Corrosion Of nZVI Research Articles

Sulfidation of Nanoscale Zero-Valent Iron by Sulfide: The Dynamic Process, Mechanism, and Role of Ferrous Iron.

Sulfidation of nanoscale zerovalent iron (nZVI) can enhance particle performance. However, the underlying mechanisms of nZVI sulfidation are poorly known. We studied the effects of Fe2+ on 24-h dynamics of nZVI sulfidation by HS- using a dosed S to Fe molar ratio of 0.2. This shows that in the absence of Fe2+, HS- rapidly adsorbed onto nZVI particles and reacted with surface iron oxide to form mackinawite and greigite (<0.5 h). As nZVI corrosion progressed, amorphous FeSx in solution deposited on nZVI, forming S-nZVI (0.5-24 h). However, in the initial presence of Fe2+, the rapid reaction between HS- and Fe2+ produced amorphous FeSx, which deposited on the nZVI and corroded the surface iron oxide layer (<0.25 h). This was followed by redeposition of colloidal iron (hydr)oxide on the particle surface (0.25-8 h) and deposition of residual FeSx (8-24 h) on S-nZVI. S loading on S-nZVI was 1 order of magnitude higher when Fe2+ was present. Surface characterization of the sulfidated particles by TEM-SAED, XPS, and XAFS verified the solution dynamics and demonstrated that S2- and S22-/Sn2- were the principal reduced S species on S-nZVI. This study provides a methodology to tune sulfur loading and S speciation on S-nZVI to suit remediation needs.

Simultaneous removal of Cd(II) and phosphate by nanoscale zero-valent iron from solution: Co-sorption and implication of corrosion

Nanoscale zero-valent iron (nZVI) has been extensively utilized in environmental remediation, but its reactivity in the presence of co-contaminants requires further investigation for effective application in complex environments. Here, we conducted batch removal experiments to systematically investigate the co-removal behaviors of Cd(II) and phosphate by nZVI. Results showed that nZVI can synergistically remove Cd(II) and phosphate in solution, with the removal efficiency of Cd(II) and phosphate in the binary system being approximately 2 and 5 times higher than those in the single system, respectively. Sequential removal experiments combined with characterization analysis revealed the co-sorption of Cd(II) and phosphate onto the corrosion product of nZVI mainly by forming the ternary complexes (≡Fe–P–Cd). The Fe(OH)2 formed as the initial nZVI corrosion product provides numerous active sites for immobilization of Cd(II) and phosphate. Such effective co-sorption of Fe(OH)2 inhibits its subsequent phase transformation to Fe3O4. Overall, our work sheds light on how nZVI, Cd(II), and phosphate interact in solution as well as highlights the influence of phase transformation on co-removal, which can broaden the potential applications of nZVI in the practical environment.

Controllable integration of nano zero-valent iron into MOFs with different structures for the purification of hexavalent chromium-contaminated water: Combined insights of scavenging performance and potential mechanism investigations

This work combined the stability of the porous structure of metal-organic frameworks with the strong reducibility of nano zero-valent iron, for the controllable integration of NZVI into MOFs to utilize the advantages of each component with enhancing the rapid decontamination and scavenging of Cr(VI) from wastewater. Hence, four kinds of MOFs/NZVI composites namely ZIF67/NZVI, MOF74/NZVI, MIL101(Fe)/NZVI, CuBTC/NZVI, were prepared for Cr(VI) capture. The results indicated that the stable structure of ZIF67, MOF74, MIL101(Fe), CuBTC, was beneficial for the dispersion of NZVI that could help more close contact between MOFs/NZVI reactive sites and Cr(VI), subsequently, MOFs/NZVI was proved to be better scavengers for Cr(VI) scavenging than NZVI alone. The Cr(VI) capture achieved the maximum adsorption capacity at pH ~ 4.0, which might be due to the participation of more H+ in the reaction and better corrosion of NZVI at lower pH. Mechanism investigation demonstrated synergy of adsorption, reduction and surface precipitation resulted in enhanced Cr(VI) scavenging, and Fe(0), dissolved and surface-bound Fe(II) were the primary reducing species. The findings of this investigation indicated that the as-prepared composites of ZIF67/NZVI, MOF74/NZVI, MIL101(Fe)/NZVI, CuBTC/NZVI, with high oxidation resistance and excellent reactivity, could provide reference for the decontamination and purification of actual Cr(VI)-containing wastewater.

