Zero-valent Iron Powder Research Articles

Kinetics and corrosion products of aqueous nitrate reduction by iron powder without reaction conditions control

Although considerable research has been conducted on nitrate reduction by zero-valent iron powder (Fe0), these studies were mostly operated under anaerobic conditions with invariable pH that was unsuitable for practical application. Without reaction conditions (dissolved oxygen or reaction pH) control, this work aimed at subjecting the kinetics of denitrification by microscale Fe0 (160-200 mesh) to analysis the factors affecting the denitrification of nitrate and the composition of iron reductive products coating upon the iron surface. Results of the kinetics study have indicated that a higher initial concentration of nitrate would yield a greater reaction rate constant. The reduction rate of nitrate increased with increasing Fe0 dosage. The reaction can be described as a pseudo-first order reaction with respect to nitrate concentration or Fe0 dosage. Experimental results also suggested that nitrate reduction by microscale Fe0 without reaction condition control primarily was an acid-driven surface-mediated process, and the reaction order was 0.65 with respect to hydrogen ion concentration. The analyses of X-ray diffractometry and X-ray photoelectron spectroscopy indicated that a black coating, consisted of Fe2O3, Fe3O4 and FeO(OH), was formed on the surface of iron grains as an iron corrosion product when the system initial pH was lower than 5. The proportion of FeO(OH) increased as reaction time went on, whereas the proportion of Fe3O4 decreased.

A closed-loop proposal for hydrogen generation using steel waste and a prototype solar concentrator

An economically viable and environmental-friendly method of generating PEM grade hydrogen has been proposed and is by the reaction of certain metals with steam, appropriately called ‘metal–steam reforming’—MSR. The drawbacks of conventional processes (hydrogen and carbothermic reduction schemes) are overcome by resorting to solution-based reduction schemes and are made economically feasible using iron oxides from steel industry's mill-scale waste. A novel aqueous-based room temperature technique using sodium borohydride (NaBH4) as the reducing agent has been developed that produces highly active nanoscale iron particles (∼40 nm). By using hydrazine as an inexpensive and, compared with NaBH4, more stable reductant, body centered cubic iron particles with ∼5 nm edges were obtained via solvothermal process under mild conditions from acid digested mill-scale waste. The nanoscale zerovalent iron (nZVI) powder showed improved kinetics and greater propensity for hydrogen generation than the coarser microscale iron. The rate constants for the MSR were obtained for all the reduction schemes employed in this work and are given by khydrogen=0.0158 min−1 kcarbon=0.0248 min−1 ksodiumborohydride=0.0521 min−1 and khydrazine=0.1454 min−1, assuming first order kinetics. Another innovative effort converted the magnetite waste directly into nZVI under solvothermal conditions, thus obviating the sluggish and time-consuming acid dissolution step. This particular aspect has significant ramification in terms of time and cost of making the iron precursor. To initiate and sustain the somewhat endothermic MSR process, a solar concentrator consisting of a convex polyacrylic bowl with reflective aluminum coating was fabricated and evaluated. This unique combination of mill-scale waste as iron source, hydrazine as reductant, mild process conditions and solar energy as the MSR actuator obviates several drawbacks plaguing the grand scheme of producing and delivering pure and humidified H2 to a PEMFC stack. Copyright © 2008 John Wiley & Sons, Ltd.

EFFECTS OF SEVERAL SURFACTANTS AND HIGH‐MOLECULAR‐WEIGHT ORGANIC COMPOUNDS ON DECOMPOSITION OF TRICHLOROETHYLENE WITH ZEROVALENT IRON POWDER

