Amorphous Iron Oxyhydroxide Research Articles

The dual gain strategy of introducing nickel doping and anchoring amorphous iron oxyhydroxide nanosheets on ZIF-67 achieves an efficient oxygen evolution reaction

A ZIF-67@Ni@FeOOH composite material was synthesized using nickel-doped ZIF-67 as a precursor and was electrochemically characterized as an efficient oxygen evolution reaction (OER) catalyst. The results indicated that Ni doping preserved the polyhedral structure of ZIF-67 while enhancing its OER activity. The introduction of amorphous FeOOH nanosheets allowed ZIF-67@Ni@FeOOH to not only retain its original polyhedral structure but also develop a hollow interior and self-remodeling surface, resulting in numerous defects. These features contribute to improved charge transfer efficiency and enhanced conductivity of the material. The dual enhancement effect is achieved by combining the doping strategy with structural defect engineering. The synergistic effects of Co, Ni, and Fe species further boost OER performance. The ZIF-67@Ni@FeOOH catalyst exhibited remarkable OER efficacy, with the lowest overpotential at a current density of 10 mA cm−2 being 329 mV and a low Tafel slope of 42.95 mV dec−1. In situ Raman spectroscopy revealed that high-valence hydroxyl oxides, specifically NiOOH and CoOOH, present on the composite surface were the active species for OER. This study offers a promising approach for developing economically viable electrocatalysts with superior efficiency for OER.

Z-scheme FeOOH/g-C3N4 nanosheets promoted PDS activation for efficient tetracycline degradation under visible light

Recently, photocatalysis combined peroxydisulfate (PDS) activation as a novel advanced oxidation processes (AOPs) was applied to remove pharmaceuticals and personal care products (PPCPs) in waterbody. Under visible light irradiation, photocatalysts, such as graphitic carbon nitride (g-C3N4, CN), could generated holes and electrons for both organic oxidation and PDS activation. However, it exhibits the drawbacks of low organics removal rate, high electron-hole recombination rate and low activation efficiency of PDS. In this study, amorphous iron oxyhydroxide (FeOOH) was intercalated into the surface of the g-C3N4 nanosheets (CNNS) to form a Z-scheme heterojunction to solve these problems. Electrochemical impedance spectroscopy (EIS) and photoluminescence spectrum (PL) tests proved the enhancement of the charge separation and migration capability of FeOOH/CNNS. The density functional theory (DFT) supported the constructive role of the Z-type heterojunction between FeOOH and CNNS in promoting photocarrier transfer and facilitating more effective PDS activation reactions. The removal rate of tetracycline (TC) achieved 98.8 % within 80 min by FeOOH/CNNS coupled PDS under visible light (FeOOH/CNNS-PDS/Vis) system. Finally, electron spin resonance (ESR) approved the pivotal role of •OH, SO4•-, and •O2- during the process.

Green Synthesis of Pure Superparamagnetic Fe3O4 Nanoparticles Using Shewanella sp. in a Non-Growth Medium

Conventional wet chemical methods for the synthesis of superparamagnetic magnetite nanoparticles (MNPs) are energy-intensive and environmentally unsustainable. Green synthesis using bacteria is a less-explored approach to MNP production. Large-scale biosynthesis of MNPs has heretofore been conducted using extremophilic bacteria that exhibit low growth rates and/or require strict temperature control. However, a decrease in material and energy costs would make such bioprocesses more sustainable. In this study, Shewanella putrefaciens CN-32, an iron-reducing bacterium, was employed to reduce amorphous iron oxyhydroxide and synthesize MNPs in a non-growth medium at ambient temperature and pressure. The synthesis was conducted using plain saline solution (0.85% NaCl) to avoid impurities in the products. X-ray diffraction and transmission electron microscopy indicated that the reduction products were MNPs with a pseudo-spherical shape and 6 ± 2 nm average size. Magnetometry showed that the particles were superparamagnetic with maximum saturation magnetization of 73.8 emu/g, which is comparable to that obtained via chemical synthesis methods. Using less than a quarter of the raw materials employed in a typical chemical co-precipitation method, we obtained a maximum yield of 3.473 g/L (>5-fold increase). These findings demonstrate that our simple and ecofriendly process can help overcome the current barriers for large-scale synthesis of high-purity magnetic nanopowders.

