Insoluble Iron Oxides Research Articles

Study on selective green leaching of rare earth elements from coal gangue using mechanochemical activation

This study proposes a sustainable method for the selective leaching of rare earth elements (REEs) from coal gangue. By combining 600 °C calcination, the addition of 5 % Fe2(SO4)3, and one hour of mechanical-chemical activation, we achieved a leaching efficiency of 65 % for REEs. This method alters the surface and crystalline structure of coal gangue, facilitating the release of rare earth phosphate minerals and the formation of water-soluble compounds (rare earth sulfates). Fe2(SO4)3 transforms into insoluble iron oxide, which immobilizes impurities and promotes the selective leaching of rare earth elements. Notably, during the leaching process, the leaching rates of aluminum (Al) and iron (Fe) were only 0.37 % and 1.27 %, respectively. Kinetic analysis indicates that this process follows a mixed reaction-controlled shrinking core model. This method effectively reduces the environmental risks associated with traditional acidic reagents, providing a sustainable pathway for the recovery of rare earth elements.

Distribution Characteristics and Genesis of Iron and Manganese Ions in Groundwater of Eastern Sanjiang Plain, China

Groundwater resources are an essential component of global water resources. Long-term consumption of groundwater exceeding the standard levels for iron and manganese can lead to chronic diseases, posing a threat to human health. The Sanjiang Plain is the largest swamp wetland area in China and has high levels of iron and manganese in the groundwater, but the cause still needs to be clarified. Based on the results of water quality tests of 41 groundwater samples in the Eastern Sanjiang Plain, this paper analyzes the distribution characteristics and causes of iron and manganese from the perspectives of the original strata environment, redox conditions, pH conditions, and hydrochemical indicator factors in the research area, using statistical methods and GIS technology. The results show that high iron and manganese content in groundwater is prevalent in the Eastern Sanjiang Plain, and the exceedance rate of manganese is higher than that of iron (87.80% and 82.90%, respectively). The primary sources of iron and manganese in groundwater are iron and manganese minerals in the original strata environment. Influenced by factors such as acidic conditions, reducing environment, and rich organic matter, insoluble high-valent iron and manganese oxides are reduced to low-valent and soluble divalent iron and manganese. At the same time, groundwater’s high mineralization and evaporation concentration are conducive to increased iron and manganese content, while the influence of human activities is small.

Conjugative plasmids inhibit extracellular electron transfer in Geobacter sulfurreducens.

Geobacter sulfurreducens is part of a specialized group of microbes with the unique ability to exchange electrons with insoluble materials, such as iron oxides and electrodes. Therefore, G. sulfurreducens plays an essential role in the biogeochemical iron cycle and microbial electrochemical systems. In G. sulfurreducens this ability is primarily dependent on electrically conductive nanowires that link internal electron flow from metabolism to solid electron acceptors in the extracellular environment. Here we show that when carrying conjugative plasmids, which are self-transmissible plasmids that are ubiquitous in environmental bacteria, G. sulfurreducens reduces insoluble iron oxides at much slower rates. This was the case for all three conjugative plasmids tested (pKJK5, RP4 and pB10). Growth with electron acceptors that do not require expression of nanowires was, on the other hand, unaffected. Furthermore, iron oxide reduction was also inhibited in Geobacter chapellei, but not in Shewanella oneidensis where electron export is nanowire-independent. As determined by transcriptomics, presence of pKJK5 reduces transcription of several genes that have been shown to be implicated in extracellular electron transfer in G. sulfurreducens, including pilA and omcE. These results suggest that conjugative plasmids can in fact be very disadvantageous for the bacterial host by imposing specific phenotypic changes, and that these plasmids may contribute to shaping the microbial composition in electrode-respiring biofilms in microbial electrochemical reactors.