We investigated the effects of coexisting surfactants and high‐molecular‐weight organic compounds on the reductive dechlorination of trichloroethylene by zerovalent iron powder to determine whether these additives had utility as washing reagents for remediation of soil and groundwater pollution. During the dechlorination reaction, the amount of trichloroethylene decreased, and the formation of cis‐1,2‐dichloroethylene was observed. The decomposition of trichloroethylene was found to be first‐order with respect to the trichloroethylene and zerovalent iron concentrations when the solution contained no additives. The rates of decomposition of trichloroethylene in the presence of the additives were lower than the rate in the absence of the additives: the rate constant was reduced by a factor of 0.7 for the cationic surfactant cetyltrimethylammonium bromide; by a factor of 0.5 for the anionic surfactants sodium n‐dodecylbenzenesulfonate, sodium n‐dodecylsulfate, and sodium n‐dodecanesulfonate and for the high‐molecular‐weight organic compounds soluble starch, β‐cyclodextrin, and polyethyleneglycol 6000; and by a factor of 0.2 for sodium laurate and the nonionic surfactants Triton X‐100, Tween 20, Tween 60, Brij 35, and Brij 58. Comparison of the concentrations of the nonionic surfactants with their critical micellar concentrations indicated that the rate‐reducing effect of these additives was due to solubilization of trichloroethylene into the micellar phase. The adsorption of trichloroethylene onto the zerovalent iron surface was also affected by the presence of the additives. Thus, our results indicated that the changes in the decomposition rate of trichloroethylene were determined by several factors.

Rapid removal of flutriafol in water by zero-valent iron powder

A study of the effect of zero-valent iron (ZVI) powder is carried out for the first time on the degradation of flutriafol (( RS)-2,4′-difluoro-α-(1 H-1,2,4-triazol-1-ylmethyl)-benzhydryl alcohol, C 16H 13F 2N 3O), a bifluorinated soil and water persistent triazole pesticide using a laboratory scale device consisting of a 20 ml pyrex serum vials fixed to a Vortex agitator. Different amounts of ZVI powder (10–50 g l −1) at pH 6.6 and room temperature were investigated. Experiments showed an observed degradation rate k obs directly proportional to the surface of contact of flutriafol with ZVI. Flutriafol degradation reactions demonstrated first order kinetic with a half-live of about 10.8 ± 0.5 min and 3.6 ± 0.2 min when experiments were conducted at [ZVI] = 10 g l −1 into oxygenated and anoxic solutions, respectively. Three analytical techniques were employed to monitor flutriafol degradation and to understand solution and by-products behaviors: (1) A UV–Vis spectrophotometer; (2) a high performance liquid chromatography (HPLC) coupled with a photo diode array (PDA) and fluorescence detectors; (3) a similar HPLC coupled with a PDA and a mass spectrometer detectors equipped with an atmospheric pressure photoionization source. Results showed a complete disappearance of flutriafol after 20 min of contact with ZVI, the loss of fluorescence properties of the final by-products, the defluorination of the triazole pesticide via hydroxylation reaction and finally the hydrogenation of the triazole ring.

Conversion of steel mill waste into nanoscale zerovalent iron (nZVI) particles for hydrogen generation via metal-steam reforming

The proton exchange membrane fuel cells (PEMFCs) are the most preferred and efficient energy conversion devices for automotive applications but demand high purity hydrogen which comes at a premium price. The currently pursued hydrogen generation methods suffer from issues such as, low efficiency, high cost, environmental non-benignity, and, in some cases, commercial non-viability. Many of these drawbacks can be overcome by resorting to metal-steam reforming using iron from steel industry's mill-scale waste. A novel solution-based room temperature technique using sodium borohydride (NaBH4) as the reducing agent has been developed that produces highly active nanoscale (30–40nm) iron particles. A slightly modified version of this technique using a surfactant and water–oil microemulsion resulted in the formation of 5nm spherical Fe particles. By using hydrazine as an inexpensive and more stable (compared to NaBH4) reductant, body centered cubic iron particles with edge dimensions ∼5nm were obtained under mild solvothermal conditions in ethanol. The nanoscale zerovalent iron (nZVI) powder showed improved kinetics and greater propensity for hydrogen generation.

