Rate Of Fe2 Research Articles

Electrochemical Analysis of Fe2+ Ions Behavior in the Metal Oxide Dispersions

Abstract This study aims at establishing how metal oxides (TiO2, Fe2O3, SiO2, and Al2O3) influence electrochemical activity of Fe2+ ions in solutions of different pH. Above pH 6.5 almost total uptake of Fe2+ ions from solution was reported for all oxides due to adsorption and oxidation of ferrous ions manifested by the reversal of the redox potential (Eh) trend. TiO2 and Fe2O3 revealed the strongest Fe2+ affinity and Al2O3 the weakest. X-ray photoelectron spectroscopy (XPS) indicated the transformation of precipitated Fe(OH)3 into FeOOH above pH 6.5. Square wave voltammetry (SWV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) have been used in experimental measurements applying the gold electrode. The changes in Ra (activation resistance of the Fe2+ electrooxidation) confirmed the beneficial effect of Fe2O3 and TiO2 on the rate of Fe2+ electrooxidation on the electrode. The linear relationship between the anodic peak current and the square root of the scanning rate proves that in the absence of oxides, the Fe2+ oxidation process is determined by the diffusion of the depolarizer to the electrode surface. In the presence of oxides, the relationships Ip = f ($\sqrt{\text{v}} $) are non-linear, and therefore the electrooxidation of Fe2+ ions is controlled by their adsorption on gold.

Kinetics of Fe(II) Oxidation in a Verticle Tube Reactor: A Pilot Scale Study

ABSTRACT A vertical tubular reactor is used for the oxidative leaching process in the mineral processing industry, especially sphalerite. Oxygen could oxidise ferrous ions (Fe2+), and ferric ions (Fe3+) are generated as the principal oxidation agent in the reactor afterward. The partial pressure of oxygen is an instrumental parameter that could change according to reactor height. Despite the extensive studies on Fe(II) oxidation in the high-pressure reactor, there is no published work on its oxidation behaviour in the tubular reactor. Hence, the Fe3+ ion's oxidation in sulfuric acid solutions was investigated in atmospheric condition. The effects of the FeSO4, H2SO4, ZnSO4 concentration, and pressure in the reactor bottom were studied on the rate of ferrous oxidation at different temperatures, i.e. T = 70, 87 and 95°C. Sulfuric acid drops the kinetic of ferrous oxidation, whereas temperature and pressure of the reactor bottom increase this criterion. The apparent activation energy obtained was 67.22 kJ/mol, and an empirical equation for the oxidation rate of Fe2+ by air is as follows:

Insight into flower-like greigite-based peroxydisulfate activation for effective bisphenol a abatement: Performance and electron transfer mechanism

Abstract This research offers insight into the activation of peroxydisulfate (PDS) by flower-like greigite (Fe3S4) (FLG) for bisphenol A (BPA) degradation in water. The as-prepared greigite was exclusively effective as a PDS activator in producing free radicals. FLG/PDS performed much better than Fe3O4/PDS and ZVI/PDS systems or some other earlier systems for BPA degradation. Only 0.02 g/L of FLG could remove more than 95% of BPA in 120 min. Cl− had little adverse impact on the BPA abatement, and 20 mg/L of NaHCO3 could decrease the BPA degradation rate to only 40%. FLG could be easily recycled by magnetic force, and it was reusable. Electron paramagnetic resonance and free radical scavenging tests demonstrated that sulfate radicals play a main role in the BPA degradation process. GC–MS and UHPLC-Q-TOF-MS were applied to detect the intermediates and the possible BPA degradation mechanism; three main pathways were proposed. The structure of nanosheets could effectively enhance the interaction between greigite and PDS and furthermore effectively produce radicals for BPA degradation. X-ray photoelectron experiments showed that the rate of Fe2+ decreased from approximately 37.0% to 19.5% and that typical peaks of S2− disappeared after PDS activation. This discovery indicated that S2− lost electrons to accelerate Fe2+/Fe3+ recycling when the Fe2+ species was changed to Fe3+. This research offered good insights into the Fe2+/Fe3+ species with sulfur elements effectively activating PDS for BPA degradation. Our study deepened the understanding of the electron transfer mechanism of sulfur-iron-based heterogeneous catalysis in environmental remediation.

