Ferrous Iron Biooxidation Research Articles

Determination of saturated dissolved oxygen concentration in iron sulfate solutions containing iron oxidizing microorganisms

Iron sulfate solutions and the extremophile lifeforms that can live within them are industrially and environmentally important in many applications and require proper assessments of solution properties. Determination of saturated dissolved oxygen concentration is an important parameter for monitoring iron biooxidation processes. However, its determination is not so straight forward using commercially available dissolved oxygen meters. Such meters utilize internal calculation models based on the saline properties of seawater which can be easily overlooked. A method for determination of the saturated dissolved oxygen concentration in acidic iron sulfate solutions with the inclusion of other inorganic salts is proposed in this work using the biooxidation of ferrous iron as an indicator measured with redox potential and converted to oxygen concentration through bioreaction stoichiometry. The technique was tested on a BioGenerator system over the course of four days and proved satisfactory in establishing a value for the saturated dissolved oxygen concentration of the bioreactor broth. Study of the lifespan properties of the microorganisms in absence of ferrous iron substrate was briefly examined to determine the effective handling period of solutions for assessment.

Ferrous iron biooxidation in a flooded packed-bed bioreactor at extreme conditions of iron concentration and acidity

The utility of ferrous iron biooxidation is to regenerate Fe(III) at required rates and conditions in specific hydrometallurgical contexts, such as metal extraction from ores/concentrates and mining and electronic waste. In these applications, considerable kinetics improvements can be achieved by increasing [Fe(III)], but pH must be decreased to avoid precipitation of this oxidant. Information about continuous biooxidation operation is limited to [Fe] < 20 g/L and 2.3 > pH > 1, therefore, it is interesting to test wider ranges for these parameters.A 1L flooded packed-bed bioreactor (30 cm in height), inoculated with Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans, was operated 60 days in continuous mode without interruptions at [Fe] up to 57 g/L and pH up to 0.44.Total Fe(II) conversion was achieved when operating at [Fe] = 57 g/L and pH = 1.2. The maximum biooxidation rate reached was 3.5 g/L·h for [Fe] = 40 g/L and 1 h of hydraulic retention time. Biooxidation rate decreases by 32 % when pH decreases from 1.2 to 0.44. Nevertheless, the biofilm remained stable at this low pH and steady state was achieved. When comparing the relative decreases in biooxidation rate and oxygen solubility, the drop of efficiency can be explained by aeration limitations and salting out effect.

Inhibitory Effect of Solvent Extractants on Growth and Metabolism of Acidophiles

ABSTRACT Due to entrainment or dissolution, organic extractants can contaminate aqueous raffinate during the solvent extraction (SX) process. This study aims to evaluate the effect of conventional SX reagents on the bio-oxidation and metabolism of industrial bacteria. Evaluating the effect of LIX 984N, Chemorex CP 150, D2EHPA, and Acorga M5640 at three concentrations on mesophiles and moderate thermophiles revealed that all extractants reduced the bacterial efficiency at different extents. It was observed that organic phases at 0.02% v/v resulted in a decrement of ferrous iron bio-oxidation rate and a negligible decrease in the bacterial population. At high dosages like 2% v/v, bio-oxidation and bacterial reproduction were utterly disrupted. The oxime-based extractants had a more significant effect on bacteria due to their lower stability and production of toxic substances by hydrolysis. Organic phases more impacted moderate thermophiles at a higher temperature compared to mesophiles. The analysis of Kendall tau-b revealed a strong inter-correlation between the concentration of organic phase and bio-oxidation parameters such as pH, ORP, bacterial population, bio-oxidation rate, and iron precipitation.