Fe@Fe2O3 Core−Shell Nanowires as Iron Reagent. 1. Efficient Degradation of Rhodamine B by a Novel Sono-Fenton Process

In this study, Fe@Fe2O3 core−shell nanowires were first used as a novel Fenton iron reagent. The nanowires were synthesized through the reduction of ferric chloride aqueous solution by sodium borohydride at ambient atmosphere, without protection of inert gases or vacuum. Rhodamine B (RhB) could be efficiently degraded in aqueous media by a novel sonochemical-assisted Fenton (sono-Fenton) system based on these Fe@Fe2O3 core−shell nanowires. The RhB degradation processes were monitored by UV−vis spectroscopy and total organic carbon (TOC) analysis. Fe@Fe2O3 core−shell nanowires showed much higher activity in the sono-Fenton system than other iron reagents such as commercial zerovalent iron powders (Fe0), ferrous ions (Fe2+), and ferric ions (Fe3+). It was found that near 100% decoloration and over 60% TOC removal of RhB (5 mg·L-1) could be achieved in 60 min by this novel sono-Fenton system with 0.018 mol·L-1 Fe@Fe2O3 core−shell nanowires. This new iron reagents before and after the sono-Fenton reaction wer...

Azo dye degradation by recycled waste zero-valent iron powder

In this paper an efficient method for azo dye degradation using an environmentally friendly zero-valent iron powder source is presented (iron particles discarded from a manufacturing process). The influence of several experimental parameters (such as pH, iron mass, particle size, substrate concentration, oxidizing and inert atmospheres) on the ability of zero-valent iron to reduce the chromophoric groups and total organic carbon content of the azo dye Remazol Black B was evaluated. Kinetic studies revealed that the azo degradation by Fe0 appeared to be first-order with respect to substrate, with an observed rate constant (kobs) of 0.153 min-1. Under the optimized operational conditions (pH 3, [Fe] = 5 g L-1, iron particle size < 250 µm), the iron-based process produced net a reduction in color and total organic carbon of about 95% and 70%, respectively. The process was also evaluated for the degradation of textile effluent. The studied process showed good characteristics, which can make it an effective alternative for polluted aquatic system remediation.

Synthesis of nanoscale reaction pits network on zerovalent iron powder surface

A neat and efficient method for controllable and reproducible synthesis of coral-shaped matrix containing abundant nanoscale reaction pits on micrometer-size zerovalent iron powder is described with the study of etching capability of dilute hydrochloric, sulfuric, and nitric acids with concentration ranges from 1 N to 6 N. Characterizations of surface morphology show that the specific surface area of this matrix increases up to 170 times that of the untreated iron powder, and that the reduction efficiency of a PCB congener in subcritical water is enhanced fivefold from 18% for the untreated iron to 92% for that with 170 times its surface area. The nanoscale pits may be a basis for enhancement of reaction cross-section via restriction of molecule mobility in the pits.

Characteristics of nitrate reduction by zero-valent iron powder in the recirculated and CO 2-bubbled system

In this study, the Fe 0/CO 2 process was investigated for removing nitrate from aqueous solution under different operating conditions such as CO 2 bubbling rate (0–400 mL/min), Fe 0 dosage (1–6 g/L), initial nitrate concentration (6–23 mg N/L), batch mode, and fresh Fe 0 supplementing (0–1 g/L). Results show that the bubbling of CO 2 flow rate at 200 mL/min was sufficient for supplying H + into solution to create an acidic environment favorable to nitrate reduction reaction. It was found that sigmoidal model equation describes the S-curve behaviors of nitrate reduction, ferrous accumulation and ammonium formation satisfactorily, and the parameter t 1/2 of the proposed model equation serves as a powerful tool for the comparison of nitrate reduction rate. Sustainability test demonstrates that Fe 0 powder began to deteriorate after three batches operation. Concerning the operating modes, the batch mode with the treated solution emptied and freshly refilled outperforms the one, which was operated by retaining the treated solution and spiking concentrated nitrate into it for the next batch treatment. To guarantee satisfactory nitrate removal using the former mode, supplement of appropriate amount of Fe 0 needs to be optimized

Degradation of phenol, into mineral compounds, in aqueous solutions using Zero-Valent Iron Powder (ZVIP)

