Fe Release Research Articles

Superior antibacterial activity of reduced graphene oxide upon decoration with iron oxide nanorods

Iron oxide (Fe2O3) nanorods (NRs) decorated reduced graphene oxide (rGO) nanocomposite, endowed with high antibacterial activity, was prepared through the one-pot calcination of pre-synthesized Fe2O3 NRs in rGO aqueous dispersion. The Fe2O3 NRs were well infused between the rGO layers as revealed by the AFM, SEM, and TGA analysis, whereas the removal and distribution of oxygen-containing functional groups were distinguished with UV–vis and FT-IR spectroscopy. The antibacterial activity of Fe2O3/rGO nanocomposite towards methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Staphylococcus aureus (VRSA), and ciprofloxacin-resistant Staphylococcus aureus (CRSA) was investigated by disk diffusion method and growth curve analysis. The nanocomposite demonstrated excellent antibacterial activity as compared to bare rGO and inhibited nearly 87 % of the bacterial growth. The CRSA was more sensitive to nanocomposite compare MRSA and VRSA. More importantly, the nanocomposite obtained was found to achieve minimum inhibitory concentration (MIC) of ∼ 5 μg/mL. Besides, measurements of the charge transfer resistance, which is used to interpret bacterial response towards rGO or Fe2O3/rGO modified glassy carbon electrode, were performed using electrochemical impedance spectroscopy (EIS). The noteworthy antibacterial performance of the Fe2O3/rGO nanocomposite was probably attributed to the synergistic effect Fe2O3 NRs decorated rGO. The mechanism study suggested that nanocomposite can induce death to the bacteria by direct contact with the sharp edges of rGO and through the release of Fe3+ ions. The data, altogether, indicated that the Fe2O3 NRS decoration of rGO resulted in nanocomposite with enhanced antibacterial performance, hence, it may be used for developing new, safe, and effective antibiotics.

Experimental evaluation of the extractability of iron bound organic carbon in sediments as a function of carboxyl content

The majority of organic carbon (OC) burial in marine sediments occurs on continental shelves, of which an estimated 10–20% is associated with reactive iron (FeR). The association of OC with FeR (OC-FeR) is thought to facilitate preservation of organic matter (OM) in sediments and therefore represents an important carbon sink. The citrate-bicarbonate-dithionite (CBD) method is used to quantify OC-FeR in marine sediments by reductively dissolving FeR, thereby releasing bound OC. While the CBD method is widely used, it may be less efficient at measuring OC-FeR than currently thought, due to the incomplete reduction of FeR, resulting from the neutral pH conditions required to prevent OM hydrolysis. Additionally, the typical range of values reported for OC-FeR in marine sediments is narrow, despite variation in OM and FeR inputs, OM source types and chemical compositions. This suggests a limitation exists on the amount of OC that can become associated with FeR, and/or that the CBD method is limited in the OC-FeR that it is able to quantify. In assessing the efficiency of the CBD method, we aimed to understand whether methodological errors or (mis)interpretation of these extraction results may contribute to the apparent limitation on OC-FeR values. Here, we synthesised OC-FeR composites with a known FeR phase and known OM moieties, varying in carboxyl content, at neutral pH. These were spiked into OC-free marine sediment, and subject to a CBD extraction to investigate i) the efficiency of CBD for OC extraction; ii) the efficiency of CBD for FeR extraction; ii) how the OC moiety affects the physical parameters of associated FeR minerals; and iii) the impact of OM moiety on OC and Fe release. We show that the CBD method results in only partial dissolution of the most susceptible FeR phase (ferrihydrite) and therefore incomplete removal of bound OC. While as little as ~20% of Fe is released from OC-free ferrihydrite, structural disorder of the mineral phase increases with the inclusion of more OC, resulting in greater losses of up to 62% Fe for carboxyl rich OC-FeR complexes. In addition, our results show that the NaCl control step performed in the CBD method is capable of removing weakly bound OC from FeR, such that inclusion of this OC in the total OC-FeR fraction may increase marine sediments OC-FeR estimates by ~33%. Finally, we suggest that the structure of OC involved in OC-FeR binding can affect quantification of the OC-FeR pool. Our results have important implications for assessing the FeR bound OC fraction in marine sediments and the fate of this OC in the global carbon cycle.

