Agglomeration Of nZVI Research Articles

Removal of Cr(VI) in groundwater by controlled release materials based on nano zero-valent iron and activated carbon

ABSTRACT The use of nano zero-valent iron (nZVI) materials for groundwater Cr(VI) removal encountered challenges of agglomeration and low removal efficiency. Controlled release materials (CRMs) gradually release reactive substances or reducing agents, prolonging the release time. Here, we report the development of novel CRMs containing nZVI and activated carbon (AC). During the removal of Cr(VI) in groundwater, the prepared AC/nZVI/CRMs slowly released nZVI, greatly reducing the agglomeration of nZVI. The adsorption capacity of AC-containing CRMs prolonged the residence time of Cr(VI) in water, improving the removal efficiency of the AC/nZVI/CRMs. We found that lower pH enhanced the removal of Cr(VI) by the AC/nZVI/CRMs from simulated groundwater. The removal efficiency of the AC/nZVI/CRMs was also affected by the simulated groundwater environment and decreased with the increasing flow rate of the groundwater. Our results suggested that these novel nZVI-containing CRMs minimized agglomeration during the removal of Cr(VI) by nZVI, exhibited enhanced efficiency under acidic conditions, and facilitated Cr(VI) removal from similar groundwater environments.

Biological self-protection inspired engineering of nanomaterials to construct a robust bio-nano system for environmental applications.

Nanomaterials can empower microbial-based chemical production or pollutant removal, e.g., nano zero-valent iron (nZVI) as an electron source to enhance microbial reducing pollutants. Constructing bio-nano interfaces is critical for bio-nano system operation, but low interfacial compatibility due to nanotoxicity challenges the system performance. Inspired by microorganisms' resistance to nanotoxicity by secreting extracellular polymeric substances (EPS), which can act as electron shuttling media, we design a highly compatible bio-nano interface by modifying nZVI with EPS, markedly improving the performance of a bio-nano system consisting of nZVI and bacteria. EPS modification reduced membrane damage and oxidative stress induced by nZVI. Moreover, EPS alleviated nZVI agglomeration and probably reduced bacterial rejection of nZVI by wrapping camouflage, contributing to the bio-nano interface formation, thereby facilitating nZVI to provide electrons for bacterial reducing pollutant via membrane-anchoring cytochrome c. This work provides a strategy for designing a highly biocompatible interface to construct robust and efficient bio-nano systems for environmental implication.

Zr4+-modified chitosan coated nZVI enhance the removal of Cr(VI) by adsorption-reduction interaction

In order to solve the problems of poor mechanical properties and stability of chitosan and easy agglomeration and oxidation of nano zero-valent iron, Zr4+ crosslinked chitosan-coated nano zero-valent iron composites (CS-Zr@nZVI) were prepared for Cr(VI) removal from wastewater. The Zr-O, Zr-N and chitosan characteristic peaks in FTIR spectrum and the nZVI characteristic peaks in XRD pattern confirmed its successful synthesis. SEM and TEM showed that nZVI was dispersed on the surface of CS-Zr@nZVI, which solved the problem of easy agglomeration of nZVI. CS-Zr@nZVI has a wide operating pH range (pH= 2.0–10.0), high pHpzc, good stability and regeneration ability. The removal of Cr(VI) by CS-Zr@nZVI accords with pseudo-second-order kinetic model and Langmuir isotherm model, and it is a spontaneous, disordered and endothermic process. The maximum adsorption capacity was 344.82 mg g−1 at 318 K and pH = 2.0. At the dosage of 1.0 g L−1, CS-Zr@nZVI can treat 134.56 mg L−1 chromium-containing wastewater (pH = 3.5) to meet the discharge standard, which proves that CS-Zr@nZVI has the application prospect of removing Cr(VI). The main mechanisms of Cr(VI) removal by CS-Zr@nZVI are electrostatic interaction, ion exchange, reduction, complexation and co-precipitation. XPS analysis showed that 84.87 % of Cr(VI) was reduced to Cr(III). The above results provide a reference for the design of efficient Cr(VI) removal materials.