A comparative study on psychrophilic and mesophilic biooxidation of ferrous iron by pure cultures of Acidithiobacillus ferrooxidans and Acidithiobacillus ferrivorans

Biological oxidation of ferrous sulfate by Acidithiobacillus ferrooxidans and Acidithiobacillus ferrivoransis an important process in the bioleaching of minerals and the treatment of acid mine drainage. The rate at which biooxidation reactions take place is directly related to the microorganisms’growth temperature. Decreasing the temperature of reaction causes both a decrease on the chemical reactions rates and a decrease on bacterial growth. In this study, the effects of pH and temperatures on oxidation of ferrous sulfate by a native At. ferrooxidans and At. ferrivorans strains were investigated. The biooxidation tests conducted in shake flasks at 28 °C and 8 °C and at initial pH 1.6 for 5 days. During the experiment, the mesophilic iron oxidizers were capable of growing on ferrous iron at concentrations of 4.5 g/L at low and optimum temperature. However, the rate of mesophilic biooxidation of ferrous iron was higher than that observed in the psychrophilic biooxidation. In conclusion, during the experiment the At. ferrivorans strain 535 showed high activity in oxidizing at low temperature than other strains. It means even at very low temperatures, microorganisms play an important role in the oxidation and leaching of sulphide ores.

Immobilization of Acidithiobacillus ferrooxidans-1333 on the Waste Ore Particles for the Continuous Oxidation of Ferrous Iron.

Background: The biooxidation of ferrous iron has a great potential for the regeneration of ferric iron, in operations such as bioleaching, bioremediation. Many natural inorganic materials were investigated for use as supports immobilizing Acidithiobacillus ferrooxidans. The waste chalcopyrite is another natural inorganic material of which particles are easy to prepare from the leached out ore heaps and the source is abundant.Objectives: The aim of this work is to investigate several characteristics of the particles of waste ore that determines possibility of use as supports for immobilization of Acidithiobacillus ferrooxidans in the packed-bed bioreactor.Materials and Methods: Acidithiobacillus ferrooxidans-1333 stored in Korean Centre for Culture Collection was used. The supports were prepared by sieving the particles of 5~30 mm in size out from the waste chalcopyrite ore heap. The cells were immobilized by the successive batch culture method and oxidation rate of the bioreactor was investigated in the continuous flow mode.Results: The cell density of Acidithiobacillus ferrooxidans-1333 immobilized on the particles of waste chalcopyrite was 2.71×108 cells g-1 and the highest oxidation rate of the packed-bed bioreactor was 3.65g.L-1.h-1. Oxidation rate of the bioreactor was less influenced by the concentration of ferrous and ferric iron in the input solution as well as by the aeration rate and dilution rate than other materials mentioned in other previous works.Conclusion: The waste chalcopyrite particle is efficient support material for immobilization of Acidithiobacillus ferrooxidans with comparable or superior characteristics to natural inorganic support materials reported before.

Iron as electron donor for denitrification: The efficiency, toxicity and mechanism.

For the treatment of low C/N wastewaters, methanol or acetate is usually dosed as electron donor for denitrification but such organics makes the process costly. To decrease the cost, iron which is the fourth most abundant element in lithosphere is suggested as the substitution of methanol and acetate. The peak volumetric removal rate (VRR) of nitrate nitrogen in the ferrous iron-dependent nitrate removal (FeNiR) reactor was 0.70±0.04kg-N/(m3·d), and the corresponding removal efficiency was 98%. Iron showed toxicity to cells by decreasing the live cell amount (dropped 56%) and the live cell activity (dropped 70%). The toxicity of iron was mainly expressed by the formation of iron encrustation. From microbial community data analysis, heterotrophs (Paracocccus, Thauera and Azoarcus) faded away while the facultative chemolithotrophs (Hyphomicrobium and Anaerolineaceae_uncultured) dominated in the reactor after replacing acetate with ferrous iron in the influent. Through scanning electron microscope (SEM) and transmission electron microscope (TEM), two iron oxidation sites in FeNiR cells were observed and accordingly two FeNiR mechanisms were proposed: 1) extracellular FeNiR in which ferrous iron was bio-oxidized extracellularly; and 2) intracellular FeNiR in which ferrous iron was chemically oxidized in periplasm. Bio-oxidation (extracellular FeNiR) and chemical oxidation (intracellular FeNiR) of ferrous iron coexisted in FeNiR reactor, but the former one predominated. Comparing with the control group without electron donor in the influent, FeNiR reactor showed 2 times higher and stable nitrate removal rate, suggesting iron could be used as electron donor for denitrification. However, further research works are still needed for the practical application of FeNiR in wastewater treatment.

