Zero-valent Iron Dosage Research Articles

Application of Recycled Zero‐Valent Iron Nanoparticle to the Treatment of Wastewater Containing Nitrobenzene

Zero‐valent iron (ZVI) was synthesized using iron oxide, a byproduct of pickling line at a steel work. ZVI with a mean particle size of 500 nm was synthesized. The reaction activity of the synthesized ZVI was much higher than commercial ZVI. When applied to the decomposition of nitrobenzene (NB), the ZVI particles underwent corrosion and passivation oxide film formation, resulting in particle size decrease. The NB decomposition rate increased with increasing ZVI dosage level and with decreasing pH. The solution pH increased monotonously with increasing reaction duration, whereas the aniline concentration showed a maximum at 50 min. Based on the GC/MS analysis, NB is presumed to be reduced into aniline via reductive intermediates such as azobenzene and azoxybenzene. When combined with a subsequent biological process, the synthesized ZVI will be able to decompose NB in wastewater effectively.

Removal of U(VI) from Leaching Process Wastewater by Zero-Valent Iron

The removing effectiveness of U(VI) in leaching process wastewater by Zero-valent iron (ZVI)(iron powder and waste scrap) has been studied. The effects of the dosage of ZVI, pH, shaking time and temperature on treatment effiency are investigated. The results showed that: ZVI has very good removal effect on U (VI), and when pH value of solution is 6, the dosage of ZVI is 1.5 g, the shaking time is 80 min, the removal rate reached 98.6%.The removing efficiency of iron powder is sightly better than waster scrap.Acorrding to the experiment, the optimum experiment conditions and the influence of these parameters are obtained. The removal mechanism of U(VI) in leaching process wastewater by ZVI is discussed.

Nitrobenzene degradation by micro-sized iron and electron efficiency evaluation

AbstractThe effect of pH, temperature, zero-valent iron (ZVI) dosage and reaction duration on nitrobenzene (NB) degradation by micro-sized ZVI was investigated in batch experiments and the electron efficiency (EE) was evaluated at constant pH. The experimental results showed that the reaction rate constant attained 0.616 min−1, which was far higher than reported in previous studies. The decrease in pH and increase in temperature of the reaction bath promoted the reaction kinetics. ZVI dosage and reaction duration were two key factors affecting NB reduction and EE. A lower ZVI dosage and a slightly longer reaction duration could afford an optimised EE and optimum NB removal. A prolonged reaction or too high a ZVI dosage resulted in increased ZVI waste.

Degradation of aniline with zero-valent iron as an activator of persulfate in aqueous solution

Zero valent iron (ZVI) can activate persulfate to generate sulfate free radicals which are a strong oxidant to degrade organic pollutants. The oxidative degradation of aniline in aqueous solution by persulfate activated with zero valent iron was studied under laboratory conditions. Batch experiments were conducted to investigate the effects of different parameters such as pH, ZVI concentration, aniline concentration, persulfate concentration and reaction temperature on aniline degradation. The results showed that aniline degradation increased with increasing temperature. The optimum dosage of ZVI was 0.4 g L−1 and 85% aniline degradation was observed. Maximum aniline degradation was observed at pH 4.0, whereas at pH above or below 4.0, aniline degradation efficiency was decreased. In the persulfate-ZVI system, the apparent energy of activation for aniline degradation was 14.85 kJ mol−1. The existence of persulfate radicals and hydroxyl radicals produced during the degradation of aniline were identified with scavenger ethanol and tert-butyl alcohol. The reaction intermediates nitrobenzene, nitroso-benzene and p-benzoquinone were detected by gas chromatography-mass spectrometry and based on these intermediates obtained a probable pathway for aniline degradation has been proposed.

Kinetics of selenite reduction by zero-valent iron

Zero-valent iron (ZVI) is an inexpensive agent that can remove many common environmental contaminants. The effects of dissolved oxygen (DO), pH, initial selenite concentration (Se(IV)), ZVI dosage and particle size as well as reaction temperature on Se(IV) removal by ZVI were systematically investigated in this study. Se(IV) removal by ZVI was more favored under oxic conditions with higher reaction rate than under anoxic conditions, ascribing to the promoted ZVI corrosion rate in the presence of DO. Moreover, Se(IV) removal by ZVI was enhanced with increasing ZVI dosage and reaction temperature but decreased with increasing pH and ZVI particle size. The removal rate of Se(IV) by ZVI experienced an increase and then a decrease with initial Se(IV) concentration ranging from 9.9 to 78.6mg L-1. To further describe the reaction rate, a pseudo-?rst-order kinetics was employed, and the calculated activation energy, by fitting the rate constants at different temperatures, was determined to be 32.86kJmol(-1). When fixing other conditions, good linear correlation could be observed between pseudo-first-order reaction rate constants (k(obs)) and ZVI dosage. Compared with other methods for Se(IV) removal reported in literatures, reduction by ZVI was considered a promising technique, which could rapidly and effectively eliminate Se(IV) from waters.

