Acidithiobacillus Research Articles

Biogenic carbon encapsulated iron oxides mediated oxalic acid for Cr(VI) reduction in aqueous: Efficient performance, electron transfer and radical mechanisms

Carbonaceous materials have a potential to mediated oxalic acid (OA) for Cr(VI) reduction, but the rational modification is needed for boosting the mediation of electron transfer. Herein, we utilized polyvinyl alcohol to envelop schwertmannite synthesized by Acidithiobacillus ferrooxidans biomineralization, and pyrolyzed them to obtain the carbon encapsulated iron oxides (C-2.0-Sch-PVA). SEM and TEM results demonstrated that a moderate calcination temperature would yield a neural network-like carbon encapsulated structure. C-2.0-Sch-PVA efficiently mediated OA to reduce Cr(VI), 98.4% of Cr(VI) (40 mg L−1) was reduced with 0.75 g L−1 C-2.0-Sch-PVA and 4 mM OA in 60 min. It still performed excellent results in a wide pH range, multiple anions and different water matrixes. The carbon encapsulated structure as electron shuttle mediated the electron transfer, and the O-moieties on its surface were a premise for initiating the Cr(VI) reduction process. The electron transfer from the inner iron oxides to the conjugated structure of the outer carbon shells facilitated Cr(VI) reduction as well. Moreover, OA raised the persistent free radicals' level in C-2.0-Sch-PVA as another important pathway for Cr(VI) reduction. Overall, C-2.0-Sch-PVA provides an excellent demonstration in the carbonaceous materials modification for mediating OA to reduce Cr(VI) in aqueous.

Hydrometallurgical Recovery of Copper Tailing Waste by Bioleaching at Hindustan Copper Limited, India

The conventional methods of refining cannot be implemented for recovery of copper from tailing waste collected from Hindustan Copper Limited, Khetri, India as it contains low copper and higher iron along with other metals present. Hence bioleaching was tested as an alternative approach for the recovery of copper from the waste. The study investigated the feasibility of using a bioleaching process for the treatment of copper tailing waste. The XRD and ED-XRF analysis confirmed that the waste contained 0.13% w/w copper, which is present in different forms including chalcopyrite (CuFeS2). Shake flask studies optimized with tailing concentration, optimum temperature, and pH showed 94.03 % w/w recovery of copper at 2 % w/v waste concentration after 40 days of exposure at pH 2.0. The study was extended to a pilot-scale glass column filled with raw copper tailing mixed with Acidithiobacillus ferrooxidans at a flow rate of 3 L h-1. A recovery of 54.71% w/w of copper was obtained by this setup. The mix-proportion clay bricks were cast with the tailing waste after bioleaching. The bricks showed better compressive strength as compared to normal bricks. A pilot scale heap leaching study with 5 kg of tailing waste mixed with Acidithiobacillus ferrooxidans showed a 64.28% w/w copper tailing in 40 days.

Effect of Biochar and Acidithiobacillus ferrooxidans on Heavy Metal Content in Soil and Lettuce

ABSTRACT The mechanism of biochar remediation of heavy metal contamination in soils has been studied quite a lot, but there are still many uncertainties about the effect of interaction between biochar and functional bacteria that adsorb and leach heavy metals. In this paper, we conducted a pot experiment to investigate in depth the effects of biochar, Acidithiobacillus ferrooxidans, and their combined treatment on heavy metal contents (Cr, As, Cd, and Pb) in soil and lettuce by using biochar and A. ferrooxidans. The results showed that biochar, A. ferrooxidans, and combined treatment increased soil pH by 42.55 ~ 51.06% and decreased the content of heavy metals in soil (0.07 ~ 60.80%). The average decrease was as follows: combined treatment (28.42%) > biochar (22.35%) > A. ferrooxidans (18.94%). All three treatments reduced the content of heavy metals in lettuce (26.19–84.42%), and the average size was combined treatment (60.82%) > biochar (52.55%) > A. ferrooxidans (44.00%). Biochar and A. ferrooxidans inhibited the enrichment of heavy metals in lettuce and promoted the growth of lettuce and the increase of nutrients. The combination of biochar and A. ferrooxidans can effectively control soil heavy metal pollution. The combined treatment can reduce the heavy metal content of lettuce and promote its growth, which is an excellent material for soil heavy metal deterrent control and has distinguished application prospects.