Effect of hydraulic retention time and pH on oxidation of ferrous iron in simulated ferruginous acid mine drainage treatment with inoculation of iron-oxidizing bacteria

The effect of hydraulic retention time (HRT) and pH on the biooxidation of ferrous iron during simulated acid mine drainage (AMD) treatment was investigated. The simulated AMD was highly acidic (pH 2.5), rich in iron (about 1700 mg/L) and copper (about 200 mg/L), and contained high concentrations of sulfate (about 4700 mg/L). The biooxidation of ferrous iron was studied in a laboratory-scale upflow packed bed bioreactor (PBR). The HRT was shortened stepwise from 40 h to 20 h, 13 h, and 8 h under the acidic environment at a pH value of 2.2. Then, the influent pH value was changed from 2.2 to 1.2 at a constant suitable HRT. Physiochemical and microbial community structure analyses were performed on water samples and stuffing collected from the bioreactor under different conditions. The results indicate that the efficiency of ferrous iron oxidation gradually decreased with the decrease of HRT, and when the HRT exceeded 13 h, ferrous iron in AMD was almost completely oxidized. In addition, the best efficiency of ferrous iron oxidation was achieved at the influent pH value of 1.8. Microbial community structure analyses show that Leptospirillum is the predominant genus attached in the bioreactor, and low influent pH values are suitable for the growth of Leptospirillum.

Hemp Fibres as Novel Green Support Material for Immobilization of Acidithiobacillus ferrooxidans

The suitability of hemp fibres as green support material for immobilization of Acidithiobacillus ferrooxidans cells in ferrous iron bio-oxidation process was investigated. A series of experiments were carried out in shake flasks and bioreactor for both cell immobilization and iron bio-oxidation. In flask experiments, five successive batch colonization cycles resulted in 6-fold increase in ferrous iron bio-oxidation rate. Evaluation of immobilized cells activity through two approaches as wet and dry storage demonstrated the higher activity of wet stored bacteria than dry ones after a period of two months. The dry stored bacteria lost almost all their activities after eight weeks. Whereas, the activity of wet stored samples was 30% at the same time. In bioreactor experiments, use of a packed-bed bioreactor with hemp fibres, the maximum ferrous iron bio-oxidation rate of 2.46 kg m-3 h-1 was obtained at dilution rate of 3.97 h-1, and retention time of 0.25 h. Our experimental results could pave a new platform for the application of hemp fibre as an inexpensive and environmentally friendly support material in bacterial cell immobilization, especially in ferrous iron bio-oxidation process using acidophilic bacteria.

A novel approach coupling ferrous iron bio-oxidation and ferric iron chemo-reduction to promote biomineralization in simulated acidic mine drainage.

A novel Acidithiobacillus ferrooxidans-mediated approach coupling biological oxidation and chemical reduction for treating acid mine drainage (AMD) was investigated. The results showed that controlled addition of zero valent iron (ZVI) into the coupling system did not exhibit a significant adverse influence on the bacterial activity of Acidithiobacillus ferrooxidans but markedly increased the formation of secondary Fe-minerals. Nutrition did not affect the efficiency of coupling process, except for the bacteria density of A. ferrooxidans. 2 days cyclic treatment performed better than that of 4 and 8 days. After 14 cycles of the coupling process, 89.4% of total iron (2.23 g L−1) was transferred into Fe-minerals finally. In addition, the combined system was highly effective in removing sulfate (63%) from a simulated AMD that contained soluble Cu, Zn, Al, and Mn. Valuable iron-sulfate material e.g. schwertmannite was formed with little co-precipitation of other metals. Therefore, the integration of A. ferrooxidans into the reduction by ZVI may have considerable potential in the enhancement of biomineralization efficiency, which may further decrease soluble TFe and sulfate loads in AMD before lime neutralization.