Chemical and Biological Reduction of PCE by Pneumatic Fracturing and Injection of ZVI in Saprolite

AbstractThis article presents a case study of the source‐area treatment of tetrachloroethene (PCE) in a low‐permeability formation using zero‐valent iron (ZVI). Evidence of the stimulation of biological reduction processes within the treatment zone occurred. Pneumatic fracturing and injection of microscale ZVI slurry in the overburden and weathered bedrock zones was performed at a commercial brownfields redevelopment site in Maryland. A 20,000‐square‐foot source area impacted with PCE at concentrations greater than 15,000 µg/L was treated at depths ranging from 10 to 70 feet bgs. An average ZVI dosage of 0.0024 iron‐to‐soil mass ratio within the overburden zone led to a 75 percent decrease in PCE mass in less than one year. For the weathered bedrock zone, an average 0.0045 iron‐to‐soil mass ratio resulted in a 92 percent decrease in PCE mass during the same period. The reducing environment and hydrogen generated by the ZVI may have stimulated Dehalobacter populations, as evidenced by concentrations up to 104 cells per milliliter measured within the treatment area despite a groundwater pH as high as 9. The biological reductive dechlorination of the chlorinated ethenes explains the temporary increase in trichloroethene and cis‐1,2‐dichloroethene concentrations. © 2013 Wiley Periodicals, Inc.

PH-dependent degradation of acid orange II by zero-valent iron in presence of oxygen

In this study, zero-valent iron (ZVI)-mediated advanced oxidation was applied to degrade the acid orange II (AOII) in the presence of oxygen. The effect of pH value, ZVI dosage, O2 concentration and added Fe2+ ions on the degradation efficiency was investigated. It was found that the increases of acidity in aqueous solution, ZVI dosage and O2 concentration were favorable to the oxidation reaction of AOII in ZVI-mediated advanced oxidation processes. The lower pH value in aqueous medium was favorable for AOII degradation in ZVI/O2 system. The AOII degradation efficiency and COD removal efficiency system could achieve more than 95% and 65% within 3h in the ZVI/O2 at initial pH 3.0, respectively. The AOII degradation in ZVI/O2 system followed the first-order reaction kinetics at pH range of 3.0–7.0, while AOII degradation followed the zero-order reaction kinetics at pH range of 9.0–11.0. The measurements of H2O2 and Fe2+ in ZVI/O2 system, and the characterization for used ZVI particles demonstrated the role of Fenton reaction in the ZVI/O2 system, which occurred favorably at low pH to generate H2O2 and Fe2+, followed by a likely species OH to degrade AOII. The involvement of OH in oxidizing AOII was examined by determining the degradation rates using OH scavenger. Moreover, the coexistence ions had no significantly influence the oxidation process, indicating the true application process. Finally, organic compounds as intermediates of the degradation process were identified by LC/MS.

Rapid decoloration of Reactive Black 5 by an advanced Fenton process in conjunction with ultrasound

The decoloration of reactive azo dye, Reactive Black 5 (RB5), by an advanced Fenton process in conjunction with ultrasound (Fenton/US) was investigated. The Fenton/US process using zero-valent iron (ZVI) aggregates as catalyst could achieve synergistic degradation of RB5, as compared to Fe(0)/US and Fenton systems. A synergy factor of 22.9 based on the first-order rate constant (k) was found. The decoloration efficiency was strongly influenced by initial pH, ZVI dose, H2O2 dose, ultrasonic input power, and the presence of salts in reaction solution. Experimental results showed that the optimum conditions for the decoloration of RB5 were ZVI 1g/L, initial pH 3.0, and H2O2 1.03×10−2mol/L with acoustic power of 120W/L at 60kHz. These conditions yielded 99% decoloration of 5.0×10−4M RB5 (ADMI 5605) solution within 10min treatment and the operation cost was only 2.25USD/m3. The dye solutions containing inorganic anions could retard the decoloration. The inhibitory effect of various inorganic anions on decoloration of RB5 followed the sequence of H2PO4-≫Cl->ClO4-≈NO3-≈SO42-. High acoustic power accelerated the reaction rate and increased decoloration efficiency. ZVI aggregates were reusable and the decoloration efficiency did not decrease substantially with repeated use of ZVI. Findings showed that the Fenton/US process could effectively decolor the reactive azo dye RB5 in wastewater.