Effect of sodium carbonate on alkaline self-leaching of gold from flotation gold ore

Oxygen pressure alkaline self-leaching of gold is an environmentally friendly and smokeless leaching process. But the insoluble iron oxide generated will precipitate on the surface of parent minerals, thus reducing the oxidation reaction and gold leaching efficiency. Simultaneously, due to the different pH requirements of pyrite oxidation and gold leaching, the pH must be strictly controlled to achieve the maximum efficiency. In this work, dissolution effect and buffering effect of sodium carbonate in the gold self-leaching process were carried out. As the addition of sodium carbonate, soluble iron-carbonate complexes would be formed to remove passivation layer and expose fresh surface of pyrite, resulting in improvement pyrite oxidation rate. Meanwhile, the buffering capacity of sodium carbonate can avoid the thiosulfate decomposition and improve the concentration of thiosulfate. The maximum gold extraction efficiency of gold-bearing flotation concentrate could achieve 91.56% under the following condition: a concentration of sodium hydroxide, sodium carbonate and sodium carboxymethyl cellulose at 0.6 M, 0.3 M and 100 mg/dm3, respectively; stirring speed at 800 rpm; temperature at 308.15 K; oxygen pressure at 0.5 Mpa; leaching time of 18 h and a liquid-solid ratio of 5:1.

Fulvic acid increases iron bioavailability in aquaponic systems: Theoretical designs and practical considerations to prevent iron deficiency in plants

Plants grown in aquaponics frequently develop iron deficiency, which is generally corrected via supplementation with iron chelates. However, the solid waste excreted by fish contains considerable amounts iron, which are lost in the system by precipitation of insoluble iron oxides. Thus, the present study proposed the use of fulvic acid (FA), a humic substance with metal complexing capacity, to prevent iron precipitation and enhance its bioavailability in the aquaculture wastewater. An aquaponic solution was added with levels of fulvic acid (0, 69, 138, 345, and 690 mg L−1), and analyzed for dissolved iron after incubation and centrifugation. Visual MINTEQ was used to characterize and quantify the effect of fulvic acid levels on iron precipitation, species of possible solid forms, and concentration of dissolved bioavailable iron forms. Dissolved iron concentration increased with the inclusion of fulvic acid in the nutrient solution, and the highest iron concentration (22.4 μM) was obtained by treating the solution with 690 mg L−1 of fulvic acid. Visual MINTEQ simulations demonstrated that, in the absence of fulvic acid, iron precipitated in the form of αFe2O3, and the concentration of available iron increased with the inclusion of FA due to its complexing properties. Solution pH had no effect on iron availability with the absence of fulvic acid; in its presence, the effect of pH was only significant at values below 4.5. This study shows that fulvic acid seems to play an important role in transporting low-soluble iron from fish tanks to plant roots in aquaponic systems.

A hybrid (iron-fat-water) phantom for liver iron overload quantification in the presence of contaminating fat using magnetic resonance imaging.

Assessment of iron content in the liver is crucial for diagnosis/treatment of iron-overload diseases. Nonetheless, T2*-based methods become challenging when fat and iron are simultaneously present. This study proposes a phantom design concomitantly containing various concentrations of iron and fat suitable for devising accurate simultaneous T2* and fat quantification technique. A 46-vial iron-fat-water phantom with various iron concentrations covering clinically relevant T2* relaxation time values, from healthy to severely overloaded liver and wide fat percentages ranges from 0 to 100% was prepared. The phantom was constructed using insoluble iron (II, III) oxide powder containing microscale particles. T2*-weighted imaging using multi-gradient-echo (mGRE) sequence, and chemical shift imaging spin-echo (CSI-SE) Magnetic Resonance Spectroscopy (MRS) data were considered for the analysis. T2* relaxation times and fat fractions were extracted from the MR signals to explore the effects of fat and iron overload. Size distribution of iron oxide particles for Magnetite fits with a lognormal function with a mean size of about 1.17µm. Comparison of FF color maps, estimated from bi- and mono-exponential model indicated that single-T2* fitting model resulted in lower NRMSD. Therefore, T2* values from the mono-exponential signal equation were used and expressed the relationship between relaxation time value across all iron (Fe) and fat concentration as [Formula: see text], with R-squared = 0.89. The proposed phantom design with microsphere iron particles closely simulated the single-T2* behavior of fatty iron-overloaded liver in vivo.

