Transformation of carbon tetrachloride by biogenic iron species in the presence of Geobacter sulfurreducens and electron shuttles

The transformation of carbon tetrachloride (CT) by biogenic iron species produced from the bioreduction of various Fe(III) oxides in the presence of Geobacter sulfurreducens and electron shuttles were investigated. Cysteine and anthraquinone-2,6-disulfonate (AQDS) at concentrations of 0.5mM and 10microM, respectively, were added as the electron shuttles. Addition of electron shuttles enhanced the extent of reduction and rate of ferric oxide reduction. The bioreduction extents of ferric oxides by G. sulfurreducens in the presence of electron shuttles were 22.8-48.3% for ferrihydrite, 6.5-17.2% for hematite, and 3.0-11.3% for goethite. After normalization to the surface areas, a higher rate of CT reduction was observed per unit of adsorbed Fe(II) on crystalline oxides. The produced biogenic Fe(II) from crystalline iron oxides was 2.8-7.6 times lower than that obtained from ferrihydrite, while the surface area-normalized rate constant for iron-mediated CT transformation in the presence of goethite and hematite were, by factors of 2-21, higher than that obtained using ferrihydrite. These results clearly depict that G. sulfurreducens drove the reduction of CT primarily through the formation of biogenic iron species in the presence of electron shuttle under iron-reducing conditions and that it is a surface area dependent process.     

Arsenate removal by resin-supported ferric ions: Mechanism,modeling, and column study

Removal of 10 mg/dm³ of As(V) by resin-supported Fe(III) was investigated in batch and column studies. The best As(V) removal was achieved at pH 3, and a high sorption density of 0.40 mmol-As/mmol-Fe was obtained after 96 h in a batch study. This sorption density could not be explained only by As(V) surface complexation with ferrihydrite. X-ray absorption near edge structure (XANES) analysis at the As K-edge suggested that over 90% of the As(V) was removed by surface precipitation as poorly crystalline ferric arsenate and the remainder was removed by surface complexation with ferrihydrite. XANES analysis at Fe K-edge suggested that 14%–35% of Fe(III) in the resin was used in the ferrihydrite and ferric arsenate. Kinetic modeling of the precipitation of ferrihydrite and ferric arsenate combined with a surface complexation model for As(V) and ferrihydrite successfully reproduced the batch experiment results. The kinetic constant for precipitation of ferrihydrite and ferric arsenate obtained by fitting of the batch experiment results successfully reproduced the column experiment results. The ratio of surface precipitation of ferric arsenate and As(V) surface complexation with ferrihydrite obtained by the constructed model was the same as in the XANES results. In the column study, a slow flow was advantageous for As(V) removal because surface precipitation of ferric arsenate took a long time.     

Iron changes in natural and Fe(III) loaded montmorillonite during carbon nanotube growth

A detailed elaboration of the transformations of iron species, present in natural and Fe(NO(3))(3) loaded montmorillonite, during carbon deposition and carbon nanotube growth is described. According to transmission electron microscopy results, deposited carbon atoms form fibres in the case of pristine montmorillonite and multiwalled carbon nanotubes in the case of Fe(III) loaded montmorillonite. M?ssbauer and x-ray diffraction analysis results point to an extensive reduction of structural and intercalated Fe(III) cations to Fe(II) with the latter migrating from the interlayer space to the vacant octahedral sites of the mineral's lattice. Such migration of the non-structural iron catalyst prohibits extensive contamination of the final composite with various metal catalyst impurities. The crucial role of the active catalytic centres in the formation of carbon nanotubes is ascribed to a minor quantity of iron, found entrapped in the carbon nanostructures, which, at the end of the reaction, is identified as iron carbide. The interesting formation of a nanometric γ-iron precipitate is also detected, which is probably stabilized through strong interactions with the lattice of montmorillonite. Finally, it is demonstrated that iron-rich natural clay minerals can serve as direct catalysts for carbon nanotube growth.     