Assessment of the ecological risk and mobility of arsenic and heavy metals in soils and mine tailings from the Carmina mine site (Asturias, NW Spain)

An evaluation of the pollution, distribution, and mobility of arsenic and heavy metals in spoil heaps and soils surrounding the abandoned Carmina lead–zinc mine (Asturias, northern Spain) was carried out. Fractionation of arsenic was performed by an arsenic-specific sequential extraction method; while, heavy metal fractionations was carried out using the protocol of the Bureau Community of Reference (BCR) (now renamed Standards, Measurements and Testing Programme). Arsenic appeared predominantly associated with amorphous iron oxyhydroxides. Among the heavy metals, lead and zinc showed high availability since significant amounts were extracted in the nonresidual fractions; whereas, chromium, copper and nickel showed very low availability, indicating their lithogenic origins. The results showed that the extractability of heavy metals in soils is influenced mainly by the presence of iron and manganese oxides as well as by pH and Eh. Multiple pollution indices, including the enrichment factor (EF), geoaccumulation index (Igeo), ecological risk index (Er) and potential ecological risk index (PERI), were used to assess the degree of soil pollution in the mine area. All results showed that lead was the key factor causing the pollution and ecological risk in the studied area, and copper, zinc and arsenic also had significant contributions. Notably, the sites at higher risk coincided with those with high availability of arsenic and heavy metals. This study provides an integrative approach that serves as a powerful tool to evaluate the metal pollution status and potential threats to the local environment of abandoned mining areas, and the results are useful for making management decisions in these areas.

Amorphous iron oxyhydroxides nano precursors used for Reactive Yellow 84 removal from aqueous solutions

In this research, we investigated the potential use of amorphous iron oxyhydroxides, ferrihydrite (FHY), for the removal of persistent pollutants from aqueous solutions. Ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N, N′-disuccinic acid (EDDS) were used as complexing agents during synthesis aiming to enhance the FHY properties. Synthesized materials were characterized by X-ray diffraction, SEM and TEM Microscopy, N2 sorption/desorption, and FT-IR Spectroscopy for their mineralogy, crystallinity, morphology and size, surface properties, and the organic content in their structure. The addition of chelating agents led to differences in nanoparticles morphology, amorphic degree, and surface properties. Reactive Yellow 84 dye was chosen as a representative refractory pollutant and laboratory-scale adsorption studies were conducted at varying dye concentrations. Ca. 100 % RY 84 dye removal efficiency was achieved within one hour at dye concentrations of 5–10 mg/L for an adsorbent dosage of 1 mg/L FHY. Adsorption kinetics and isothermal studies were considered, the uptake capacity was calculated for each nanomaterial and empiric mechanistic information was derived. The results showed that ferrihydrite exhibits the best performance, with a maximum uptake capacity of 40.73 mg Reactive Yellow 84 dye per gram adsorbent followed by FHY_EDTA and FHY_EDDS (up to 35.86 mg/g). Coupling the adsorption with photodegradation processes led to a significant increase in removal efficiencies of persistent RY 84 from polluted aqueous solution, in good timing, suggesting a feasible alternative at sites where dye concentration in effluents is elevated.

Ce Site in Amorphous Iron Oxyhydroxide Nanosheet toward Enhanced Electrochemical Water Oxidation.

Iron oxyhydroxide has been considered an auspicious electrocatalyst for the oxygen evolution reaction (OER) in alkaline water electrolysis due to its suitable electronic structure and abundant reserves. However, Fe-based materials seriously suffer from the tradeoff between activity and stability at a high current density above 100mA cm-2 . In this work, the Ce atom is introduced into the amorphous iron oxyhydroxide (i.e., CeFeOx Hy ) nanosheet to simultaneously improve the intrinsic electrocatalytic activity and stability for OER through regulating the redox property of iron oxyhydroxide. In particular, the Ce substitution leads to the distorted octahedral crystal structure of CeFeOx Hy , along with a regulated coordination site. The CeFeOx Hy electrode exhibits a low overpotential of 250mV at 100mA cm-2 with a small Tafel slope of 35.1 mVdec-1 . Moreover, the CeFeOx Hy electrode can continuously work for 300h at 100mA cm-2 . When applying the CeFeOx Hy nanosheet electrode as the anode and coupling it with the platinum mesh cathode, the cell voltage for overall water splitting can be lowered to 1.47V at 10mA cm-2 . This work offers a design strategy for highly active, low-cost, and durable material through interfacing high valent metals with earth-abundant oxides/hydroxides.