Comparison of the reaction kinetics and mechanisms of Sb(III) oxidation by reactive oxygen species from pristine and surface-oxidized pyrite

With the rapid increase in the antimony (Sb) concentration in the environment, the environmental risk and pollution control of Sb has gradually attracted wide attention. The oxidation of Sb by pyrite influences its toxicity and mobility. Pyrite is oxidized by dissolved oxygen (DO) in an aerobic environment to form a surface oxide coating. However, the effect of the surface oxide coating on the reaction activity of pyrite is poorly understood. In this study, the influence of oxidation products on the surface morphology of pyrite and its interfacial reaction with Sb were investigated comprehensively. The amount of surface oxide coating increased with increasing pH. The main oxidation products under acidic conditions were mainly iron (II) hydroxy complex, and those under neutral conditions were iron (III) hydroxy complex. In a suspension of surface-oxidized pyrite (SOP), the oxidation efficiency of Sb(III) decreased significantly, and inhibition became more significant with increasing pH. As a result of the formation of the surface oxide coating, the contents of hydrogen peroxide (H2O2) and hydroxyl radicals (·OH), which are the main oxidants of Sb(III), were found to be lower in the SOP suspension than in pristine pyrite. The reasons are as follows. On the one hand, surface oxidation products decompose H2O2. On the other hand, they retard the production of H2O2 and ·OH by inhibiting Fe(II) release into the solution and O2 diffusion into the surface of pyrite. In addition, the adsorption capacity of Sb was enhanced after aqueous oxidation because Fe hydroxy complex have a strong affinity to Sb and large specific surface area. Aqueous oxidation of pyrite greatly influences the geochemical cycling and existence of Sb in the environment. The study lays a solid foundation for assessing the environmental risk of and developing pollution controls for Sb.

Selective removal of phosphate from aqueous solution by MIL-101(Fe)/bagasse composite prepared through bagasse size control

MIL-101(Fe)/sugarcane bagasse (SCB) with high adsorption capacity and selectivity toward phosphate was prepared through in-situ synthesis method. Effects of bagasse size on the morphology and performances of the composites were investigated, and adsorption behavior and mechanism of phosphate on the composite prepared at the optimum bagasse size were studied. Results showed that composite prepared with bagasse size of 200–300 mesh (MIL-101(Fe)/SCB3) showed much higher adsorption capacity than SCB, blank MIL-101(Fe) and the composites prepared with the other bagasse size, which was due to the more positively charged surface and the more exposed adsorption active sites including FeOHx and exchangeable Cl−. Co-ions experimental results illustrated that the as prepared MIL-101(Fe)/SCB3 showed high adsorption affinity toward phosphate, and the common cationic and anionic ions exhibited negligible effects on phosphate adsorption capacity and rate. The optimum pH range for phosphate adsorption on MIL-101(Fe)/SCB3 was from 3.0 to 10.0, and in this range Fe release was less than 0.03%. Adsorption mechanism showed that phosphate was adsorbed mainly through electrostatic force, ion-exchange, and inner-sphere surface complex. Simulated wastewater treatment experiment showed that MIL-101(Fe)/SCB3 could efficiently remove phosphate from aqueous solution.

Association between dexamethasone treatment and alterations in serum concentrations of trace metals.

Previously, a significant elevation in the serum levels of iron (Fe) was observed within a few days after the initiation of cisplatin (CDDP)-based chemotherapy. To clarify the underlying mechanisms, the serum concentration of hepcidin, a negative regulator of Fe release, was determined in the clinical samples obtained from six patients with cancer. The result showed that the serum concentration of hepcidin in patients receiving CDDP-based chemotherapy was significantly increased after 4-6 days of treatment, in comparison to the baseline level, suggesting that aforementioned excessive systemic Fe was not explained by the change of serum hepcidin level. All these patients received antiemetic premedication. We next evaluated of the effects of Pt-containing drugs and prophylactic antiemetic dexamethasone medication on the serum concentration of trace metals in mice, and on the hepatic and renal concentration of trace metals. The serum concentrations of Fe, Cu, and Zn in the CDDP-treated and oxaliplatin-treated mice were not significantly altered in comparison to those of the vehicle-treated control group. The serum concentrations of Fe, Cu, and Zn were increased after 24 h of dexamethasone treatment, compared to those of the control group (P < 0.05). The hepatic concentration of Mn was significantly reduced, whereas those of Fe and Cu inclined to diminish. The present findings suggest that dexamethasone can partly contribute to the changes in the serum concentrations of trace metals during anticancer chemotherapy.