Bio-Assisted Leaching of Non-Ferrous Metals from Waste Printed Circuit Boards—Importance of Process Parameters

The effect of varying process parameters during bio-catalyzed leaching of metals from end-of-life printed circuit boards (PCBs) was investigated. Fragmented PCBs (under 2 mm) were subjected to an indirect bioleaching in a stirred tank reactor while pulp density, pH and initial ferric iron content were varied. An iron oxidizing Acidithiobacillus ferrooxidans 61 microbial strain was used to generate the lixiviant through oxidizing Fe(II) to Fe(III). Chemically generated Fe(III) was tested as lixiviant under the same conditions as the biological one for comparative purposes. Cell enumeration during leaching and microscopic observations of the input and leached PCBs were conducted in parallel to shed light on the observed phenomena. The degree of bringing metals in solution was found to depend mainly on ferric iron concentration and pH. For the entire duration being always kept as 24 h, substantial portion of Cu (~87%) was extracted respectively at 1% pulp density (PD), 15.5 g/L Fe3+ and pH 1. For Zn and Ni, nearly 100% recovery was observed at 5% PD, 18 g/L Fe3+ and pH 1.1. The achieved results offer possibilities for further studies at higher pulp density, to ultimately render the bioleaching approach as enabling economical and environmentally friendly technology for urban mining of non-ferrous metals.

An integrated biohydrometallurgical approach for the extraction of base metals from printed circuit boards

This study evaluated a novel two-step process for biological lixiviant generation to facilitate base metals leaching from waste printed circuit boards (PCBs). In the first step, crushed waste sulfur pastilles, a by-product of the petroleum industry, were biologically oxidised to produce biogenic H2SO4. The acidified effluent containing biogenic H2SO4 was then supplemented with ferrous iron (20 g L−1) in the second step, where it was biologically oxidised to produce ferric iron. The recovered biolixiviant was then used for base metal leaching from PCBs. The biological sulfur oxidation rate was 0.43 g L−1 d−1 with oxidation efficiency 43%, and the biological iron oxidation rate was 5.93 g L−1 d−1 with oxidation efficiency 96.5%. Acidithiobacillus caldus was primarily responsible for the oxidation of waste sulfur, whereas the iron oxidation was achieved by a microbial consortium dominated by Acidithiobacillus ferrooxidans. The leaching of base metals from PCBs using the biogenic lixiviant was investigated at various experimental conditions to determine leaching efficiency. Leaching parameters tested in this study included temperature (25-45 °C), aeration, PCB pulp density (PD, 1 and 5%), pH control, leaching reactor configuration, and pre-treatment of PCBs by ashing. The results showed that increasing temperature significantly increased (p < 0.05) metal extraction from PCBs using biogenic lixiviants. Aeration did not improve leaching efficiency when compared to vigorous mixing. High leaching efficiencies for Cu (97.9%), Ni (80.1%), Al (91.0%) and Zn (99.7%) were obtained at 45 °C without aeration at a 1% PD and a pH range of 1.25 to 1.64. Controlling pH to a set point of pH 1.4 with feedback-dosing of 2 M H2SO4 significantly increased (p < 0.05) the leaching efficiencies (78.8% Cu, 71.3% Ni, 85.3% Al and 90.6% Zn) at 35 °C as compared to leaching without pH control. Changing the leaching process from batch to sequential leaching (5% PD) also enabled higher extraction for Cu (92.4%), Ni (92.6%), Al (82.2%) and Zn (99.8%) when two cycles of lixiviant replacement were undertaken over 96 h. Pre-treatment of PCBs by ashing at 500 °C for 1 h resulted in high leaching efficiencies for Cu (93.7%), Ni (76.1%), Al (85.4%) and Zn (95.8%) using biogenic H2SO4 at 1% PD. This study showed that by separating the unit processes for biogenic lixiviant generation from the leaching process, the optimisation of biogenic lixiviant production and PCB leaching parameters could be effectively achieved without compromising the growth and activity of the microorganisms.