Fluoride adsorption studies on mixed-phase nano iron oxides prepared by surfactant mediation-precipitation technique

Mixed nano iron oxides powder containing goethite (α-FeOOH), hematite (α-Fe(2)O(3)) and ferrihydrite (Fe(5)HO(8)·4H(2)O) was synthesized through surfactant mediation-precipitation route using cetyltrimethyl ammonium bromide (CTAB). The X-ray diffraction, FTIR, TEM, M?ssbauer spectroscopy were employed to characterize the sample. These studies confirmed the nano powder contained 77% goethite, 9% hematite and 14% ferrihydrite. Fluoride adsorption onto the synthesized sample was investigated using batch adsorption method. The experimental parameters chosen for adsorption studies were: pH (3.0-10.0), temperature (35-55°C), concentrations of adsorbent (0.5-3.0 g/L), adsorbate (10-100 mg/L) and some anions. Adsorption of fluoride onto mixed iron oxide was initially very fast followed by a slow adsorption phase. By varying the initial pH in the range of 3.0-10.0, maximum adsorption was observed at a pH of 5.75. Presence of either SO(4)(2-) or Cl(-) adversely affected the adsorption of fluoride in the order of SO(4)(2-)>Cl(-). The FTIR studies of fluoride loaded adsorbent showed that partly the adsorption on the surface took place at surface hydroxyl sites. M?ssbauer studies indicated that the overall absorption had gone down after fluoride adsorption that implies it has reduced the crystalline bond strength. The relative absorption area of ferrihydrite was marginally increased from 14 to 17%.     

Adsorption and aggregation of Fe(III)-hydroxy complexes during the photodegradation of phenol using the iron-added-TiO(2) combined system

The behavior of Fe(III) aquacomplexes in TiO(2) suspensions in the degradation of phenol has been investigated. The most active Fe(OH)(2+) species adsorbed on the surface of TiO(2) retards the conversion of Fe(OH)(2+) into oligomers and therefore increases the percentage of Fe(OH)(2+) with irradiation time, with a consequent enhancement in the catalytic cycle of Fe(III)/Fe(II) and excited charge traps by Fe(III) in the iron-TiO(2) system. The influence of iron addition on TiO(2) was obtained when the regeneration of [Fe(OH)(2+)] remained continuous with irradiation time. In an optimum TiO(2) suspension (0.5g/L) with the addition of 0.1mM Fe(III), the measured k(obs) values for phenol degradation were enhanced for the higher adsorption of Fe(OH)(2+) on the reactive surface of TiO(2) at a specified irradiation time.     

Adsorption of arsenate on synthetic goethite from aqueous solutions

Goethite was synthesized from the oxidation of ferrous carbonate precipitated from the double decomposition of ferrous sulfate doped with sodium lauryl sulfate (an anionic surfactant) and sodium carbonate in aqueous medium. The specific surface area and pore volume of goethite were 103 m(2) g(-1) and 0.50 cm(3) g(-1). Batch experiments were conducted to study the efficacy of removal of arsenic(V) using this goethite as adsorbent for solutions with 5-25 mg l(-1) of arsenic(V). The nature of adsorption was studied by zeta-potential measurements. The adsorption process followed by Langmuir isotherm and diffusion coefficient of arsenate was determined to be 3.84 x 10(11)cm(2)s(-1). The optimum pH of adsorption was found to be 5.0. The kinetics of adsorption was evaluated with 10 mg l(-1) and 20 mg l(-1) of As(V) solutions and activation energy of adsorption, as calculated from isoconversional method was in the range of 20 kJ mol(-1) to 43 kJ mol(-1). This suggests that the adsorption process is by diffusion at the initial phase and later through chemical control. FT-IR characterization of arsenic treated goethite indicated the presence of both AsOFe and AsO groups and supported the concept of surface complex formation.     

Mössbauer effect study of the microscopic properties of separated hydrolysed Fe(III) products

Fe(III) hydrolysed products, obtained after ageing the separated high and low molecular weight fractions in the presence NO₃^? and Cl ions, were studied by Mössbauer spectra. The nitrate high molecular fractions precipitate as α -FeOOH while the chloride give β-FeOOH particles. Low molecular weight nitrate fractions precipitate as Fe(III) hydroxide and ferrihydrite. By heating the solution, they can be transformed into goethite.     

Interaction of caffeine with montmorillonite

In this study, caffeine was adsorbed onto montmorillonite and the surface of the montmorillonite was observed before and after the adsorption. Observations were performed by X-ray diffractometry (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and scanning probe microscopy (SPM). Measurement of the interlayer distance by XRD revealed that it narrowed to 1.09?nm after caffeine adsorption. Adsorption of a small amount of caffeine causes a broadening of d₀₀₁ peaks. This suggested that caffeine molecules were adsorbed into the interlayer space in part, resulting in an irregular layer stacking. The results of SPM observations of caffeine-adsorbed montmorillonite showed the existence of protrusions that are different from minerals on the surface of montmorillonite and suggested a possibility that the protrusions were caffeine molecules adsorbed onto the surface of montmorillonite. DRIFTS demonstrated that the intensity of peaks assigned to Si–OH and siloxane decreased with the increase in the amount of caffeine adsorbed. These results suggested that caffeine molecules were adsorbed both into the interlayer space and onto the surface and interacted with Si–OH and siloxane, in particular. These findings will help us to select ions to be held in the interlayer space and organic compounds to improve the amount of adsorption when montmorillonite is used in the manufacture of caffeine-free drinks and foods.     