Two-step biohydrometallurgical technology of copper-zinc concentrate processing as an opportunity to reduce negative impacts on the environment

Polymetallic concentrates obtained during ore beneficiation pose a significant problem for the mining and metallurgy industry due to an increase in load on subsequent comminution steps and a high loss of metals in slag during smelting. Storage of such slag can lead to pollution of groundwater due to weathering. Biohydrometallurgy is an option for the processing of sulfidic raw materials that has a low impact on the environment. Processing of sulfidic concentrates of copper-zinc ore via bioleaching techniques was studied in this paper. Three mixed microbial cultures of acidophilic microorganisms were enriched from industrial mining sites: two autotrophic mesophilic cultures containing Acidithiobacillus ferroxidans and Leptospirillum spp. (grown at 30 and 35 °C), and a mixotrophic moderate thermophilic culture containing Sulfobacillus thermotolerans, Leptospirillum ferriphilum, as well as the archaea Ferroplasma acidiphilum and Acidiplasma spp. (grown at 40 °C). The autotrophic microbial culture growing at 30 °C was used to generate an iron-containing biosolution for ferric leaching of a copper-zinc concentrate. Zinc and iron extracted into solution faster than copper during high-temperature (80 °C) ferric leaching of the concentrate due to galvanic interactions between minerals, redox conditions of the medium, and differences between mineral oxidation mechanisms. Weight loss of the leach residue was 34.0%, with relative copper content increased by 1.0%, zinc content decreased by 6.18%, and iron content decreased by 15.1%. Biooxidation of ferrous iron in the pregnant leach solution by three microbial cultures was also studied. The most effective culture was moderate thermophilic. The results of studies on the bioregeneration of leaching solutions are relevant to the development of a two-step biohydrometallurgical technology for processing of copper-zinc concentrate with a closed cycle of technological flows. The ferrous iron biooxidation rate by the moderate thermophilic culture reached 20 g L−1 day−1. The leach residue obtained can be considered a high-grade copper concentrate able to be processed via smelting. This bioleaching process would make it possible to reduce pollution of groundwater by some toxic metals stored in slags. An environmentally friendly technology flow sheet for copper-zinc sulfidic ore processing using two-step bioleaching treatment was proposed.

Effect of Organic Nutrients on the Activity of Archaea of the Ferroplasmaceae Family

The effect of different organic compounds (glucose, fructose, ribose, glycine, alanine, pyruvate, acetate, citrate, and yeast extract) as well as of the wastes of food production (molasses, stillage, sweet whey), on the growth of iron-oxidizing acidophilic microorganisms and biooxidation of ferrous iron was studied. Representatives of the microorganisms predominating in biohydrometallurgical processes—archaea of the family Ferroplasmaceae (A. aeolicum V1T, A. cupricumulans BH2T, Acidiplasma sp. MBA-1, Ferroplasma acidiphilum B-1) and bacteria of the genus Sulfobacillus (S. thermosulfidooxidans SH 10–1, S. thermotolerans Kr1T)—were the subjects of the study. All studied strains most actively grew and oxidized ferrous iron in the presence of yeast extract, which is probably due to the presence of a large number of different growth factors in its composition, while others substrates provided growth of microorganisms and ferrous iron oxidation.

Biological Oxidation and Removal of Iron in Copper-Containing Acidic Mine Drainage by Using Siliceous Stones as Carrier Materials

Acid mine drainage is detrimental to the environment, which is rich of a variety of heavy metals, and has a low pH value and high acidity. The purpose of this paper is to study the bio-oxidation of ferrous iron and the selective precipitation of ferric iron, to gain a long-term effective solution to the environmental problem. The maximum ferrous iron bio-oxidation rate (76.19mg/L·h) was obtained at a low pH value of 3.0 and culture temperature of 30°C. In addition, we found a relatively higher ferric iron removal rate (99.18%) and the lowest copper loss rate (4.59%) at a pH value of 3.2 and reaction temperature of 30°C and stirring time of 4h.