This paper presents an original approach to the treatment of phenolic aqueous solution by using zero-valent iron powder (ZVIP). In batch reactors under water treatment conditions (room temperature and pH: 4-7), a rapid degradation of phenol in the presence of iron powder 40-60 mesh (40 gL -1 ) was observed. The decline in the phenol concentration was monitored by a spectrofluorometer (Shimadzu RF 5301 PC), a spectrophotometer (UV-Vis Shimadzu 1650 PC) and GC (Gas Chromatography). Due to the degradation reaction, a large decrease in the total organic carbon (TOC) value, which was measured by a Shimadzu TOC analyzer model 5000 A, had been observed. The degradation enthalpy was measured by a micro-calorimeter SETARAM C80 and was compared to the formation enthalpy of phenol. In addition, experiments were run in buffer solutions. With different pH values, different degradation rates were obtained indicating that the pH plays an important role in the degradation process. Moreover, a kinetic study was performed and a potential mechanism of the degradation process is proposed.

Treatment of Aqueous Nitrate by Zero Valent Iron Powder in the Presence of CO2 Bubbling

AbstractThis paper investigates a process for the removal of nitrate from ground water by combination of Fe° and CO2 bubblin*** The bubbling of CO2 effectively creates an acidic environment favorable to Fe° corrosion, which results in nitrate reduction. I 10 min, the solution pH dropped to 3.2 with CO2 inflow rate of 500 mL/min. In the presence of Fe° (2 g/L), the CO2 bubblin (500 mL/min) induced conversion of nitrate‐N (∼7 mg/L) by 85% in 40 min. In addition, the end product in the reaction mi***xture was ammonium, which accounts for 90% to 104% of nitrate conversion with the presence of various iron dosages (0.5 t 2.0 g/L). Though the formation of ammonium is a drawback, the ammonium was eliminated from aqueous phase by a follow up treatment of settling (30 min) and air aeration (50 min).

Alternative chromium reduction and heavy metal precipitation methods for industrial wastewater

AbstractA study of alternative chromium‐reduction and heavy‐metal precipitation methods was performed on wastewater generated by a metal‐cleaning facility. Four existing chromium‐reduction treatment methods were tested on the wastewater samples: treatment with (1) sodium metabisulfite, (2) ferrous sulfate, (3) zero‐valent iron, and (4) dimethyl dithio carbamate, ferrous sulfate, and aluminum/chloride. We found that the first two methods are more effective in chrome reduction, while the last method achieved similar reduction results but produced more sludge than any of the other methods. Our results also indicated that when ferrous sulfate was used as a chrome reduction reagent at a low initial pH (2 to 3), the competitive oxidation reaction of ferrous ions with dissolved oxygen in solution is insignificant.When iron powder was used to reduce hexavalent chromium to trivalent chromium, we found that (a) when the sample containing low levels of total chromium (⩽ 1.54 × 10− 4 mole/liter) was mixed properly with zero‐valent iron powders at a low pH (4 to 5), the total chromium concentration could be reduced to 1 mg/l in 3 hours; and (b) the chrome absorption‐reduction efficiency is limited by the transport process of Cr(VI) from the bulk of the wastewater to the surface of the iron powder. In a leaching test of used iron powder filtered from the treated wastewater, we also found that most of chromium absorbed on the iron powder was very stable, and only low Cr(VI) was detected in the leachate.