High surface area solids obtained by intercalation of iron oxide pillars in montmorillonite

When montmorillonite is dispersed in aqueous solutions of trinuclear acetato-hydroxo iron(III) nitrate, [Fe₃(OCOCH₃)₇OH]NO₃, the interlayer cations of the montmorillonite are exchanged with the partially hydrolyzed trinuclear acetato complex ions. On heating the exchanged complex ions are converted into iron oxide pillars which keep the silicate layers apart and form micropores between the layers. The resulting product has a basal spacing of 16.7 Å and a specific surface area of about 300 m²/g at 500°C. Adsorption isotherms for various vapors on the product have been measured.     

Arsenic sorption onto natural hematite, magnetite, and goethite

In this work the sorption of As(III) and As(V) on different natural iron oxides (hematite, magnetite, and goethite) has been studied as a function of different parameters. The sorption kinetics for the three iron oxides shows that equilibrium is reached in less than 2 days and the kinetics of sorption seems to be faster for goethite and magnetite than for hematite. The variation of the arsenic sorbed on the three different sorbents as a function of the equilibrium arsenic concentration in solution has been fitted with a non-competitive Langmuir isotherm. The main trend observed in the variation of the arsenic sorbed with pH is the decrease of the sorption on the three sorbents at alkaline pH values, which agrees with results found in the literature. Highest As(III) sorption was observed on hematite surface in all the pH range compared to goethite and magnetite. Natural minerals studied in this work had similar sorption capacities for arsenic than synthetic sorbents.     

Adsorptive removal of As(V) and As(III) from water by a Zr(IV)-loaded orange waste gel

Orange waste, produced during juicing has been loaded with zirconium(IV) so as to examine its adsorption behavior for both As(V) and As(III) from an aquatic environment. Immobilization of zirconium onto the orange waste creates a very good adsorbent for arsenic. Adsorption kinetics of As(V) at different concentrations are well described in terms of pseudo-second-order rate equation with respect to adsorption capacity and correlation coefficients. Arsenate was strongly adsorbed in the pH range from 2 to 6, while arsenite was strongly adsorbed between pH 9 and 10. Moreover, equimolar (0.27 mM) addition of other anionic species such as chloride, carbonate, and sulfate had no influence on the adsorption of arsenate and arsenite. The maximum adsorption capacity of the Zr(IV)-loaded SOW gel was evaluated as 88 mg/g and 130 mg/g for As(V) and As(III), respectively. Column adsorption tests suggested that complete removal of arsenic was achievable at up to 120 Bed Volumes (BV) for As(V) and 8 0BV for As(III). Elution of both arsenate and arsenite was accomplished using 1 M NaOH without any leakage of the loaded zirconium. Thus this efficient and abundant bio-waste could be successfully employed for the remediation of an aquatic environment polluted with arsenic.     

The comprehensive investigation on removal mechanism of Cr(VI) by humic acid-Fe(II) system structured on V,Ti-bearing magnetite surface

The Cr(VI) could be adsorbed and reduced by the humic acid (HA)-Fe(II) system structured on the V, Ti-magnetite (VTM) surface. The Cr(VI) removal process included adsorption and reduction stages. First, the Cr(VI) was adsorbed on the VTM-HA surface via the ionic bonds between the Ti atoms of VTM core and the O atoms of the HCrO₄^?. The adsorption of Cr(VI) is uniform, monolayer, and controlled by Cr(VI) diffusion. Subsequently, the adsorbed Cr(VI) was reduced by the HA-Fe(II) system on the VTM-HA surface. During the Cr(VI) reduction process, the HA and Fe(II) have a synergistic effect. The Cr(VI) was reduced to the Cr(III) by the HA and Fe(II). Meanwhile, the HA could also reduce Fe(III) to Fe(II), making Fe(II) continue to participate in the Cr(VI) reduction. The olefin, hydroxyl, and aldehyde groups of HA were the primary electron donors during the Cr(VI) reduction. The Fe(II) acted as an electron bridge, transferring the electron from HA to Cr(VI). The reduced Cr(III) was deposited on the VTM-HA surface via the complexation with the carboxyl and hydroxyl groups of HA. The results demonstrated that the Cr(VI) could be adsorbed, reduced and complexed by the HA-Fe(II) system on the VTM-HA surface synchronously.     