The impact of heteroaggregation between nZVI and SNPs on the co-transport of Cd(II) in saturated sand columns

This study investigated the co-transport behaviors of nano zero-valent iron (nZVI) and Cd(II) in the presence of soil nanoparticles (SNPs) under various SNPs/nZVI mass ratios. It was illustrated that the mobility of colloidal Cd(II) was highly dependent on the nZVI-SNPs heteroaggregation behavior. In the case of 40 mg/L nZVI with SNPs/nZVI mass ratios > 1, the formation of stable SNPs-nZVI heteroaggregates with hydrodynamic diameters (Dh) < 500 nm facilitated the nZVI and colloidal Cd(II) transport at their effluent mass recoveries of 34.76–37.82 % and 9.81–17.17 %, respectively. However, in the case of 100 mg/L nZVI with SNPs/nZVI mass ratios of 0.4–2, the interception of nZVI-SNPs heteroaggregates with Dh > 1500 nm by quartz sands led to almost complete retention of nZVI and colloidal Cd(II) in the columns. Combined with analytical results of zeta potentials and XRD spectrum, it was revealed that the Cd(II) ions could accelerate nZVI corrosion. The positively charged Fe3O4 and γ-FeOOH on corroded nZVI surface could facilitate the heteroaggregation of nZVI-SNPs by the patch-charge attraction, which further reduced the environmental risk of colloidal Cd(II) transport. These findings revealed the important effects of heteroaggregation between nZVI and SNPs on the transport risk of Cd(II) in groundwater.

Integrated influence of sulfide modification on the reactivity of nanoscale zero-valent iron towards decabromodiphenyl ether under an electromagnetic field

Individual application of sulfide modification and electromagnetic field (EMF) can enhance the reactivity of nanoscale zero-valent iron (nZVI), yet the potential of both in combination is not clear. This work found that the reactivity of nZVI towards decabromodiphenyl ether was significantly enhanced by the combined effect of sulfidation and EMF. The specific reaction rate constant of nZVI increased by 7 to 10 times. A series of characterization results revealed that the sulfidation level not only affects the inherent reactivity but also the magnetic-induced heating (MIH) and corrosion (MIC) of nZVI. These collectively influence the degradation efficiency of nZVI under EMF. Sulfidation generally diminished the MIH effect. The low degree of sulfidation (S/Fe = 0.1) slightly reduced the MIC effect by 21.4%. However, the high degree of sulfidation (S/Fe = 0.4) led to significantly enhanced MIC effect by 107.1%. For S/Fe = 0.1 and 0.4, the overall enhancement in the reactivity resulting from EMF was alternately dominated by the contributions of MIH and MIC. This work provides valuable insights into the MIH and MIC effects about the sulfidation level of nZVI, which is needed for further exploration and optimization of this combined technology.

Simultaneous removal of Cr, Cu, Zn, and Cd by nano zero-valent iron modified sludge biochar in high salinity wastewater

Cr, Cu, Zn, and Cd commonly coexisted in the electroplating wastewater with high salinity and organics, while their removal was often investigated individually. In this study, the simultaneous removal of Cr, Cu, Zn, and Cd was investigated by nano zero-valent iron modified sludge biochar (nZVI@SBC). The results showed that nZVI@SBC could significantly improve the removal efficiency of the four heavy metals (HMs) in high salinity wastewater. NO3– (N-NO3–) and humic acid (HA) could promote the removal of Cr, Cu, Zn, and Cd, and PO43- (P-PO43-) could enhance the removal of Cd. EPR analysis demonstrated the generation of 1O2 in different water matrices. The 1O2 intensity increased in the presence of NO3– and HA, which indicated the acceleration of the nZVI corrosion and the promoted electron transfer in the system. To further understand the reaction mechanism, the variation of nZVI@SBC structures and compositions during the treatment process were characterized by SEM-EDS, XRD, BET, and XPS. Cr and Cu were removed through adsorption and co-precipitation after reduction by nZVI, while Cd and Zn were removed by alkali precipitation and complexation. This work improves the understanding of simultaneous removal of HMs by nZVI@SBC and provides a cost-effective approach for the electroplating wastewater treatment.