Characteristic study of biological CaCO3-supported nanoscale zero-valent iron: stability and migration performance

ABSTRACT nZVI has attracted much attention in the remediation of contaminated soil and groundwater, but the application is limited due to its aggregation, poor stability, and weak migration performance. The biological CaCO3 was used as the carrier material to support nZVI and solved the nZVI agglomeration, which had the advantages of biological carbon fixation and green environmental protection. Meanwhile, the distribution of nZVI was characterised by SEM-EDS and TEM carefully. Subsequently, the dispersion stability of bare nZVI and CaCO3@nZVI composite was studied by the settlement experiment and Zeta potential. Sand column and elution experiments were conducted to study the migration performance of different materials in porous media, and the adhesion coefficient and maximum migration distances of different materials in sand columns were explored. SEM-EDS and TEM results showed that nZVI could be uniformly distributed on the surface of biological CaCO3. Compared with bare nZVI, CaCO3@nZVI composite suspension had better stability and higher absolute value of Zeta potential. The migration performance of nZVI was poor, while CaCO3@nZVI composite could penetrate the sand column and have good migration performance. What’s more, the elution rates of bare nZVI and CaCO3@nZVI composite in quartz sand columns were 5.8% and 51.6%, and the maximum migration distances were 0.193 and 0.885 m, respectively. In summary, this paper studies the stability and migration performance of bare nZVI and CaCO3@nZVI composite, providing the experimental and theoretical support for the application of CaCO3@nZVI composite, which is conducive to promoting the development of green remediation functional materials.

Research Progress on the Degradation of Organic Pollutants in Water by Activated Persulfate Using Biochar-Loaded Nano Zero-Valent Iron.

Biochar (BC) is a new type of carbon material with a high specific surface area, porous structure, and good adsorption capacity, which can effectively adsorb and enrich organic pollutants. Meanwhile, nano zero-valent iron (nZVI) has excellent catalytic activity and can rapidly degrade organic pollutants through reduction and oxidation reactions. The combined utilization of BC and nZVI can not only give full play to their advantages in the adsorption and catalytic degradation of organic pollutants, but also help to reduce the agglomeration of nZVI, thus improving its efficiency in water treatment and providing strong technical support for water resources protection and environmental quality improvement. This article provides a detailed introduction to the preparation method and characterization technology, reaction mechanism, influencing factors, and specific applications of BC and nZVI, and elaborates on the research progress of BC-nZVI in activating persulfate (PS) to degrade organic pollutants in water. It has been proven experimentally that BC-nZVI can effectively remove phenols, dyes, pesticides, and other organic pollutants. Meanwhile, in response to the existing problems in current research, this article proposes future research directions and challenges, and summarizes the application prospects and development trends of BC-nZVI in water treatment. In summary, BC-nZVI-activated PS is an efficient technology for degrading organic pollutants in water, providing an effective solution for protecting water resources and improving environmental quality, and has significant application value.

Boron-doped biochar-nano loaded zero-valent iron to activate persulfate for the degradation of oxytetracycline

Oxytetracycline has posed a serious environmental nuisance, and seeking environmental decontamination materials is the priority task to deal with antibiotic water contamination. Herein, boron-doped biochar loaded nano zero-valent iron composites (nZVI/BBC) were fabricated as activators of PDS for oxidative degradation of oxytetracycline hydrochloride (OTC), and the main removal mechanism was explored in detail. The results showed that Boron-doped biochar with borate ester structure (BC2O) and degree of defects are the main active sites for improving PDS activation properties. BBC could effectively prevent nZVI agglomeration and reduce nZVI passivation. The effects of calcination temperature of BBC, loading ratio and dosage of nZVI/BBC, PDS concentration, initial solution pH, pollutant concentration, and interfering ions on OTC removal by nZVI/BBC were also systematically investigated, and the optimal reaction conditions were screened: 10 wt% loading of nZVI in the composite, 1 g/L dosage of nZVI/BBC, 1 mM dosage of PDS and solution pH= 5. The cycling test showed that the removal rate of OTC by nZVI/BBC decreased from 95.3% to 70.2% after five cycles, indicating that there is excellent stability of this material. Among them, the catalyst of 10%nZVI/BBC displayed the optimal PDS activation performance, owing to the synergistic adsorption-double oxidation system, BBC as well as nZVI. The free radical quenching experiment and free radical trapping experiment proved that the degradation of OTC mainly followed the free radical pathway and SO4•− and •OH were the primary active species in the catalytic system. This study provides a practical reference for the treatment of actual antibiotic wastewater.