Kinetics of oxidation of iron(II) ions with lipid hydroperoxides

AbstractOne of the pathways for excessive production of free radicals is the decomposition of lipid hydroperoxides catalyzed by iron. A number of hydroperoxides of unsaturated fatty acids (LOOH), some prepared in our laboratory and others extracted from biological materials, were used to determine the rate constants of Fe2+ oxidation by measuring the formation rate of Fe3+ ions in the presence of simple unidentate ligands, chloride, and thiocyanate as the [FeCl]2+ and [FeNCS]2+ complexes, in a deoxygenated dichloromethane:methanol (2:1, v/v) mixture. The rates of Fe2+ oxidation with prepared LOOHs via the [FeNCS]2+ complex were approximately the same‐the average second‐order reaction rate constant was 1390 ± 340 dm3 mol−1 s−1; the rate constants of LOOHs from different biological materials were in the same range. The rates measured as the [FeNCS]2+ complex were somewhat higher than the rates measured as the [FeCl]2+ complex, indicating that ligands could interact in the transition state, thus affecting the disruption of the intermediate complex. Since there were no significant differences in the activation thermodynamic parameters for reactions within the reaction series of studied hydroperoxides, it was assumed that the oxidation proceeded by an inner sphere mechanism, considering that the breakdown of the successor inner sphere complex with the homolytic cleavage of peroxide bonds of hydroperoxides forming reactive alkoxyl radicals was the rate‐limiting step. Based on this research, an indirect spectrophotometric method for quantitative determination of LOOH was reestimated. The microprocedure proposed for the lipid hydroperoxide assay could be applied to follow the early stages of lipid peroxidation processes in real biological samples.

Treatment of the Basic Yellow 2 Dyestuff with Fenton Advanced Oxidation Process

In this study, the removal of Basic Yellow 2 (BY2) dyestuff used in textile dyeing industry by Fenton process which is one of the Advanced Oxidation Processes (IOP) was investigated. Effect of pH, Fe2+, hydrogen peroxide (H2O2) and temperature was evaluated on oxidation process. Removal of the colorant (BY2) was monitored by considering color and Chemical Oxygen Demand (COD). A COD removal efficiency of 62.05% and color of 90.71% were obtained under optimum experimental conditions where baseline solution pH is 3, the concentration of (BY2) colorant is 200 mgL-1, rates of Fe2+ and H2O2 are 150 mgL-1 and 400 mgL-1, reaction temperature is 200C and experiment time is 30min. Keywords : Fenton, Basic Yellow 2, H2O2, pH DOI : 10.7176/JSTR/5-2-45

Solid State Synthesis of Spinel-Type Metal Oxide Mg1.5Fe0.5MnO4 and Study of Its Exchange Capability for Li+

The spinel-type composite metal oxide, magnesium-manganese-titanium oxide (Mg1.5Fe0.5MnO4), was prepared by the method of solid state crystallization. As a spinel-type structure, it is versatile in chemical composition and its stoichiometric number. It could keep crystal structure stability by changing stoichiometric number method to insert or extract some substitutable ions. This characteristic can be special studied to meet some requirements. This spinel-type composite metal oxide was detected by XRD and SEM for the valuating partition coefficient of saturated exchange capacity and the other parameters to confirm certain characteristics. The dissolution rate of Fe2+ and Mn4+ from Mg1.5Fe0.5MnO4 which was treated by acid were less than 9.3%, meanwhile the extraction rate of Mg2+ was more than 75%. The experimental data showed that the acidifying of MgFeMn-620 (H) can reach 12.1 mmol g–1 ion exchange capacity for Li+ in solution.

Bioregeneration of Leaching Solutions during Two-Step Processing of Copper-Zinc Concentrate

A comparative study of the oxidation of ferrous iron ions by various cultures of acidophilic chemolithotrophic microorganisms in solutions obtained after ferric leaching of copper-zinc concentrate at 80°C has been carried out. It was shown that the use of a moderately thermophilic culture for bioregeneration of leaching solutions was preferable. At the same time, the oxidation rate of Fe2+ ions reached 0.88 g/(L h), or 21.1 g/(L day). We propose that the activity of the moderately thermophilic culture was due to the presence of the mixotrophic bacteria Sulfobacillus spp., which used organic products of the microbial lysis for their growth. These products were formed during high-temperature ferric leaching of the copper-zinc concentrate with the biosolution.

