Biological Oxidation Of Ferrous Iron Research Articles

Synthesis and properties of ternary (K, NH4, H3O)-jarosites precipitated from Acidithiobacillus ferrooxidans cultures in simulated bioleaching solutions

The purpose of this study was to synthesize a series of solid solution jarosites by biological oxidation of ferrous iron at pH2.2–4.4 and ambient temperature in media containing mixtures of K+ (0, 1, 4, 6, 12, 31mM) and NH4+ (6.1, 80, 160, 320mM). The starting material was a liquid medium for Acidithiobacillus ferrooxidans comprised of 120mM FeSO4 solution and mineral salts at pH2.2. Following inoculation with A. ferrooxidans, the cultures were incubated in shake flasks at 22°C. As bacteria oxidized ferrous iron, ferric iron hydrolyzed and precipitated as jarosite-group minerals (AFe3(SO4)2(OH)6) and/or schwertmannite (idealized formula Fe8O8(OH)6(SO4)·nH2O). The precipitates were characterized by X-ray diffraction (XRD), elemental analysis, and Munsell color. Schwertmannite was the dominant mineral product at low combinations of K+ (≤4mM) and NH4+ (≤80mM) in the media. At higher single or combined concentrations, yellowish jarosite phases were produced, and Munsell hue provided a sensitive means of detecting minor schwertmannite in the oxidation products. Although the hydrated ionic radii of K+ and NH4+ are similar, K+ greatly facilitated the formation of a jarosite phase compared to NH4+. Unit cell and cell volume calculations from refinements of the powder XRD patterns indicated that the jarosite phases produced were mostly ternary (K, NH4, H3O)-solid solutions that were also deficient in structural Fe, especially at low NH4 contents. Thus, ferric iron precipitation from the simulated bioleaching systems yielded solid solutions of jarosite with chemical compositions that were dependent on the relative concentrations of K+ and NH4+ in the synthesis media. No phase separations involving discrete, end-member K-jarosite or NH4-jarosite were detected in the un-aged precipitates.

Recovery of Metals and Stabilization of Arsenic from (Bio-)Leaching Operations by Engineered Biological Processes

This paper focuses on the application of biotechnological stabilization of arsenic from (bio-) leaching operations. One of the latest applications of the Thioteq technology is arsenic immobilization. The Thioteq-scorodite biorecovery reactor is an aerobic system to immobilise arsenic in bio-scorodite crystals. In this patented process, biological arsenite oxidation, biological ferrous iron oxidation and crystallisation reactions are simultaneously taking place. Bio-scorodite crystals can be easily harvested by sedimentation due to their relative large size of up to 160 μm. This biogenic material is classified as non-hazardous due to its very low arsenic leaching rates. Furthermore, bioscorodite crystals resemble the colour, crystal morphology, iron and arsenic content, structural water of the mineral scorodite. The operational costs related to scorodite bio-crystallization can be reduced at least 50% compared to chemical precipitation because the use of biological reactions to induce the crystallization of scorodite and the good stability properties of the produced crystals. The Thioteq-scorodite process is a reliable cost effective solution to arsenic removal and immobilization by using biological processes. The stabilization of arsenic in the form of biologically produced scorodite is an attractive technology for the compact and safe immobilization of arsenic from medium to high concentrations of arsenic in acidic process streams.

Bioscorodite Crystallization in an Airlift Reactor for Arsenic Removal

Bioscorodite (FeAsO4·2H2O) crystals were crystallized in an airlift reactor fed at pH 1.2 and 72 °C. Arsenic removal was limited by the biological ferrous iron oxidation. In continuous operation, the iron oxidation initially was 30% and increased to 80% in few days when the iron and dissolved oxygen concentration were increased. The bioscorodite yield was 3 g/g of arsenic removed. The first precipitates were identified as scorodite having a dipyramidal octahedron habit with an Fe/As molar ratio of 1.55. The stability test (TCLP) classified the crystals as suitable for storage with a leached arsenic concentration of 0.5 mg L–1 after 60 days. Settling rates of bioscorodite crystals between 50 and 140 m h–1 were measured. Size distribution frequency indicates that bioscorodite crystals grew from an average size of 30 μm during batch operation to 160 μm at the end of the continuous operation phase. The morphology and size of the crystals guarantee their free-flowing nature, avoiding scaling. The biggest and most stable crystals can be harvested by sedimentation, to select the material best suited for final disposal.