Emission of iron and aluminum oxide particles from ultrasonic humidifiers and potential for inhalation

Ultrasonic humidifier use is a potential source of human exposure to inhalable particulates. This research evaluated the behavior of insoluble iron oxide and aluminum oxide particles in water used to fill room-sized ultrasonic humidifiers. Solutions of 10 mg/L Fe, as iron oxide particles, or 5 mg/L Al, as aluminum oxide suspension, were added into tap water used to fill ultrasonic humidifiers. The humidifiers were operated for 14 h; samples were obtained over time and monitored for soluble and particulate Fe and Al, as well as particle sizes in the humidifier reservoir and emitted in aerosols. Denser, settleable particles of approximately 1.5 μm diameter of iron or aluminum oxides accumulated at the bottom of the humidifier reservoir. Smaller, suspended metal oxide particles of 0.22–0.57 μm diameter were emitted as aerosols from the humidifier. Soluble anions and cations in tap water were also present in the aerosols emitted from humidifiers. The results indicate that a typical 1.6 MHz ultrasonic humidifier can emit 0.22–0.57 μm particles and dissolved minerals from fill water into breathable air.

Extracellular Electron Transfer via Outer Membrane Cytochromes in a Methanotrophic Bacterium Methylococcus capsulatus (Bath).

Electron exchange reactions between microbial cells and solid materials, referred to as extracellular electron transfer (EET), have attracted attention in the fields of microbial physiology, microbial ecology, and biotechnology. Studies of model species of iron-reducing, or equivalently, current-generating bacteria such as Geobacter spp. and Shewanella spp. have revealed that redox-active proteins, especially outer membrane c-type cytochromes (OMCs), play a pivotal role in the EET process. Recent (meta)genomic analyses have revealed that diverse microorganisms that have not been demonstrated to have EET ability also harbor OMC-like proteins, indicating that EET via OMCs could be more widely preserved in microorganisms than originally thought. A methanotrophic bacterium Methylococcus capsulatus (Bath) was reported to harbor multiple OMC genes whose expression is elevated by Cu starvation. However, the physiological role of these genes is unknown. Therefore, in this study, we explored whether M. capsulatus (Bath) displays EET abilities via OMCs. In electrochemical analysis, M. capsulatus (Bath) generated anodic current only when electron donors such as formate were available, and could reduce insoluble iron oxides in the presence of electron donor compounds. Furthermore, the current-generating and iron-reducing activities of M. capsulatus (Bath) cells that were cultured in a Cu-deficient medium, which promotes high levels of OMC expression, were higher than those cultured in a Cu-supplemented medium. Anodic current production by the Cu-deficient cells was significantly suppressed by disruption of MCA0421, a highly expressed OMC gene, and by treatment with carbon monoxide (CO) gas (an inhibitor of c-type cytochromes). Our results provide evidence of EET in M. capsulatus (Bath) and demonstrate the pivotal role of OMCs in this process. This study raises the possibility that EET to solid compounds is a novel survival strategy of methanotrophic bacteria.

Synchronous extraction of nickel and copper from a mixed oxide-sulfide nickel ore in a low-temperature roasting system

Abstract Mixed oxide-sulfide nickel ore is becoming the major source of nickel produced in the nickel smelting enterprise due to the increasing global demand of nickel and the depletion of high-grade nickel sulfide ore. Low temperature roasting technique by ammonium sulfate is a potential cleaner production process with high metal recovery, high reaction selectivity and low energy consumption. In this work, Chinese mixed oxide-sulfide nickel ores were roasted by ammonium sulfate at low temperatures of 300–500 °C to extract valuable metals directly and synchronously. Some influence factors including roasting temperature, ammonium-to-ore mole ratio, roasting time and particle size of the ore samples were studied in the roasting process. Sodium sulfate was added to improve the extraction of nickel by converting into Na-pyrosulfate. The results showed that more than 97% Cu, 97% Ni and 82% Fe are extracted, under the conditions of roasting temperature 450 °C, roasting time 4 h, ammonium-to-ore mole ratio 2.2:1, particle size −160 + 180 mesh, sodium sulfate dosage 3 g. The evolution behavior and mechanism of various minerals were elucidated using X-ray Diffraction, Thermogravimetric Analysis, Differential Thermal Analysis, Scanning Electron Microscope and Energy Dispersive Spectrometer. It is found that pyrite (FeS2), pyrrhotite (Fe7S8), pentlandite ((Fe,Ni)9S8) and chalcopyrite (CuFeS2) can react sufficiently with ammonium sulfate to form the corresponding metallic ammonium sulfate salts. Ammonium ferric sulfate can be decomposed to produce insoluble iron oxide by increasing the roasting temperature to higher than 500 °C to realize the separation from copper and nickel in the leaching liquid. The ammonium sulfate roasting-water leaching technique provides an effective approach for the extraction of nickel and copper from Chinese low grade mixed oxide-sulfide nickel ores.