Sulfidation of nano-Fe/Pd bimetal for highly efficient remediation of Cr (VI) from water: Enhanced reactivity and applicability

Sulfidation of zero-valent iron nanoparticles (S-nZVI) has been considered as a common means to improve its reactivity. In this paper, Pd and Na2S were chosen as the catalyst and sulfidation regent via a modified post sulfidation approach to fabricate a kind of sulfidated bimetallic Fe/Pd nanoparticles (S-nZVIPd). The structure and composition have been clearly confirmed by a combination of various techniques. Morphology analysis showed that S-nZVIPd had a core–shell framework and hierarchical structure. The reactivity performance of S-nZVIPd, nZVIPd and S-nZVI toward Cr (VI) remediation from aqueous solution was compared, and the underlying mechanisms for the improvement effect of Cr (VI) removal were also investigated. S-nZVIPd exhibited a superior remediation reaction to remove Cr (VI) with higher removal capacity of 234.9 mg/g, with the comparison of nZVIPd (192.3 mg/g) and S-nZVI (137.5 mg/g). Additionally, the effects of common anions and cations, pH, and temperature on Cr (VI) removal were also investigated in batch experiments. Also, kinetic fitting of results revealed that remediation obeyed a pseudo-second-order model, where the apparent activation energy was 37.7 KJ/mol, illustrating that the removal of Cr (VI) was mainly dominated by chemical reduction. The enhanced removal rate of Cr (VI) by S-nZVIPd suggested that Pd and FeSx played a dual role in accelerating the corrosion of nZVI, and were facilitated to electron transfer between nZVI and Cr (VI). The results indicated that the research of the novel S-nZVIPd composite delivered new ideas theoretically for specific inquiries in the future.

Phase transformation of nanoscale zero-valent iron and concurrent arsenite sequestration under oxic water environment

Nanoscale zero-valent iron (nZVI) may partially or completely transform to iron (hydr)oxides when it is used to remove arsenite [As(Ⅲ)]. It is necessary to explore the dynamic phase transformation of nZVI and concurrent arsenic valent changes since reactivity is relevant to the exiting species. In this study, X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), Raman spectrum, and scanning electron microscope (SEM) were used to probe the phase transformation of nZVI under the varied simulated polluted water, including different As(Ⅲ) concentration, pH, and co-existing anions. The mainly final product of nZVI corrosion was lepidocrocite (γ-FeOOH) evaluated by XRD. Because of proton release, As(Ⅲ) made more Fe0 corroded in the initial reaction and the corrosion process was faster in the later stage. The formation of iron (hydr)oxides was the main factor affecting the removal of As(Ⅲ) between pH 2–8. And the co-existing anions promoted the corrosion of Fe0, which weakened the negative effect of competitive adsorption on As(Ⅲ) removal to some extent. This research will provide vital information on the evolution and fate of nZVI under environmental conditions, as well as As(Ⅲ) stabilization and mobilization for nZVI treatment system.

Molybdenum disulfide co-catalysis boosting nanoscale zero-valent iron based Fenton-like process: Performance and mechanism