Bioleaching of rare-earth elements from phosphate rock using Acidithiobacillus ferrooxidans

Phosphate rock containing rare earth elements (REEs) is considered one of the most promising potential secondary sources of REEs, as evidenced by large tonnages of phosphate rock mined annually. The bioleaching of REEs from phosphate rock using A. ferrooxidans was done for the first time in this study, and it was found to be greater than abiotic leaching and was more environmentally friendly. The result showed that the total leaching rate of REEs in phosphate rock was 28.46% under the condition of 1% pulp concentration and pH=2, and the leaching rates of four key rare earths, Y, La, Ce, and Nd, were 35.7%, 37.03%, 27.92%, and 32.53%, respectively. The bioleaching process was found to be accomplished by bacterial contact and Fe2+ oxidation. The blank control group which contained Fe2+ was able to leach some of the rare earths, indicating that the oxidation of Fe2+ may affect the leaching of rare earths. X-Ray Diffraction (XRD)analysis showed that the minerals were significantly altered and the intensity of the diffraction peaks of dolomite and apatite decreased significantly after microbial action compared to the blank control, and it was observed that bacteria adhere to the mineral surface and the minerals become smooth and angular after bioleaching by Scanning electron microscope (SEM), indicating that bacteria have a further effect on the rock based on Fe2+ oxidation.Finally.Fourier Transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix (3DEEM) fluorescence spectra analysis showed that extracellular polymeric substances (EPS) participate in the bioleaching process.

Bioleaching of carbide waste using spent culture of Acidithiobacillus bacteria: Effective factor evaluation and ecological risk assessment

This study investigates the bioleaching of Li, Ni, Cu, Zn, and Ba from carbide slag using presecreted metabolites (spent cultures) of Acidithiobacillus ferrooxidans ( A. ferrooxidans ) and Acidithiobacillus thiooxidans (A. thiooxidans ). The effects of pH (1–3), pulp density (0.1%–2% w/v), and contact time (up to 8 days) in achieving high metal recovery were determined. The highest metal biosolubilize rate was achieved at a pH of 1.5, pulp density of 0.5% w/v, and retention time of 6 days. Results showed that the spent cultures of A. ferrooxidans and A. thiooxidans recovered 100% of Ni and Li, respectively. In addition, the results of the spent of mixed culture revealed an improved metal recovery compared with individual strain mediums. Furthermore, investigations on the pollution indexes of the leached slag revealed that leaching using spent of mixed culture was more effective than other leaching methods. Investigation of the contamination factor, ecological risk factor, pollution load index, and geo-accumulation index demonstrated that the metabolites of A. ferrooxidans and the spent of mixed culture significantly improved the waste quality in terms of reducing heavy metals pollution. • Bioleaching of carbide slag waste using spent culture was studied. • Pure A. ferrooxidans and A thiooxidans and mixed culture were examined. • The optimum condition was pH: 1.5, pulp density: 0.5% w/v, and contact time: 6 days. • Ecological risk assessment before and after bioleaching was demonstrated.

Bioleaching of tellurium from mine tailings by indigenous Acidithiobacillus ferrooxidans.

Tellurium (Te) is a scarce and valuable metalloid, which can be found in some mine tailings. In this work, an indigenous Acidithiobacillus ferrooxidans strain was used to leach Te from mine tailings collected in the Shimian Te mine region, China. Under the optimized conditions of initial pH of 2·0, pulp density of 4% and temperature of 30°C, 47·77% of Te can be dissolved after 24 days of bioleaching. The leaching of Te by different systems such as bioleaching, Ferric ion (Fe(III)) leaching and acid leaching was compared. The results showed that the leaching behaviour of Te is similar to that of sulphur in sulphide minerals, that is, Fe(III) first oxidizes telluride (Te(-II)) in minerals to elemental Te, and then elemental Te can be oxidized by bacteria to Te(IV) and Te(VI). Besides, it was also showed by scanning electron microscope observation and Fourier transform infrared spectroscopy analysis of the ore sample before and after bioleaching that some bedded structure covered on the surface of the ore after bioleaching acting as a reaction compartment, and the changing of active groups indicated a possible attachment between bacteria and ore. There is an indirect mechanism involved in bioleaching of Te.