Phyllosilicate-based adsorbents decorated with iron oxyhydroxides: Application for lead, chromates and selenites removal

Expanded vermiculite (EVer) was acid activated and silanized in order to obtain suitable substrate?s surface for decoration with iron oxyhydroxides (IO). Obtained activated sample (EVa), was decorated by deposition of either prevailing goethite or amorphous iron oxyhydroxides (AIO) resulting in EV-A and EV-B adsorbent, respectively. Modifications of EVa showed improved adsorption performances when used as adsorbent of lead, chromates and selenites. Adsorption experiments conducted in a batch and column system demonstrated good potential for purification of water contaminated with Pb2+, Cr(VI), and Se(IV). Equilibrium adsorption capacity of EV-A in relation to Pb2+ and Cr(VI) were 48 and 54 mg g-1, respectively, while EV-B showed even better effectiveness for Se(IV) achieving 120 mg g-1 capacity. Regeneration of pollutant saturated adsorbents approved that prepared adsorbents possess fine removal potency even after five adsorption/desorption cycles from 87.58 (for Pb2+/EV-A) to 92.81 % (for Cr(VI)/EV-A) of initial adsorption capacity.

Modern authigenic amorphous and crystalline iron oxyhydroxides in subsurface Ordovician dolostones (Jinan, North China Block): Biomineralization and crystal morphology

Iron oxide/oxyhydroxide precipitation in nature can involve various mechanisms that are associated with environmental conditions. Amorphous and crystalline Fe oxyhydroxides associated with extracellular polymeric substances (EPS) are common in some of the pores and fractures of subsurface Ordovician dolostone (Jinan, North China Block). These precipitates, dominated by ferrihydrite nanogranules (20–30 nm), acicular goethite nanorods and nanofibers (>200 nm), and various twinned goethite polymorphs (~1–3 mm), record a series of crystallization stages that reflect the mechanisms of iron mineralization. For Fe oxyhydroxide formation this involved: (1) biogenic ferrihydrite and goethite nanoparticle formation, (2) ferrihydrite–goethite transformation and development of nanogranule-attached goethite, (3) goethite twin development, and (4) multi-generation overgrowths on twined goethite. This process shows that the Fe was fixed biogenically with crystallization taking place via a nonclassical nanogranule-aggregation pathway. As such, it highlights the complex mechanisms of crystal growth and morphological development involved with Fe oxyhydroxide mineralization in nature. The distribution of the precipitates, concentrated in larger voids ~11 m below ground surface, demonstrates their sensitivity to ambient conditions such as redox and Fe supply.

Recovered mine drainage passive treatment residuals address legacy sediment pollution: A field mesocosm study at Grand Lake o' the Cherokees, Oklahoma

Grand Lake o' the Cherokees, Oklahoma is a large multipurpose reservoir that receives both elevated metals concentrations from the upstream Tri-State Lead-Zinc Mining District (TSMD) and excess nutrients from its agricultural watershed along with significant internal phosphorus (P) legacy loads. Mine drainage residuals (MDRs), amorphous iron oxyhydroxides recovered from passive treatment systems, may serve as phosphorus sinks. To evaluate the role of MDRs on reservoir sediment dynamics, a field mesocosm study (20-L vessels) was designed with four different mine drainage residuals (MDR) treatments: sediment control (no addition), mixed (MDR mixed with sediment), layered (MDR on top of sediment, no mixing) and bagged (MDR inside a fine mesh bag on top of sediment, no mixing) with phosphorus-spiked water. Soluble reactive P (SRP) concentrations demonstrated decreasing trends and the control treatment showed greater concentrations than all MDR treatments. P adsorption capacity (PAC) was determined to be approximately 0.7 mg/g and > 30 mg/g for sediments and MDRs, respectively. At Day 135, SRP reached >99% removal for all four treatments. Aqueous lead and cadmium concentrations were below detection limits and zinc concentrations were below the National Recommended Water Quality Criteria. Sediment lead, zinc and cadmium concentrations were below the TSMD-specific sediment quality guidelines, except for final Mixed MDR treatment sediment with 16.7% of samples exceeding both Cd and Pb criteria. Results showed that MDRs removed excess P from the water column and by using the recommended bagged addition method, trace metal release to both the water column and sediment layer were minimized.