The conventional Fenton process has the drawbacks of low efficiency of Fe3+/Fe2+ conversion, low utilization of H2O2, and narrow range of pH. In this paper, molybdenum sulfide (MoS2) was used as a co-catalyst to boost the nanoscale zero-valent iron (nZVI) based heterogeneous Fenton-like process for the degradation of Rhodamine B (RhB). The catalytic performance, influences of parameters, degradation mechanism, and toxicity of intermediates were explored. Compared with the conventional like-Fenton process, the existence of MoS2 accelerated the decomposition of H2O2 and the RhB degradation rate constant of MoS2/nZVI/H2O2 reached more than six times that of nZVI/H2O2. In addition, the effective pH range of MoS2/nZVI/H2O2 was broadened to 9.0 with 84.9% of RhB being removed within 15 min. The co-catalytic system of MoS2 and nZVI was stable and had high reusability according to the results of four consecutive runs. Quenching tests and electron paramagnetic resonance (EPR) demonstrated that hydroxyl radical (·OH), superoxide anions (·O2−), and singlet oxygen (1O2) were all involved in MoS2/nZVI/H2O2. Compared with nZVI/H2O2 system, MoS2 not only increased the corrosion of nZVI but also accelerated the conversion of Fe3+/Fe2+. ECOSAR analysis suggested that the overall acute and chronic toxicity of the degradation products decreased after treatment. Hence, this MoS2 co-catalytic nZVI based Fenton-like process can be used as a promising alternative for the treatment of organic wastewater.

One-stop rapid decomplexation and copper capture of Cu(II)-EDTA with nanoscale zero valent iron

Heavy metal complexes widely exist in the industrial wastewater, imposing significant threat to public health. Conventional treatment of heavy metal complexes usually requires two-step procedures, including the advanced oxidation process for decomplexation and the subsequent precipitation to remove the released metal ions. Herein, we developed a one-stop technique for simultaneous Cu(II)-EDTA decomplexation and copper capture using nano zero-valent iron (nZVI). The dissolved Fe3+ from nZVI corrosion could rapidly complex with EDTA to destroy the Cu(II)-EDTA, while •O2- and •OH generated via the reaction of nZVI and molecular oxygen, would degrade the EDTA ligand. The liberated Cu2+ were subsequently reduced to metallic Cu or adsorbed by the iron hydroxides. Impressively, 99 % of Cu(II)-EDTA was removed within 10 min with the rate constant up to 0.49 min−1 and 70–90 % of Cu captured by nZVI. More importantly, this nZVI based one-stop technique was effective in an extremely broad pH range of 1–12 and could also realize the one-stop removal of Cu complexes from actual wastewater, producing effluent that stably meets the discharge standard of electroplating wastewater. This study provides a facile method to simultaneously destruct Cu(II)-EDTA and capture Cu, and also sheds light on the decomplexation mechanism of heavy metal wastewater.

Enhanced elimination of Cr(VI) from aqueous media by polyethyleneimine modified corn straw biochar supported sulfide nanoscale zero valent iron: Performance and mechanism

A novel polyethyleneimine modified corn straw biochar supported sulfide nanoscale zero-valent iron (S-nZVI@PBC) was developed to enhance Cr(VI) removal from aqueous media. The characteristics of morphology, chemical composition, and functional groups of S-nZVI@PBC, as well as its kinetics and mechanism for Cr(VI) removal were explored. Characterization verified S-nZVI was successfully loaded onto PEI modified biochar. The adsorption process was well represented pseudo-second-order model (R2 = 0.990) and Langmuir isotherm model (R2 = 0.962), indicating it was a monolayer chemical adsorption process. The Cr(VI) removal was affected by pH and achieved the maximum when pH = 3.0, which may be ascribed to the better corrosion of nZVI and release of Fe(II) from the S-nZVI@PBC in acidic condition. The primary mechanisms were adsorption, reduction, and co-precipitation. S-nZVI@PBC exhibited higher stability and reusability than nZVI, which makes it more promising in environmental application. Overall, S-nZVI@PBC is of great potential for treating Cr(VI)-containing wastewater.

Critical layer in liquid-solid system influencing the remediation of chromium using zeolite-supported sulfide nano zero-valent iron