Magnetosome yield characteristics modeling of acidithiobacillus ferrooxidans in airlift bioreactor using response surface methodology.

Bacterial magnetosomes had been proved to have great application potential in medicine and biotechnology. The objective of the present study was to obtain high yield of magnetosomes from Acidithiobacillus ferrooxidans (A. ferrooxidans) BYM in an airlift bioreactor using response surface methodology (RSM). The magnetosomes from A. ferrooxidans BYM were characterized using a transmission electron microscope and scanning electron microscopy. The maximum magnetosome yield of 0.4267mg/L was achieved at ventilation capacity of 3.6L/min and gluconic acid concentration of 10mmol/L at 25oC. The correlation coefficient (R2) value of 0.8676 of the obtained model suggested a good correlation between the actual and predicted magnetosome yield. The confirmation experiment confirmed that the actual magnetosome yield of 0.391mg/L obtained were in agreement with the predicted value of 0.398mg/L. These results suggested that RSM can be employed to find out the optimum conditions for magnetosome formation in airlift bioreactor.

Exploring the role of extracellular polymeric substances in the antimony leaching of tailings by Acidithiobacillus ferrooxidans.

The concentration of Sb bearing tailings in water located in abandoned antimony mines was found to be a big problem, as they contaminate other water resources and entire food chain. Microorganisms were found to be key in tailing leaching and reaction speeding in the presence of extracellular polymeric substances (EPS) produced by bacteria. Herein, we investigated the pattern of the Sb leaching from Sb bearing tailings using Acidithiobacillus ferrooxidans, and analyzed the mechanism of EPS in the leaching process of Sb. To completely and deeply understand the functions of EPS in the bioleaching of antimony tailings, the generation behavior of EPS produced by Acidithiobacillus ferrooxidans (A. ferrooxidans) during bioleaching was characterized by three-dimensional excitation-emission matrix (3D-EEM). Meanwhile, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) were used to show the changes of EPS functional groups before and after leaching. Compared with the functional groups in EPS produced by A. ferrooxidans before leaching, the content of hydroxyl and amino groups that reduce high-valent metals to low-valent metals in EPS decreases after leaching, and the carbonyl content increases, corresponding to the ratio of trivalent antimony increased, indicating that EPS could reduce the risk of pentavalent antimony to trivalent one. At the same time, with biological scanning electron microscopy and energy spectrum scanning, the observation of EPS on the mineral surface showed that Sb was adsorbed in the EPS, and the XPS of Sb was fine. Spectral analysis showed that the Sb adsorbed in EPS contained both Sb(III) and Sb(V). Besides, for revealing the influence of EPS in the leaching process of Sb from tailings, this work provided an in-depth understanding of the mechanism of Sb released from tailings under the action of A. ferrooxidans and further provides a basis for the biogeochemical cycle of Sb.

Mineral weathering of iron ore tailings primed by Acidithiobacillus ferrooxidans and elemental sulfur under contrasting pH conditions

The acidophilic sulfur oxidizing bacterium (SOB), Acidithiobacillus ferrooxidans, has been found to stimulate elemental sulfur (S0) oxidation and mineral weathering in alkaline Fe ore tailings. However, A. ferrooxidans growth and activities depend on the pH conditions surrounding their interfaces with minerals. The present study aimed to investigate how pH influences bacterial growth and functions in Fe ore tailings. A simulated aquatic ‘homogeneous’ incubation system was initially adjusted into acidic (pH 4), neutral (pH 7) and alkaline (pH 9) conditions, which mimicked the microenvironmental conditions of the water-cell-mineral interfaces in the tailings. It was found that A. ferrooxidans grew well and oxidised S0 under the prevailing and initially acidic conditions (pH < 6). These stimulated the weathering of biotite and amphibole-like minerals and the formation of nanosized jarosite and ferrihydrite-like minerals mediated by extracellular polymer substrate (EPS). In contrast, the initially neutral/alkaline pH conditions (i.e., pH > 7) with the presence of the alkaline tailings restricted SOB growth and functions in S0-oxidation and mineral weathering. These findings suggest that it is essential to prime acidic conditions in microenvironments to support SOB growth, activities, and functions toward mineral weathering in tailings, providing critical basis for involving SOB in eco-engineered pedogenesis in tailings.