Reduction of nitroaromatic pesticides with zero-valent iron

Reduction of eleven nitroaromatic pesticides was studied with zero-valent iron powder. Average half-lives ranged from 2.8 to 6.3 h and the parent compounds were completely reduced after 48–96 h. The di-nitro groups of the 2,6-dinitroaniline herbicides were rapidly reduced to the corresponding diamines, with a negligible amount of partially reduced monoamino or nitroso products. Low levels of de-alkylated products were observed after 10 days. The nitro group of the organophosphorus insecticides was reduced dominantly to the monoamines but in a slower rate than the 2,6-dinitroanilines. A trace amount of oxon products was found. Reduction of nitro to amino was also the predominant reaction for the diphenyl ether herbicides. Aromatic de-chlorination and de-alkylation were minor reactions. These amine products were more stable than the parent compounds and 60% or more of the amines were detected after two weeks. Humic acid decreased the reduction rates of pendimethalin, and dichlone (a known quinone redox mediator) counteracted the effect of humic acid on the reactivity. Storage of iron powder under air decreased the reactivity very rapidly due to iron oxidation. Repeated use of iron powder also showed similar results. The reduced activity of air-oxidized iron was recovered by purging with hydrogen, but not nitrogen. Integration of iron powder with hydrogen- and quinone-producing microbial technologies may be a viable mean for remediation of highly oxidized xenobiotics in the environment.

Degradation of benomyl, picloram, and dicamba in a conical apparatus by zero-valent iron powder

Reduction of some pesticides (benomyl, picloram, and dicamba) was studied in an aerobic batch conical pilot system to investigate the disappearance of these pesticides on contact with iron powder (20 g/l, 325-mesh). Aqueous buffered solutions of the compounds were added to the system followed by zero-valent iron powder (ZVIP), and the decline in the pesticide concentrations was monitored over time. HPLC analyses show a complete disappearance of picloram (1.20 mg/l) after 20 min of reaction. Benomyl (1.00 mg/l) and dicamba (1.25 mg/l) disappear after 25 and 40 min, respectively. The t 50 values ranged from 3 to 5.5 min, and were about slightly less than the t 1/2 values reported when the log of the relative HPLC peak area was plotted versus time, where the relative peak area was calculated by dividing the measured peak area by the initial peak area. Pathways for the degradation of the studied pesticides by ZVIP are proposed.

Reductive degradation of carbaryl in water by Zero-valent iron

Reduction of carbaryl solution by zero-valent iron powder (ZVIP) was studied in a rotator batch system (70 rpm) in order to evaluate the utility of this reaction in remediation of carbamate contaminated water. Degradation with different amount of ZVIP: 0.01, 0.02, 0.03, 0.04 g/ml at pH 6.6 and at ambient temperature was investigated. The results show that the process exhibits a degradation rate appearing to be directly proportional to the surface contact area of ZVIP (325-mesh) with the carbaryl molecules. Three analytical techniques were used to monitor carbaryl degradation: (1) A UV–Vis diode array spectrophotometer was used to record all spectra. (2) A high performance liquid chromatography was used to separate by-products and examine the evolution of breakdown products. (3) A home-built spectrophosphorimeter that uses the solid surface room temperature phosphorescence (SSRTP) was employed to observe selectively the decline of the carbaryl concentration at different amount of ZVIP on Whatman no. 1 filter paper. Results show that the reducing degradation of carbaryl with ZVIP as the source of electrons is effective with a half-life close to several minutes.

Remediation of s-triazines contaminated water in a laboratory scale apparatus using zero-valent iron powder

Atrazine, propazine and simazine were tested separately and in mixture by batch procedure in a laboratory-constructed apparatus. 3.75 l of a buffered s-triazines pesticide solution was treated at room temperature by 325-mesh zero-valent iron powder (ZVIP) (20 g/l). High performance liquid chromatography was used to separate by-products and study the decline in the pesticide’s concentrations. Results obtained show that the order of degradation was simazine, atrazine and then propazine. The half-lives ( t 1/2) of the s-triazines pesticides are, respectively, 7.4, 9.0 and 10.6 min when they are treated separately, and 9.8, 11.2 and 13.7 min when they are treated together under the same conditions. The final by-product obtained after 50 min of contact of simazine with ZVIP shows a shift to longer wavelength in its UV spectrum. A similar phenomenon is shown for atrazine and propazine. Identical primary by-products are produced and subsequently degraded to 4,6-(diamino)- s-triazine, which seems to be the major by-product of the reductive treatment process. Pathways for the degradation of the studied s-triazines by ZVIP are proposed.