Sulfidated nano zero-valent iron particles were immobilized on ZSM-5 zeolite (Z/S-nZVI) and used for hexavalent chromium (Cr(VI)) remediation. The performance of Z/S-nZVI improved with the increase in Cr(VI) concentration (< 60 mg/L), while the performance significantly decreased for a Cr(VI) concentration of more than 60 mg/L. The adsorption behavior for Cr(VI) was different from that reported in previous studies. The improved performance can be tailored for increasing efficiency of nano zero-valent iron (nZVI) corrosion, while the degree of corrosion of nZVI was affected by the concentration of the pollutant as discussed by kinetics, X-ray diffraction (XRD) and X-ray photoelectron spectrometer (XPS) analyses. The experiments for the dissolution of ferrous ions and the dosage of adsorbent demonstrated that the critical layer in the liquid-solid system changed with the increase in the concentration of Cr(VI) (Cr(VI): Z/S-nZVI > 0.6). Moreover, the removal mechanisms of Cr(VI) were elucidated through XRD, transmission electron microscopy (TEM) and XPS techniques. This results demonstrate that the species of chromium in the critical layer changed from Cr(III) to Cr(VI) as the concentration of chromium increased from low to high. Furthermore, the critical layer was composed of Cr(VI), Fe(II), O and H elements. Additionally, the experiments of coexisting ions and aging time confirmed that Z/S-nZVI possessed high selectivity and stability to ensure efficiency and cost-effectiveness in practical applications.

The enhanced biological methanation performance in trickle-bed reactor by different continuous hydrogen supply from nano-zero valent iron corrosion

In this paper, the hydrogen (H2) supply to trickle-bed reactor (TBR) in endogenous and exogenous ways by nano-zero-valent iron (nZVI) corrosion was indicated, in order to increase the biogas generation and methane (CH4) content from wastewater. The results showed that the nZVI corrosion H2 supply method increased the biogas generation in TBR. The daily average CH4 yields of TBR in stages 1–4 increased by 23.99 %, 35.76 %, 49.40 % and 56.13 % compared with control stage, respectively, and the highest CH4 content of 90.72 % was achieved in stage 3. The changes of enzyme concentration indicated that iron from nZVI enhanced the activities of acetate kinase and dehydrogenase, however, the activity of coenzyme F420 was lower due to the presence of homoacetogenic acetate formation that enhanced the acetoclastic methanogenesis pathway. Changes in the structure of the microbial community played an important role in the mechanism of CH4 enhancement, and the analysis of microbial abundance showed that the additions of nZVI and ferrous iron (Fe2+) changed the microbial communities, with increased abundances of hydrogenotrophic methanogens and homoacetogen.

Nano- and micro-scale zerovalent iron-activated peroxydisulfate for methyl phenyl sulfoxide probe transformation in aerobic water: Quantifying the relative roles of SO4·−, Fe(IV), and ·OH

Multiple reactive intermediates have been proposed to be involved in peroxydisulfate (PDS) activation by zerovalent iron (ZVI), including sulfate radical (SO4·−) produced via iron-oxide shell mediated electron transfer, ferryl ion species (Fe(IV)) formed from Fe(II)-PDS interaction, and hydroxyl radical (·OH) generated by ZVI aerobic oxygenation. In this study, evolution of the relative role of these intermediates in microscale and nanoscale ZVI (mZVI vs. nZVI) activated PDS processes is comparatively investigated by using a methyl phenyl sulfoxide (PMSO) probe that selectively reacts with Fe(IV) to produce methyl phenyl sulfone (PMSO2). Interestingly, during PMSO transformation by mZVI/PDS process, yields of PMSO2 (η(PMSO2)) exhibit three-stage behavior that they first increase to a maximum (∼80% but lower than 100%) (Stage I) and then plateau for a period (Stage II) followed by a decrease phase (Stage III). Accordingly, the relative role of Fe(IV) in PMSO transformation is unceasingly improved in Stage I and subsequently reaches equilibrium with that of free radicals in Stage II, while it finally decreases in Stage III. Similar η(PMSO2) evolution trends are obtained in nZVI/PDS process, except that the η(PMSO2) increase in Stage I is negligible, possibly due to the exceptional fast nZVI dissolution. It was further clarified by tert-butyl alcohol scavenging assay that, in addition to Fe(IV), the free radical involved in Stages I and II is SO4·−, while ·OH was dominant in Stage III. Moreover, studies on O2 effect reveal that ZVI aerobic oxygenation participates in mZVI corrosion during the entire process, while it is only involved in nZVI corrosion when PDS content is reduced to a low concentration, indicating that the reactivities of PDS and O2 are similar in mZVI corrosion, but differ greatly in nZVI corrosion. Additionally, effects of reactant dose and pH on η(PMSO2) evolution are also explored. Dynamics of the relative role of different reactive oxidants should be taken into account in further applications of ZVI/PDS in situ chemical remediation technology considering their different chemistries.

