Valent Iron Research Articles

Persulfate activation with biochar supported nanoscale zero- valent iron: Engineering application for effective degradation of NCB in soil

Nitrochlorobenzene (NCB) is very common in pesticide and chemical industries, which has become a major problem in soil environment. However, the remediation of NCB contaminated soil is received finite concern. Using biochar as a substrate for nanoscale-zero valent iron (nZVI/p-BC) to activate peroxodisulfate (PDS), a novel heterogeneous oxidative system had been applied in the current study to remediate NCB contaminants in soil. The degradation efficiencies and kinetics of m-NCB, p-NCB, and o-NCB by various systems were contrasted in soil slurry. Key factors including the dosage of nZVI/p-BC, the molar ratio of nZVI/PDS, initial pH and temperature on degradation of NCB were further examined. The results confirmed that the nZVI/p-BC/PDS displayed the remarkable performance for removing NCB compared with other systems. Higher temperature with nZVI/PDS molar ratio of 2:1 under the acidic condition favored the reduction of NCB. The treatment for NCB with optimal conditions were evaluated for the engineering application. The mechanism of nZVI/p-BC/PDS indicated that electron transfer between p-BC and nZVI was responsible for activation of PDS, generating active species (SO4•−, •OH and 1O2) via both the free and non-free radical pathways. Experimental results revealed prominent availability of nZVI/p-BC/PDS system in remediation of actual contaminated field by NCB.

One-step strategy for efficient Cr(VI) removal via phytate modified zero-valent iron: Accelerated electron transfer and enhanced coordination effect

The toxic Cr(VI) from industrial wastewater pose serious threat to the human beings and eco-systems. To reduce the operation processes and enhance the removal efficiency of Cr(VI), targeted design of functionalized material is critical in practical applications. Herein, we developed a one-step strategy for simultaneous Cr(VI) reduction and total Cr capture by a novel phytate modified zero-valent iron (PA-ZVI). The reaction kinetics of Cr(VI) removal by PA-ZVI (0.2225 min−1) was 53 times higher compared to ZVI (0.0042 min−1). The Fe(0) content on the surface of PA-ZVI increased from 2.2% to 15.6% compared to ZVI. Meanwhile, Cr(VI) was liable to adsorb on the surface of PA-ZVI due to its lower adsorption energy compared with the original ZVI (−2.09 eV vs −0.85 eV). The incorporation of the phytate ligand promoted electron transfer from iron core to Cr(VI), leading to the rapid in-situ reduction of Cr(VI) adsorbed on the surface of PA-ZVI to Cr(III). PA-ZVI exhibited a satisfactory performance for Cr(VI) removal at a broad pH range (3−11) and in the presence of coexisting ions and humic acid. Moreover, the reactor with the addition of PA-ZVI achieved more than 90% Cr(VI) removal within 72 h in continuous flow experiments. The feasibility of PA-ZVI for the removal of Cr(VI) is also validated in authentic wastewater. This work provides novel ZVI materials that can effectively address decontamination challenges from Cr(VI) pollution.

The influence of biochar supported nano‐zero valent iron on the anaerobic digestion of sulfate wastewater

AbstractIn this study, the effect of biochar supported nano‐zero valent iron (nZVI/BC) on anaerobic digestion of sulfate wastewater including methane yield, total volatile fatty acids, COD balance, sulfur balance, variation of iron (Fe2+) and microbial community structure was investigated by a batch‐scale experiment. The results showed that nZVI/BC could effectively maintain the stability of anaerobic digestion even at a high sulfate concentration. At SO42−/COD = 0.1 with 2 g nZVI/BC, the maximum methane yield (Bmax) and maximum methane production rate (Rmax) were obtained with a value of 3940.6648 mL and 553.6266 mL/day, respectively. When the SO42−/COD ratio was increased from 0.1 to 2, the ratio of COD converting to CH4 was decreased from 80.85% to 20.16%, while the ratio of COD used for SO42− reduction was increased from 8.79% to 77.96%. Meanwhile, nZVI/BC could enrich the hydrogentrophic Methanobacterium especially Methanobacterium with an average relative abundance of 75.86%.