Heterogeneous fenton oxidation of methylene blue with Fe-impregnated biochar catalyst

Fe-impregnated biochar (Fe-BC) as high-efficiency heterogeneous Fenton catalyst was synthesized and evaluated in detail for its catalytic activity, stability and reusability under various conditions. The optimal conditions for the Fenton oxidation of methylene blue (MB) as model dye were determined as 0.075 g/L H2O2, 0.5 g/L Fe-BC for 0.1 g/L MB, which resulted in optimum Dye:Fecat:H2O2 ratio of 1:5:0.75 (on g/L basis) or [Dye]:[Fetotal]:[H2O2] molar ratio of 1:6.2:7.0 respectively. The effective degradation of MB was identified over a wider pH range, and even after four consecutive runs Fe-BC maintained above 95% MB removal rate within 3 min of treatment with low Fe release, indicating strong stability and reusability. Under the optimum Dye:Fecat:H2O2 (g/L) condition at initial pH 4, the Fe-BC achieved 99.9% removal efficiency of MB within 3 min in heterogeneous Fenton reaction (HEFR) with much less H2O2 concentration and low catalyst dosage, demonstrating its efficiency and cost-effectiveness compared to other Fenton reaction catalysts. The removal velocity of MB showed two rate steps: a fast first stage followed by a slow stage with the rate in the order of H2O2/Fe-BC ⋙ H2O2/biochar > biochar > H2O2. Overall, the developed Fe-BC is more economical with strong stability and recyclability for use in HEFR for treating recalcitrant pollutants.

Soluble Fe release from iron-bearing clay mineral particles in acid environment and their oxidative potential

Soluble iron from atmospheric aerosol particles has toxicological effects on ambient environment due to their oxidative potential. However, the dissolution process and factors affecting this process are poorly understood. In this study, by solid phase characterization and aqueous dissolution experiments, we investigated the influence of acids, including HCl, H2SO4 and HNO3, and H+ concentration on iron dissolution rate, solubility and speciation of iron in chlorite, illite, kaolinite and pyrite. The dissolution of iron-bearing clay minerals, i.e. chlorite, illite and kaolinite, was a multi-stage process with a rapid rate in the initial stage and then decreasing rate in the following stages. In contrast, the regularly crystallized pyrite proceeded with an extremely rapid dissolution rate at very beginning and then remained almost constant. In all acid solutions, the dissolution rate was in the order of pyrite > illite > chlorite > kaolinite. H2SO4 was stronger than HCl and HNO3 in the destruction of mineral structures to release iron, while HNO3 dissolved more iron in pyrite (FeS2). High H+ concentration easily destroyed the mineral structures to release the structural or interlayer iron, whereas low H+ concentration increased the proportion of Fe (II) in clay minerals. Non-linear fitting of continuous dissolution models showed that the iron dissolution rates and iron redox speciation as functions of time were well predicted, with r2 > 0.99 for chlorite and illite, and r2 > 0.96 for kaolinite. Oxidative potential analysis proved that the dissolved iron possessed a considerable potential to generate reactive oxygen species.