Sequential biologically assisted extraction of Cu and Zn from printed circuit boards (PCB)

ABSTRACT The increased production and use of electrical and electronic equipment leads to obsolescence and disposal problems, necessitating materials recovery and recycling. This paper reports results on metal bioleaching from printed circuit boards (PCBs) using chemolithotrophic bacteria isolated at different sulphide ore biotopes in Armenia. Different ways of generating lixiviants were investigated, namely using combination of Acidithiobacillus ferrooxidans 61 and Acidithiobacillus thiooxidans SO-1 bacteria generating biogenic Fe2(SO4)3 and biogenic H2SO4. The sequence between these leaching agents permitted design of a 2-step process based on acidolysis and redoxolysis to leach non-ferrous metals from PCBs. To compare the efficiency of the sequential bioleaching of PCBs, several experimental runs were realised under the six modes at 10% pulp density. The flasks-based tests have witnessed almost complete recovery of Cu with the rest of the metals reaching extraction degree above 80%.

Acidithiobacillus ferrooxidans and mixed Acidophilic microbiota oxidation to remove sulphur impurity from iron concentrate

This study reports the bacterial properties of mixed Acidophilic microbiota with sulfur as electron donor and Acidithiobacillus ferrooxidans (A. ferrooxidans) with FeS2 as electron donor and conducted microbial desulfurization experiments. The results showed that mixed Acidophilic microbiota and A.ferrooxidans could effectively reduce the sulfur content in iron concentrate, with the desulfurization efficiency of 79.8 % and 45.7 % in 30 days. And the recovery rates were above 90 % and 88 % respectively. The results of the Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) showed that both bacteria oxidized the iron concentrate and removed the sulfur-containing impurity from the surface of the ore sample. According to the enrichment of elemental phosphorus on the sulfur of the ore sample, it can be deduced that the bacteria were oxidized. After the leaching of A.ferrooxidans, it was found that jarosite was generated, which was consistent with the conclusion of Stereomicroscope morphological observation. Based on X-ray photoelectron spectroscopy analysis, it was concluded that mixed Acidophilic microbiota could reduce the deposition on the surface of iron concentrate after the leaching of sulfate and improve the bioleaching efficiency. The conversion route of sulfur was identified to be from S2-/S22- to Sn2-/S0, and finally SO42-. In conclusion, a model for the oxidation of iron concentrate by A.ferrooxidans and Mixed Acidophilic Microbiota during bioleaching has been proposed.

Copper recovery through biohydrometallurgy route: chemical and physical characterization of magnetic (m), non-magnetic (nm) and mix samples from obsolete smartphones.

The more modern electronics are, the smaller and complex printed circuit boards are. Thus, these materials are continually changed (physicochemically), increasing the copper concentrations in smartphones. In this sense, it is challenging to set standardized recycling processes to improve metal recovery. In addition, biohydrometallurgy is a clean and cheap process to obtain critical metals from low-grade sources and waste electronic equipment. Therefore, the aim of this work was to characterize, physicochemically, 21 PCBs from smartphones manufactured from 2010 to 2015, and then to recover the copper by Acidithiobacillus ferrooxidans (biohydrometallurgy). The PCBs were comminuted and separated into Magnetic (M), Nonmagnetic (NM) and without magnetic separation (MIX) samples. It was identified 217.8; 560.3 and 401.3mg Cu/g of PCBs for M, NM and MIX samples, respectively. Regarding biohydrometallurgy, the culture media iron-supplemented (NM + Fe and MIX + Fe) increased the copper content by 2.6 and 7.2%, respectively, and the magnetic separation step was insignificant.