Enhanced transformation and dechlorination of p-chloronitrobenzene in the combined ZVI–anaerobic sludge system

The combination of zero-valent iron (ZVI) with anaerobic sludge for enhancing reductive transformation and dechlorination of p-chloronitrobenzene (p-ClNB) was investigated in this study. p-ClNB was quickly reduced into p-chloroaniline (p-ClAn) and subsequently dechlorinated into aniline in the complex system, and the strengthening factor for pseudo-first-order transformation rate constant of p-ClNB (Q, k ZVI + sludge/(k sludge + k ZVI)) was above 3. The Q values for the different ZVI types with anaerobic sludge were as following: Reduced ZVI (RZVI) > Industrial ZVI > Nanoscale ZVI (NZVI). Thereinto, the aggregation of NZVI occurred, and its reaction activity declined. Furthermore, the increase of ZVI dosage promoted the p-ClNB transformation, but the p-ClAn dechlorination rate and Q value were not improved. With the anaerobic biomass increasing, the dechlorination rate of p-ClAn was significantly enhanced, and the Q value had positive relation with the mass ratio of anaerobic sludge to RZVI.

Coagulation enhancement of nonylphenol ethoxylate by partial oxidation using zero-valent iron/hydrogen peroxide

Coagulation enhancement of nonionic surfactant nonylphenol polyethoxylate with 9 mol of ethoxylate (NP9EO), was conducted by partial oxidation using zero-valent iron (ZVI)/hydrogen peroxide (H2O2) since coagulation is a typical process in many small-scale wastewater treatment plants but it is difficult to remove NP9EO due to micelle formation, and partial oxidation as pretreatment using the proposed process might be adequate and economically feasible. In this study, effects of pH, ZVI dosage, and H2O2 concentration were all investigated. The results show, highest NP9EO removal was observed at pH 2 instead of pH 1.5, since the presence of extra ferrous ion in the lower pH consumed the hydroxyl radicals, resulting in low removal efficiency. In addition, ferrous ion was converted to ferric ion for pH higher than 2 which reduced the efficiency of Fenton reaction. NP9EO removal efficiency by coagulation with ZVI/H2O2 pretreatment was as high as 99%, which is 40% higher than that without ZVI/H2O2 pre-treatment. The optimum dosages for ZVI/H2O2 oxidation were about 125 mg/L of H2O2 and 3 g/L of ZVI with NP9EO removal higher than 85%. But considering the following coagulation, the optimum dosages were about 125 mg/L of H2O2 and 2.5 g/L of ZVI with NP9EO removal efficiency of 95%. Besides, the dissolution of ferric ion from ZVI/H2O2 was able to reduce/replace the requirement of the traditional ferric chloride.

Zero Valent Iron Particles for the Degradation of Polycyclic Aromatic Hydrocarbons in Contaminated Soil

The removal of polycyclic aromatic hydrocarbons (PAHs) from contaminated soil through oxidative degradation by zero valent iron (ZVI) has been investigated in this study. The results showed a fast decrease of PAHs within the first 30 minutes of treatment followed by a slow degradation. The degradation rates coefficient (k) of PAHs analysed using pseudo first-order rate model showed the rate of reaction increased with the increase of ZVI concentrations from 0.003 min-1 at 1% ZVI concentration to 0.011 min-1 at 3% ZVI. However, the normalized surface area constant (kSA) decreased when the ZVI dosage above 3% was applied.

Degradation of p-chloroaniline by persulfate activated with zero-valent iron

The degradation of p-chloroaniline (PCA) by persulfate (S2O82-) activated with zero-valent iron (ZVI) was investigated through batch experiments. Effects of pH, temperature, and dosages of ZVI on PCA degradation were also examined. The degradation of PCA increased with higher dosage of ZVI due to increased activation of persulfate by zero-valent iron which generates strong oxidizing species (sulfate radicals) in aqueous solution. The PCA degradation was higher under acidic conditions (pH 2.0 and 4.0) when compared to alkaline conditions. Complete degradation of PCA was obtained by ZVI-activated persulfate at pH 4.0 at 12min. An increase in reaction temperature from 15 to 50°C significantly enhanced the PCA degradation. The aniline, N-(4-chlorophenyl)-p-phenylene di-imine, 1-(4-Chlorophenyl)-3-phenylurea and 5-chloro-2-(4-chlorophenyl diazenyl) phenol were identified as the major intermediates of PCA oxidation by persulfate.