In situ prepared Chlorella vulgaris-supported nanoscale zero-valent iron to remove arsenic (III).

Nanoscale zero-valent iron (nZVI) has a high removal affinity toward arsenic (As). However, the agglomeration of nZVI reduces the removal efficiency of As and, thus, limit its application. In this study, we report an environmentally friendly novel composite of Chlorella vulgaris-supported nanoscale zero-valent iron (abbreviated as CV-nZVI) that exhibits a fast and efficient removal of As(III) from As-contaminated water. Scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometry (XRD), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) were used to characterize and analyze the CV-nZVI. These results indicated that the stabilization effect of C. vulgaris reduced the nZVI agglomeration and enhanced the reactivity of nZVI. The experiments showed a removal efficiency of 99.11% for As(III) at an optimum pH of 7.0. The adsorption kinetics and isotherms followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm with the superior maximum adsorption capacities of 34.11mg/g for As(III). The FTIR showed that the As(III) was adsorbed on the CV-nZVI surface by complexation reaction, and XPS indicated that oxidation reaction was also involved. After five reuse cycles, the removal efficiency of As(III) by CV-nZVI was 32.93%, suggesting that the CV-nZVI had some reusability and regeneration. Overall, this work provides a practical and highly efficient approach for As remediation in As-contaminated water, and simultaneously resolves the agglomeration problems of nZVI nanoparticles.

Reduced graphene oxide supported Fe/Ni bimetallic nanoparticles for the rapid adsorption and dechlorination of 2,4-dichlorophenol

Agglomeration and passivation of nanoscale zerovalent iron (nZVI) can result in significant decrease of reactivity with contaminants. In this paper, reduced graphene oxide supported Fe/Ni bimetallic composites (Fe/Ni@rGO) were synthesized. Electron microscopy characterization showed that the spherical Fe/Ni bimetallic nanoparticles with the size of 70–150 nm were successfully loaded on the graphene sheets and mainly distributed at the edges and folds of the graphene sheets. The agglomeration of nZVI decreased significantly and more active sites were exposed. The removal efficiency of 2,4-dichlorophenol by nZVI, reduced graphene oxide supported nZVI (Fe@rGO) composites and Fe/Ni@rGO composites were 14.4%, 71.8% and 95.0% within 180 min, respectively. The results showed that when the pH was 5–7 and humic acid concentration was 60 mg/L, the removal efficiency of 2,4-dichlorophenol was higher. According to the correlation coefficient R2, the removal of 2,4-dichlorophenol by Fe/Ni@rGO followed the pseudo second order model instead of the pseudo first order model. The anti-oxidation and cycle test showed that Fe/Ni@rGO composites had high stability and recycling value. The removal mechanism of 2,4-dichlorophenol by Fe/Ni@rGO composites was the synergistic effect of adsorption by rGO and dechlorination by Fe/Ni.

Removal of p-nitrophenol by double-modified nanoscale zero-valent iron with biochar and sulfide: Key factors and mechanisms

In this study, the mechanisms and key factors of p-nitrophenol (PNP) removal by biochar (BC) and sulfide double-modified nanoscale zero-valent iron (nZVI) were systematically investigated. The results showed that the residence time of the hydrothermal carbonization of waste bamboo chopsticks was the key factor affecting the removal of PNP by nZVI/BC. The biochar derived from waste bamboo chopsticks prepared at a hydrothermal temperature of 240 °C for 1 h was the most suitable nZVI loading material. The hydrophobicity of the biochar had a greater impact on S-nZVI/BC. Biochar effectively alleviated the agglomeration of nZVI and formed a miniature galvanic cell with nZVI to promote its corrosion. The effective reducing agents in the S-nZVI/BC system were Fe0, Fe2+, S2−, and S22−, and the system had stronger reducibility then nZVI. The reaction rate of S-nZVI/BC for PNP removal was 2.6 times higher than that of nZVI. In addition, the double modification of nZNI reduced the energy barrier of the PNP removal reaction and alleviated the surface passivation of nZVI. The apparent activation energy of the reaction under anaerobic conditions after sulfidation treatment was reduced by 23.7 %, while the PNP removal efficiency increased by 8 % under aerobic conditions. Density Function Theory (DFT) calculations revealed that PNP was more easily adsorbed and participated in the reaction on the surface of the sulfide shell layer than oxidized shell layer. This work confirms that biochar loading and surface sulfidation can enhance the reactivity and stability of nZVI.