Study of the Oxidation Rate of Fe2+ Ions in Water during Air Bubbling

The influence of the specific surface area of air bubbles in the process of bubbling on the oxidation rate of Fe2+ ions of model solutions prepared using distilled water with the addition of Fe2+ ions in the form of iron(II) sulfate (pure grade). The dependences of the rate of Fe2+ oxidation in water during air bubbling have been found.

Interactive influence of Fe–Mn and organic matter on pentachlorophenol sorption under oxic and anoxic conditions

This study examined the adsorption of pentachlorophenol (PCP) on geosorbents (original bulk soil and soils treated to significantly remove organic carbon and oxides of Fe and Mn) under oxic and anoxic experimental conditions. pH effects on adsorption capacities were maximal at pH<pKa of PCP (4.7). Decrease in redox potential and an increase in dissolve organic carbon inhibited PCP sorption. While contribution of Mn oxide to PCP sorption was negative due to decreasing charge interference, the study equally implied negligible role of surface area compared to organic matter contents and oxides of Fe with R2≤0.825. The rate of Fe2+ and Mn2+ release under anoxic condition reduced interactions of phenolate with iron oxides and consequently, the distribution coefficients coupled with increased dissolve organic carbon. Pseudo second order and Langmuir isotherm provided the best kinetic and isotherm models respectively, although adsorption processes appeared to involve more than one kinetic stage based on intra-particle diffusion model (R2≤0.982). The study suggests that soil treatment to remove Mn oxide may encourage transitory PCP sinks in some reductomorphic environments.

Constraints on biotic and abiotic role in the formation of Fe-Si oxides from the PACMANUS hydrothermal field

Fe-Si oxide deposits were recovered from the PACMANUS (Papua New Guinea-Australia-Canada-Manus) hydrothermal field in Eastern Manus basin. Samples were loose and fragile. Optical and scanning electron microscopy showed that the samples had abundant rod-like or twisted filamentous and granular structures. Electron probe microanalysis revealed that these filaments and grains were mainly composed of Fe and Si. The presence of spherical grains on the surface of the filaments suggests the intergrowth of biotic and abiotic reactions. Biotic and abiotic kinetics competition always exists in the redox gradient. Based on the physico-chemical conditions of PACMANUS hydrothermal fluids, we calculated a strict abiotic oxidation rate of Fe2+ to Fe3+, which is approximately 0.0123 g/min. If the fluids had been erupting consistently and the concentration of Fe2+ was constant, 3.232 kg per year of Fe would be deposited in this vent. The amount of Fe oxides around the studied vent was larger than the amount determined by strict abiotic kinetic calculation. Bacteria may also play an important role in Fe oxidation. A mesh-like microenvironment constructed by biogenic filaments ensured adequate Fe2+ and low oxygen content for the growth of bacteria. Moreover, this structure promoted the deposition of abiotic Fe-Si oxides.

Treatment of iron(II)-rich acid mine water with limestone and oxygen.

The main components of acid mine water are free acid, sulphate, and Fe²⁺. Limestone is the most cost-effective alkali that can be used for neutralization. The purpose of this investigation was to identify conditions where Fe²⁺ is removed with limestone and simultaneously oxidized with oxygen to Fe³⁺, in a polyvinyl chloride pipe under pressure. Gypsum scaling is prevented by passing rubber balls through the pipe of the so-called Oxygen-Pipe-Neutralization (OPeN) process pilot plant. Two synthetic waters were treated: (A) acid mine water containing 123 mg L⁻¹ Fe²⁺ representing gold mine water, and (B) acid mine water containing 6,032 mg L⁻¹ Fe²⁺ representing coal mine water. Batch studies were carried out in a pipe reactor and showed that the rate of Fe²⁺ oxidation depended on the Fe²⁺ concentration, oxygen pressure, amount of recycled sludge, limestone dosage and the mixing rate. Continuous studies in an OPeN process pilot plant resulted in 100% removal of total acidity from synthetic coal mine water and a 98% removal from synthetic gold mine water. Fe²⁺ was removed completely as precipitated Fe(OH)₃ from both synthetic coal and gold mine water at around pH 7 at 200 and 100 kPa oxygen pressure, respectively.