Reusability of zero-valent iron particles for zinc ion separation

Abstract Zero-valent iron (ZVI) is known to be effective in separating heavy metals from aqueous solution. However, used ZVI particles are usually discarded in heavy metal-containing sludge. Therefore, an appropriate technique for the reactivation of used ZVI for reuse is discussed in this work. A series of zinc desorption tests from zinc-adsorbed ZVI revealed that zinc desorption required both acidic conditions to dissolve zinc-containing iron hydroxide layers on ZVI and reductants to remove insoluble iron oxide layers from the ZVI surface. Organic acid reductants, such as citric acid, satisfy both these requirements. The ZVI particles that were reactivated by the desorption of zinc using 10.0-mM citric acid were applied repeatedly for zinc removal. Reusing the ZVI particles four times did not affect their zinc removal performance relative to that of virgin ZVI. Furthermore, the used 10.0-mM citric acid could be reused to desorb zinc from the used ZVI particles after separating the zinc and iron ions by hydroxide precipitation at pH 12 and re-acidifying the solution to pH 2.5 by the addition of sulfuric acid. Thus, both the ZVI particles and the 10.0-mM citric acid cleansing liquid were found to be reusable for zinc separation from aqueous solution.

Air pollution-aerosol interactions produce more bioavailable iron for ocean ecosystems.

It has long been hypothesized that acids formed from anthropogenic pollutants and natural emissions dissolve iron (Fe) in airborne particles, enhancing the supply of bioavailable Fe to the oceans. However, field observations have yet to provide indisputable evidence to confirm this hypothesis. Single-particle chemical analysis for hundreds of individual atmospheric particles collected over the East China Sea shows that Fe-rich particles from coal combustion and steel industries were coated with thick layers of sulfate after 1 to 2 days of atmospheric residence. The Fe in aged particles was present as a "hotspot" of (insoluble) iron oxides and throughout the acidic sulfate coating in the form of (soluble) Fe sulfate, which increases with degree of aging (thickness of coating). This provides the "smoking gun" for acid iron dissolution, because iron sulfate was not detected in the freshly emitted particles and there is no other source or mechanism of iron sulfate formation in the atmosphere.

Tertiary treatment of a municipal wastewater toward pharmaceuticals removal by chemical and electrochemical advanced oxidation processes

This study focuses on the degradation of pharmaceuticals from a municipal wastewater after secondary treatment by applying various advanced oxidation processes (AOPs) and electrochemical AOPs (EAOPs) like UVC, H2O2/UVC, anodic oxidation (AO), AO with electrogenerated H2O2 (AO-H2O2), AO-H2O2/UVC and photoelectro-Fenton (PEF) using either UVC radiation (PEF-UVC) or UVA radiation (PEF-UVA). The municipal wastewater after secondary treatment was spiked with 5.0 mg L−1 of trimethoprim (TMP) antibiotic. The efficiency of processes to remove TMP followed the order UVC < AO-H2O2 < PEF-UVA << AO ≈ PEF-UVC < AO-H2O2/UVC < PEF-UVA (pH = 2.8) < H2O2/UVC ≈ PEF-UVC (pH = 2.8), using neutral pH, except when identified. While the UVC radiation alone led to a very low TMP removal, the H2O2/UVC process promoted a very high TMP degradation due to the production of hydroxyl radicals (OH) by H2O2 cleavage. In the AO-H2O2/UVC process, the electrogeneration of H2O2 can avoid the risks associated with the transportation, storage and manipulation of this oxidant and, furthermore, OH at the anode surface are also formed. Nevertheless, low contents of H2O2 were detected mainly at the beginning of the reaction, leading to a lower initial reaction rate when compared with the H2O2/UVC system. In the PEF-UVC, the addition of iron at neutral pH led to the visible formation of insoluble iron oxides that can filter the light. At pH 2.8, the iron remained dissolved, thereby promoting the Fenton's reaction and increasing the organics removal. The UVA-driven processes showed limited efficiency when compared with those using UVC light. For all processes with H2O2 electrogeneration, the active chlorine species can be scavenged by the H2O2, diminishing the efficiency of the processes. This can explain the lower efficiency of AO-H2O2 when compared with AO. Moreover, the degradation of the MWWTP effluent spiked with 18 pharmaceuticals in μg L−1 during AO process was assessed as well as the influence of the following operational variables on the process efficiency: (i) H2O2 concentration on H2O2/UVC, (ii) current density on AO, AO-H2O2, AO-H2O2/UVC, PEF-UVC and PEF-UVA, and (iii) pH on PEF-UVA.