Kinetics of ferrous iron oxidation by Sulfobacillus thermosulfidooxidans

The biological oxidation of ferrous iron is an important sub-process in the bioleaching of metal sulfides and other bioprocesses such as the removal of H 2S from gases, the desulfurization of coal and the treatment of acid mine drainage (AMD). As a consequence, many Fe(II) oxidation kinetics studies have mostly been carried out with mesophilic microorganisms, but only a few with moderately thermophilic microorganisms. In this work, the ferrous iron oxidation kinetics in the presence of Sulfobacillus thermosulfidooxidans (DSMZ 9293) was studied. The experiments were carried out in batch mode (2L STR) and the effect of the initial ferrous iron concentration (2–20 g L −1) on both the substrate consumption and bacterial growth rate was assessed. The Monod equation was applied to describe the growth kinetics of this microorganism and values of μ max and K s of 0.242 h −1 and 0.396 g L −1, respectively, were achieved. Due to the higher temperature oxidation, potential benefits on leaching kinetics are forecasted.

Biooxidation and precipitation for iron and sulfate removal from heap bioleaching effluent streams

Effluents from bioleaching processes cause severe problems if dispersed in the environment since they typically have very low pH values and high sulfate and ferric iron concentrations. Dissolved iron may also interfere with the metal recovery. In the bioleaching circuit, partial removal of dissolved iron and sulfate is needed to alleviate process disturbances. In this study, an integrated, bench-scale process comprising a fluidized-bed reactor (FBR) and a gravity settler was developed for controlled biological oxidation of ferrous iron and precipitative removal of ferric iron and sulfate for use in waste management of heap bioleaching processes. The FBR for iron oxidation by an enrichment culture dominated by Leptospirillum ferriphilum was operated at 37 ± 2 °C. The FBR recycle liquor was partially neutralized with 10 M KOH or 50 g/L CaCO 3 slurry to promote ferric iron and sulfate precipitation. With 6 ± 1.5 g Fe 2+/L in the feed and KOH-adjusted pH 3.5, the oxidation rate of Fe 2+ was 3.7 g/L h and 99% precipitation of ferric iron was achieved in the process. Adjustment with CaCO 3 to pH 3.2 slightly decreased the oxidation rate to 3.3 g/L h and 98% of ferric iron precipitated. With 15 g Fe 2+/L in the feed, the oxidation rate was 7.0 g Fe 2+/L h coupled with 96% precipitation of ferric iron. A solid solution of jarosite was the main product of ferric iron precipitation with KOH adjustment and with minor amounts of goethite at the higher pH range. Adjustment of the pH with CaCO 3 precipitated ferric iron also as a solid solution of jarosite, and sulfate precipitated also in the form of gypsum (CaSO 4·2H 2O) especially at the higher pH values.

Experimental Study of Ferrous Iron Biooxidation by <i>Leptospirillum Ferriphilum </i>in Different Biofilm Reactors

The process of biological oxidation of ferrous iron by the microorganism Leptospirillum ferriphilum was studied in different types of biofilm reactors. A total of 12 bioreactor types with both fixed and mobile support were used. The biofilm supports used had different shapes and were made of: polyethylene, nylon, polystyrene, polyvinylidene difluoride, polyester, ceramics, carbon and PVC. The pH of the microbial medium was maintained around 1.0, the temperature was 40°C while the influent ferrous iron concentration was 20 g/L. Iron oxidation rates of up to 4.5 g/L/h were obtained. The most efficient were the bioreactors with polyethylene and nylon woven fabric support. However, they oxidized ferrous iron at high rate for relatively short time periods - 40 to 60 days. While the bioreactor with a fixed bed of Raschig rings support had lower iron oxidation rate, their long-term stability was much higher. Of all the biofilm support materials tested, it was found that only polyvinylidene difluoride did not allow the formation of biofilm. Since no significant amounts of jarosite were formed at pH of 1.0 and below, the biofilm formed was very weak mechanically. For that reason the moving support, such as inverse fluidized bed, was not very appropriate because of the high shear stress.

