Bioleaching Research Articles

Characterization of Oxidizing Activity of a Microbial Community in an Industrial Bioleaching Heap

In order to explore new options to optimize the low-grade copper ore bioleaching process, it is important to understand the kinetics of microbial oxidation at industrial level. This work studies the changes of iron and sulfur oxidation rates of microbial communities in solution from an industrial low grade copper bioleaching heap process at Escondida Mine in Chile. Pregnant leach solution (PLS) samples were analyzed periodically to determine physico-chemical parameters. The total numbers of the different microorganism species in industrial samples were determined by Real Time PCR. In addition, Most Probable Number assays (MPN) were performed for iron and sulfur oxidizing microorganisms. Kinetics incubation tests of PLS in the presence of iron or sulfur were performed to study the iron and sulfur oxidation, in total, 102 oxidation profile tests were obtained. Based on the oxidation profiles obtained, the tests were divided into four groups, labeled as fast, normal, stepped shape, and incomplete. The grouping system was established by considering oxidation time and rates, during the initial oxidation stages and accounted for any lag phase. A data mining technique, called decision trees was used to analyze the data and to generate rules that represented patterns in the data. Strong correlations were found between the predominant microorganisms and the behavior of the oxidation tests. Preliminary results indicate that the magnitude order of MPN of the iron oxidizing microorganisms is an important factor in the microbial oxidizing activity, followed by the predominant specie within the microbial population, PLS temperature and Eh.

Comparative Genomics Begins to Unravel the Ecophysiology of Bioleaching

The metabolic potential of 16 bioleaching microorganisms (Eubacteria and Archaea) has been investigated, allowing the prediction of potential inter- and intra-species physiological interactions (ecophysiology) during spatial and temporal changes that are known to occur within industrial bioleaching heaps. Genome analysis has allowed preliminary models to be built for genes and pathways involved in key processes such as nitrogen and carbon cycling, sulfur and iron uptake and homeostasis, extra-cellular polysaccharide biosynthesis, heavy metal resistance and energy metabolism. This paper will focus on the diverse ways that microorganisms obtain carbon from their environment with a particular emphasis on elucidating how these processes might be expected to vary over space and time during the lifetime of a bioleaching operation. It is anticipated that this knowledge will improve our understanding of fundamental biological processes in extremely acidic environments and it is hoped that it will capture usable knowledge that can be applied to bioleaching. Comparative genomics between two strains of Acidthiobacillus ferrooxidans highlights the importance of lateral gene transfer in increasing genetic and metabolic potential and suggests that classical molecular DNA techniques, such as rDNA typing, significantly underestimate the microbial diversity of bioleaching heaps.

Leaching of Ni and Cu from Mine Wastes (Tailings and Slags) Using Acid Solutions and <i>A. Ferrooxidans</i>

The objective of this work is to evaluate the acidic and biological leaching of tailings containing Ni/Cu from a flotation and smelting plant. Acidithiobacillus ferrooxidans, strain LR, was used for bioleaching at pH 1.8 and chemical controls were run parallel to that. The acidic leaching was done within 48 hours at pH 0.5 and 1.0. In the slag inoculated flasks the redox potential was high (600 mV), thus indicating oxidative bacterial activity, however, the obtained results after 15 days showed only around 13% Ni and 8% Cu extractions, which were not different to those of the controls. For the flotation tailings bioleaching extractions were approximately 45% for Ni and 16% for Cu while differing figures were obtained for the chemical controls. These were 30% and 12% respectively. Here we could observe that the presence of bacterial activity led to a higher solubility of Ni. Acid leaching of slag showed higher nickel and copper extractions: 56% and 24% respectively at pH 0.5 and 21% and 11% at pH 1.0. However, the acid consumption was 320 and 150 Kg/ton of slag, respectively, both much higher than in bacterial assays. These results indicated that Ni and Cu solubilization from the slag is acid dependent no matter the redox potential or ferric iron concentration of the leaching solution. For flotation tailings, acid treatment showed extractions of 23% for Ni and 16% for copper at pH 0.5 and 22% and 28%, respectively at pH 1.0. The acid consumption was also higher: 220 and 120 Kg/ton, at pH 0.5 and 1.0, respectively. Based on own findings we could observe that acid leaching is found to be more effective for slag, though the acid consumption is much higher, while for the flotation tailings, bacterial leaching seems to be the best alternative.