Safety and efficacy of iron oxide black, red and yellow for all animal species

Iron oxides black, red and yellow are intended to be used as colourings to add and restore colour to feedingstuffs at a recommended concentration between 500 and 1,200 mg/kg. No data on the tolerance of target animals were provided. The iron oxides black, red and yellow are excreted essentially unchanged in the faeces of the target animals. Iron absorption from these water insoluble iron oxides is low. However, no conclusion on the safety of the iron oxides under assessment for the target animals could be made as a sufficient biological and toxicological database, particularly genotoxicity data, was not available. The use of the iron oxides in animal nutrition is unlikely to result in a direct exposure of the consumer and would not influence the iron content of edible tissues and products from animals treated with iron oxides. Consequently, the supplementation of feed for food-producing animals with the iron oxides under assessment would not provide a risk to consumers. Iron oxide black, red and yellow should be considered as irritant to skin and eyes. In the absence of any information, the Panel on Additives and Products or Substances used in Animal Feed FEEDAP cannot conclude on the potential of the additives to be a skin sensitiser. As the inhalation of iron oxides could cause unspecific lung inflammation, inhalation exposure of users should be considered to be a hazard. As there is concern about the possible genotoxicity of iron oxides, any route of exposure should be considered as hazardous. The use of iron oxide black, red and yellow in animal nutrition does not pose a risk to the environment. The iron oxides are effective in colouring feedingstuffs.

Formate Metabolism in Shewanella oneidensis Generates Proton Motive Force and Prevents Growth without an Electron Acceptor.

Shewanella oneidensis strain MR-1 is a facultative anaerobe that thrives in redox-stratified environments due to its ability to utilize a wide array of terminal electron acceptors. Conversely, the electron donors utilized by S. oneidensis are more limited and include products of primary fermentation such as lactate, pyruvate, formate, and hydrogen. Lactate, pyruvate, and hydrogen metabolisms inS. oneidensis have been described previously, but little is known about the role of formate oxidation in the ecophysiology of these bacteria. Formate is produced by S. oneidensis through pyruvate formate lyase during anaerobic growth on carbon sources that enter metabolism at or above the level of pyruvate, and the genome contains three gene clusters predicted to encode three complete formate dehydrogenase complexes. To determine the contribution of each complex to formate metabolism, strains lacking one, two, or all three annotated formate dehydrogenase gene clusters were generated and examined for growth rates and yields on a variety of carbon sources. Here, we report that formate oxidation contributes to both the growth rate and yield of S. oneidensis through the generation of proton motive force. Exogenous formate also greatly accelerated growth on N-acetylglucosamine, a carbon source normally utilized very slowly by S. oneidensis under anaerobic conditions. Surprisingly, deletion of all three formate dehydrogenase gene clusters enabled growth of S. oneidensis using pyruvate in the absence of a terminal electron acceptor, a mode of growth never before observed in these bacteria. Our results demonstrate that formate oxidation is a fundamental strategy under anaerobic conditions for energy conservation inS. oneidensis. Shewanella species have garnered interest in biotechnology applications for their ability to respire extracellular terminal electron acceptors, such as insoluble iron oxides and electrodes. While much effort has gone into studying the proteins for extracellular electron transport, how electrons generated through the oxidation of organic carbon sources enter this pathway remains understudied. Here, we quantify the role of formate oxidation in the anaerobic physiology of Shewanella oneidensis Formate oxidation contributes to both the growth rate and yield on a variety of carbon sources through the generation of proton motive force. Advances in our understanding of the anaerobic metabolism of S. oneidensis are important for our ability to utilize and engineer this organism for applications in bioenergy, biocatalysis, and bioremediation.