Ultrafast removal of Cr(VI) by chitosan coated biochar-supported nano zero-valent iron aerogel from aqueous solution: Application performance and reaction mechanism

Chitosan coated biochar-supported nano zero-valent iron aerogel (C-nZVI@BC) was successfully synthesized for the efficient removal of Cr(VI) from aqueous solution. Results showed that the C-nZVI@BC has a 2.1-fold higher adsorption capacity of Cr(VI) than the uncoated sample. Chitosan coating on nZVI@BC and BC support could prevent the oxidation and agglomeration of nZVI. Ultrafast adsorption of Cr(VI) with 61 %, 77 %, and 87 % of the maximum adsorption capacities were achieved within 1 min with the initial concentrations of Cr(VI) at 100 mg/L, 300 mg/L, and 600 mg/L, respectively. The C-nZVI@BC exhibited high adsorption performance under aerobic conditions, and showed high Cr(VI) removal rates (>83 %) in a wide pH range (2–8). Cr(VI) and Cr(III) could be simultaneously removed by C-nZVI@BC, and the key mechanisms were adsorption, reduction, and complexation. The acid and alkali resistance experiment of C-nZVI@BC showed that C-nZVI@BC still has better adsorption capacity of Cr(VI) (96.7 mg/g) in acid environment. The application of C-nZVI@BC in the simulated electroplating wastewater treatment indicated a high removal rate of Cr(VI). C-nZVI@BC could effectively reduce the low concentration of Cr(VI) below the standard of the World Health Organization. The syringe filtration and column adsorption experiments implied the potential of C-nZVI@BC for Cr(VI) removal in groundwater. In addition, C-nZVI@BC could be a direct reducing agent for Cr(VI) and an activator of persulfate (PS) for the degradation of antibiotics, and C-nZVI@BC + PS showed 77 % and 82 % removal of tetracycline and chlortetracycline within 5 min. Overall, C-nZVI@BC was a suitable adsorbent for pollutant removal.

Enhanced removal of Cd2+ by nano zero-valent iron modified attapulgite from aqueous solution: Optimal design，characterization and adsorption mechanism

Nano zero-valent iron (nZVI) modified attapulgite composite (nZVI@ATP) was prepared by liquid phase reduction method for Cd2+ removal from aqueous solution. A series of characterization methods confirmed that nZVI particles with a particle size of 50–100 nm were evenly distributes on the surface of attapulgite after pickling, which greatly overcomes the agglomeration of nZVI. Composite material had the optimum removal rate of Cd2+ when the ratio of iron to attapulgite was 1: 2. More than 98% of Cd2+ was removed from aqueous solution using nZVI@ATP at an initial condition of 100 mg/LCd2+ under the conditions of 1 g/L of nZVI@ATP, pH 5.0 and a temperature of 25 ℃, much higher than that of attapulgite. Kinetic studies revealed that Cd2+ adsorption process followed the pseudo-second-order model, and basically reached the adsorption equilibrium after 2 h, indicating that chemisorption was the dominant adsorption mechanism. Adsorption thermodynamics showed that the adsorption process was a spontaneous endothermic reaction, accompanied by the increase in entropy. The Freundlich adsorption isotherm model could well fit the adsorption process. The presence of Na+, Ca2+ and Mg2+ in the solution strongly inhibited the removal of Cd2+. The mechanism of Cd2+ removal by nZVI@ATP involved multiple processes, mainly including surface-complexation adsorption and precipitation/co-precipitation. The results exhibited that nZVI@ATP has excellent potential as an adsorbent for the removal of Cd2+ from the contaminated water.