Traditional and novel geochemical extractions applied to a Cu–Zn soil anomaly: a quantitative comparison of exploration accuracy and precision

ABSTRACT Partial extractions have been employed and promoted as geochemical exploration tools, but assessment of performance is infrequently undertaken. Minimum probability statistics were used to quantitatively compare twelve extractions and document the level of exploration precision and accuracy. These methods were valuable in comparing the different digestion methods, identifying the best performance level and determining an appropriate geochemical threshold for future exploration. Eight ‘conventional’ reagents were tested, namely ‘four-acid’, aqua regia, bacterial leach (LocatOre ® ), Genalysis ® proprietary leach (TL3), cold hydroxylamine hydrochloride, Mehlich I reagent, hydrogen peroxide, deionized water, together with four new digestible digests (Coke ® , Pepsi ® , Diet Coke ® and a Tempranillo red wine). These tests involved analysis of thirty ® leach and the hydroxylamine hydrochloride leach performed the best in terms of both accuracy and precision. The new extractions were particularly effective for Cu, whereas the hydroxylamine hydrochloride leach was best for Zn. The Coke ® , Pepsi ® and Diet Coke ® extractions exhibited some buffering effects. In contrast, the Tempranillo wine is exceptionally well buffered and the most robust of the new digestions. Results indicate that even over marginally anomalous soils, many partial extraction techniques will confidently identify the location of mineralization. The use of expensive and proprietary procedures may not produce any better result than using standard reagents or even common beverage solutions as soil extraction reagents.

An Experimental Approach for Studying Chalcopyrite Leaching and Passivation in Column Bioleaching

The effect of different microbial consortia on the leaching of chalcopyrite was studied at different temperatures and solution compositions with Boliden’s Aitik ore in column reactors simulating heap bioleaching. The columns were equipped with sampling chambers and chalcopyrite mineral electrodes in order to investigate the passivation of chalcopyrite. The sampling chambers were filled with agglomerated ore and pieces of chalcopyrite-rich ore. In addition to chemical analysis of the leaching solution and solids the progress of leaching of chalcopyrite was studied by continuous potential measurements with chalcopyrite electrodes. The occurrence and composition of potentially passivating layers on the surfaces of the electrodes and the samples taken from sample chambers were examined by optical and scanning electron microscopy.

Impacts of Mineralogy on the Chemistry and Microbiology of Heap Bioleaching

The microbial microenvironment in heaps is strongly influenced by ore mineralogy. While laboratory studies on microbial activity under controlled conditions provide a good understanding how bioleaching organisms might assist in metal extraction, examination of the ore, its mineralogy and leaching chemistry offer additional valuable insights. Some examples are discussed and illustrated with data for a copper-nickel sulfide ore.

Differential Gene Expression of Industrial Bioleaching Transcriptomes by <i>Leptospirillum Ferrooxidans</i> DNA Microarray

Heap bioleaching is presently the most successful technology for copper extraction from low-grade sulfide ores. Metabolic behaviors and adaptation mechanisms of microbial communities to this system remain unknown. A combination of molecular approaches has been used to determine the key microorganisms in the Escondida Sulphide Heap. This work reports the global gene expression in industrial bioleaching samples by using a specific DNA microarray of Leptospirillum ferrooxidans to better understand the metabolic functions displayed by Leptospirillum spp. iron oxidizers as mineral leaching proceeds. Quantitative real-time PCR analysis showed low cell numbers of Leptospirillum species during the first part of the irrigation period, however, it became the most abundant and active in the second part of the cycle. Transcriptome analysis by DNA microarray could provide specifics transcription patterns in the different stages of the industrial process. We studied the gene expression from bioleaching heap samples with variable Leptospirillum cell numbers, operation times and with different chemical and physical conditions. The results showed induction of genes involved in energetic metabolism, electron transport, ribosomal proteins, DNA repair and response to heavy metals when Leptospirillum species were most abundant and active. We suggest that up- and down-regulation of specifics genes could be used as indicators of physiological responses to operational conditions in the bioleaching systems.