Effective degradation of para-chloronitrobenzene through a sequential treatment using zero-valent iron reduction and Fenton oxidation

In this study, zero-valent iron (ZVI) was used to pretreat para-chloronitrobenzene (p-CNB), and the major product was para-chloroaniline (p-CAN). By adding H(2)O(2) directly, further p-CAN degradation can be attributed to Fenton oxidation because ferrous ions (Fe(2+)) released during the ZVI corrosion could be used as an activator for H(2)O(2) decomposition. In the reduction process, the reduction efficiency of p-CNB as well as Fe(2+) concentration increased with increasing iron dosage and decreasing solution pH. Under the optimal conditions, 25 mg L(-1) of p-CNB could be transformed in 3 h when initial solution pH was 3.0 and ZVI dosage was 2.0 g L(-1). A sufficient amount of Fe(2+) (50.4 mg L(-1)) was obtained after the above reaction to activate H(2)O(2). In the Fenton process, the oxidization of p-CAN was also more effective in acidic conditions and it increased with increasing H(2)O(2) concentration. The control experiments showed that the sequential treatment was more effective than Fenton oxidation alone in treating p-CNB wastewater since the removal rate of total organic carbon (TOC) was improved by about 34%. It suggested that the amino function group is more susceptible to oxidative radical attack than the nitro function group. Therefore, sequential treatment using zero-valent iron reduction followed by Fenton oxidation is a promising method for p-CNB degradation.

The comparative study on the rapid decolorization of azo, anthraquinone and triphenylmethane dyes by zero-valent iron

The comparative study was carried out for the decolorization of three kinds of dyes: azo dye, Reactive Brilliant Red K-2G (RBR); anthraquinone dye, Reactive Brilliant Blue KN-R (RBB); and triphenylmethane dye, Malachite Green (MG) from aqueous solution by zero-valent iron (ZVI) as an effective reductant. ZVI was synthesized with a modified method of reduction in liquid phase, in which the macromolecule stabilizer polyvinylpyrrolidone was added. The effects of solution pH, ZVI dosage and initial dye concentration on the decolorization were investigated. The results showed that pH value had little effect on dye decolorization. With increasing dosage of ZVI, decolorization efficiency increased, but reduction capacity and reaction time showed descending trends. High decolorization efficiency (95.74–99.22%) was achieved within 2 min for 698.24 mg/L for RBR, 10 min for 691.69 mg/L for RBB and 30 min for 686.10 mg/L for MG at optimal pH. The first-order kinetic model was found to fit the experimental data well. The UV–vis spectra and FTIR spectra analysis indicated that chromophores of dyes were destroyed and some functional groups such as amino and aromatic ring were transformed in the decolorization process. ZVI was proved to be a universal and efficient reductant for rapid decolorization of the three dyes.

Degradation of azo dye direct sky blue 5B by sonication combined with zero-valent iron

The degradation of azo dye direct sky blue 5B by sonication combined with zero-valent iron (US-Fe 0)was investigated and an evident synergistic effect was observed. The synergetic effect is mainly due to the increase of OH radical concentration from Fenton’s reaction. The OH radical concentrations in sole sonication and US-Fe 0 process were detected by using terephthalic acid as a fluorescent probe and found that OH radicals were generated continuously during sonication and the production of OH radicals in US-Fe 0 process was much higher than that in sole sonication. The degradation of direct sky blue 5B followed a pseudo-first-order kinetics and the degradation rate constants were found to be 0.0206 and 0.169 min −1 with sole sonication and US-Fe 0 process respectively. It was also found that the degradation ratio of direct sky blue 5B increased with the increase of zero-valent iron dosage and decrease of pH value of the dye aqueous solution. The degradation mechanism of direct sky blue 5B with US-Fe 0 process was discussed by the changes of UV–Vis spectrogram of the dye during degradation. The dramatic changes of UV spectra showed a disappearance of both azo and aromatic groups during the degradation.

Treatment of Distillery Wastewater by the Nano‐Scale Zero‐Valent Iron and the Supported Nano‐Scale Zero‐Valent Iron

The treatment of wastewater from the distillery industry was carried out by using nano-scale- and supported nano-scale zero-valent iron at a laboratory scale and ambient temperature. Effects of dilution, pH, mixing rate, zero-valent iron dosage, and amount of support for the zero-valent iron were investigated. All parameters had a significant effect on the removal efficiency of all investigated pollutants. Increasing the number of dilutions and the nano-scale zero-valent iron dosage led to the increase of removal efficiency of pollutants. Higher removal efficiency was achieved in an acidic initial pH of wastewater. The reduction of all pollutants was limited by the kinetics of the pollutant destruction/reduction by nano-scale zero-valent iron particles at a mixing rate greater than 170 rpm. At optimum condition, greater than 95, 94, and 64% of color, chemical oxygen demand, and biochemical oxygen demand were removed, respectively, within 6 hours. Additionally, the presence of a support had a significant effect on pollutant removal.

