Biooxidation Rate Research Articles

Ferrous iron oxidation efficiency and kinetics by indigenous iron-oxidizing bacteria in acid mine drainage

Biological Fe(II) oxidation by iron-oxidising bacteria (FeOBs) at low pH is a cost-effective treatment for acid mine drainage (AMD). However, treatments based on this process are limited because of uncertainties regarding the ability and rate of oxidation of Fe(II) from AMD. In the present study, an indigenous FeOBs consortium was enriched in AMD, and its ability to oxidise Fe(II) is described. The bio-oxidation rate of Fe(II) was 39.1 mg/(L·h) under optimal culture conditions [35 ℃, pH 2.0, 500 mg/L Fe(II)]. In addition, the oxidation rate equation of Fe(II) could be fitted to a zero-order kinetic model, indicating that Fe(II) was oxidised at a constant rate. Furthermore, a continuous-flow bioreactor was developed to simulate the Fe(II) oxidation efficiency of indigenous FeOBs for in situ AMD biological treatment. The maximum Fe(II) oxidation rate was 22.8 mg/(L·h) when the influent Fe(II) load was 32.3 mg/(L·h). Acidithiobacillus and Acidiphilium were the dominant species contributing to Fe(II) oxidation in the bioreactor, accounting for 67.7 % and 32.8 %, respectively. The results will help promote the application of FeOBs in AMD treatment.

Effects of Fe(II) bio-oxidation rate and alkali control on schwertmannite microstructure and adsorption of oxyanions: Characteristics, performance and mechanism

Schwertmannite has attracted increasing interest for its excellent sorption of oxyanions such as AsO43−, CrO42−, and Sb(OH)6−. Controlling biomineralization by adjusting the Fe(II) oxidation rate and implementing alkali control can enhance the yield and adsorption performance of schwertmannite. However, the adsorption improvement mechanism is still unclear. The morphology, crystallinity, specific surface area (SSA) and oxyanion adsorption of schwertmannite synthesized with alkali control of solution pH and different Fe(II) oxidation rates were analyzed in this study. The differences in the adsorption mechanisms of As(V), Cr(VI) and Sb(V) on schwertmannite obtained under different synthesis conditions were also studied. Reducing the Fe(II) oxidation rate or maintaining the solution pH through alkali control significantly increased the SSA of schwertmannite and the proportion of outer-sphere sulfate. Alkali-controlled schwertmannite (Sch-C) exhibited superior As(V) and Sb(V) adsorption performance and slightly greater Cr(VI) adsorption than non-alkali-controlled schwertmannite. The As(V) and Sb(V) adsorption capacities of Sch-C greatly improved because the ultra-high SSA increased the surface hydroxyl content and reduced the passivation effect of amorphous precipitates on the mineral surface, allowing continuous sulfate exchange at inner mineral sites. An increased surface hydroxyl content had little effect on Cr(VI) adsorption, but an increased proportion of outer-sphere sulfate caused a slight increase in Cr(VI) adsorption. Sb(V) has a stronger hydroxyl exchange ability than As(V), but due to its octahedral structure, it exchanges only with outer-sphere sulfate on schwertmannite and hardly exchanges with inner-sphere sulfate.

A high productivity bioprocess for obtaining metallic copper from printed circuit boards (PCBs)

PCBs constitute a residue rich in metals, among which copper stands out due to its majority content, much higher than that found in natural deposits, so that it is a potential secondary resource. Many attempts have been made to recover copper via biohydrometallurgy because it is an environmentally friendly route, however, one of its main drawbacks is the low productivity achieved.A global process based on circularity for obtaining copper cathodes from PCBs is proposed. First, PCBs from end-of-life mobile phones are shred to sizes between 800 and 2000 µm. Copper is leached from these pieces in a continuous stirred tank reactor (CSTR) at high ferric concentration, at a moderate temperature of 60 °C reaching dissolution rate higher than 1 g/L·h and a yield of 99 %. The solution that leaves the CSTR with concentrations of up to 10 g/L of Cu is passed through a high-performance bioreactor for the regeneration of Fe(III). A biooxidation rate of 1.3 g/L⋅h was achieved, and no inhibition was observed.Concurrently, copper is recovered in metallic state by solvent extraction and electrowinning with recirculation streams becoming a more profitable and sustainable complete global process.