Integrated green complexing agent and biochar modified nano zero-valent iron for hexavalent chromium removal: A characterisation and performance study

In this study, nano zero-valent iron (nZVI) was loaded on biochar (BC) prepared from recycled waste peanut shells. The loaded BC in the nZVI@BC composite was assumed to weaken the agglomeration of nZVI and the environmentally-friendly complexing agents sodium citrate (Cit) and sodium carboxymethyl cellulose (CMC) were used to establish Cit-nZVI@BC and CMC-nZVI@BC for the effective removal of Cr(VI) from aqueous environments. The characterisation results suggested that Cit and CMC not only inhibited the oxidation of nZVI, but also effectively improved its reactivity. The experimental results demonstrated that the Cr(VI) removal efficiency by nZVI was less than 20%, while CMC-nZVI@BC enhanced the Cr(VI) removal efficiency to 80.73%, because CMC was coated on the nZVI surface for anti-passivation and improved the surface activity of nanoparticles. In addition, the Cr(VI) removal efficiency reached almost 100% with Cit-nZVI@BC, and the citrate dissociated the passivation layer on the surface of the zero-valent iron particles to ensure the reactivity of the zero-valent iron. The reaction mechanism of Cit-nZVI@BC includes adsorption, reduction, and co-precipitation, whereas CMC-nZVI@BC also involves surface complexation reactions. The kinetic studies revealed that the removal of Cr(VI) by Cit-nZVI@BC and CMC-nZVI@BC followed the second-order reaction kinetic model, and the reaction rates of Cit-nZVI@BC and CMC-nZVI@BC were both higher than that of nZVI. The results indicate that the prepared systems are promising for Cr(VI) remediation in contaminated environments.

Biochar-loaded nZVI/Ni bimetallic particles for hexavalent chromium removal from aqueous solution

The biochar-loaded nZVI/Ni bimetallic nanoparticles (BC@nZVI/Ni) was synthesized by liquid phase co-reduction method and evaluated for its potential Cr(VI) removal capacity. BC@nZVI/Ni had a good removal effect in a wide pH range (2.1-9.2). The removal efficiency reached 100% for 20 mg L−1 Cr(VI) at pH ≤ 3.1. The maximum adsorption capacity of 55.52 mg g−1 was obtained at 298 K. Its excellent removal performance was mainly attributed to the abundant surface functional groups of BC and its prevention effect on nZVI agglomeration, and the reduction effect of Ni(0) on Fe(II). The main mechanism of BC@nZVI/Ni for Cr(VI) removal was electrostatic attraction, ligand exchange, surface complexation, reduction and co-precipitation. The adsorption process fitted well with Freundlich and pseudo-second-order models. It was a spontaneous and endothermic process.

Activation of persulfate by green nano-zero-valent iron-loaded biochar for the removal of p-nitrophenol: Performance, mechanism and variables effects

In this study, with the green tea extraction solution as a reducing agent and green tea residues as a raw material of biochar, green nano zero-valent iron biochar (G-nZVI-BC) was prepared with the green synthesis method and then combined with potassium persulfate to degrade p-nitrophenol in water. Compared with zero-valent iron-loaded biochar (C-nZVI-BC) prepared by the traditional chemical liquid phase synthesis method, G-nZVI-BC containing tea polyphenols further improved dispersibility of Fe0 on biochar, prevented nZVI agglomeration on BC, and promoted PNP degradation. The system constructed by G-nZVI-BC/PDS showed the high oxidation resistance than the C-nZVI-BC/PDS system, thus endowing the synthesis material with long-term reactivity. Both the radical pathway and non-radical pathways contributed to catalytic degradation and free radicals played a key role. The G-nZVI-BC/PDS system realized the good removal effect on PNP in the pH range of 3.06–9.23. The reusability of G-nZVI-BC and the PNP removal effect in water body conditions indicated that G-nZVI-BC had a good application prospect in the field of water treatment.

