell dimensions. The dissimilarity of corrosion patterns observed on the surfaces of samples indicates a variation in cell–surface interaction from one crystal plane to the other. Subsequent correlation between the surface corrosion patterns associated with the dissolution process and the changes occuring in the leaching solution indicated that the most signficant aspect in the early stages of leaching is the recognition and subsequent attachment of the bacteria to active sites on the immediate surfaces. This initial process consequently controls the leaching progression and defines the type and evolution of pits occurring on the surfaces. The overall analysis indicates that the surface properties of pyrite may control the initial oxidation kinetics and the evolution of corrosion patterns in acid bacterial leaching.

Bacterial Leaching of Metals from Tannery Sludge by Indigenous Sulphur-Oxidizing Bacteria—Effect of Sludge Solids Concentration

An investigation on the effect of sludge solids concentration on bioleaching of Cr(III) and other metals from tannery sludge by indigenous sulphur-oxidizing bacteria was carried out. The sludge solids concentrations ranged from 13 to 60 g/L. The concentration of elemental sulphur was fixed at 30 g/L. The results showed that the lowest pH reached after 25 days of bioleaching at all studied sludge solids concentration was about 1.3. The optimum sludge solids concentration for maximum metal leaching from tannery sludge was 40 g/L and about 87% of Cr(III), 73% of Al, 72% of Fe, 62% of Mg, and 73% of Zn could be leached in this case. During bioleaching, the concentrations of total and volatile suspended solids of the tannery sludge significantly decreased. The sulphur-oxidizing bacteria could tolerate a Cr(III) concentration as high as 5,930 mg/L at pH 1.3. The leaching efficiencies of Cr(III), Al, and Fe for both chemical leaching and bioleaching of tannery sludge were similar at pH 1.3. The leaching efficiency of Ca, Mg, and Zn in both leaching processes were identical for pH values in the range of 1.3 to 3.0.

BPMA rewards pump sector excellence

Heap bioleaching of low grade chalcopyrite (CuFeS2) was carried out in 1000 tons scale over a time period of 383 days. 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 (2.37 kg d− 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.