Sequential bioleaching of copper from brake pads residues using encapsulated bacteria

Bioleaching of copper from pure granular shots and from a “pre-consumer” secondary resource from automotive industry (Brake Pads Powder, “BPP”) was carried out in a comparative study with conventional planktonic and PVA-encapsulated micro-organisms using a mixed culture of iron oxidizing bacteria: A. ferrooxidans, L. ferrooxidans and L. ferriphilum. The global process is characterized as “sequential” since a preliminary acid leaching is performed for ferrous iron extraction from the BPP material before the copper bioleaching itself.Prior to bioleaching experiments, resistance to dissolved copper has been quantified at various concentrations to assess a potential protective effect of the biomass by the PVA-matrix. PVA-encapsulated bacteria showed a better resistance to dissolved copper with a linear progression in the ferrous iron oxidation kinetic up to 40gCu2+/L concentrations while planktonic cells presented a drastic decrease in this kinetic between 10 and 40gCu2+/l, resulting in a 2 to 3-fold kinetic increase for the encapsulated bacteria depending on the strain. Bioleaching of elemental granular copper in 9K medium (Fe2+: 10g/L) showed significant enhancement of copper leaching kinetic with encapsulated biomass (1.9·10−1gCu2+/Lh) in comparison with the planktonic mode (8.2·10−2gCu2+/Lh). These tests demonstrated thereby the role of ferrous iron bio-oxidation and acid consumption values close to the stoichiometric ratio. Finally, the bioleaching with encapsulated bacteria was applied to copper extraction from BPP and showed a 150% enhanced kinetic in comparison with equivalent planktonic system and a 300% increase vs abiotic mode with respective leaching rates of 4.43·10−2; 2.9·10−2 and 1.48·10−2gCu2+/Lh.Cell immobilization offers complementary benefits as continuous process and permanent bacteria acclimation. This technology presents an interesting alternative to conventional planktonic and “two-step” processes.

Solution pH and Jarosite Management during Ferrous Iron Biooxidation in a Novel Packed-Column Bioreactor

Jarosite formation is undesirable in bioleaching processes as it depletes the needed ferric reagent for the oxidation of most sulfide minerals. Although it creates kinetic barriers thereby retarding the leach rates of most minerals, jarosite serves as support for the attachment of bioleaching microbes, facilitating biooxidation rate. Microbial ferrous-oxidation by mesophilic microbe was studied in a recently reported novel packed-column bioreactor with a view to investigate the potential of using solution pH to manage jarosite accumulation in the bioreactor in addition to establishing a base case data for the bioreactor. Experiments were conducted in the bioreactor packed with glass balls (15mm diameter) at constant temperature of 38.6 °C, residence time of 18 hours, airflow rate of 20 mLs-1and pH values of 1.3, 1.5 and 1.7. The results showed that the amount of jarosite accumulation is proportional to the solution pH, and to the duration of operation of the bioreactor. Jarosite precipitation concentrations of 4.95, 5.89 and 7.08 gL-1were obtained after 10 days of continuous operation at solution pH values of 1.3, 1.5 and 1.7 respectively, while after 15 days the precipitations concentrations increased to 5.50, 7.90, 9.98 gL-1respectively. The results also showed that 33% and 52% precipitate reduction could be achieved by gradual decrease in the bioreactor solution pH to 1.5 and 1.3 after being continuously operated for 10 days at pH 1.7 respectively after an addition of 5 days. A maximum ferrous oxidation rate (), 6.85 mmol.L-1.h-1and the affinity kinetic constants (,), of 0.001 and 0.006 for Hansford and Monod models respectively. Although a directly relationship exist between jarosite formation and pH, the results of this study may be relevant in bioleach heaps or at least in column bioreactors to manage/control jarosite accumulation thereby improving the leach kinetics of mineral sulfides.