Sedimentary iron cycling in the Benguela upwelling system off Namibia

Iron (Fe) is an essential micronutrient and its availability controls primary production in large parts of the ocean. Further, the variability of oxygen minimum zones (OMZ) exerts a major control on the availability of Fe, concentrations of which are elevated off Namibia. Therefore, to understand the sources and processes involved in the cycling of Fe off Namibia, we determined major and trace element contents (Fe, Al, Si, K, P, organic carbon, Mn, Co, Zr) and the isotopic composition of Fe (δ56Fe) in seven sediment cores along a transect from the shelf to the abyssal plain at ∼5 km water depth (Meteor cruise M76-1) as well as in the local lithogenic background (Namibian river bed sediments and dust).The depletion of Mn vs. the local lithogenic background (LLB) reflects the reducing character of sediments from the shelf to the lower slope. While depletion of Mn and enrichment of Co indicates the anoxic–sulfidic environment on the shelf, the enrichment of both elements in abyssal sediments documents highly oxidizing conditions there.Iron/Al ratios are elevated (0.6 to 1.6) and therefore equal to, or higher than the LLB. The highest Fe enrichment is seen on the shelf (core 1) and the shelf break (core 2) with a clear decrease towards the abyss. The bulk δ56Fe values range from +0.30 to −0.05‰ in the marine sediments, with an average of ∼0.08‰, which is slightly lighter than the δ56Fe of the LLB (0.16 to 0.21‰). Further, combined enrichments of K and Fe suggest the presence of detrital biotite (core 1) and authigenic glauconite (core 2), both of which are perfectly correlated with Zr/Al ratios reflecting the highly dynamic conditions of the shelf environment (0-300 m water depth).The absent large sedimentary Fe isotope fractionation in the sediments of this study compared to Peru sediments is likely due to a combination of the following: (i) a highly variable OMZ leading to random re-oxidation of any sediment-sourced Fe which prevents the export of larger amounts of dissolved Fe to the interior of the ocean, and which also prevents focused enrichments of Fe, and (ii) an enhanced dust flux, which frequently resupplies terrestrial Fe dampening any Fe isotope fractionation.This study is a snapshot on sedimentary Fe cycling in one area from the vast Namibian margin. Compared to the Peruvian margin, the data suggest little sedimentary Fe release, transport and redeposition. However, previous water column data suggest substantial Fe release. Hence, for a more subtle investigation of the Fe loss and re-supply a higher sampling resolution of multiple cores across the shelf and slope will be required.

The iron records and its sources during 1990–2017 from the Lambert Glacial Basin shallow ice core, East Antarctica

In this study, a shallow ice core (12.5 m, called LGB) was drilled at the Lambert Glacial Basin, East Antarctica. The major ion and metal elements were measured at 5–6 cm resolution in this shallow core, which covered the period 1990–2017. Therefore, an annual-resolution record of iron (Fe) concentrations and fluxes were reconstructed in this shallow ice core. Although the Fe data is comparable to previous results, our results emphasized that much more dissolved Fe (DFe) from the Cerro Hudson volcanic event (August 1991) was transported to the East Antarctic ice sheet, in comparison with the Pinatubo volcanic event (June 1991). The aeolian dust may be the primary DFe source during 1990–2017. In particular, the DFe variations may be affected by the biomass burning emissions in two periods (1990–1998 and 2014–2017). While total dissolved Fe (TDFe) variations were controlled by the climatic conditions since 2000 because of the temperature (δ18O) decreasing at East Antarctica. These Fe data will be useful to assess the modern bioavailable Fe release for the Antarctica ice sheet.

Long-term electrode behavior during treatment of arsenic contaminated groundwater by a pilot-scale iron electrocoagulation system

Iron electrocoagulation (Fe-EC) is an effective technology to remove arsenic (As) from groundwater used for drinking. A commonly noted limitation of Fe-EC is fouling or passivation of electrode surfaces via rust accumulation over long-term use. In this study, we examined the effect of removing electrode surface layers on the performance of a large-scale (10,000 L/d capacity) Fe-EC plant in West Bengal, India. We also characterized the layers formed on the electrodes in active use for over 2 years at this plant. The electrode surfaces developed three distinct horizontal sections of layers that consisted of different minerals: calcite, Fe(III) precipitates and magnetite near the top, magnetite in the middle, and Fe(III) precipitates and magnetite near the bottom. The interior of all surface layers adjacent to the Fe(0) metal was dominated by magnetite. We determined the impact of surface layer removal by mechanical abrasion on Fe-EC performance by measuring solution composition (As, Fe, P, Si, Mn, Ca, pH, DO) and electrochemical parameters (total cell voltage and electrode interface potentials) during electrolysis. After electrode cleaning, the Fe concentration in the bulk solution increased substantially from 15.2 to 41.5 mg/L. This higher Fe concentration led to increased removal of a number of solutes. For As, the concentration reached below the 10 μg/L WHO MCL more rapidly and with less total Fe consumed (i.e. less electrical energy) after cleaning (128.4 μg/L As removed per kWh) compared to before cleaning (72.9 μg/L As removed per kWh). Similarly, the removal of P and Si improved after cleaning by 0.3 mg/L/kWh and 1.1 mg/L/kWh, respectively. Our results show that mechanically removing the surface layers that accumulate on electrodes over extended periods of Fe-EC operation can restore Fe-EC system efficiency (concentration of solute removed/kWh delivered). Since Fe release into the bulk solution substantially increased upon electrode cleaning, our results also suggest that routine electrode maintenance can ensure robust and reliable Fe-EC performance over year-long timescales.