Electrochemical Characterization of a Novel Exoelectrogenic Bacterium Strain SCS5, Isolated from a Mediator-Less Microbial Fuel Cell and Phylogenetically Related to Aeromonas jandaei.

A facultative anaerobic bacterium, designated as strain SCS5, was isolated from the anodic biofilm of a mediator-less microbial fuel cell using acetate as the electron donor and α-FeOOH as the electron acceptor. The isolate was Gram-negative, motile, and shaped as short rods (0.9–1.3 μm in length and 0.4–0.5 μm in width). A phylogenetic analysis of the 16S rRNA, gyrB, and rpoD genes suggested that strain SCS5 belonged to the Aeromonas genus in the Aeromonadaceae family and exhibited the highest 16S rRNA gene sequence similarity (99.45%) with Aeromonas jandaei ATCC 49568. However, phenotypic, cellular fatty acid profile, and DNA G+C content analyses revealed that there were some distinctions between strain SCS5 and the type strain A. jandaei ATCC 49568. The optimum growth temperature, pH, and NaCl (%) for strain SCS5 were 35°C, 7.0, and 0.5% respectively. The DNA G+C content of strain SCS5 was 59.18%. The isolate SCS5 was capable of reducing insoluble iron oxide (α-FeOOH) and transferring electrons to extracellular material (the carbon electrode). The electrochemical activity of strain SCS5 was corroborated by cyclic voltammetry and a Raman spectroscopic analysis. The cyclic voltammogram of strain SCS5 revealed two pairs of oxidation-reduction peaks under anaerobic and aerobic conditions. In contrast, no redox pair was observed for A. jandaei ATCC 49568. Thus, isolated strain SCS5 is a novel exoelectrogenic bacterium phylogenetically related to A. jandaei, but shows distinct electrochemical activity from its close relative A. jandaei ATCC 49568.

Functional role of PilA in iron acquisition in the cyanobacterium Synechocystis sp. PCC 6803.

Cyanobacteria require large quantities of iron to maintain their photosynthetic machinery; however, in most environments iron is present in the form of insoluble iron oxides. Whether cyanobacteria can utilize these sources of iron, and the potential molecular mechanisms involved remains to be defined. There is increasing evidence that pili can facilitate electron donation to extracellular electron acceptors, like iron oxides in non-photosynthetic bacteria. In these organisms, the donation of electrons to iron oxides is thought to be crucial for maintaining respiration in the absence of oxygen. Our study investigates if PilA1 (major pilin protein) may also provide a mechanism to convert insoluble ferric iron into soluble ferrous iron. Growth experiments supported by spectroscopic data of a strain deficient in pilA1 indicate that the presence of the pilA1 gene enhances the ability to grow on iron oxides. These observations suggest a novel function of PilA1 in cyanobacterial iron acquisition.

Effect of γFe2O3 nanoparticles on photosynthetic characteristic of soybean (Glycine max (L.) Merr.): foliar spray versus soil amendment

There is an urgent need to address comprehensive biosafety issues associated with the use of Fe2O3 nanoparticles (IONPs). The present study was performed to investigate the effect of 6-nm IONPs and citrate-coated IONPs (IONPs-Cit) on photosynthetic characteristics and root elongation during germination of Glycine max (L) Merr. Plant physiological performance was assessed after foliar and soil IONPs fertilization. No adverse impacts at any growth stage of the soybeans were observed after application of IONPs. The Fe2O3 nanoparticles produced a significant positive effect on root elongation, particularly when compared to the bulk counterpart (IOBKs) suspensions of concentrations greater than 500 mg L−1. Furthermore, IONPs-Cit significantly enhanced photosynthetic parameters when sprayed foliarly at the eight-trifoliate leaf stage (P < 0.05). The increases in photosynthetic rates following spraying were attributed to increases in stomatal opening rather than increased CO2 uptake activity at the chloroplast level. We observed more pronounced positive effects of IONPs via foliar application than by soil treatment. This study concluded that IONPs coated with citric acid at IONPs to citrate molar ratio of 1:3 can markedly improve the effectiveness of insoluble iron oxide for Fe foliar fertilization.