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.

Effect of As(III) on kinetics of Fe2+ bio-oxidation

Fe2+ bio-oxidation influenced by toxic metal ions released from the dissolution of arsenic-bearing gold ores was investigated. Fe2+ bio-oxidation by moderately thermophilic microorganisms was studied under different initial concentrations of Fe2+ and As(III), and Monod equation was used to fit the Fe2+ bio-oxidation under different conditions. Results showed that the Fe2+ bio-oxidation rate increased as the initial Fe2+ concentration increased until it reached 12 g/L. As(III) severely inhibited Fe2+ bio-oxidation. When the As(III) concentration was 8 g/L, 9 g/L Fe2+ was more than 200 h. The Monod equation fitted the Fe2+ bio-oxidation well. In the absence of As(III), the maximum specific growth rate of the culture and the substrate affinity constant were 0.142 h-1 and 0.053 g/L, respectively. As(III) inhibited Fe2+ bio-oxidation via competitive inhibition, and the inhibition constant was 0.0035 g/L.

Green extraction of nickel and valuable metals from pyrrhotite samples with different crystallographic structures through acidophilic bioleaching.

Nowadays, due to the strategic status of nickel in the global market, utilizing its disregarded resources like low-grade nickel containing pyrrhotite is of significant importance. A comprehensive set of experiments and analyses were performed to determine the bioleaching capability and mechanism for nickel extraction from hexagonal and monoclinic pyrrhotite. Over 95% Ni extraction was achieved from the hexagonal pyrrhotite sample. Ni extraction from the monoclinic sample reached its maximum value of 67% and 90% at 3% pulp density, with mixed mesophilic and moderately thermophilic cultures, respectively. Characterization analyses indicated that jarosite and elemental sulfur formation in mixed mesophilic bioleaching reduced the samples' bio-oxidation rate and metal dissolution. The kinetics study revealed that the controlling step in thermophilic bioleaching is the chemical reaction; however, the mixed control model was best fitted on mesophilic data. Electrochemistry studies confirmed bioleaching results and indicated that monoclinic pyrrhotite's oxidation rate under the operating conditions is faster than hexagonal pyrrhotite, and the temperature positively correlates with the oxidation rate. Toxicity assessment analysis showed that the final residues of both bioleached samples could be considered environmentally safe.

Process dynamics in a hydrogen-based energy storage system

The BioGenerator is a technology that was recently invented and is used for the biological conversion of hydrogen to electricity. Its main application is in the re-electrification of hydrogen in hydrogen-based energy storage systems for the smoothing of the variability in wind and solar power generation. Therefore, BioGenerator operation is highly dynamic. The core of the BioGenerator is a bioreactor where principal microorganisms Leprospirillun ferriphilum oxidize Fe2+ to Fe3+. The dynamics of the process of energy storage affects the temporal characteristics of the bioreactor. The BioGenerator remains idle during the peaks of power generation of renewable power where Fe2+ remaining in the bioreactor is continuously consumed biologically. Likewise during the valleys in power generation Fe3+ is consumed electrochemically and Fe2+ accumulates. The effect of periodic interruption on the operation of the iron-oxidizing bioreactor was studied in this work. Our results show that idling of the BioGenerator for less than half a day has no negative effect on returning to the initial performance, while longer idling periods result in a small temporary reduction in bioreactor performance. Similar dynamics were observed in both stand-alone bioreactor as well as in a bioreactor incorporated in a complete BioGenerator system for hydrogen re-electrification. Additionally, operation of the closed loop BioGenerator system revealed hysteresis effects on the steady state bio-oxidation rate correctable with brief interruption of operation.

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.