Unravelling the roles of Ginkgo biloba L. for modification of nanoscale zero valent iron in persulfate system to remove antibiotic resistance genes by the tool of metabonomic analysis

• Ginkgo biloba L. extract increased content of surface Fe 2+ of G-nZVI by 1.66 times. • Ginkgo biloba L. could increase active sites, but not prevent agglomeration of nZVI. • Ginkgo biloba L. produced synergistic effect with nZVI to activate persulfate. • Seven metabolites became the most important contributors to modify nZVI. • Electron transfer and redox reactions arose with lipids of Ginkgo biloba L. extract. Antibiotic resistance genes (ARGs) are often detected in secondary effluents of wastewater treatment plants. Nanoscale zero valent iron (nZVI) modified by Ginkgo biloba L. leaf extract (G-nZVI) as an effective catalyst exhibited excellent activation of sodium persulfate (PS), which could achieve higher removal efficiency of ARGs than PS + nZVI system. However, the roles and specific components of Ginkgo biloba L. leaf ( Ginkgo biloba L.) for nZVI modification are still not understood. X-ray diffraction and X-ray photoelectron spectroscopy of nZVI and G-nZVI indicated content of surface Fe 2+ of G-nZVI increased by 1.66 times. Under such circumstances, removal efficiencies of genes were further compared by two systems (G + nZVI + PS/G-nZVI + PS). However, the degradation efficiencies of sul 1, intI 1 and bacterial 16S rRNA gene did not significantly differ. Therefore, the role of Ginkgo biloba L. extract was probably to increase active sites of nZVI by electron transfer, but not to prevent agglomeration of nZVI. Additionally, the findings of electron spin resonance elucidated that PS could be activated by Ginkgo biloba L. extract to produce radicals. Notably, metabolic interactive pathways (iPath) showed that there were accumulated lipids in nZVI, which may arise electron transfer and redox reactions. Additionally, the seven significantly down regulation metabolites might reduce the Fe 3+ to Fe 2+ and became the most important contributors to modify nZVI.

Optimization of preparation of montmorillonite nanometer zero-valent iron and the degradation of amoxicillin by response surface methodology

Abstract Three-factor and three-level tests were carried out by Box–Behnken response surface methodology, with amoxicillin as the target pollutant, nanometer zero-valent iron (nZVI) materials loaded with montmorillonite prepared by liquid phase reduction method and the concentration of FeSO4 and NaBH4 and montmorillonite dosage as influencing factors. It revealed that the interaction between FeSO4 concentration and NaBH4 concentration had a significant effect on the preparation of montmorillonite-loaded nanometer zero-valent iron material, playing a key role in the removal of amoxicillin, and the effect of FeSO4 concentration was even more significant. In addition, the shape, structure and characteristic groups of the prepared materials were analyzed by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), etc. The nanometer zero-valent iron loaded with montmorillonite can effectively slow down the nZVI agglomeration effect and improve the effect of material degradation of pollutants. For the same concentration of amoxicillin wastewater, the removal rate of amoxicillin wastewater, after 1 h reaction, is as follows: Mont/nZVI > nZVI > Mont. The optimal conditions for the reaction are: pH is 3, the initial concentration is 60 mg/L, and the dosage is 2 g/L. The higher the temperature, the more amoxicillin is degraded by Mont/nZVI.

A novel stabilized carbon-coated nZVI as heterogeneous persulfate catalyst for enhanced degradation of 4-chlorophenol

Nano zero-valent iron (nZVI) and its composite materials have been extensively studied in the field of environmental remediation. However, the oxidation and agglomeration of nZVI limits the large-scale application of nZVI in environmental remediation. This study developed a two-step method to prepare stable carbon-coated nZVI (Fe0@C) which combined hydrothermal carbonization and carbothermal reduction methods and used glucose and iron oxide (Fe3O4) as precursors. When the carbothermal reduction temperature was 700 °C and the elemental molar ratio of carbon to iron was 22:1, stable Fe0@C can be generated. The nZVI particles are encapsulated by mesoporous carbon and embedded in the carbon spheres. The unique structure of carbon coating not only inhibits the agglomeration of nZVI, but also makes nZVI stable in air for more than 120 days. Not only that, the as-synthesized Fe0@C exhibited high catalytic activity toward the degradation of 4-chlorophenol (4-CP) by activating persulfate. Different from conventional nZVI catalysts in generation of sulfate radicals, Fe0@C selectively induced hydroxyl radicals for 4-CP degradation. Moreover, Fe0@C has been shown to efficiently degrade 4-CP by using the dissolved oxygen in water to form hydroxyl radicals. This study not only provides a simple, green method for the preparation of stabilized nZVI, but also provides the possibility of large-scale application of nZVI in the field of environmental remediation.