Removal Efficiency and Performance Optimization of Organic Pollutants in Wastewater Using New Biochar Composites

The purpose is to optimize the catalytic performance of biochar (BC), improve the removal effect of BC composites on organic pollutants in wastewater, and promote the recycling and sustainable utilization of water resources. Firstly, the various characteristics and preparation principles of new BC are discussed. Secondly, the types of organic pollutants in wastewater and their removal principles are discussed. Finally, based on the principle of removing organic pollutants, BC/zero valent iron (BC/ZVI) composite is designed, among which BC is mainly used for catalysis. The effect of BC/ZVI in removing tetracycline (TC) is comprehensively evaluated. The research results reveal that the TC removal effect of pure BC is not ideal, and that of ZVI is general. The BC/ZVI composite prepared by combining the two has a better removal effect on TC, with a removal amount of about 275 mg/g. Different TC concentrations, ethylene diamine tetraacetic acid (EDTA), pH environment, tert-butanol, and calcium ions will affect the TC removal effect of BC composites. The overall effect is the improvement of the TC removal amount of BC composites. It reveals that BC has a very suitable catalytic effect on ZVI, and the performance of BC composite material integrating BC catalyst and ZVI has been effectively improved, which can play a very suitable role in wastewater treatment. This exploration provides a technical reference for the effective removal of organic pollutants in wastewater and contributes to the development of water resource recycling.

Efficient removal of Sb(Ⅴ) from water using sulphidated ferrihydrite via tripuhyite (FeSbO4) precipitation and complexation

Elevated concentrations of antimony (Sb) in the ecological environment have received considerable attention due to the harmful consequence involved. This study synthesized sulphidated ferrihydrite with different S:Fe molar ratios to efficiently remove Sb(V) from water. As the S:Fe molar ratio ranged from 0.00 to 1.48, the removal efficiency of Sb(V) by sulphidated ferrihydrite first decreased before increasing considerably. Sulphidated ferrihydrite with an S:Fe molar ratio of 0.74 exhibited a strong affinity towards Sb(V) with an optimal removal capacity of 963.74 mg Sb/g, which was 3.2−fold higher than that of ferrihydrite. In the kinetic experiments, the removal behavior of Sb(V) was well described by the pseudo−second−order model, suggesting that the removal process was controlled via chemisorption. Moreover, Sb(V) was efficiently removed over a wide pH range of 3.00–11.00, and coexisting anions (NO3−, Cl−, SO42−, SiO32−, CO32− and PO43−) exhibited marginal impact on the Sb(V) removal by sulphidated ferrihydrite (S:Fe ≥ 0.44). The characterization results of XRD, SEM, TEM mapping and etched XPS revealed goethite to be the dominant phase of sulphidated ferrihydrite with an S:Fe molar ratio of 0.15, while a mixed constitution of mixed−valent iron (hydro)oxides and iron sulphide was formed when the S:Fe molar ratio exceeded 0.44. Moreover, sulphidated ferrihydrite acted as a donor for Fe and S for the effective retention of Sb(V) by two main pathways: precipitation (tripuhyite, FeSbO4) and complexation (≡S–H and ≡Fe–OH). Therefore, sulphidated ferrihydrite is a promising material for eliminating Sb(V) contamination from water.

Comparison of different valent iron on anaerobic sludge digestion: Focusing on oxidation reduction potential, dissolved organic nitrogen and microbial community

Comparison of different valent iron on anaerobic sludge digestion: Focusing on oxidation reduction potential, dissolved organic nitrogen and microbial community

Preparation and Application of Sewage Sludge Bio-char/Zero Valent Iron (SSBC/ZVI) Composite for Improving the Biodegradability of a Real Chemical Synthesis-Based Pharmaceutical Wastewater

A new kind of micro-electrolysis filler sewage sludge biochar/zero valent iron (SSBC/ZVI) composite was prepared for a real chemical synthesis based pharmaceutical wastewater pretreatment for improving the biodegradation index (BI). The optimal operation condition of micro-electrolysis system was obtained at HRT of 2 h, the initial pH of 3.0 and filler dosage of 100 g/L, with COD removal rate of 30.5%. Characterization analysis of raw/used SSBC/ZVI filler and GC–MS analysis of raw/treated pharmaceutical wastewater were conducted to reveal the pollutant removal mechanisms by micro-electrolysis, and the results suggested that the pollutants removal was mainly attributed to the combination of reduction and oxidation, absorption of SSBC and flocculation of iron sludge. SSBC/ZVI exhibited relative high stability and excellent reusability for COD removal and BI improvement of real pharmaceutical wastewater after 4 runs. Moreover, the leaching tests of heavy metals (HMs) were conducted to investigate their release of the constituents in SS, and the results indicated that HMs leaching into the liquid from the filler was at a relative low level. This study provided new ideas of sewage sludge utilization for real wastewater pretreatment.