Bacterial Diversity in a Mine Water Treatment Plant

We investigated the microbial community in a pilot plant for treatment of acid mine water by biological ferrous iron oxidation using clone library analysis and calculated statistical parameters for further characterization. The microbial community in the plant was conspicuously dominated by a group of Betaproteobacteria affiliated with "Ferribacter polymyxa".

Kinetic measurement of biological oxidation of ferrous iron at low ferric to ferrous ratios in a controlled potential batch reactor

Traditionally, the kinetics of microbial ferrous iron oxidation have been studied in continuous or in batch culture. Both methods have drawbacks: in continuous culture experiments have to be repeated at a number of dilution rates to cover the entire spectrum of ferrous to ferric ratios, which is time-consuming. Furthermore, experiments at very low ferric-to-ferrous ratios require high dilution rates which are close to or exceed those at which wash-out occurs. In batch experiments, on the other hand, the prevalent ferric to ferrous ratio rapidly changes due to substrate depletion while the microbial population continually grows, making determination of specific momentary rates difficult. The present paper describes initial work with a novel device, the Redostat™, which allows careful electrochemical control of ferric to ferrous ratio in a batch reactor. A culture of Leptospirillum ferriphilum was grown at 35 °C and 5 g dm − 3 total iron by maintaining the ferric to ferrous ratio at 0.17, 0.51 and 1.65 (corresponding to redox potentials of 419, 452 and 482 mV vs. Ag/AgCl), respectively. The correlation of data obtained from off-gas and current measurements was excellent, and fitted Monod kinetics with ferric inhibition. A hitherto unobserved effect indicates the onset of ferric iron inhibition at the low redox potentials employed here. It was also noted that the biomass concentration has an effect on the biomass specific ferrous iron consumption rate and the biomass yield on ferrous iron.

Experiments and CFD simulation of ferrous biooxidation in a bubble column bioreactor

In the present attempt a set of experiments and a 3D simulation using a commercially available computational fluid dynamics package (FLUENT) were adopted to investigate complex behavior involving hydrodynamics and ferrous biological oxidation in a gas–liquid bubble column reactor. By combining the hydrodynamics and chemical species transport equations, the velocity field, air volume fraction and ferrous biooxidation rate in the column were simulated. The kinetic model proposed by Nemati and Webb [Nemati, M., & Webb, C. (1997). A kinetic model for biological oxidation of ferrous iron by Thiobacillus ferrooxidans. Biotechnology and Bioengineering, 53, 478–486] was used to simulate the biooxidation rate in the column. Gas–liquid interactions were modeled using an Eulerian model in three dimensions. The effects of inlet air velocity and initial substrate (Fe 2+) concentration on the velocity field, air volume fraction and biooxidation rate of ferrous iron in the column were investigated. To validate the model, simulation was compared with the experimental data in the presence of Acidithiobacillus ferrooxidans in an aerated column where the superficial gas velocity was adjusted between 0 and 0.5 m/s. It was found that the initial ferrous concentration and the inlet air velocity had a pronounced effect on the ferrous biooxidation rate. The results indicated that the maximum biooxidation rate can be obtained at superficial air velocity of 0.1 m/s and initial ferrous concentration of 6.7 g/L.