Integration of cascaded aeration and neutralization for the treatment of acid mine drainage: Insights into the formation of jarosite

Acid mine drainage (AMD) treatment has become a major environmental issue confronting the global mining industry. For treating AMD economically and efficiently, a novel AMD passive treatment system consisting of cascaded aeration based biomineralization process driven by Acidithiobacillus ferrooxidans (A. ferrooxidans) LX5 followed by lime neutralization was developed. Compositions and structures of precipitates were measured through a scanning electron microscope equipped with an energy-dispersive X-ray spectrometry (SEM-EDS) and X-ray powder diffraction (XRD). Results showed that the biogenic Fe-minerals, with 1–1.5 μm diameter and 17.5 m2/g specific surface area, belonged to jarosite expressed as KFe3(SO4)2(OH)6 with Fe/S molar ratios between 1.61 and 1.68. The density and Fe2+ bio-oxidation rate of A. ferrooxidans LX5 immobilized on the surface of jarosite (namely immobilized cells) were approximately 8.3 × 108 cells/g and 7.3 mmol L−1 h−1, which were approximately 10 and 2.2 times higher than those of cultivating A. ferrooxidans LX5 solution used as the control (namely suspension cells). The constructed water-dropping system could supply sufficient oxygen for the Fe2+ bio-oxidation. The initial Fe2+ in the AMD was completely oxidized into Fe3+ and 41.8% of total Fe was removed during biomineralization. In addition, it was found that 34% of Zn2+, 21% of Cd2+, 42.7% of Cr3+, and 23.8% of Cu2+ were removed by co-precipitation or adsorption to jarosite simultaneously. With this novel treatment system, the amounts of lime addition required for AMD neutralization and toxic solid waste production were drastically decreased by about 70 wt% and 81.3 wt%, respectively, in comparison to the control (without biomineralization). These results show water-dropping aeration and A. ferrooxidans LX5 play a significant role in the Fe2+ bio-oxidation and removal of metal ions, and the integration of cascaded aeration and neutralization is a possibility for cost-effective treatment of highly acid and toxic metal-loaded AMD.

Effect of organic nutrients on bioleaching of low-grade copper concentrate at different temperatures

The goal of the present work was to study the effect of different organic nutrients (yeast extract and molasses) on the biooxidation of copper concentrate containing chalcopyrite, tennantite, sphalerite, and pyrite in batch experiments at different temperatures (of 40 to 55°C). For the experiments, representatives of microbial groups predominant in biohydrometallurgical processes, bacterium of the genus Sulfobacillus, Acidithiobacillus caldus, and archaea of the genus Acidiplasma, were used. It was shown that both temperature and addition of organic nutrients in the medium affected the activity of the bioleaching. In the same time, the effect of organic nutrients was significant only at high temperatures (50 and 55°C). In all experiments, biooxidation rate decreased at the highest temperature, 55°C. Since among the strains used in the study, only A. caldus MBC-1 is autotroph, which is able to provide the population with organic nutrients and is not active at 55°C, at this temperature it was not able to maintain activity of other strains. Therefore at 55°C, biooxidation activity strongly depended on the presence of organic nutrients. Despite temperature and presence of organic nutrient affected activity of concentrate biooxidation that was revealed by the differences in pH, Eh values and iron ions concentrations in the medium, copper, zinc and arsenic extraction rates depended on these factors to a lesser extent.

Biological and acid leaching of low-grade sulfide concentrate containing Cu and Ni at different temperatures

In this study, the bioleaching of low-grade nickel-copper concentrate was carried out using the nutrient medium containing yeast extract (YE) at temperature range of from 40 to 60°C in order to study the dependence of biooxidation rate and Cu and Ni extraction levels on the temperature and the presence of organic compounds. Mixed culture of the strains Sulfobacillus thermosulfidooxidans, Acidithiobacillus caldus, and Acidiplasma sp., moderately-thermophilic acidophiles, which oxidize sulfide minerals, was used in the experiments. Temperature and organic carbon source were shown to affect bioleaching. At 40−50°C, the influence of YE addition was insignificant. At 55 and 60°C bioleaching depended on YE presence. Nevertheless, microbial activity affected mainly iron leaching and allowed maintaining comparatively low pH of medium. Both Cu and Ni extraction rates almost was not affected by biooxidation activity. Thus, the leaching of the base metals form the concentrate was mainly determined by abiotic factors (acidity and temperature). Regardless of this fact, bioleaching may play a significant role for processing of similar sulfide concentrates, since to maintain favourable pH, abiotic acid leaching could require a large amounts of H2SO4, while biooxidation provides sulfuric acid generation.