Adhesion of <i>Acidithiobacillus Caldus</i> and <i>Leptospirillum Ferriphilum</i> on Pyrite and their Effect on Surface Properties of Sulfide Minerals

Acidithiobacillus caldus and Leptospirillum ferriphilum cells grown in different energy substances (ferrous ion, sulfur and pyrite) were used. The adhesion of A. caldus and L. ferriphilum cells on pyrite and their effect on pyrite surface properties were studied by adsorption, zeta-potential and FT-IR methods, and the corrosion images of pyrite interaction with bacteria were examined using atomic force microscopy. Research showed that pyrite isoelectric point (IEP) after interaction with bacterial cells shifted towards cells isoelectric point, and the shift degree in case of interaction with A. caldus was observed to be much more pronounced than for interaction with L. ferriphilum, which can be due to higher affinity of A. caldus towards pyrite. The FT-IR spectra of pyrite treated with bacterial cells revealed the presence of the cell functional groups signifying cells adsorption. Although the adsorption density of A. caldus on pyrite was higher than that of L. ferriphilum, L. ferriphilum with strong ability to oxidize ferrous ion showed better leaching efficiency than A. caldus with strong ability to oxidize sulfur for pyrite leaching. The results demonstrated that more important of indirect action (L. ferriphilum) than direct action (A. caldus) on pyrite.Introduction Bacterial adsorption to minerals is an initial step in bacterial leaching for metal recovery [1]. It has been reported that bacterial adhesion is dependent not only on the biochemical properties of the organism but also on the interfacial properties of the various interfaces existing in a bioleaching system[2].The bacteria-mineral interactions result in the changes of their surface properties. The elucidation of their alternate will be beneficial for bioleaching processes. Both Acidithiobacillus caldus and Leptospirillum ferriphilum are known for their ability to inhabit acidic environments and derive energy from oxidation of inorganic substances with natural occurrence in ore deposits and acid mine drainage and high affinity towards sulfide minerals [3-5]. In this work, the alterations of surface properties of pyrite after interaction with L. ferriphilum and A. caldus are studied, and the changes in surface properties caused by bacterial adsorption are discussed with reference to bioleaching behavior of pyrite.

The Microbial Assisted Leaching of Nickel Laterites Using a Mixed Culture of Chemolithotrophic Microorganisms

Nickel laterite contains metal values but is not capable of participating in the primary chemolithotrophic bacterial oxidation because it contains neither Fe2+ iron nor substantial amount of reduced sulphur. Its metal value can, however, be recovered by allowing the primary oxidation of FeS2, or similar iron/sulphur minerals to provide H2SO4 acid solutions, which solubilise the metal content. This study investigated the possibility of treating nickel laterites using chemolithotrophic microorganisms. Preliminary studies conducted using H2SO4 acid, citric acid and acidified Fe2(SO4)3 gave an insight on the use of chemolithotrophic bacteria in this process,. Results showed that H2SO4 acid performed better, in terms of nickel recovery, than citric acid or acidified Fe2(SO4)3. In the bacterial leaching test works, mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus caldus and Leptospirillum ferrooxidans were used in the presence of elemental sulphur and FeS2 as energy sources. The sulphur substrate exhibited better effects in terms of bacterial growth, acidification and nickel recovery than the FeS2 substrate. Using response surface methodology, the theoretical optimum conditions for maximum nickel recovery (79.8%) within the conditions studied was an initial pH of 2.0, 63μm particle size and 2.6% pulp density.