Preparation of adsorbent based on water treatment residuals and chitosan by homogeneous method with freeze-drying and its As(V) removal performance

Although the chitosan-WTRs particulate adsorbent prepared by embedding method has been proved to have arsenic adsorption capacity, the capacity of it is greatly weakened compared with the original water treatment residuals (WTRs). In this study, WTRs and chitosan were used as raw materials to prepare a new kind of adsorbent beads by a homogeneous method. At the same time, in order to enhance the adsorption capacity and reduce the limitation of kinetics, freeze-drying method was chosen to dry the adsorbent. The WTRs-chitosan beads by homogeneous method (WCB) were characterized by SEM, XRD, XPS and other methods. According to the characterization results, there are regularly arranged pores inside the particles, and the iron in the particles mainly exists in the form of amorphous iron oxyhydroxide. According to the results of batch experiment, the pseudo-second-order kinetic model has a higher degree of fit, indicating that the WCB adsorbs As(V) mainly by chemical adsorption. The maximum adsorption capacity estimated from the Langmuir isotherm model is 42.083 mg/g, which is almost same as the WTRs. Weak acid and neutral conditions are conducive to adsorption, while alkaline conditions have a significant inhibitory effect on arsenic adsorption.

Effect of Cr on Aqueous and Atmospheric Corrosion of Automotive Carbon Steel.

This study investigated the effect of Cr alloying element on the corrosion properties of automotive carbon steel (0.1C, 0.5Si, 2.5Mn, Fe Bal., composition given in wt.%) in aqueous and atmospheric conditions using electrochemical measurement and cyclic corrosion tests. Three steels with 0, 0.3, and 0.5 wt.% Cr were studied by electrochemical impedance spectroscopy. Polarization resistance (Rp) of 0.3 Cr and 0.5 Cr steels was higher than that of 0 Cr steel, and the Rp also increased as the Cr content increased. Therefore, Cr increases the corrosion resistance of automotive carbon steel immersed in a chloride ion (Cl−)-containing aqueous solution. In the cyclic corrosion test results, Cl− was concentrated at the metal/rust interface in all of the steels regardless of Cr content. The Cl− was uniformly concentrated and distributed on the 0 Cr steel, but locally and non-uniformly concentrated on the Cr-added steels. The inner rust layer consisted of β-FeOOH containing Cl− and Cr-goethite, while the outer rust layer was composed of amorphous iron oxyhydroxide mixed with various types of rust. FeCl2 and CrCl3 are formed from the Cl− nest developed in the early stage, and the pitting at CrCl3-formed regions are locally accelerated because Cr is strongly hydrolyzed to a very low pH.

Geochemical signatures of lignite mining products in sediments downstream a fluvial-lacustrine system

As a result of the open-cast lignite mining in the Lusatian region of north-eastern Germany, large amounts of iron, sulphate, trace metals, and aluminium are fed into the groundwater and small streams that discharge into the River Spree, which ultimately flows through urban Berlin. In this study, we examined whether the input of these mining products leads to longitudinal gradients in element compositions and mineral formations in the riverine sediments. The signatures of fluvial and interconnected lacustrine sediments along a 190-km flow section were evaluated via principal component analysis to define the impact range of the open-cast products. These products clearly showed a sediment impact range of at least ~90 km downstream of the mining area. In particular, nickel and cobalt readily co-precipitate with iron, while sedimentary sulphur initially increases and therefore shows a longer impact range than amorphous iron oxy-hydroxides. These findings further demonstrate that sulphur and iron have different transport mechanisms. Although sulphate concentrations in the river waters of Berlin are still high, sedimentary iron and sulphur contents at the city border are only slightly higher than at the reference point close to the source of River Spree. The strongly diminished but still present mining signature in urban Berlin is replaced by an urban signature characterised by high levels of zinc, chromium, lead, and copper.

Identifying Iron-Bearing Nanoparticle Precursor for Thermal Transformation into the Highly Active Hematite Photo-Fenton Catalyst

The hematite photo-Fenton catalysis has attracted increasing attention because it offers strong oxidation of organic pollutants under visible light at neutral pH. In the present work, aqueous synthesis of hematite photo-Fenton catalysts with high activity is demonstrated. We compare photo-Fenton activity for hematite obtained by hydrolyzation at 60 °C or by a thermally induced transformation from iron-bearing nanoparticles, such as amorphous iron oxyhydroxide or goethite. A link between their structure and visible light photo-Fenton reactivity is established. The highest activity was observed for hematite obtained from goethite nanowires due to oblong platelet-like structure, high surface area and the presence of nanopores.