Bio-oxidation of a high-sulfur refractory gold concentrate with a two-stage chemical-biological approach

A two-stage chemical-biological oxidation approach, which applied a high temperature chemical oxidation stage prior to the bio-oxidation stage, was employed to accelerate the bio-oxidation rate of Axi gold concentrate with pyrite as the main sulfide phase. The extraction levels of Fe and S were 67.0% and 72.9% in the traditional one-stage bio-oxidation approach, while the values were elevated respectively to 78.0% and 79.6% with the two-stage approach. Accordingly, the extraction rate of gold was increased from 83.6% to 90.3% when subjected to the two-stage approach. The intensification mechanism of the two-stage approach was carried out by using Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM- EDX), X-ray photoelectron spectroscopy (XPS) and particle size analysis. The results indicated that pyrite on the surface of the concentrate was partly oxidized and particle size of the concentrate diminished after the first stage (chemical oxidation), which would facilitate the subsequent bio-oxidation process.

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 rapid method to quantify the biomass of viable Acidithiobacillus ferrooxidans in iron-based bioleaching matrix of sewage sludge

Overlay plate counting is the traditional way to determine the biomass of viable Acidithiobacillus ferrooxidans in iron-based bioleaching matrix of sewage sludge. However, the time required is 12 days at a minimum. Here, a rapid method based on a quantitative relationship between the extant rate of iron bio-oxidation by Acidithiobacillus ferrooxidans and the CFU counts was developed. The method reduces the time to ∼3 h. In the new method, the biomass is calculated by dividing the extant iron bio-oxidation rate by the specific rate of iron oxidation by Acidithiobacillus ferrooxidans. The extant rate of iron bio-oxidation was determined in a 2-h iron oxidation test. The effects of environmental factors such as pH on iron oxidation in all tests were the same. The basal specific rate of iron oxidation by Acidithiobacillus ferrooxidans was 10−9 mg/h/CFU. During bioleaching, the specific rate increased by 10−10 mg/h/CFU when the net contact time between Acidithiobacillus ferrooxidans and available ferrous iron increased by one hour. Therefore, according to the law, the biomass can be rapidly determined by the extant rate and the net contact time.

EFFECT OF Acidithiobacillus thiooxidans-CYSTEINE INTERACTIONS ON PYRITE BIOOXIDATION BY Acidithiobacillus ferrooxidans IN THE PRESENCE OF COAL COMPOUNDS

Abstract This study evaluated the biooxidation of pyrite contained in a Colombian coal (2.38 mm < particle size < 0.50 mm). The variables were cysteine concentration (0-600 mg/L) and culture type (pure Acidithiobacillus ferrooxidans (ATCC 23270) and a consortium of Acidithiobacillus thiooxidans (ATCC 15494) and Acidithiobacillus ferrooxidans). Pyrite oxidation for the assays without cysteine was 31.14% after 12 days. In the presence of pure A. ferrooxidans, oxidation increased by 8.18% in the assays containing 60 mg Cys/L. In contrast, the counterpart using the consortium exhibited a significant increase in redox potential, which improved oxidation by 28.44%. Since all the assays had a similar kaolinite removal (around 31.45%), and the experiments without cysteine did not show differences in behaviour, the A. thiooxidans-cysteine interactions might have been responsible for increasing Fe3+ regeneration, alleviating the toxic effect of Al3+ ion dissolution, thus improving pyrite oxidation. The consortium-cysteine-coal interactions contrasted with those proposed by other authors for A. ferrooxidans-cysteine-pure pyrite and A. thiooxidans-cysteine, indicating different metabolic pathways in the presence of inorganic and organic coal matrices. On the other hand, the biooxidation rate decreased for both cultures in the presence of 600 mg Cys/L, showing similar inhibition to that reported in the literature.