Application of nanoscale zero-valent iron in hexavalent chromium-contaminated soil: A review

Abstract Chromium (Cr) is a common toxic heavy metal that is widely used in all kinds of industries, causing a series of environmental problems. Nanoscale zero- valent iron (nZVI) is considered to be an ideal remediation material for contaminated soil, especially for heavy metal pollutants. As a material of low toxicity and good activity, nZVI has been widely applied in the in situ remediation of soil hexavalent chromium (Cr(vi)) with mobility and toxicity in recent years. In this paper, some current technologies for the preparation of nZVI are summarized and the remediation mechanism of Cr(vi)-contaminated soil is proposed. Five classified modified nZVI materials are introduced and their remediation processes in Cr(vi)-contaminated soil are summarized. Key factors affecting the remediation of Cr(vi)-contaminated soil by nZVI are studied. Interaction mechanisms between nZVI-based materials and Cr(vi) are explored. This study provides a comprehensive review of the nZVI materials for the remediation of Cr(vi)-contaminated soil, which is conducive to reducing soil pollution.

Persulfate activation by sulfide-modified nanoscale iron supported by biochar (S-nZVI/BC) for degradation of ciprofloxacin

Antibiotics ciprofloxacin pollution has become a major problem in the aqueous environment. Advanced oxidation processes (AOP) have been recognized as promising technology to treat wastewater contaminated by antibiotics. In this study, biochar-supported sulfided nanoscale zero- valent iron (S-nZVI/BC) was employed as a catalyst to activate persulfate (PS) to remove the ciprofloxacin (CIP). The effects of S/Fe molar ratio, PS dosage, initial pH value and CIP concentration, and coexisting anion were investigated. Results showed that S-nZVI/BC exhibited excellent performance in removing CIP when combined with PS. S-ZVI/BC with an S/Fe mole ratio of 0.25 exhibited the highest CIP removal efficiency. CIP could be efficiently removed when the initial solution pH ranged from 2.5 to 8.5, and chloride was found to have a negative effect on degradation. The batch experimental data agreed well with the pseudo-second-order model. Radical scavenger studies revealed that SO4− and HO were the crucial reactive species, which contributed to the high CIP degradation performance. A possible degradation pathway was proposed with the elimination of the piperazine ring based on the LC-MS analysis. Moreover, the catalytic ability of S-nZVI/BC could be maintained at 87% after five turnovers. In all, this study indicates that S-nZVI/BC is an ideal catalyst for PS activation for antibiotics treatment.

Degradation of organic pollutants by photoelectro-peroxone/ZVI process: Synergistic, kinetic and feasibility studies

In this study a novel hybrid process was employed for the degradation of Metanil Yellow (MY). The operational parameters of photoelectro-peroxone/zero valent iron (PEP/ZVI) process were studied and the complete decoloration was found at pH = 3.0, 100 mg/L ZVI, 33.2 mg/L ozone, 300 mA applied current and 25 min reaction time. The combination of UV, ozone, electrogenerated H2O2 and ZVI showed high synergistic effect for MY degradation. ZVI showed high reusability in PEP/ZVI process. Among anions, nitrite ion demonstrated high inhibitory effect while chloride ions had no significant effect on MY degradation. Scavenging tests depicted that hydroxyl radical and singlet oxygen were the main agents of MY degradation. PEP/ZVI process was tested for several emerging pollutants (benzotriazole, 4-chlorophenol, carmoisine and tetracycline); the results presented the effectiveness of the process for the degradation of pollutants in a way that complete degradation occurred at only 30 min. Moreover, the performance of PEP/ZVI was examined for the treatment of two actual wastewaters. PEP/ZVI demonstrated an excellent function in terms of the removal of organic compounds to achieve discharging standards.

Fine structural features of nanoscale zero-valent iron characterized by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM).