Heap bioleaching of a complex sulfide ore: Part I: Effect of pH on metal extraction and microbial composition in pH controlled columns

The effect of pH on the bioleaching of a low-grade, black schist ore from Finland containing pyrrhotite, pyrite, pentlandite, chalcopyrite and other mineral sulfides was studied using columns containing 9.0 kg of agglomerated ore that was irrigated with nutrient supplemented surface water from the deposit at ambient temperature. Iron and sulfur-oxidizing enriched culture was used to inoculate the columns. Iron oxidation and metal leaching increased with decreasing pH. At pH 1.5, 59% Ni was bioleached after 140 days together with 59% Zn, 13% Cu and 16% Co. In comparison, at pH 3.0 only 15% Ni, 10% Zn, 5% Cu and 0.5% Co were leached; while at pH 2, 53% Ni was bioleached after 230 days. Based on an optimization between the leaching of metals, the acid consumption, the concentration of soluble iron and the dissolution of other gangue minerals, leaching at pH of 2.0 were recommended for this heap bioleaching application. The microbial composition as determined by a combination of Polymerase Chain Reaction (PCR)–Denaturing Gradient Gel Electrophoresis (DGGE)-sequencing approach was not significantly affected by pH. Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans were the dominant species in all the leach liquors. In addition, L. ferriphilum was detected for the first time in extracted leach residue liquor after 300 days of bioleaching. Sulfobacillus thermotolerans, A. caldus, A. thiooxidans and some unknown species were found to lesser extent. Archaeal species were also present in all leach liquors.

Heap bioleaching of a complex sulfide ore: Part II. Effect of temperature on base metal extraction and bacterial compositions

The effect of low to moderate temperatures (7 to 50 °C) on the bioleaching of a low-grade, multi-metal black schist ore from Finland in which pentlandite was the main valuable mineral, was studied using columns at set temperatures. The iron and sulfur-oxidizing microbial culture used were enriched from the ore deposit water samples. At 7 °C and 21 °C, the leach liquor redox potential stabilized to 500–600 mV, whereas at 35 °C and at 50 °C it varied between 300 and 500 mV. Microbial iron oxidation started after a lag phase of 20 days at 7 °C and after 60 days of operation, total iron and Fe tot/Fe 2+-ratio were higher in the 7 °C column leach liquor than at other temperatures. At 50 °C, all dissolved iron remained in ferrous form and did not indicate microbial activity. Highest bioleaching recoveries of Ni (26%), Zn (18%) and Co (6%) were obtained after 140 days at 21 °C. At 50 °C, bioleaching decreased due to the lack of ferric ion. The microbial composition, as measured by Polymerase Chain Reaction (PCR)–Denaturing Gradient Gel Electrophoresis (DGGE)-sequencing approach, was affected by temperature. Acidithiobacillus ferrooxidans was the most common species in the leach liquor at 7 °C; while at 35 °C Leptospirillum ferrooxidans dominated and at 50 °C, Sulfobacillus thermotolerans was the most common organism. Total liquid-phase cell counts were higher at 7 °C than at other temperatures. Thus the boreal ore deposit enrichment culture was composed of microorganisms capable of being active over a wide temperature range.

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

This work investigates the heap bioleaching of a low-grade nickel sulfide ore containing rather high levels of olivine, chlorite and antigorite (MgO 30–35%) present in the main gangue minerals. A 500-ton heap bioleaching system was developed and the microorganisms used in the test were a mixture of mesophiles, Acidithiobacillus ferrooxidans ( FJ164046; DQ321745), Acidithiobacillus thiooxidans ( EF059760) and Leptospirillum ferrooxidans (DSM2391). The inoculum used was obtained from a three-stage progressive scale-up (from 25 L to 500 L and finally to 10 m 3) culture. Industrial grade concentrated sulfuric acid and acid wastewater (pH 0.0–0.3) produced from off-gas treating during the smelting process were also used during bioleaching. A nickel (84.6%) and cobalt (75.0%) extraction was achieved after 350 days of heap leaching, including 80 days of acid pre-leaching and 270 days of bioleaching. The economical feasibility model predicted that the process was feasible.