Kinetics of Fe&lt;sup&gt;2+&lt;/sup&gt; Oxidization at Different Initial Fe&lt;sup&gt;2+&lt;/sup&gt; and Fe&lt;sup&gt;3+&lt;/sup&gt; Concentration in the Presence of Moderate Thermophilic Bacteria

In the bacterial leaching, the oxidation of Fe2+ is very important process. According to the results of this paper, Fe2+ and Fe3+ concentration effect on the growth of moderate thermophile. The optimum conditions for growth of moderate thermophile are the initial concentration of Fe2+ at 0.16mol/l. It indicates the existence of the optimum conditions including initial concentrations of Fe2+ and Fe3+ for the bio-oxidation Fe2+. To increase the initial concentration of Fe3+ can enhance the oxidation rate of Fe2+. The dynamic model of the moderate thermophile oxidation Fe2+ has been established by analyzing and calculating test data with the Matlab software.

Nitrate-Dependent Ferrous Iron Oxidation by Anaerobic Ammonium Oxidation (Anammox) Bacteria

We examined nitrate-dependent Fe(2+) oxidation mediated by anaerobic ammonium oxidation (anammox) bacteria. Enrichment cultures of "Candidatus Brocadia sinica" anaerobically oxidized Fe(2+) and reduced NO3(-) to nitrogen gas at rates of 3.7 ± 0.2 and 1.3 ± 0.1 (mean ± standard deviation [SD]) nmol mg protein(-1) min(-1), respectively (37°C and pH 7.3). This nitrate reduction rate is an order of magnitude lower than the anammox activity of "Ca. Brocadia sinica" (10 to 75 nmol NH4(+) mg protein(-1) min(-1)). A (15)N tracer experiment demonstrated that coupling of nitrate-dependent Fe(2+) oxidation and the anammox reaction was responsible for producing nitrogen gas from NO3(-) by "Ca. Brocadia sinica." The activities of nitrate-dependent Fe(2+) oxidation were dependent on temperature and pH, and the highest activities were seen at temperatures of 30 to 45°C and pHs ranging from 5.9 to 9.8. The mean half-saturation constant for NO3(-) ± SD of "Ca. Brocadia sinica" was determined to be 51 ± 21 μM. Nitrate-dependent Fe(2+) oxidation was further demonstrated by another anammox bacterium, "Candidatus Scalindua sp.," whose rates of Fe(2+) oxidation and NO3(-) reduction were 4.7 ± 0.59 and 1.45 ± 0.05 nmol mg protein(-1) min(-1), respectively (20°C and pH 7.3). Co-occurrence of nitrate-dependent Fe(2+) oxidation and the anammox reaction decreased the molar ratios of consumed NO2(-) to consumed NH4(+) (ΔNO2(-)/ΔNH4(+)) and produced NO3(-) to consumed NH4(+) (ΔNO3(-)/ΔNH4(+)). These reactions are preferable to the application of anammox processes for wastewater treatment.

Fast microbial reduction of ferrihydrite colloids from a soil effluent

Recent studies on the microbial reduction of synthetic iron oxide colloids showed their superior electron accepting property in comparison to bulk iron oxides. However, natural colloidal iron oxides differ in composition from their synthetic counterparts. Besides a potential effect of colloid size, microbial iron reduction may be accelerated by electron-shuttling dissolved organic matter (DOM) as well as slowed down by inhibitors such as arsenic. We examined the microbial reduction of OM- and arsenic-containing ferrihydrite colloids. Four effluent fractions were collected from a soil column experiment run under water-saturated conditions. Ferrihydrite colloids precipitated from the soil effluent and exhibited stable hydrodynamic diameters ranging from 281 (±146)nm in the effluent fraction that was collected first and 100 (±43)nm in a subsequently obtained effluent fraction. Aliquots of these oxic effluent fractions were added to anoxic low salt medium containing diluted suspensions of Geobacter sulfurreducens. Independent of the initial colloid size, the soil effluent ferrihydrite colloids were quickly and completely reduced. The rates of Fe2+ formation ranged between 1.9 and 3.3fmolh−1cell−1, and are in the range of or slightly exceeding previously reported rates of synthetic ferrihydrite colloids (1.3fmolh−1cell−1), but greatly exceeding previously known rates of macroaggregate-ferrihydrite reduction (0.07fmolh−1cell−1). The inhibition of microbial Fe(III) reduction by arsenic is unlikely or overridden by the concurrent enhancement induced by soil effluent DOM. These organic species may have increased the already high intrinsic reducibility of colloidal ferrihydrite owing to quinone-mediated electron shuttling. Additionally, OM, which is structurally associated with the soil effluent ferrihydrite colloids, may also contribute to the higher reactivity due to increasing solubility and specific surface area of ferrihydrite. In conclusion, ferrihydrite colloids from soil effluents can be considered as highly reactive electron acceptors in anoxic environments.