An angstrom-resolution physical model of nanoscale zero-valent iron (nZVI) is generated with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) on the Fe L-edge. Bright-field (BF), high-angle annular dark-field (HAADF) and secondary electron (SE) imaging of nZVI acquired by a Hitachi HD-2700 STEM show near atomic resolution images and detailed morphological and structural information of nZVI. The STEM-EDS technique confirms that the fresh nZVI comprises of a metallic iron core encapsulated with a thin layer of iron oxides or oxyhydroxides. SAED patterns of the Fe core suggest the polycrystalline structure in the metallic core and amorphous nature of the oxide layer. Furthermore, Fe L-edge of EELS shows varied structural features from the innermost Fe core to the outer oxide shell. A qualitative analysis of the Fe L(2,3) edge fine structures reveals that the shell of nZVI consists of a mixed Fe(II)/Fe(III) phase close to the Fe (0) interface and a predominantly Fe(III) at the outer surface of nZVI.

Qualitative Analysis of the Effect of Polymer Solution and Suspension Properties on the Electrospinning of Nanocomposite Fibers

Nanocomposite fibers produced via electrospinning have very large surface area by virtue of their nanometer diameter sizes thereby making them very attractive for various applications such as for adsorption of contaminants from wastewater. In this study, a highly adsorbing nanoparticle, iron-modified montmorillonite was used as filler in the nanocomposite. The effects of polymer solution and suspension properties such as polymer concentration, clay loading, and filler type on the electrospinning of the nanocomposite were investigated using a 2k factorial design of experiment. The types of montmorillonite used were zero valent iron-MMT (ZVIMMT) and iron (III)-MMT (FeMMT). It was found from the SEM images that finer fibers were generated from suspensions with lower polymer concentration in the solution specifically at 5 wt% and from suspensions with ZVIMMT particles as filler. However, a common defect in nanofibers called beads was also observed in the fibers produced from 5 wt% polymer concentration. TEM micrographs confirmed that the ZVIMMT fibers have smaller diameter than the FeMMT fibers. In addition, it was recognized that the layered structure of the clay is still intact after the electrospinning process. The XRD pattern of the fibers revealed that the clay particles were intercalated with the polymer molecules based on the calculated d-spacing. Furthermore, elemental analysis on the bead and string regions of the electrospun fibers confirmed the presence of polymer and montmorillonite particles in both regions.

Evaluation of Granular Surfactant-Modified/Zeolite Zero Valent Iron Pellets As a Reactive Material for Perchloroethylene Reduction

The use of permeable reactive barriers (PRBs) for groundwater remediation is based on two distinct mechanisms: sorption and transformation. With sorption as the main mechanism, contaminants sorb on the PRB materials and are retarded. With transformation as the main mechanism, the contaminants react with the PRB materials and then converted to less toxic or innocuous substances. In this study, we tested surfactant-modified zeolite/zero valent iron (SMZ/ZVI) pellets as a PRB material to retard and degrade perchloroethylene (PCE), utilizing both sorption and transformation processes. Batch PCE kinetic studies showed instantaneous PCE removal from the aqueous phase due to sorption and subsequent removal with time due to reduction. The separation of sorption from reduction can be used to obtain both the PCE distribution coefficient ( Kd ) and the pseudofirst-order reduction rate constant ( μobs ) from a single batch experiment. The calculated Kd and μobs values are 3.0 and 0.5 L∕kg and 0.14 and 0.05 h−1 for SM...

Zero-Valent Iron for Water Treatment

The use of zero-valent iron in the treatment of hazardous water contaminants is reviewed. The review concentrates on experimental procedures employed in the investigation of a range of applications for zero -valent iron and the efficacy of the processes. Investigations reviewed include those performed with halogenated aliphatic compounds, halogenated aromatic compounds, nitro-aromatic organic compounds, and high-valency toxic metals. Experiments employing bimetallic and cementation reductants as well as zero-valent iron alone are covered. The need for zero-valent iron technology is discussed, as is the need for more rigorous investigation of operational parameters. Despite a paucity of information from the literature it has been shown that efficacy is greatest for well-mixed batch or continuous column systems employing neutral to acidic pH and a high specific surface area of iron. The literature also reveals a need to focus future work on enhancing the chemical reaction taking place on the iron surface in order to enhance the rate of reductive remediation.