Development of a novel oxidative stress-amplifying nanocomposite capable of supplying intratumoral H2O2 and O2 for enhanced chemodynamic therapy and radiotherapy in patient-derived xenograft (PDX) models.

Radiotherapy (RT) is a potent approach to cancer treatment, but the tumor microenvironment (TME) in solid tumors is often highly hypoxic and contains high levels of antioxidant enzymes, thereby reducing the RT efficacy. In this study, we developed an oxidative stress amplifier (termed CFM) capable of self-sufficient H2O2 and O2 delivery that can be used in concert with RT and chemodynamic therapy (CDT) to treat tumors in patient-derived xenograft (PDX) model systems. Upon exposure to the hypoxic and acidic TME, CFM undergoes rapid degradation that results in the release of Fe3+, Ca2+, O2, and H2O2. Glutathione can subsequently reduce Fe3+ to Fe2+, which is then able to react with H2O2via the Fenton reaction to yield high levels of hydroxyl radicals which subsequently damage mitochondria. CaO2-derived O2 also modulates intratumoral hypoxia, while excessive Ca2+ levels within mitochondria result in apoptotic cell death. Altogether, these properties sensitize PDX tumors to RT. Importantly, the Fe, Zn, and Ca generated by CFM degradation are essential elements in humans. Altogether, these properties make this approach to oxidative stress amplification a promising means of amplifying oxidative stress within tumors while overcoming hypoxia-related resistance to RT, thereby providing a framework for the design of potent radiosensitizing therapeutic approaches.

The Effect of Mixing Method on Preparing Chitosan-Zeolite-Fe Composites on Fe(III) Release

&lt;p&gt;Preparation of an Fe(III) slow-release materials using chitosan and zeolite and evaluation of their release behavior in the 0.33 M citric acid has been done. The composite synthesis was carried out by varying the method of mixing basic ingredients. The first method was done by mixing chitosan gel, zeolite and Fe solution altogether (composite A). The second method was done by mixing chitosan gel with Fe solution and stirring, after that adding zeolite (composite B). The last method was done by interacting zeolite with Fe solution then stirring and then adding chitosan gel (composite C). The structure of the composite was characterized using an infrared spectrophotometer (FTIR), X-Ray diffractometer (XRD), and SEM. Evaluation of release in the citric acid 0.33 M for composite showed that the order of release of Fe(III) from the fastest was chitosan-Fe, composite A, composite B, composite C, zeolite-Fe with values of k are 0.049 mg/g; 0.016 mg/g; 0.015 mg/g; 0.011 mg/g; and 0.006 mg/g, respectively. The SEM images of composite showed rough surface morphology of composites due to the presence of zeolite-Fe which was not coated by the chitosan framework. Thus, it can be concluded that the chitosan-zeolite-Fe composite can be used as a Fe(III) slow-release composite but the variation of mixing method of the materials does no effect on the Fe(III) slow-release properties.&lt;/p&gt;

Oscillatory cAMP signaling rapidly alters H3K4 methylation

Epigenetic variation reflects the impact of a dynamic environment on chromatin. However, it remains elusive how environmental factors influence epigenetic events. Here, we show that G protein-coupled receptors (GPCRs) alter H3K4 methylation via oscillatory intracellular cAMP. Activation of Gs-coupled receptors caused a rapid decrease of H3K4me3 by elevating cAMP, whereas stimulation of Gi-coupled receptors increased H3K4me3 by diminishing cAMP. H3K4me3 gradually recovered towards baseline levels after the removal of GPCR ligands, indicating that H3K4me3 oscillates in tandem with GPCR activation. cAMP increased intracellular labile Fe(II), the cofactor for histone demethylases, through a non-canonical cAMP target-Rap guanine nucleotide exchange factor-2 (RapGEF2), which subsequently enhanced endosome acidification and Fe(II) release from the endosome via vacuolar H+-ATPase assembly. Removing Fe(III) from the media blocked intracellular Fe(II) elevation after stimulation of Gs-coupled receptors. Iron chelators and inhibition of KDM5 demethylases abolished cAMP-mediated H3K4me3 demethylation. Taken together, these results suggest a novel function of cAMP signaling in modulating histone demethylation through labile Fe(II).