High-dispersion zero-valent iron particles stabilized by artificial humic acid for lead ion removal

Nano zero-valent iron (nZVI), as a high-efficiency adsorbent for heavy metals, often suffers being oxidized and assembling together due to small size and super reactivity, further decreasing its adsorption performance and limiting application ranges. Herein, we have designed a novel adsorbent with high-dispersion nZVI stabilized by as-prepared artificial humic acid (AHA-nZVI) derived from hydrothermal humification (HTH) technology. Introduction of artificial humic acid (A-HA) can effectively reduce the oxidation and agglomeration of nZVI, leading to superior kinetic removal efficiency of Pb2+ (> 99.2%) and huge Langmuir removal capacity of 649.0 mg/g. The combination of nZVI and A-HA (contained abundant functional groups, i.e. −OH and −COOH) via C–O-Fe bonding makes nZVI have good dispersion and oxidation resistance. Multiple interaction mechanisms including reduction reaction, complexation and co-precipitation between heavy metals and AHA-nZVI samples are realized. Overall, AHA-nZVI is a promising material for high-performance heavy metal contaminated water treatment.

Field demonstration of enhanced removal of chlorinated solvents in groundwater using biochar-supported nanoscale zero-valent iron

The application of biochar-supported nanoscale zero-valent iron (biochar-nZVI) was successfully implemented in a field demonstration for the first time. To overcome the significant shortcomings of nZVI agglomeration for in-situ groundwater remediation, biochar-nZVI was injected into groundwater using direct-push and water pressure driven packer techniques for a site impacted by chlorinated solvents in the North China Plain. The field demonstration comprising two-step injections was implemented to demonstrate the effectiveness of nZVI and biochar-nZVI respectively. The outcome of the demonstration revealed a sharp reduction of contaminant concentrations of chlorinated solvents in 24 h following the first injection of nZVI, but the rebound of the concentrations of these contaminants in groundwater has occurred within the next two weeks. However, application of biochar-nZVI greatly enhanced the removal of chlorinated solvents in groundwater over the longer period of 42 days. The enhanced removal of chlorinated solvents in groundwater by biochar-nZVI is mainly attributed to the synergistic effects of adsorption and reduction. The adsorption by biochar significantly reduced the level of chlorinated solvents in groundwater. Overall increases in ferrous iron and chloride concentrations after the injections indicated that the reduction has occurred during the removal of chlorinated solvents in groundwater. In summary, biochar-supported nZVI could be potentially used for the effective remediation of chlorinated solvents in groundwater.

Methylene Blue Removal of Fixed-Bed Column Reactor with Pumice and nZVI-Pumice: Experimental and Modeling Study

Nano zero-valent iron (nZVI) emerges as a low cost and eco-friendly adsorbent to treat textile wastewater, which is rich in dye content. However nZVI particles can easily agglomerate in aqueous environment due to electrostatic interaction, decreasing their treatment efficiency. Therefore pumice, a low-cost and naturally found porous material with lower specific surface area (2m2/gr), can be used as support material to reduce agglomeration of nZVI. Treatment efficiencies of pumice/nZVI packing (10:0 and 9:1 (w/w)) in column reactor for specified initial methylene blue concentrations (25, 50, 75 and 100 mg/L) were investigated in this study. Adsorption capacities of the adsorbents were calculated as 2.8 and 4.2 mg/g-adsorbent, respectively at 100 mg/L initial methylene blue concentration. Mixed bed column performed significantly better than its pumice-only counterpart for low initial concentrations. Thomas adsorption model was applied to experimental results with a moderate to high predictive power.