Development of the mathematical model of the kinetics of the stationary process of bio-cleaning with substratic inhibition

A scientifically sound method for calculating the parameters of bio-cleaning should contain as a basic a reliable mathematical description of the stationary process. The results of stationary laboratory experiments are presented in the coordinates “specific rate of destruction V – concentration ρ”. Statistical processing proves the presence of substrate inhibition for both gaseous and soluble and dissolved harmful substances in water. For an analytical description of the dependence of the biooxidation rate on the concentration of contaminants, a phenomenological approach is applied, taking into account in a simple form two obvious phenomena: the contact of a microorganism with a substrate molecule and the inhibitory effect of the medium on it. The numerical values of empirical dependency coefficients for the studied processes are calculated. A differential equation is proposed at the macro level that describes the kinetics of biochemical destruction. The concept of a macrokinetic mathematical model of bioremediation is defined as a system of two functions that quantitatively reflect the dependence of the specific oxidation rate of pollution on its concentration and concentration on time, as well as satisfying the relationship between the relationships of the same parameters in differential form. The dependence of concentration on time is defined both in the form of a numerical integration algorithm and in the form of an approximate formula. The adequacy and universality of the proposed model for the studied processes is proved. The advantage of the proposed model of substrate inhibition kinetics is the simplicity of the structure of the basic formula and the ease of determining empirical coefficients based on this. In addition to numerical integration for determining the time of destruction, an approximate analytical solution is found, which can be adequately used in the concentration range of the experimental study. Further research is aimed at developing methods for calculating non-stationary processes in biochemical purification plants of certain specific types

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.

Continuous production of a biogenic ferric iron lixiviant for the bioleaching of printed circuit boards (PCBs)

Ferric iron is a low-cost oxidant frequently used in hydrometallurgy and is particularly suitable to leach various metals from printed circuit boards (PCBs). This paper presents the use of the BRGM-KCC acidophilic consortium to generate ferric iron solution in a bubble column run in continuous mode. The influence of influent ferrous iron concentration, ranging from 1 to 9 g L−1 on the bio-oxidation rate was studied in the presence of a solid support. The impacts of the quantity of solid support, the hydraulic residence time (HRT), the culture medium and the type of support were established. Stable performance was achieved over an extended period with a Fe2+ oxidation rate of 1400 mg L−1 h−1. Cryogenic scanning electron microscopy was used to observe the attachment of cells on the solid support in different operating conditions and showed that the clogging of the solid support with jarosite precipitates influenced its colonization by the micro-organisms and the stability of the bioprocess. The operating conditions, and especially the influent ferrous iron concentration and nutritive medium composition, also influenced the structure and the abundance of the microbial community.

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.

Treatment of tetrathionate effluents by continuous oxidation in a flooded packed-bed bioreactor

Thiosalts are compounds commonly present in process plant liquor for the concentration of metal sulphide ores by milling and flotation. Since thiosalts are metastable species that are oxidized to sulphuric acid as an end product, they cannot be discharged nor recycled into the process. Therefore, the development of a cost-effective process for the treatment of these effluents is necessary. In this paper, the continuous bio-oxidation of tetrathionate is carried out in a flooded packed-bed reactor by an immobilized microbial consortium. Batch tests show that the initial tetrathionate concentration and pH slightly affect the tetrathionate bio-oxidation process in the ranges 3 to 5g/L and 1.5 to 2, respectively. The specific bio-oxidation rate is 0.08h−1. Only sulphate ions and protons have been detected as end products. For the starting up of the bioreactor, a new method of biofilm formation for tetrathionate bio-oxidation is implemented. The maximum bio-oxidation rate in continuous operation is 0.415gh−1 (0.830kgh−1m−3). The biofilm was stable for the whole period studied, i.e. 35days. These results indicate that a flooded packed-bed reactor is an interesting option from an economic point of view for the treatment of waters contaminated by thiosalts.