Distribution character of localized iron microniche in lake sediment microzone revealed by chemical image.

DGT (diffusive gradients in thin films) technique and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) for heterogeneous distribution of the soluble labile iron (Fe) at submillimeter resolution in lake sediment porewater are reported. The soluble labile Fe species include ion and labile organic complexes. The chemical images in two dimensions (2D) for DGT concentration of Fe (CDGT(Fe)) are investigated for Fe remobilization character. There are 902 CDGT(Fe) values between 1000 and 2000 μg L-1, 463 values between 2000 and 3000 μg L-1, and 112 values over 3000 μg L-1 in all chemical maps. Based on the linear correlation relationships between CDGT (Fe) and total Fe (TFe), total organic carbon (TOC), acid-volatile sulfide (AVS), Eh, concentrations of the soluble reactive phosphorus (P) (SRP), and soluble labile trace metals (Zn, Cu, Pb, and Zn) in a vertical 1D profile of sediment or porewater, Fe release mechanisms are mainly due to the reductive Fe release from iron oxyhydroxides and the decomposition of organic matter in algae biomass and deep sediment layer. It can be used to explain the formation mechanisms of Fe microniches in chemical maps with heterogeneous character to a great extent. CDGT(Fe) peak flux in the center of Fe microniche and the low CDGT (Fe) at the edge of a microniche are due to the formation of the insoluble iron sulfide and the abundant acid-volatile sulfide (AVS) in sediment. The verified co-remobilization of the soluble labile Fe and trace metals or SRP in sediment porewater can be used to predict their simultaneous release from Fe microniches with the large CDGT (Fe) peaks. The different kinds of Fe microniche zones and hot spots from sediment/water interface (SWI) to deep sediment correspond to the formation mechanisms of microniches mentioned above. Moreover, some narrow Fe microniche zones with the large CDGT (Fe) across chemical maps are due to the desorption of Fe(II) from the freshly formed oxide on Myriophyllum verticiilatur roots, which are located at sites of microniche zones.

Micron-scale distribution controls metal(loid) release during simulated weathering of a Pennsylvanian coal shale

Coal mine spoil is a long-lasting legacy of historic coal mining operations that continues to impact water quality across Appalachia. Metal(loid) release from abandoned coal mine spoil, which can be a significant source of acid mine drainage (AMD), is dependent on speciation and distribution within the parent coal shale. This work aimed to determine how the micron- and sub-micron scale mineralogy, morphology, and texture of metal(loid)-bearing phases in a coal-shale control the rate and release of metal(loid)s during subsequent weathering through two primary objectives: (1) determine the microscale speciation and distribution of Fe and other metal(loid)s in a parent coal shale, and (2) determine the amount of metal(loid)s released during simulated weathering of shale physically crushed into silt- to sand-sized particles. This work was accomplished through a combination of electron microscopy and synchrotron-based X-ray microprobe analyses. This suite of techniques also provides insight into the geochemical history of the coal shale that could not be determined by bulk techniques. Trace elements were associated with either Fe-sulfides or with other phases that included metal(loid)-sulfides, aluminosilicates, and organic matter. Three distinct pools of Fe-sulfides were present: (i) larger mm-scale grains, with minimal internal fractures; (ii) μm- to mm-scale aggregates of μm-scale crystals forming secondary coatings on the larger mm-scale grains, and (iii) μm- to mm-scale aggregates forming framboidal grains. Fe-sulfide mineralogy was dominated by pyrite with minor contributions of marcasite and a S(-II)-bearing phase. Larger pyrite grains and their secondary coatings contained homogeneous distributions of Fe and Mn as well as other trace metal(loids) including V, Ti, Cr, As, Se, Cu, and Zn. The fine-grained pyrite aggregates were strongly enriched in As and Se and contained discrete Cu- and Zn-bearing particles. Clays and organic matter surrounding the sulfide minerals were identified by micro-XRD and FT-IR spectroscopy. Simulated batch weathering of the physically crushed shale resulted in metal(loid) release that varied as function of size fraction and time. Metal(loid) release increased with decreasing particle size from sand-sized to silt-sized fractions. Although small amounts of Fe were released into solution after two days, the bulk of Fe release occurred after 10 days and continued for six months, after which Fe was gradually removed from solution. The weathering trends for Mn, Cu, Zn, and Ni were similar to Fe. In contrast, As and Se were characterized by rapid release into solution followed by removal prior to 10 days. These results indicate that micrometer-scale metal(loid) distribution within Fe sulfides controlled metal(loid) release into solution during simulated weathering of a coal shale. Specifically, elements concentrated in mineral coatings (As, Se) were rapidly mobilized in a short-lived pulse whereas elements associated with the larger grains (Fe, Mn, Cu, Zn, and Ni) exhibited a delayed but prolonged release into solution. The non-concomitant contaminant release indicates that an understanding of the textural relationships in the source material is required to understand weathering trends. This work highlights the importance of non-point sources of AMD, and addressing these sources is a critical step in improving water quality in the region.