Bioleaching of Complex Sulfides Concentrate and Correlation of Leaching Parameters Using Multivariate Data Analysis Technique

Bacterial leaching was applied to recover metal values from complex sulfide concentrates. The leaching kinetics were observed to depend on various leaching parameters, including Fe(II) concentration, pH and pulp density. The rate of leaching decreased with increase of iron precipitation rate. The leaching results indicated good bacterial activity. A Principle Component Analysis showed all the variables can be classified into four groups which account for more than 79.7% of the variance. The four groups were described as factors like leaching kinetics, bacterial activity, leaching parameters and bacterial metabolites. [doi:10.2320/matertrans.M2009125]

Biological leaching of nickel and cobalt from lateritic nickel ore of Sukinda mines

In the present study lateritic nickel ore was used for bacterial leaching using a mixed consortium of mesophilic acidophiles. The microorganisms were adapted to 1 gram nickel/L prior to leaching. For the experiments, lateritic ore in different forms such as raw, roasted, roasted ore presoaked in dilute sulphuric acid and palletized pretreated roasted (400 °C and 600 °C) ore were taken. The leaching experiments were conducted in 9 K+ with 40 L capacity bioreactor using 10% (v/v) inoculum concentration at 10% (w/v) pulp density. The aeration was maintained at 2–3 L/min and the speed of agitator and temperature at 400–500 rpm and 35 °C. The maximum extraction of nickel and cobalt was observed with pretreated ore (600 °C) at 10% pulp density (77.23% and 73.22%) respectively within 31 days at pH 1.5 and least extraction in case of raw ore i.e., 9.47% nickel and 41.12% cobalt respectively.

Large-scale experiments for copper extraction by bacterial heap leaching of the chalcopyrite predominant ore of Rosia Poieni.

The paper presents the principal aspects of the researches, from lab work to large-scale experiments, achievements for the elaboration of the technology for the recovery of copper from low-grade ores extracted in the quarry, from the copper deposit of Rosia Poieni, using bacterial leaching procedures. On the basis of the research, „The technology for the recovery of copper from low-grade with predominant content of primary sulphides, through bacterial leaching processes recovery extraction with the organic extractant Acorga M 5640” has been homologated.

Silicate mineral dissolution in the presence of acidophilic microorganisms: Implications for heap bioleaching

Silicate minerals are found with sulfide minerals and therefore, can be present during heap bioleaching for metal extraction. The weathering of silicate minerals by chemical and biological means is variable depending on the conditions and microorganisms tested. In low pH metal rich environments their dissolution can influence the solution chemistry by increasing pH, releasing toxic trace elements, and thickening of the leach liquor. The amenity of five silicate minerals to chemical and biological dissolution was tested in the presence of either ‘ Ferroplasma acidarmanus’ Fer1 or Acidithiobacillus ferrooxidans with olivine and hornblende being the most and least amenable, respectively. A number of the silicates caused the pH of the leach liquor to increase including augite, biotite, hornblende, and olivine. For the silicate mineral olivine, the factors affecting magnesium dissolution included addition of microorganisms and Fe 2+. XRD analysis identified secondary minerals in several of the experiments including jarosite from augite and hornblende when the medium contained Fe 2+. Despite acidophiles preferentially attaching to sulfide minerals, the increase in iron coupled with very low Fe 2+ concentrations present at the end of leaching during dissolution of biotite, olivine, hornblende, and microcline suggested that these minerals supported growth. Weathering of the tested silicates would affect heap bioleaching by increasing the pH with olivine, fluoride release from biotite, and production of jarosite during augite and hornblende dissolution that may have caused passivation. These data have increased knowledge of silicate weathering under bioleaching conditions and provided insights into the effects on solution chemistry during heap bioleaching.