Mind the gap: long range charge transfer across the periplasm of Shewanella oneidensis

Shewanella oneidensis a gram negative proteobacteria, is capable of the dissimilatory metal reduction (DMR) of insoluble iron and manganese oxides, through the deployment of multiple strategies, including using multiple multi‐heme c‐type cytochromes that electrochemically wire the cellular interior to the exterior. In order to harness the remarkably biological chemistry of Shewanella in bioenergy and microbial fuel cells, we examined the molecular details of long‐range electron transfer within and between Shewanella multi‐heme cytochromes that are implicated in the DMR pathway. To probe the model of Mtr cytochrome interactions, we have developed new analytical methods to quantify the directionality and stoichiometry of redox reactions in the Shewanella Mtr cytochromes. We have modified traditional PFE methods to probe the protein:protein interactions that may be at work in the Shewanella DMR pathway, revealing an unforeseen unidirectionality for electron transfer. These data, coupled to structural studies of MtrA using small angle x‐ray scattering (SAXS) and analytical ultracentrifugation (AUC), elucidate a model of long‐range electron transfer that occurs from the quinol pool of Shewanella to the cell surface, as mediated by a series of multi‐heme cytochromes c. For each multi‐heme cytochrome, the high number of redox cofactors and their similar reduction potentials, convolutes the routine assignment of specific macroscopic reduction potentials to individual hemes. Here, novel Mtr cytochrome mutants where predicted heme ligands have been mutated from His to Met/Ala mutagenically “map” the nature of each heme center. The electrochemical, spectroscopic and physiological impact of such mutations will be presented.

Persistence of commercial nanoscaled zero-valent iron (nZVI) and by-products

The use of nanoscale zero-valent iron (nZVI) for in situ remediation of a wide scale of environmental pollutants is increasing. Bench and field pilot studies have recorded successful cleanup of many pollutants using nZVI and other iron-mediated nanoparticles. However, a major question remains unanswered: what is the long-term environmental fate of the iron nanoparticles used for remediation? We aged three types of commercial nZVI in different aqueous media, including a groundwater sample, under aerobic and anaerobic conditions for 28 days, and found that the bulk of the nZVI injected into polluted sites will end up in the sediment phase of the aquifer. This is mainly due to aggregation-induced sedimentation of the nZVI and the insoluble iron oxides formed when nZVI undergoes corrosion. Iron concentrations >500 g/kg were detected in sediment, a loading level of iron that may potentially affect some organisms and also reduce the permeability of aquifers. Dissolved and suspended iron concentrations initially surged when nZVI was applied, but iron decreased steadily in the supernatant and suspended sediment as the bulk of the iron partitioned into the sediment. Solution and surface chemistry of the iron species showed that nZVI remains reactive for more than 1 month, and that the reactivity of iron and its transformations are governed by environmental factors, including the presence of different ions, ionic strength, natural organic matter, and pH.

Bio-current as an indicator for biogenic Fe(II) generation driven by dissimilatory iron reducing bacteria

Microbial reduction of insoluble iron minerals by dissimilatory iron reducing bacteria (DIRB) is an important environment process in the iron biogeochemical cycle. We reported that the bio-current generated from oxidation of organic matter by these bacteria in the presence of iron oxides can be used as an indicator for microbial dissolution of insoluble iron oxides. Bioelectrochemical experiments were conducted to investigate the effects of the specific bacteria and the phase identity of iron oxides on bio-current generation by recording the current response as a result of a poised constant potential. Experimental results indicated that the bio-current generation can be greatly enhanced by iron oxide addition under all the conditions varying in the type of pure culture or iron oxide. The increase in the bio-current was linearly correlated with the increased concentration of biogenic Fe(II) detected either by chemical analysis or cyclic voltammetry (CV) tests. This can be understood based on the proposed mechanism that the Fe(II)/Fe(III) couple functions as the electron mediator shuttling electrons from the microbes to the electrodes.