Sticky bacteria: Combined effect of galactose and high ferric iron concentration on extracellular polymeric substances production and the attachment of Acidithiobacillus ferrooxidans on a polymetallic sulfide ore surface.

Adaptation and microbial attachment mechanisms for the degradation of sulfide ores are mediated by the production of extracellular polymeric substances (EPS) and their role in biofilm formation. EPS production responds to induction mechanisms associated with environmental conditions. In this study, the double induction of EPS with galactose and high ferric iron concentrations in planktonic cells of Acidithiobacillus ferrooxidans, and their attachment on the surface of a polymetallic sulfide ore from Bella Rica-Azuay in Ecuador were evaluated. A. ferrooxidans cells were previously adapted to different concentrations of galactose [0, 0.15, and 0.25% (w/v)], using two ferrous iron concentrations as an energy source (9 and 18 g L–1) in a 9K culture medium. EPS production and its effect on mineral attachment were determined at the time point of maximal growth. The results obtained show a maximum cell attachment of 94.1% within 2 h at 0.15% of galactose and 18 g⋅L–1 of ferric iron concentration, compared to 71.4% without galactose and 9 g⋅L–1 of ferric iron. The maximum concentration of EPS was obtained with a 0.25% galactose concentration; however, it did not result in greater attachment compared to 0.15% galactose concentration. Through the combined induction of low galactose concentration and high ferric iron concentration, the percentage of bacterial attachment can be increased and, therefore, a possible increase in the rate of biooxidation and bioleaching could be obtained.

Inhibition of humic acid on copper pollution caused by chalcopyrite biooxidation

Humic acid has the advantages of wide source, easy availability and environmental friendliness, which may be a good choice for inhibiting chalcopyrite biooxidation and alleviating copper pollution. However, there are few researches on the inhibitory effect and mechanism of humic acid on the biooxidation of chalcopyrite. In order to fill this knowledge gap, this study proposed and validated a novel method for inhibiting chalcopyrite biooxidation by means of humic acid. The results showed that the biooxidation of chalcopyrite could be effectively inhibited by humic acid, which consequently decreased the release of copper ions. Humic acid with a concentration of 120 ppm had the best inhibitory effect, which reduced the biooxidation efficiency of chalcopyrite from 40.7 ± 0.5 % to 29.3 ± 0.8 %. This in turn suggested that humic acid could effectively suppress the pollution of copper under these conditions. The analysis results of solution parameters, mineral surface morphology, mineral phases and element composition showed that humic acid inhibited the growth of Acidithiobacillus ferrooxidans, promoted the formation of jarosite and intensified the passivation of chalcopyrite, which effectively hindered the biooxidation of chalcopyrite, and would help to alleviate the pollution of copper.

Characterization and genomic analysis of two novel psychrotolerant Acidithiobacillus ferrooxidans strains from polar and subpolar environments.

The bioleaching process is carried out by aerobic acidophilic iron-oxidizing bacteria that are mainly mesophilic or moderately thermophilic. However, many mining sites are located in areas where the mean temperature is lower than the optimal growth temperature of these microorganisms. In this work, we report the obtaining and characterization of two psychrotolerant bioleaching bacterial strains from low-temperature sites that included an abandoned mine site in Chilean Patagonia (PG05) and an acid rock drainage in Marian Cove, King George Island in Antarctic (MC2.2). The PG05 and MC2.2 strains showed significant iron-oxidation activity and grew optimally at 20°C. Genome sequence analyses showed chromosomes of 2.76 and 2.84 Mbp for PG05 and MC2.2, respectively, and an average nucleotide identity estimation indicated that both strains clustered with the acidophilic iron-oxidizing bacterium Acidithiobacillus ferrooxidans. The Patagonian PG05 strain had a high content of genes coding for tolerance to metals such as lead, zinc, and copper. Concordantly, electron microscopy revealed the intracellular presence of polyphosphate-like granules, likely involved in tolerance to metals and other stress conditions. The Antarctic MC2.2 strain showed a high dosage of genes for mercury resistance and low temperature adaptation. This report of cold-adapted cultures of the At. ferrooxidans species opens novel perspectives to satisfy the current challenges of the metal bioleaching industry.