Kinetic Measurement of Biological Oxidation of Ferrous Iron at Low Ferric to Ferrous Ratios in a Controlled Potential Batch Reactor

Traditionally, the kinetics of microbial ferrous iron oxidation have been studied in continuous culture or in batch. Both methods have drawbacks: in continuous culture experiments have to be repeated at a number of dilution rates to cover the entire spectrum of ferrous to ferric ratios, which is time-consuming. Furthermore, experiments at very low ferric to ferrous ratios generally fail due to microbial wash-out at the high dilution rates needed to achieve these. In batch experiments, on the other hand, the prevalent ferric to ferrous ratio rapidly changes due to substrate depletion while the microbial population continually grows, making determination of specific momentary rates difficult. The present paper describes initial work with a novel device, the Redostat™, which allows careful electrochemical control of ferric to ferrous ratio in a batch reactor. A culture of Leptospirillum ferriphilum was grown at 35°C and 5 g/L total iron by maintaining the ferric to ferrous ratio at 0.17, 0.51 and 1.65 (corresponding to redox potentials of 419, 452 and 482 mV vs. Ag/AgCl), respectively. The correlation of data obtained from off-gas and current measurements was excellent, and fitted Monod kinetics with ferric inhibition. A hitherto unobserved effect indicates the onset of ferric iron inhibition at the low redox potentials employed here.

Microbial Diversity in a Pilot Plant for Producing Iron Hydroxysulfates

The microbial community of a pilot plant for the production of iron hydroxysulfates by biological oxidation of ferrous iron was studied using molecular techniques. The 16S rRNA gene libraries were dominated by one sequence type, which can be classified phylogenetically to the class of Betaproteobacteria. These bacteria have no close cultivated relatives and were also proved as the dominating species in other mine waters. The microbial community was observed over a period of 18 months using TRFLP to investigate the influence of different process parameters on the composition of the microbial diversity. These studies verified the dominance of the Betaproteobacteria in the pilot plant.

Microbial Fuel Cell Operation with Continuous Biological Ferrous Iron Oxidation of the Catholyte

The oxygen reduction rate at the cathode is a limiting factor in microbial fuel cell (MFC) performance. In our previous study, we showed the performance of an MFC with ferric iron (Fe3+) reduction at the cathode. Instead of oxygen, ferric iron was reduced to ferrous iron (Fe2+) at the cathode with a bipolar membrane between the anode and cathode compartment. This resulted in a higher cathode potential than is usually obtained with oxygen on metal-based chemical catalysts in MFCs. In this study, we investigated the operation of the same MFC with ferric iron reduction at the cathode and simultaneous biological ferrous iron oxidation of the catholyte. We show that the immobilized microorganism Acidithiobacillus ferrooxidans is capable of oxidizing ferrous iron to ferric iron at a rate high enough to ensure an MFC power output of 1.2 W/m2 and a current of 4.4 A/m2. This power output was 38% higher than in our previous study at a similar current density without ferrous iron oxidation. The bipolar membrane is shown to split water into 65-76% of the needed protons and hydroxides. The other part of the protons was supplied as H2SO4 to the cathode compartment. The remaining charge was transported by K+ and HSO4-/SO4(2-) from the one compartment to the other. This resulted in increased salt concentrations in the cathode. The increased salt concentrations reduced the ohmic losses and enabled the improved MFC power output. Iron could be reversibly removed from the bipolar membrane by exchange with protons.

Mineral and iron oxidation at low temperatures by pure and mixed cultures of acidophilic microorganisms

An enrichment culture from a boreal sulfide mine environment containing a low-grade polymetallic ore was tested in column bioreactors for simulation of low temperature heap leaching. PCR-denaturing gradient gel electrophoresis and 16S rRNA gene sequencing revealed the enrichment culture contained an Acidithiobacillus ferrooxidans strain with high 16S rRNA gene similarity to the psychrotolerant strain SS3 and a mesophilic Leptospirillum ferrooxidans strain. As the mixed culture contained a strain that was within a clade with SS3, we used the SS3 pure culture to compare leaching rates with the At. ferrooxidans type strain in stirred tank reactors for mineral sulfide dissolution at various temperatures. The psychrotolerant strain SS3 catalyzed pyrite, pyrite/arsenopyrite, and chalcopyrite concentrate leaching. The rates were lower at 5 degrees C than at 30 degrees C, despite that all the available iron was in the oxidized form in the presence of At. ferrooxidans SS3. This suggests that although efficient At. ferrooxidans SS3 mediated biological oxidation of ferrous iron occurred, chemical oxidation of the sulfide minerals by ferric iron was rate limiting. In the column reactors, the leaching rates were much less affected by low temperatures than in the stirred tank reactors. A factor for the relatively high rates of mineral oxidation at 7 degrees C is that ferric iron remained in the soluble phase whereas, at 21 degrees C the ferric iron precipitated. Temperature gradient analysis of ferrous iron oxidation by this enrichment culture demonstrated two temperature optima for ferrous iron oxidation and that the mixed culture was capable of ferrous iron oxidation at 5 degrees C.