Reduction swelling behaviour of haematite/magnetite agglomerates with addition of MgO and CaO

The influence of three kinds of CaO and MgO additives (dolomite, burnt lime and serpentine) on the reduction swelling behaviour of haematite–magnetite (H–M) concentrates pellets was studied. Burnt lime and dolomite increased the reduction swelling index of H–M oxidised pellets, while the reduction swelling index was able to be reduced when serpentine was added. CaO accelerated the formation and growth of metallic iron whiskers and led to abnormal swelling of the magnetite briquettes, while MgO was able to be dissolved in wüstite and reduced the migration rate of Fe2+; therefore, there was no catastrophic swelling in either the haematite or magnetite briquettes. As far as H–M concentrate pellets were concerned, because the solubility of CaO in magnetite was greater than that in the primary haematite and the secondary haematite generated from magnetite during the oxidation was easy to be reduced to wüstite, there was abnormal swelling in the reduced H–M pellets with CaO addition.

Attenuation and diel cycling of coal-mine drainage constituents in a passive treatment wetland: A case study from Lambert Run, West Virginia, USA

Abstract This study reports changes in coal-mine drainage constituent concentrations through a passive treatment wetland and over diel cycles. The purpose of the study was to determine what physiochemical mechanisms control attenuation of metals and if they varied by location and through time. The source water was slightly acidic (average pH 5.43); downstream degassing of CO2 contributed to an increase in pH prior to discharge from the site (average pH 7.05). Aluminum, Fe, rare earth elements (REE) and Y were removed to a greater extent than were Mn, Co and Ni. At acidic pH, the REE and Y were generally complexed by SO4. At higher pH, carbonate complexes became more important. The REE and Y concentrations were normalized to the North American Shale Composite standard; the normalized patterns were coherent near the source but anomalies of Ce and Y were present further downstream indicating oxidation and sorption processes. Four sets of diel-based samples were collected, one from a shallow, surface-flow wetland and three from a deeper, newly constructed wetland. Well-defined diel cycles were observed for concentrations of Si, Mn, Fe, Co, Ni, As, REE and Y in the shallow wetland. In all cases, the concentrations increased (up to 863%) during night and decreased during the day. These cycles had an inverse relationship with the temperature cycle (pH had no discernable cycle). The consistency of concentration cycles suggests a common mechanism, most likely associated with the formation of Fe oxyhydroxides. The increased rate of Fe2+ oxidation in warm water can account for the cycles in Fe; scavenging of the other elements by the Fe precipitate can account for the consistency of the cycles even though the elements include cations, anions ( H 2 AsO 4 - or HAsO 4 - 2 ), and neutral species ( H 4 SiO 4 0 ). While REE and Y had clear cycles in the constructed wetland, the other elements did not. This is partially due to the lower elemental concentrations (including Fe) but the cycles may also be damped by the deeper, slower-moving water. This study illustrates the dynamic nature of metal removal in passive treatment systems. Furthermore, it suggests that grab samples collected during daytime hours may underestimate the concentrations and flux of metals in these systems.

Kinetics of iron oxidation upon polyphenol binding

Polyphenol prevention of iron-mediated DNA damage occurs primarily through iron binding. Once bound, iron in the Fe(2+)-polyphenol complex autooxidizes to Fe(3+) in the presence of O(2). To determine the correlation between the rate of Fe(2+)-polyphenol autooxidation and polyphenol antioxidant ability, kinetic studies at pH = 6.0 in the presence of oxygen were performed using UV-vis spectrophotometry. Initial rates of iron-polyphenol complex oxidation for epigallocatechin gallate (EGCG), methyl-3,4,5-trihydroxybenzoate (MEGA), gallic acid (GA), epicatechin (EC), and methyl-3,4-dihydroxybenzoate (MEPCA) were in the range of 0.14-6.7 min(-1). Polyphenols with gallol groups have faster rates of iron oxidation than their catechol analogs, suggesting that stronger iron binding results in faster iron oxidation. Concentrations of polyphenol, Fe(2+), and O(2) were varied to investigate the dependence of the Fe(2+)-polyphenol autooxidation on these reactants for MEGA and MEPCA. For these analogous gallate and catecholate complexes of Fe(2+), iron oxidation reactions were first order in Fe(2+), polyphenol, and O(2), but gallate complexes show saturation behavior at much lower Fe(2+) concentrations. Thus, gallol-containing polyphenols promote iron oxidation at a significantly faster rate than analogous catechol-containing compounds, and iron oxidation rate also correlates strongly with polyphenol inhibition of DNA damage for polyphenol compounds with a single iron-binding moiety.