Bioprocess for Leaching of Copper Concentrate

A bioprocess for oxide-sulfide copper flotation concentrates has been proposed. It includes: i) chemical step – leaching with sulfuric acid solution and subsequent high temperature ferric leaching with microbially produced Fe3+-containing solution, and ii) biological step – bioregeneration of ferric iron along with additional biooxidation of the sulfide minerals using moderately thermophilic acidophilic microorganisms. The flotation copper concentrates contained 27.0–37.4% copper as sulfide (digenite, bornite, etc.) and oxide (malachite, azurite, tenorite, etc.) minerals. The acid leaching under batch conditions at 50°C and pH 1.2 during 22 hours led to 40.6% of copper recovery from the concentrate. Subsequent ferric leaching of the acid leach residue at 80°C, pulp density 9%, initial concentration of Fe3+ 30.7 g/L, and pH 1.2–1.3 during 7 hours increased the total copper recovery to 94.5%. Bioregeneration of the Fe3+ was conducted using moderately thermophilic microorganisms including bacteria of the genus Sulfobacillus at 40°C in the presence of 3% leach residue. The average ferrous iron biooxidation rate and total copper recovery within 2 days were 1.0 g/L∙h and 97%, respectively.Leaching of copper under semi-continuous conditions with bioregeneration of Fe3+ at 40°C was studied. It was found that copper recovery achieved 90% within 22 hours and the average oxidation rate of ferrous iron was up to 0.95 g/L·h.

A novel microwell-based analytical technique for studying ferrous iron biooxidation activity

The broad range of complexities in bioleaching includes the use of mixed microbial communities with diversity of species and strains with different windows of operating conditions. Empirical approaches to characterise these currently use cumbersome experimental systems; hence the need to develop a high throughput research tool, analogous to the techniques used in high throughput pharmaceutical research. In this study, a microwell research tool was evaluated as a growth and measurement tool for mixed autotrophic bioleaching cultures. The tool was assessed by comparing its performance to conventional shake flask apparatus. Mixed mesophilic cultures of predominantly Leptospirillum ferriphilum and Acidithiobacillus ferrooxidans were used. Growth and ferrous iron oxidation kinetics were quantified and assessed. Microwell plates performed similarly to conventional shake flasks with respect to growth and iron oxidation kinetics. The microwell plate apparatus was also used as a measurement system in combination with a microwell plate reader (measuring absorbance change at 428nm over time). Progressive colour change of growth experiments correlated to ferrous iron oxidation within a defined operating window. We conclude that, using this measurement as a proxy for trends iron oxidation, the microwell research tool is well-suited for high throughput scoping studies to map operating windows for different cultures, in both an unadapted and adapted context. This was confirmed through an activity test utilising fluoride as an inhibitor. Where absorbance measurements at 428nm are used to track oxidation progress, the research tool has limitations with respect to pH (<2.0) and total iron concentration (<8.0gl−1).

Investigation of ferrous-iron biooxidation kinetics by Leptospirillum ferriphilum in a novel packed-column bioreactor: Effects of temperature and jarosite accumulation

The kinetics of microbial ferrous-iron by Leptospirillum ferriphilum was studied at substrate loading rate of 3–90mmolL−1h−1 in a novel packed column bioreactor. The study was conducted with a view to providing an understanding of the reaction kinetics in a flow-through system which may be assumed to mimic bioheap solution flow, rather than the more typical batch reactors. The bioreactor was maintained at pH of 1.45±0.05 and constant air flow rate of 15mLs−1. The Boon and Hansford, and the Monod models accurately described the experimental data. The effect of temperature on the kinetic parameters was investigated at 25, 30 and 35°C. The maximum oxidation rate, rFe2+max=15.10mmolL−1h−1, was highest at 35°C. The activation energy, Ea=20.97kJmol−1, of ferrous-iron biooxidation in the novel bioreactor is indicative of a system that is limited by both biochemical and diffusion factors. The result also showed about 38.80% increase in the maximum microbial ferrous-iron oxidation,rFe2+max, due to accumulation of jarosite. However, the decreasing values of substrate affinity constant, KFe2+, and the apparent affinity constant, K′Fe2+ revealed that the microbial affinity for ferrous biooxidation increases with increase in jarosite formation. This study reveals that jarosite maybe beneficial to bioleach heaps if it is carefully managed.