Adsorption capacities of poorly crystalline Fe minerals for antimonate and arsenate removal from water: adsorption properties and effects of environmental and chemical conditions

Antimonate (Sb(V)) and arsenate (As(V)) pollution frequently occur in aqueous environment and can be absorbed by poorly crystalline Fe minerals (i.e., ferrihydrite). In this study, the adsorption capacity and rate of Sb(V) and As(V) from water with fresh ferrihydrite were compared by establishing adsorption isotherms and kinetics, and the effects of ferrihydrite dosage, solution pH and humic substances on Sb(V) and As(V) adsorption were also investigated. The adsorption isotherms results showed that the equilibrium and maximum adsorption capacities of Sb(V) on ferrihydrite were approximately equal to those of As(V) under different temperatures. The results of adsorption kinetics showed that the adsorption rate of Sb(V) derived from the pseudo-second-order equation was much lower than that of As(V). In addition, the adsorption capacity and rate of Sb(V) and As(V) were greatly affected by various ferrihydrite dosage and solution pHs. The presence of humic acid and fulvic acid (FA) significantly affected the adsorption process of Sb(V) due to competition adsorption, whereas the adsorption properties of As(V) were little affected by FA under this experimental conditions.     

Mechanism of arsenate coprecipitation at the solid/liquid interface of ferrihydrite: A perspective review

Arsenate (As(V)) is a toxic element in acid mine drainage and has to be removed during the neutralization process. Coprecipitation with ferrihydrite is the main mechanism for As(V) removal from acid mine drainage. To improve treatment efficiency, a quantitative understanding of the coprecipitation mechanism is required. Coprecipitation can incorporate more As(V) into ferrihydrite than adsorption. The results of XRD (X-ray Diffraction) and XANES (X-ray Adsorption Near Edge Structure) analysis confirmed that the formation of poorly crystalline ferric arsenate increased when the initial As/Fe molar ratio increased in the coprecipitation with ferrihydrite. EXAFS (Extended X-ray Adsorption Fine Structure) analysis at the iron K-edge showed that the proportion of octahedral structures in ferrihydrite increased when the initial As/Fe molar ratio increased. Moreover, EXAFS analysis at the arsenic K-edge, assuming three kinds of surface complexes for the AsFe bond, revealed that the coordination number for AsFe with an atomic distance of 2.85 × 10⁻¹⁰ m increased and that for As-Fe with an atomic distance of 3.24 × 10⁻¹⁰ m decreased as the initial As/Fe molar ratio increased. Thus, for more efficient wastewater treatment, active control of coprecipitation phenomena according to mechanistic details is essential.     

Understanding removal of phosphate or arsenate onto water treatment residual solids

Chemical and physical characterization methods were used to analyze ferric, alum, and lime water treatment residual solids (WTRSs) in order to describe why phosphate or arsenate adsorption occurred on the WTRSs, and why ferric WTRSs were the stronger adsorbent for both phosphate and arsenate. In total, five WTRSs, two ferric, two alum, and one lime, were analyzed. Elemental analysis of the WTRSs showed lime residuals contained the greatest molar amount of the primary element (7.04 mol Ca/kg solid), followed by the ferric residuals (4.86-4.96 mol Fe/kg solid) whereas alum residuals contained the least amount of primary element as compared to the ferric or alum residual solids (3.62-4.67 mol Al/kg solid). Mercury porosimetry identified more small pores (<0.006 μm) in a ferric WTRSs when compared to an alum WTRSs, indicating that a more detailed pore structure allowing for intraparticle phosphate or arsenate diffusion might be present in the ferric solid. Similarly, SEM images at 1000 times magnification showed a porous surface in both ferric WTRSs, whereas the alum WTRSs showed a smooth surface at the same magnification. Several general equations to describe phosphate or arsenate adsorption on WTRSs were provided.     

Removal of Supranol Yellow 4GL by adsorption onto Cr-intercalated montmorillonite

Cr(III)-intercalated montmorillonite was utilized as an adsorbent for the removal of the organic pollutant, Supranol Yellow 4GL, a synthetic dye used for chemical fibres. The material was prepared by the reaction of Na montmorillonite with a base-hydrolyzed solution of Cr nitrate salt (OH(-)/Cr(3+) molar ratios of 2). XRD data showed that the interlayer spacing (d(001)) of montmorillonite was increased from 12.35 to 23.06 Angstroms. The kinetics and mechanism of the adsorption of the acid dye, Supranol Yellow 4GL, on Cr(III)-intercalated montmorillonite was investigated. The equilibrium time was reached within 30 min. The process follows pseudo-second-order rate kinetics. The Langmuir isotherm described the adsorption data over the concentration range (20-160 mg/l). The separator factor R(L) revealed the favourable nature of this adsorption process. Also, the thermodynamic parameters such as DeltaS degrees, DeltaH degrees, DeltaG degrees were determined.     