In situ construction of amorphous hierarchical iron oxyhydroxide nanotubes via selective dissolution-regrowth strategy for enhanced lithium storage

The low-cost and high-capacity metal oxides/oxyhydroxides possess great merits as anodes for lithium-ion batteries (LIBs) with high energy density. However, their commercialization is greatly hindered by insufficient rate capability and cyclability. Rational regulations of metal oxides/oxyhydroxides with hollow geometry and disordered atomic frameworks represent efficient ways to improve their electrochemical properties. Herein, we propose a fast alkalietching method to realize the in-situ fabrication of iron oxyhydroxide with one-dimensional (1D) hierarchical hollow nanostructure and amorphous atomic structure from the iron vanadate nanowires. Benefiting from the improved electron/ ion kinetics and efficient buffer ability for the volumetric change during the electro-cycles both in nanoscale and atomic level, the graphene-modified amorphous hierarchical FeOOH nanotubes (FeOOH-NTs) display high rate capability (~650 mA h g−1 at 2000 mA g−1) and superior long-term cycling stability (463 mA h g−1 after 1800 cycles), which represents the best cycling performance among the reported FeOOH-based materials. More importantly, the selective dissolutionregrowth mechanism is demonstrated based on the time tracking of the whole transition process, in which the dissolution of FeVO4 and the in-situ selective re-nucleation of FeOOH during the formation of FeOOH-NTs play the key roles. The present strategy is also a general method to prepare various metal (such as Fe, Mn, Co, and Cu) oxides/oxyhydroxides with 1D hierarchical nanostructures.

Influence of pH on the Kinetics and Mechanism of Photoreductive Dissolution of Amorphous Iron Oxyhydroxide in the Presence of Natural Organic Matter: Implications to Iron Bioavailability in Surface Waters.

In this study, we investigate the influence of pH on the kinetics and mechanism of photoreductive dissolution of amorphous iron oxyhydroxide (AFO) in view of the recognition that the light-mediated dissolution of iron oxides controls Fe availability in many natural waters. Our results show that both ligand-to-metal charge transfer (LMCT) and photogenerated superoxide (O2•-) play an important role in AFO photoreductive dissolution in the presence of the chosen surrogate of natural organic matter, Suwannee river fulvic acid (SRFA). The pH dependence of LMCT-mediated AFO photoreductive dissolution is mainly controlled by the influence of pH on AFO solubility. A decrease in pH increases the concentration of the dissolved and more photolabile Fe(III)-SRFA complex present in equilibrium with AFO, a complex in which Fe(III) is readily reduced by LMCT. The pH dependence of superoxide-mediated Fe(III) reduction (SMIR) is also controlled by the influence of pH on AFO solubility with an increase in the dissolved inorganic Fe(III) concentration with the decrease in pH resulting in an increased rate of SMIR. No influence of pH was observed on the steady-state O2•- concentration generated on SRFA irradiation as well as the O2•- decay rate in the presence of SRFA, suggesting that the concentration and lifetime of O2•- are not important factors in controlling the pH dependence of O2•--mediated AFO dissolution. Overall, the results of this study show that the impact of acidification of natural waters on Fe availability will be much more pronounced when Fe is present as iron oxyhydroxide compared to that observed when organically bound Fe dominates with this effect because of the strong dependency of iron oxyhydroxide solubility on pH. The increased rate and extent of dissolution of iron oxyhydroxides on the acidification of natural waters will also have implications to the fate of other contaminants (such as heavy metals and organic compounds) that may be present on the iron oxyhydroxide surface.

Major, trace, and rare earth element geochemistry of the Ayder and İkizdere (Rize, NE Turkey) geothermal waters: Constraints for water–rock interactions

This study aims to determine the sources of rare earth elements (REEs) in the geothermal and cold waters of the Ayder and İkizdere (Rize) geothermal fields (NE Turkey). The differentiation stages of REEs in water–rock interactions as well as the migration processes of aqueous complexes of rare earth elements (REEs) in the waters were evaluated. Based on results for major ions, the İkizdere geothermal water with a temperature of 61 °C can be classified as Na-Ca-HCO3 type water, whereas the Ayder geothermal water with a temperature of 54 °C can be classified as Na-Ca-CO3−SO4 type water. ∑REE concentrations were between 0.64–2.13 μg/L in the İkizdere geothermal field and between 0.01–0.32 μg/L in the Ayder geothermal field. As well as lower pH values, the waters in the İkizdere geothermal field were found to have higher REE concentrations than those of the Ayder geothermal field. Geochemical characteristics of REEs from the host rocks and water samples indicate that the REEs are derived from granite and granodiorite host rocks. Normalized REE plots for the host rocks and waters showed similar patterns, and in particular, the waters interacting with granitic rocks display a pronounced positive Eu anomaly and a less clear Ce anomaly. The positive Eu anomaly in the altered surrounding rocks is associated with argillization of feldspars in the granitic host rocks that the waters have passed through. Application of a speciation model showed that amorphous iron oxy-hydroxide complexes of REEs were significant for a pH value of nearly 9 in the Ayder geothermal waters whereas fluoride complexes are dominant in the İkizdere geothermal waters whose pH is just below 7.