Kinetics of reductive denitrification by nanoscale zero-valent iron

Zero-valent iron powder (Fe 0) has been determined to be potentially useful for the removal of nitrate in the water environment. This research is aimed at subjecting the kinetics of denitrification by nanoscale Fe 0 to an analysis of factors affecting the chemical denitrification of nitrate. Nanoscale iron particles with a diameter in the range of 1–100 nm, which are characterized by the large BET specific surface area to mass ratio (31.4 m 2/g), removed mostly 50, 100, 200, and 400 mg/l of nitrate within a period of 30 min with little intermediates. Compared with microscale (75–150 μm) Fe 0, endproduct is not ammonia but N 2 gas. Kinetics analysis from batch studies revealed that the denitrification reaction with nanoscale Fe 0 appeared to be a pseudo first-order with respect to substrate and the observed reaction rate constant ( k obs) varied with iron content at a relatively low degree of application. The effects of mixing intensity (rpm) on the denitrification rate suggest that the denitrification appears to be coupled with oxidative dissolution of iron through a largely mass transport-limited surface reaction (<40 rpm).

Reducing degradation of azo dye by zero-valent iron in aqueous solution

The reducing degradation kinetics of five azo dyes, Acid orange II , Acid orange IV, Acid orange GG, Acid red 3B and Orange I , by zero-valent iron powder in aqueous solution were studied. It showed that the degradation is a two-step reaction, with the first step being reversible. Solution acidity and iron surface area are the factors greatly influencing the degradation rates, and with increasing of acidity and iron surface area, the degradation rates increase

The effects of pH and addition of an organic buffer (HEPES) on nitrate transformation in Fe0-water systems

The feasibility of using zero-valent iron (Fe0) powder to remediate nitrate-contaminated water was studied using bench-scale batch reactors. Operational parameters, such as Fe0 dosage (w/v), initial concentration of nitrate-nitrogen, pH, and the use of an organic buffer (HEPES) were studied, specifically focusing on the effects of pH and the addition of HEPES on nitrate transformation using zero-valent iron powder. Nitrate-nitrogen was removed by 94% when 0.01M of HEPES was added to a non-shaking batch reactor containing 20 mg/l nitrate-nitrogen and 4% (w/v) of Fe0. Shaking was proved to be more efficient than no shaking. Using the response surface methodology it was found that nitrate removal was closely related to pH. At low pH (e.g., pH &amp;lt; 2), the nitrate removal was fast and efficient (95% to 100%). At high pH (e.g., pH &amp;gt; 11), the transformation of nitrate was fast and efficient only for low concentration of nitrate in the Fe0-H2O system. At normal pH range (pH = 6 to 8), nitrate removal was usually lower than 50% without buffer treatment. The addition of the organic buffer (HEPES) could greatly enhance the nitrate transformation in a wide pH range (e.g., pH = 2 to 11).

The effects of pH and addition of an organic buffer (HEPES) on nitrate transformation in Fe0-water systems

The feasibility of using zero-valent iron (Fe0) powder to remediate nitrate-contaminated water was studied using bench-scale batch reactors. Operational parameters, such as Fe0 dosage (w/v), initial concentration of nitrate-nitrogen, pH, and the use of an organic buffer (HEPES) were studied, specifically focusing on the effects of pH and the addition of HEPES on nitrate transformation using zero-valent iron powder. Nitrate-nitrogen was removed by 94% when 0.01M of HEPES was added to a non-shaking batch reactor containing 20 mg/1 nitrate-nitrogen and 4% (w/v) of Fe0. Shaking was proved to be more efficient than no shaking. Using the response surface methodology it was found that nitrate removal was closely related to pH. At low pH (e.g., pH < 2), the nitrate removal was fast and efficient (95% to 100%). At high pH (e.g., pH > 11), the transformation of nitrate was fast and efficient only for low concentration of nitrate in the Fe0-H2O system. At normal pH range (pH = 6 to 8), nitrate removal was usually lower than 50% without buffer treatment. The addition of the organic buffer (HEPES) could greatly enhance the nitrate transformation in a wide pH range (e.g., pH = 2 to 11).