Effect of model ligands on iron redox speciation in natural waters using flow injection with luminol chemiluminescence detection

The effects of dissolved organic compounds on the determination of nanomolar concentrations of Fe(II) have been compared using two luminol-based flow injection chemiluminescence (FI-CL) methods. One used the direct injection of sample into the luminol reagent stream, and the other incorporated on-line solid-phase extraction of the analyte on an 8-hydroxyquinoline microcolumn. The CL signals from analyses of dissolved iron species (Fe(II) and Fe(III)) with model ligands and organic compounds were examined in high-purity water and seawater. The organic compounds included natural reducing agents (e.g., ascorbic acid), nitrogen sigma-donor/pi-acceptor compounds (e.g., 1,4-dipyridine, protoporphyrin IX), aromatic compounds (e.g., 1,4-dihydroxybenzene), synthetic iron chelators (e.g., EDTA), and natural iron binding compounds (e.g., desferrioxamine B, ferrichrome A). Fe(II) determinations for both luminol FI-CL methods were affected by submicromolar concentrations of redox-active compounds, strong iron binding ligands (i.e., log K(FeL) > 6), and compounds with electron-donating functional groups in both high-purity water and seawater. This was due to reactions between organic molecules and iron species before and during analysis, rather than chemiluminescence caused by the individual organic compounds. In addition, the effects of strong ligands and size speciation on Fe(II) recoveries from seawater following acidification (pH 2) and reduction (100 microM sodium sulfite) were investigated.     

Arsenic removal by adsorption on iron(III) phosphate

Under natural conditions, arsenic is often associated with iron oxides and iron(III) oxidative capacity towards As(III) is well known. In this study, As(III) and As(V) removal was performed using synthesised iron(III) phosphate, either amorphous or crystalline. This solid can combine (i) As(III) oxidation by iron(III) and (ii) phosphate substitution by As(V) due to their similar properties. Results showed that adsorption capacities were higher towards As(III), leading to Fe2+ and HAsO4(2-) leaching. Solid dissolution and phosphate/arsenate exchange led to the presence of Fe3+ and PO4(3-) in solution, therefore various precipitates involving As(V) can be produced: with Fe2+ as Fe3(AsO4)2.8H2O(s) and with Fe3+ as FeAsO4.2H2O(s). Such formations have been assessed by thermodynamic calculations. This sorbent can be a potential candidate for industrial waste treatment, although the high release of phosphate and iron will exclude its application in drinking water plants.     

Effects of ferrous ions on the reductive dechlorination of trichloroethylene by zero-valent iron

The surface characteristics of zero-valent iron (ZVI) and the efficiency of reductive dechlorination of trichloroethylene (TCE) in the presence of ferrous ions were studied. The experimental results indicated that the acid-washing of a metallic iron sample enhanced the efficiency of TCE degradation by ZVI. This occurred because acid-washing changed the conformation of oxides on the surface of iron from maghemite (gamma-Fe(2)O(3)) to the more hydrated goethite (alpha-FeOOH), as was confirmed by XPS analysis. However, when ferrous ions were simultaneous with TCE in water, the TCE degradation rate decreased as the concentration of ferrous ion increased. This was due to the formation of passive precipitates of ferrous hydroxide, including maghemite and magnetite (Fe(3)O(4)), that coated on the surface of acid-washed ZVI, which as a result inhibited the electron transfer and catalytic hydrogenation mechanisms. On the other hand, in an Fe(0)-TCE system without the acid-washing pretreatment of ZVI, ferrous ions were adsorbed into the maghemite lattice which was then converted to semiconductive magnetite. Thus, the electrons were transferred from the iron surface and passed through the precipitates, allowing for the reductive dechlorination of TCE.     

Fe增强Ni2(CO3)(OH)2臭氧分解抗湿性与催化性能

臭氧污染已成为我国继PM2.5之后的主要污染物,传统的臭氧分解催化材料在湿润环境中性能不稳定.本工作采用水热法制备了一种铁掺杂改性的碱式碳酸镍催化剂(NiCH-Fe),该催化剂可在60％相对湿度下稳定分解2.14μg/L臭氧12 h,去除率达99％.水分子吸附质量检测结果表明,NiCH-Fe表面的水分子吸附量比纯NiC...