Reactive iron isotope signatures of the East Asian dust particles: Implications for iron cycling in the deep North Pacific

Iron released from wind-blown dust has been widely suggested to be an important nutrient source for oceanic primary productivity. Once introduced into the seawater, the reactive Fe might get dissolved and impart its isotope signature into the water column. Characterization of the reactive iron isotope signatures of eolian dust will thus help to understand the budget of Fe in the global ocean. Yet, there are few systematic studies on the Fe isotope systematics of the dust sources across large spatial scale. Here, we report Fe isotope data from HCl leaching experiment on surficial samples from deserts and loess deposits of different locations spanning >3000 km spatially in east Asia, one of the most important dust source regions. Our data suggest most of the samples have relatively similar leaching signatures (δ56Fe = –0.09±0.07‰, n=9, 2 SD). To understand the kinetics of Fe release during proton promoted leaching of natural particles, a synthetic model taking into account of different dissolution dynamics of easily dissolvable Fe and silicate Fe was developed. The model was tested by continuous leaching of two representative pelagic sediment samples recovered from core LL44-GPC3 in the North Pacific. When introducing only one tunable parameter (i.e., the initial dissolution rate of Fe from hydro(oxides), with other parameters constrained by the dissolution kinetics), the model successfully reproduces leachate δ56Fe evolution and agrees reasonably well with Fe speciation in the studied marine sediment samples. We thus suggest that the leaching process can be well characterized by our kinetic model, while Fe isotopes in the initial leachates of the samples are dominated by endmember composition of the easily dissolvable Fe species. The small but distinct fractionation of Fe isotopes in the desert/loess samples from the parental upper continental silicate materials are suggested to record signatures of the secondary Fe species produced during weathering in the oxic environment. The significantly lighter Fe isotope compositions in the initial leachates of the North Pacific pelagic sediment samples compared to the east Asian desert/loess deposits indicate apparent isotope exchange of the dust reactive components with seawater dissolved species. The sedimentary light reactive Fe isotope signatures in turn point toward the contribution of sources characterized by low δ56Fe to the deep North Pacific and/or preferential uptake of 56Fe by seawater ligands from the dust reactive components particularly at the seawater-sediment interface.

Highly robust La1-xTixFeO3 dual catalyst with combined photocatalytic and photo-CWPO activity under visible light for 4-chlorophenol removal in water