Effective degradation of C.I. Acid Red 73 by advanced Fenton process

The degradation of C.I. Acid Red 73 (AR 73) was investigated by advanced Fenton process based on zero-valent iron and hydrogen peroxide. The effect of zero-valent iron dosage, hydrogen peroxide concentration, initial pH, initial dye concentration, mixing rate and temperature on the degradation of AR 73 was studied. The results showed that AR 73 removal efficiency increased with the increase of zero-valent iron addition, hydrogen peroxide concentration, mixing rate and temperature, but decreased with the increase of initial pH value. The residual concentration of AR 73 was only 6.4 mg/L after 30 min treatment at optimum conditions for 200.0 mg/L AR 73 initial concentration. And advanced Fenton process can partly remove COD values of AR 73. The activation energy of the degradation reaction is 31.98 kJ/mol.

Dechlorination of γ-hexachlorocyclohexane by zero-valent metallic iron

This study investigated the rates and pathways of gamma-hexachlorocyclohexane (gamma-HCH) dechlorination by granular zero-valent iron under different pH, iron dosage and temperature conditions. It was found that gamma-HCH was rapidly reduced to benzene and chlorobenzene (CB) with benzene as the major product and that the dechlorination likely follows three steps of dichloroelimination to benzene, or two steps of dichloroeliminations and one step of dehydrohalogenation to CB. The calculated pseudo-first-order rate of gamma-HCH degradation was 0.0125 min(-1) at pH 6.73, 25 degrees C and 10 gL(-1) iron dosage, corresponding to 55.5 min of half-life. It was also found that the rate of gamma-HCH dechlorination increases as a function of reaction temperature and zero-valent iron dosage and decreases as a function of solution pH. The calculated activation energy is 33.5 kJ mol(-1) at pH 6.73, which is much lower than that of dehydrohalogenation facilitated by hydroxyl under basic conditions. The study suggested that zero-valent iron could be used to effectively and efficiently transform gamma-HCH.

Heavy metal removal from wastewater using zero-valent iron nanoparticles

Because of having a high reduction potential, the zero-valent iron (ZVI) is often applied for the remediation of wastewater or groundwater with heavy metals. The purpose of this study was aimed to investigate the reaction behavior of heavy metals with ZVI nanoparticles in the wastewater. The affecting factors, such as initial pH, dosage of nanoscale ZVI and initial concentration of heavy metal, on the removal efficiency of heavy metals by ZVI in the wastewater were examined by the batch experiments in this study. It was found that the removal of heavy metals was affected by initial pH. The rate and efficiency of metal removal increased with decreasing initial pH. Greater than 90% of the heavy metals were removed when the initial pH was controlled at 2. In addition, the rate and efficiency of metal removal increased as the dosage of nanoscale ZVI increased. The removal efficiency of heavy metal was higher than 80% when 2.0 g/L of ZVI was added in the wastewater. On the other hand, the slow rate and low efficiency of metal removal from the wastewater treated by nanoscale ZVI was found in the wastewater with high concentration of heavy metal.

Removal of EDTA from low pH printed-circuit board wastewater in a fluidized zero valent iron reactor

Fluidized zero valent iron (ZVI) process was adopted to reduce ethylenediaminetetraacetic acid (EDTA) from low pH printed-circuit board (PCB) wastewater for two reasons: (1) low pH of the wastewater favoring the ZVI reaction; (2) higher ZVI utilization for fluidized process due to abrasive motion of the ZVI. The results showed that the degradation of EDTA was greatly enhanced under acidic pH, longer hydraulic detention time (HRT) and presence of dissolved oxygen (DO). Without addition of oxygen, 65% of EDTA was removed with capacity of 7.33 mg EDTA/g ZVI at pH 2, ZVI dosage of 424 g/L and HRT 10 min. With 6.8 mg/L of DO, 83% of EDTA was reduced with capacity of 19.01 mg EDTA/g ZVI for the same experimental condition. The presence of oxygen/ZVI initiated a Fenton type reaction to reduce EDTA. The end product after EDTA degradation was analyzed by high performance liquid chromoagraphy (HPLC), where propionic acid (C(2)H(5)COOH) was observed, indicating EDTA (oxidation number for carbon is 2) was oxidized to propionic acid (oxidation number for carbon is 3). Nitrogen species was also measured and the nitrogen in EDTA was converted to ammonium instead of nitrate and nitrite.