Point mutation consideration in CcO protein of the electron transfer chain by MD simulation

In Acidithiobacillus ferrooxidans, proteins such as CcO are present in the electron transport pathway. They cause ferrous iron oxidation to ferric leading to the electron release. CcO has two copper atoms (CuA, CuB). CuA plays an important role in electron transfer. According to previous studies, the conversion of histidine to methionine in a similar protein increased the redox potential and was directly related to the number of electrons received. Also, the binding of methionine 233 to CuA and CuB in the wild protein structure is the reason for the selection of the H230 M mutation in the CuA site. Then, wild-type and H230 M mutant were simulated in the presence of a bilayer membrane POPC using the gromacs version 5.1.4. The changes performed in the H230 M mutant were evaluated by MD simulations analyzes. CcO and CoxA proteins are the last two proteins in the chain and were docked by the PatchDock server. By H230 M mutation, the connection between CuA and M230 weakens. The M230 moves further away from CuA, resulting become more flexible. Therefore, the Methionine gets closer to E149 of the CoxA leading to the higher stability of the CcO/CoxA complex. The results of RMSF analysis at the mutation point showed a significant increase. This indicates more flexibility in the active site. And leads to an increase in E0 in the mutation point, an increase in the rate of electron reception, and an improved bioleaching process.

Attempts to Stimulate Leaching Activity of Acidithiobacillus ferrooxidans Strain TFBk

Autotrophic acidophilic bacteria Acidithiobacillus ferrooxidans is a model species for studying metal bioleaching from low-grade sulfide ores and concentrates. Arsenopyrite gold-bearing concentrates are refractory and often processed using biohydrometallurgical approaches; therefore, it is important to develop methods to improve arsenopyrite bioleaching. In the present work, we have studied the possibility of improving arsenopyrite concentrate bioleaching by the strain of A. ferrooxidans. For this purpose, we have analyzed the genome of the strain A. ferrooxidans TFBk to reveal the genes potentially important in the bioleaching process. Genes determining resistance to arsenic, as well genes involved in the utilization of C1-compounds and resistance to oxidative stress, were revealed. Therefore, the possibility of increasing the rate of arsenopyrite concentrate bioleaching using C1-compounds (methanol and formate) was studied. Formate was able to increase both the biomass yield of the strain A. ferrooxidans TFBk as well as the bioleaching rate. In addition, the effect of redox potential increase by means of the addition of sodium persulfate in the medium on arsenopyrite concentrate bioleaching was studied. It was shown that the addition of 0.1% sodium persulfate stimulated strain growth, while a higher concentration inhibited it. Despite this, the rate of concentrate bioleaching increased in the presence of 0.5–1.0% of persulfate, which may be explained by the interactions of added oxidizer with concentrate components.

A sustainable approach for gold recovery from refractory source using novel BIOX-TC system

This study developed a sustainable method for gold extraction from low-grade refractory ore by combining acidic biooxidation and thiocyanate (SCN) leaching (BIOX-TC) in one system to avoid neutralization and minimize the complexity of the process. Among leachant candidates, thiocyanate was proposed as a less toxic reagent for gold leaching. Furthermore, thiocyanate requires ferric iron as an oxidant for gold extraction and ferric iron can be provided by the microorganisms during biooxidation. In the first step, acidic biooxidation was done using a mixture of acidophiles including Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans resulting in 59.6% sulfur oxidation. A preliminary static incubation of Acidithiobacillus thiooxidans also improved biooxidation efficiency achieving higher sulfur oxidation of 87.8%. Following biooxidation, thiocyanate leaching using 0.2 M SCN was performed under three different conditions: (1) in a separate flask with 0.01 M ferric iron addition; (2) in-situ leaching, in the biooxidation flask with the mixed bacterial culture); (3) in-situ leaching in the biooxidation flask with the bacterial culture and with 0.01 M additional ferric iron. It was found that in-situ thiocyanate leaching of the biooxidized ore in the presence of the bacterial culture and without ferric iron addition resulted in the highest gold recovery (86.9%). The biooxidation mechanism and its kinetics have been extensively discussed in this paper.