Biotic factor does not limit operational pH in packed-bed bioreactor for ferrous iron biooxidation

Ferrous ion biooxidation is a process with many promising industrial applications: mainly regeneration of ferric ion as an oxidizing reagent in bioleaching processes and depuration of acid mine drainage. The flooded packed-bed bioreactor (FPB) is the design that leads to the highest biooxidation rate. In this bioreactor, biomass is immobilized in a biofilm that consists of an inorganic matrix, formed by precipitated ferric compounds, in the pores of which cells are attached. This biofilm covers the surface of particles (siliceous stone) that form the bed. The chemical stability of this inorganic matrix defines the widest possible pH range in FPBs. At pH below 1, ferric matrix is dissolved and cells are washed out. At pH higher than 2, ferric ion precipitates massively, greatly hindering mass transfer to cells. Thus, among other parameters, pH is recognised as a key factor for operational control in FPBs. This paper aims to explain the effect of pH on FPB operation, with an emphasis on microbial population behaviour. FPBs seeded with mixed inocula were assayed in the pH range from 2.3 to 0.8 and the microbial population was characterised. The microbial consortium in the bioreactor is modified by pH; at pH above 1.3 Acidithiobacillus ferrooxidans is the dominant microorganism, whereas at pH below 1.3 Leptospirillum ferrooxidans dominates. Inoculum can be adapted to acidity during continuous operation by progressively decreasing the pH of the inlet solution. Thus, in the pH range from 2.3 to 1, the biotic factor does not compromise the bioreactor performance.

Immobilization of Acidithiobacillus ferrooxidans on sulfonated microporous poly(styrene–divinylbenzene) copolymer with granulated activated carbon and its use in bio-oxidation of ferrous iron

The immobilization efficiencies of Acidithiobacillus ferrooxidans cells on different immobilization matrices were investigated for biooxidation of ferrous iron (Fe2+) to ferric iron (Fe3+). Six different matrices were used such as the polyurethane foam (PUF), granular activated carbon (GAC), raw poly(styrene–divinylbenzene) copolymer (rawSDVB), raw poly(styrene–divinylbenzene) copolymer with granular activated carbon (rawSDVB-GAC), sulfonated poly(styrene–divinylbenzene) copolymer (sulfSDVB) and sulfonated poly(styrene–divinylbenzene) copolymer with granular activated carbon (sulfSDVB-GAC). The sulfSDVB-GAC polymer showed the best performance for Fe2+ biooxidation. It was used at packed-bed bioreactor and the kinetic parameters were obtained. The highest Fe2+ biooxidation rate (R) was found to be 4.02g/Lh at the true dilution rate (Dt) of 2.47 1/h and hydraulic retention time (τ) of 0.4h. The sulfSDVB-GAC polymer was used for the first time as immobilization material for A. ferrooxidans for Fe2+ biooxidation.

The effects of fluoride and aluminum ions on ferrous-iron oxidation and copper sulfide bioleaching with Sulfobacillus thermosulfidooxidans

Microorganisms that grow at high temperatures can improve Fe(II) bio-oxidation and thereby its technological applications, such as bioleaching and H2S removal. Conversely, elements present in industrial growth media, such as fluoride, can inhibit bacterial growth and iron bio-oxidation. In this work, the influence of fluoride on the kinetics of ferrous-iron bio-oxidation with Sulfobacillus thermosulfidooxidans was investigated. The effects of fluoride concentrations (0–0.5mmolL−1) on both iron oxidation and bacterial growth rates were assessed. In addition, the effect of the addition of aluminum, which was intended to complex free fluoride and reduce the concentration of HF through the formation of aluminum–fluoride complexes, was also investigated. The results show that 0.5mmolL−1 NaF completely inhibited bacterial growth within 60h. Nevertheless, fluoride toxicity to S. thermosulfidooxidans was minimized by control of the aluminum–fluoride ratio in the system because, at a 2:1 aluminum–fluoride molar ratio, bacterial growth was similar to that observed in the absence of fluoride ions. Despite a slower bacterial growth rate, fluoride concentrations less than the inhibitory concentration increased the Fe(II) oxidation rate. Successful copper bioleaching (80–100%) from fluoride-containing sulfide ores (1% total fluoride) was demonstrated in the presence of aluminum.