TiO2/Fe2O3 photoanodes for solar water oxidation prepared via electrodeposition of amorphous precursors

Hematite-titania thin films with various ratios of Ti/Fe have been prepared on FTO substrate via cathodic and anodic deposition of amorphous Ti oxyhydroxide gel (TiOx) and iron oxyhydroxide (FeOOH) films, respectively followed by annealing processes. TiOx underlayer behaved as a template for FeOOH electrodeposition. The photocatalytic behavior of the photoanodes based on the prepared structures was studied. An increased photocurrent density was obtained without anodic shifting of the photocurrent onset potential. Mott-Schottky studies showed that Ti contributes little to donor density in hematite-titania photoanodes prepared by this technique. The impedance measurements suggest that both separation and transfer of charge carriers are promoted in these hematite-titania photoanodes. For comparative studies, hematite-titania photoanodes have been prepared from TiOx and FeOOH precursors formed by spin-coating technique and anodic deposition method, respectively. The photoelectrochemical performance of these photoanodes in the presence of cobalt-phosphate catalyst was also evaluated.

Persulfate activation by Fe(III) with bioelectricity at acidic and near-neutral pH regimes: Homogeneous versus heterogeneous mechanism.

The combination of persulfate (PS) activation by iron ions with electrochemical process (electro/Fe3+/PS) is a promising advanced oxidation process. However, almost all these systems were performed in an unbuffered solution and actually under acidic pH condition, with the electricity being frequently supplied by external power. Considering the high buffering capacity of wastewater and energy saving, peroxydisulfate (PDS) activation by Fe(III) species with bioelectricity provided by microbial fuel cell (MFC) for bisphenol A (BPA) oxidation was investigated at fixed near-neutral pH as well as acidic pH. The results indicate that 90.8% of BPA could be removed at pH 2.5. Though the iron existed in the form of precipitate, BPA could still be efficiently removed at pH 6.0. The precipitate formed in the system at pH 6.0 was identified as the amorphous iron oxyhydroxides. Sulfate radicals in the bulk solution and that adsorbed on the precipitate were the dominant reactive species responsible for the oxidation of BPA in the homogeneous and heterogeneous MFC/Fe(III)/PDS processes, respectively. The mechanisms of BPA degradation at both pH values were proposed via EPR and quenching tests as well as XPS analysis. The effects of operating parameters, the mineralization, the mineralization current efficiency and energy consumption were also explored.

Uptake of Sb(V) by Nano Fe3O4-Decorated Iron Oxy-Hydroxides

The presence of antimony in water remains a major problem for drinking water technology, defined by the difficulty of available adsorbents to comply with the very low regulation limit of 5 μg/L for the dominant Sb(V) form. This study attempts to develop a new class of water adsorbents based on the combination of amorphous iron oxy-hydroxide with Fe3O4 nanoparticles and optimized to the sufficient uptake of Sb(V). Such a Fe3O4/FeOOH nanocomposite is synthesized by a two-step aqueous precipitation route from iron salts under different oxidizing and acidity conditions. A series of materials with various contents of Fe3O4 nanoparticles in the range 0–100 wt % were prepared and tested for their composition, and structural and morphological features. In order to evaluate the performance of prepared adsorbents, the corresponding adsorption isotherms, in the low concentration range for both Sb(III) and Sb(V), were obtained using natural-like water. The presence of a reducing agent such as Fe3O4 results in the improvement of Sb(V) uptake capacity, which is found around 0.5 mg/g at a residual concentration of 5 μg/L. The intermediate reduction of Sb(V) to Sb(III) followed by Sb(III) adsorption onto FeOOH is the possible mechanism that explains experimental findings.

Impact of ferrous iron dosing on iron and phosphorus solids speciation and transformation in a pilot scale membrane bioreactor

Dosing of a pilot scale MBR with a ferrous salt for P removal results in a mix of FePO4(s)and P adsorbed to amorphous iron oxyhydroxides. Increase in the proportion of FePO4(s)is desired given the higher ratio of P : Fe in the biosolids produced.