A highly robust Ti-substituted LaFeO3 dual catalyst was synthesized via a facile Pechini sol-gel route using a dried amorphous sol-gel titania as titanium source and a final calcination at 800 °C that enabled solid-solid diffusion of titanium atoms within the perovskite network. Using an amorphous precursor instead of crystallized titania nanocrystals increased the Ti → La atomic substitution degree in the crystalline network from 5 at% to 11 at%, together with a strong increase in the catalytic activity. The partially substituted La1-xTixFeO3 catalyst with a 11 at% substitution degree allowed pure heterogeneous surface reactions to take place under pure visible light (λ > 420 nm), with an increase in the catalyst robustness by more than two orders of magnitude compared to the unmodified LaFeO3 counterpart, evidenced by the absence of any Fe release, the structural stability of the substituted catalyst and the absence of any loss of catalytic activity with test cycles. Further, the strategy of combining both photocatalysis and H2O2-mediated heterogeneous photo-Fenton advanced oxidation processes within one single heterogeneous catalyst allowed the dual La1-xTixFeO3 catalyst to simultaneously take advantage from the higher reaction rate of photo-Fenton and from the higher mineralization yield of photocatalysis in water treatment. As a result, the dual 11 at% Ti-substituted La1-xTixFeO3 catalyst clearly outperformed its unmodified LaFeO3 counterpart and led to a complete mineralization of the 4-chlorophenol substrate under pure visible light, with strongly enhanced H2O2 decomposition, 4-chlorophenol and TOC conversion rates. Finally, the activity of the La1-xTixFeO3 catalyst under visible light contributed significantly to its overall activity obtained using the full solar spectra.

High sulfate concentration enhances iron mobilization from organic soil to water

Widespread increases in iron (Fe) concentrations are contributing to ongoing browning of northern freshwaters, but the driver/s behind the trends are not known. Fe mobilization in soils is known to be controlled by redox conditions, pH, and DOC availability for complexation. Moreover, high sulfate concentrations have been suggested to constrain Fe in transition from soil to water, and declining sulfate deposition to have the opposite effect. We studied the effect of these Fe mobilization barriers in a microcosm experiment, applying high (peak S deposition) and low (present day) sulfate treatments and oxic versus anoxic conditions to boreal (O horizon) soil slurries. We hypothesized that anoxic conditions would favor Fe release. On the contrary we expected high sulfate concentrations to suppress Fe mobility, through FeS formation or by lowering pH and thereby DOC concentrations. Anoxia had positive effects on both Fe and DOC concentrations in solution. Contrasting with our hypothesis, Fe concentrations were enhanced at high sulfate concentrations, i.e. increasing acidity in high sulfate treatments appeared to promote Fe mobilization. Establishment of the basidiomycete fungus Jaapia ochroleuca in the oxic treatments 44 days into the experiment had a major impact on Fe mobilization by increasing total Fe concentrations in solution. Thus, anoxia and acidity, along with fungi mediated mobilization, were important in controlling Fe release from soil to the aqueous phase. While Fe is often assumed to precipitate as Fe(oxy)hydroxides in the transition from anoxic to oxic water in the riparian zone, Fe from anoxic treatments remained in solution after introduction of oxygen. Our results do not support reduced atmospheric S deposition as a driver behind increasing Fe concentrations in boreal freshwaters, but confirm the importance of reducing conditions—which may be enhanced by higher soil temperature and moisture—for mobilization of Fe across the terrestrial-aquatic interphase.

Comparison of microwave and furnace melting for glasses to immobilise Fe-corrosion products

ABSTRACTThis study reports a comparison between Fe-based corrosion products immobilised by direct vitrification through furnace melting versus microwave melting. Although microwave melting is faster, the Fe-corrosion product does not dissolve in the melt and is encapsulated by the vitreous phase. In comparison, for furnace melting, complete dissolution of the corrosion product in the glass is obtained till the solubility limits are exceeded. In both cases, Fe release is low indicating that either strategy may be employed for immobilisation depending upon the species captured in the Fe-corrosion product.

The role of concentrations gradients on phosphorus and iron dynamics from chemically-dosed horizontal flow wetlands for tertiary sewage treatment.

This study examined the dynamics of iron (Fe) and phosphorus (P) transformations from the surface sludge accumulated in tertiary horizontal flow (HF) treatment wetlands (TW) chemically dosed for P removal. Site surveys showed P was stored in HF TW with and without artificial aeration on average, with instances of P release in the non-aerated site. Controlled experiments revealed storing TW surface sludge for over 24 hours resulted in limited oxygen and nitrate concentrations, resulting in both P and Fe release. The rate of P release increased with increasing water-sludge P concentration gradients, and the reaction could take as little as 10 minutes. Convection had no impact on P transformation rates. The findings suggest mitigation strategies could include the manipulation of the biogeochemical environment by managing oxygen and nitrate concentrations within the wetlands. A better understanding of links between Fe, P, and nitrate is needed to test proactive mitigation strategies for small wastewater treatment plants.