Continuous biological ferrous iron oxidation in a submerged membrane bioreactor

Microbial oxidation of ferrous iron may be available alternative method of producing ferric iron, which is a reagent used for removal of H2S from biogas. In this study, a submerged membrane bioreactor (MBR) system was employed to oxidize ferrous iron to ferric iron. In the submerged MBR system, we could keep high concentration of iron-oxidizing bacteria and high oxidation rate of ferrous iron. There was membrane fouling caused by chemical precipitates such as K-jarosite and ferric phosphate. However, a strong acidity (pH 1.75) of solution and low ferrous iron concentration (below 3000 mg/I) significantly reduced the fouling of membrane module during the bioreactor operation. A fouled membrane module could be easily regenerated with a 1 M of sulfuric acid solution. In conclusion, the submerged MBR could be used for high-density culture of iron-oxidizing bacteria and for continuous ferrous iron oxidation. As far as our knowledge concerns, this is the first study on the application of a submerged MBR to high acidic conditions (below pH 2).

Comparison of different bioreactor systems for indirect H 2S removal using iron-oxidizing bacteria

Microbial oxidation of ferrous iron may be available alternative method of producing ferric sulphate, which is a reagent used for removal of H 2S from biogas. For practical use of this process, this study evaluated some of the most efficient bioreactor systems for continuous ferrous iron oxidation by iron-oxidizing bacteria. Performances of various bioreactor systems were compared based on the ferrous iron oxidation efficiency according to the stepwise increase of hydraulic loading rates and ease of operation. A submerged-membrane bioreactor and immobilized bioreactor systems were used to increase the cell concentration. In the immobilized bioreactor system, various support media such as a granular activated carbon, polyurethane foam and honeycomb-type ceramics were tested with respect to the cell immobilizing performance. To improve the stability of biofilm, airlift-type immobilized bioreactor system was also developed. In this study, both the membrane bioreactor system and the immobilized bioreactor system using polyurethane foam achieved very good performance of biological ferrous iron oxidation. However, in consideration of economical and operational aspects, the immobilized bioreactor using polyurethane foam is the most practical and efficient system for indirect H 2S removal using iron-oxidizing bacteria.

Biological oxidation of ferrous iron: study of bioreactor efficiency

AbstractThe bio‐oxidation of ferrous iron is a potential industrial process for the regeneration of ferric iron in the removal of H2S. In the first stage, H2S is selectively oxidized to elemental sulfur using ferric sulfate. The ferrous sulfate produced is oxidized to ferric sulfate using Thiobacillus ferrooxidans for recycle and reuse in the process. The aim of the work described here was to investigate continuous oxidation of ferrous iron by immobilized T ferrooxidans and the factors which can directly affect the oxidation rate in order to assess the feasibility of this technique on an industrial scale. An analysis of the evolution of bioreactor performance with time (125 days) was performed in order to assess the feasibility of this technique on an industrial scale. A good oxidation rate was obtained despite the transport problems encountered due to occlusion of the porous support. On the other hand, the toxic effects due to absorption in the ferric solution of one or more compounds from the gas digester were studied using a ferric iron solution from the absorption process. The results indicate the feasibility of the biological system for the regeneration of the ferric‐absorbing solution. Finally, a previous study for the design of an industrial bioreactor to regenerate ferric sulfate solutions, used to remove H2S from biogas in a wastewater‐treatment plant (Jerez de la Frontera, Spain), is introduced. Good biological oxidation performances have been obtained using a pilot plant bioreactor of 500 dm3. Copyright © 2003 Society of Chemical Industry

Mathematical model of the oxidation of ferrous iron by a biofilm of Thiobacillus ferrooxidans.