Oxidation and immobilization of iron and manganese by a fluidized bed reactor

An iron and manganese species immobilization technology was developed in a fluidized bed reactor (FBR) with a new fluidized media, immobilized iron oxide (namely FeOx-30). The FeOx-30 catalyst exhibited excellent performance as a catalyst for the oxidation of Mn2 + . About 95% and 30% of the manganese species were immobilized on FeOx-30 and silica sand in FBR, respectively. The oxidation rates of Fe2 + and Mn2 + and the immobilization efficiencies of iron and manganese oxides strongly depend on pH value. Usually during oxidization the pH values of the solution containing Fe2 + must be above 7, and Mn2 + must be above 9. During this study, large amounts of iron species leached from the surface of FeOx-30 only when manganese was in the system. The surface of the FeOx-30 became fragile in a single system. However, the removal of iron and manganese species simultaneously was better than only the removal of manganese in an FBR. In the binary system, the optimum pH condition for immobilization of both iron and manganese species was pHi 9. The higher catalyst loading in the binary system led to a higher removal efficiency of iron and manganese.

Iron solids formed from oxidation precipitation of ferrous sulfate solutions

AbstractThe oxidation and precipitation of iron from ferrous sulfate solutions was studied at high Fe2+ concentrations, as found in typical South African acid mine drainage, and at high pH, as practised in the removal of iron from acid mine drainage (AMD) by the high‐density sludge process. The results obtained showed that the nature of the precipitates formed was largely determined by the rate of Fe2+ oxidation. High pH promoted higher‐oxidation rates resulting in high‐nucleation rates, and the consequent formation of finer particles. The precipitation process in all cases was found to produce nanosized, growth limited primary particles. These primary particles later aggregated, producing particles several hundreds of nanometres in size. At pH 8.0, these fine particles aggregated due to Van der Waals forces, while at pH 10.0, ferrihydrite was found to transform into goethite. The settling rates of the precipitates showed little dependence on the pH. The precipitate formed at pH 6.0 contained consistently higher proportions of Fe2+ compared to the precipitates formed at higher pHs. Interestingly, particles formed at higher pH gave lower final BET surface areas, contrary to the trend that would be predicted from the evolution of the population based average particle size. © 2007 American Institute of Chemical Engineers AIChE J, 2007.

Evaluation of Mixed Valent Iron Oxides as Reactive Adsorbents for Arsenic Removal

The objective of this research was to determine if Fe(II)-bearing iron oxides generate ferric hydroxides at sufficient rates for removing low levels of arsenic in packed-bed reactors, while at the same time avoiding excessive oxide production that contributes to bed clogging in oxygenated waters. Column experiments were performed to determine the effectiveness of three media for arsenic removal over a range in empty bed contact times, influent arsenic concentrations, dissolved oxygen (DO) levels, and solution pH values. Corrosion rates of the media as a function of the water composition were determined using batch and electrochemical methods. Rates of arsenic removal were first order in the As(V) concentration and were greater for media with higher corrosion rates. As(V) removal increased with increasing DO levels primarily due to faster oxidation of the Fe2+ released by media corrosion. To obtain measurable amounts of arsenic removal in 15 mM NaCl electrolyte solutions containing 50 microg/L As(V), the rate of Fe2+ released by the media needed to be at least 15 times greater than the As(V) feed rate into the column. In waters containing 30 mg/L of silica and 50 microg/L of As(V), measurable amounts of arsenic removal were obtained only for Fe2+ release rates that were at least 200 times greater than the As(V) feed rate. Although all columns showed losses in hydraulic conductivity overthe course of 90 days of operation, the conductivity values remained high, and the losses could be reversed by backwashing the media. The reaction products produced by the media in domestic tap water had average As-to-Fe ratios that were approximately 25% higher than those for a commercially available adsorbent.