Bioleaching of anilite by Acidithiobacillus ferrooxidans

In order to characterize the efficiency of copper bioleaching from anilite using pure cultures of Acidithiobacillus ferrooxidans in the absence and presence of ferrous sulphate, the experiments were carried out in shake flasks with or without 4 g/L ferrous sulphate (FeSO 4·7H 2O) at pH 2.0, 150 r/min and 35°C. The tests show that Acidithiobacillus ferrooxidans is unable to attack anilite in iron-free 9K medium. Anilite is rapidly oxidized by bacterial leaching when ferrous sulphate is added. Chemical oxidation of anilite is slow compared with Acidithiobacillus ferrooxidans initiated solubilization in the presence of iron. The EDAX analysis of the surfaces of anilite confirms that sulfur coating layer is present as a reaction product on the surface of the bacterially leached mineral.

Bacterial leaching of chalcopyrite and bornite with native bioleaching microorganism

A native mesophilic iron-oxidizing bacterium, Acidithiobacillus ferrooxidans, has been isolated (30°C) from a typical, lead-zinc concentrate of Dachang Mine in the region of Liuzhou located in the southwest of China. Two typical copper sulfide minerals, chalcopyrite and bornite, were from Meizhou Copper Mine in the region of Guangdong Province, China. Variation of pH and cell growth on time and effects of some factors such as temperature, inoculation cell number, and pulp density on the bioleaching of chalcopyrite and bornite were investigated. The results obtained from the bioleaching experiments indicate that the efficiency of copper extraction depends on all of the mentioned variables, especially the pulp density has more effect than the other factors on the microorganism. In addition, the results show that the maximum copper recovery was achieved using a mesophilic culture. The copper dissolution reached 51.34% for the chalcopyrite while it was 72.35% for the bornite at pH 2.0, initial Fe(II) concentration 9 g/L and pulp density 5%, after 30 d.

The oxidative dissolution of arsenopyrite (FeAsS) and enargite (Cu 3AsS 4) by Leptospirillum ferrooxidans

Arsenopyrite (FeAsS) and enargite (Cu 3AsS 4) fractured in a nitrogen atmosphere were characterised after acidic (pH 1.8), oxidative dissolution in both the presence and absence of the acidophilic microorganism Leptospirillum ferrooxidans. Dissolution was monitored through analysis of the coexisting aqueous solution using inductively coupled plasma atomic emission spectroscopy and coupled ion chromatography–inductively coupled plasma mass spectrometry, and chemical changes at the mineral surface observed using X-ray photoelectron spectroscopy and environmental scanning electron microscopy (ESEM). Biologically mediated oxidation of arsenopyrite and enargite (2.5 g in 25 ml) was seen to proceed to a greater extent than abiotic oxidation, although arsenopyrite oxidation was significantly greater than enargite oxidation. These dissolution reactions were associated with the release of ∼917 and ∼180 ppm of arsenic into solution. The formation of Fe(III)-oxyhydroxides, ferric sulphate and arsenate was observed for arsenopyrite, thiosulphate and an unknown arsenic oxide for enargite. ESEM revealed an extensive coating of an extracellular polymeric substance associated with the L. ferrooxidans cells on the arsenopyrite surface and bacterial leach pits suggest a direct biological oxidation mechanism, although a combination of indirect and direct bioleaching cannot be ruled out. Although the relative oxidation rates of enargite were greater in the presence of L. ferrooxidans, cells were not in contact with the surface suggesting an indirect biological oxidation mechanism. Cells of L. ferrooxidans appear able to withstand several hundreds of ppm of As(III) and As(V).

Bioleaching of Zinc and Iron from Steel Plant Waste using Acidithiobacillus Ferrooxidans

The bacterial leaching of zinc and iron from solid wastes at the Isdemir iron and steel plant has been investigated using Acidithiobacillus ferrooxidans as the bacterial agent. The effects of a range of operational parameters, including particle size, solids concentration and pH, on the efficiency of the bioleaching process were investigated. In each test, several variables were determined to assess the efficiency of leaching, including slurry pH and redox potential, temperature, bacteria population and concentrations of zinc and iron in solution. Experimental results demonstrated that pulp solids concentration, slurry pH and solids particle size were all important parameters in the bacterial leaching process. Maximum extraction was achieved at pH values around 1.3 and a solids concentration of 1% w/v, with 35% of the Zn content and 37% of the Fe being dissolved.