Microbial oxidation of ferrous iron may be a viable alternative method of producing ferric sulfate, which is a reagent used for removal of H(2)S from biogas. The paper introduces a kinetic study of the biological oxidation of ferrous iron by Thiobacillus ferrooxidans immobilized on biomass support particles (BSP) composed of polyurethane foam. On the basis of the data obtained, a mathematical model for the bioreactor was subsequently developed. In the model described here, the microorganisms adhere by reversible physical adsorption to the ferric precipitates that are formed on the BSP. The model can also be considered as an expression for the erosion of microorganisms immobilized due to the agitation of the medium by aeration.

Bacterial ferrous iron oxidation of acid mine drainage as pre-treatment for subsequent metal recovery

Mining activities at Falu copper mine in Sweden started around the year 1080 AD and continued until 1993. During all these centuries, the acid mine drainage has caused low pH values and high metal levels in the nearby Falu river and it's surroundings. This work is part of a plan to achieve a long-term solution to this environmental problem, where the aim is to treat the mine water overflow in such a way that a neutral pH and an essentially metal free aqueous effluent is obtained. The idea is to first oxidise the ferrous iron with bacteria, in order to be able to make a selective ferric iron precipitation at a pH of around 3. One possible process option is to use the precipitated ferric hydroxide for the production of red pigment. Thereafter, zinc will be recovered in such a way that it will be suitable for recycling. In this paper, only the initial stage of bacterial ferrous iron oxidation is discussed. The ferrous iron oxidation was initially studied in laboratory scale using batch cultures of mesophilic (35°C), moderate thermophilic (45°C) and extreme thermophilic (65°C) microorganisms. The ferrous iron oxidation kinetics was determined with two different concentrations of ferrous iron. The moderate thermophilic culture did not grow well on ferrous iron only. Since the mesophilic and extreme thermophilic microorganisms showed approximately the same oxidation kinetics, the mesophilic bacteria was selected for further studies in pilot scale, due to their lower operating temperature which reduces the heating cost. A pilot plant was erected at the mine site with three 500 l reactors in series with a treatment capacity of up to approximately 500 l h −1. The reactors were filled with plastic bodies in order to support the formation of a permanent biofilm to avoid bacterial washout. The pilot plant has been operating continuously for several months and the influence of flow rate, ferrous concentration, pH and temperature was investigated. The feasibility for a biological ferrous iron oxidation step was successfully demonstrated. With a ferrous concentration of 3.5 g l −1, 35°C, pH 1.8 and a flow rate of 330 l h −1 a ferrous iron oxidation rate of 750 mg l −1 h −1 was achieved. The results obtained will be used to calculate the capital and operating cost for a full scale plant, capable of treating 25 m 3 of acid mine drainage per hour. Before the final decision, regarding the ferrous iron oxidation step is made, alternative processes such as hydrogen peroxide and ozone oxidation will be evaluated.

Continuous ferrous iron biooxidation in flooded packed bed reactors

In this paper the biological ferrous iron oxidation in flooded packed bed reactors is studied. Bacterial oxidation of ferrous iron is a potential industrial process for the treatment of acid mine drainage and in the regeneration of ferric iron as a leaching agent in hydrometallurgical processes. The aim of this work is the development of a reactor capable of attaining the oxidation rates demanded by industrial processes, which are higher than those shown in the literature. The bioreactor consists of a polymethylmetacrylate column randomly packed with siliceous stone particles with inlets for fresh medium and air at the bottom from where they flood the reactor. The performance of ferrous iron biooxidation reactors is strongly improved by applying this bioreactor design.

Inhibition effect of ferric iron on the kinetics of ferrous iron

Ferric iron acted as a non-competitive inhibitor for the biological oxidation of ferrous iron and decreased the inhibitory effects of high concentrations of ferrous iron as well as the auto-inhibitive effect the bacterial cells. A previously developed kinetic model for this reaction was modified to incorporate the inhibition effects of ferric iron. © Rapid Science Ltd. 1998