Coupled mechanism of enhanced and inhibitory effects of nanoscale zero-valent iron on methane production and antibiotic resistance genes in anaerobic digestion of swine manure

In this study, the turning point for nanoscale zero-valent iron’s (NZVI) promotion and inhibition effects of methane production coupled with the reduction of antibiotic resistance genes (ARGs) was investigated. Adding 150 mmol/L NZVI increased methane production by maximum of 23.8 %, which was due to the chemical reaction producing H2 and enhancement of direct interspecies electron transfer (DIET) by NZVI. NZVI350 dramatically repressed methane generation by 48.0 %, which might be associated with the large quantity of reactive oxygen species (ROS) and excessive H2 inhibiting the functioning of microorganisms. The fate of ARGs was significantly related to daily methane production, indicating that the more methane production finally generated, the less the abundance of ARGs at last left. The reduction of ARGs was enhanced by maximum of 61.0 %, which was attributed to the inhibition of vertical gene transfer (VGT) and horizontal gene transfer (HGT) caused by steric hindrance associated with NZVI corrosion.

Insight into the action of magnetite loaded with nano Ni/Fe bimetallic particles (Ni4/Fe@Fe3O4) toward carbon tetrachloride degradation in aqueous solution

Nanometer zero-valent iron (nZVI), Fe2+ and H2 were potential electron donors for CT removal by nZVI. However, the action of these electron donors in CT reduction was often ambiguous. In this study, the actual catalytic activity of Ni4/Fe@Fe3O4 under common ions and humic acid (HA) was investigated. The results showed that Na+ and K+ had no effect on CT removal, Cl‐, SO42‐ and low concentration of Mg2+ was beneficial to CT removal, while NO3‐, HCO3‐, Ca2+ and HA exhibited the negative effects. According to the analysis results of gas chromatography (GC) and ion chromatography (IC), a possible dechlorination pathway of CT was proposed. Furthermore, the action mechanism of nZVI, Ni0 and magnetite (Fe3O4) on CT removal were explored. Among the three possible nZVI reducing mechanism, the use of H2 by Ni0 for the hydrodechlorination was dominant, while the direct reduction of nZVI was secondary. Fe2+, the product of nZVI corrosion, contributed little to CT degradation and required longer reaction time. Ni0 could not only utilize H2 but also form galvanic cells with nZVI to accelerate CT dechlorination. In addition, the support Fe3O4 significantly improved the dispersion of Ni/Fe nanoparticles and its corrosion product Fe2+ also promoted the CT removal. These findings were significant for comprehending the mechanisms of bimetallic nanocomposites in reducing CT, and might guide to the development of nZVI based technology for repairing polluted water or soil with organochlorine pollutants.

Effect of Spatial Distribution of nZVI on the Corrosion of nZVI Composites and Its Subsequent Cr(VI) Removal from Water.

There have been many studies on contaminant removal by fresh and aged nanoscale zero-valent iron (nZVI), but the effect of spatial distribution of nZVI on the corrosion behavior of the composite materials and its subsequent Cr(VI) removal remains unclear. In this study, four types of D201-nZVI composites with different nZVI distributions (named D1, D2, D3, and D4) were fabricated and pre-corroded in varying coexisting solutions. Their effectiveness in the removal of Cr(VI) were systematically investigated. The results showed acidic or alkaline conditions, and all coexisting ions studied except for H2PO4− and SiO32− enhanced the corrosion of nZVI. Additionally, the Cr(VI) removal efficiency was observed to decrease with increasing nZVI distribution uniformity. The corrosion products derived from nZVI, including magnetite, hematite, lepidocrcite, and goethite, were identified by XRD. The XPS results suggested that the Cr(VI) and Cr(III) species coexisted and the Cr(III) species gradually increased on the surface of the pre-corroded D201-nZVI with increasing iron distribution uniformity, proving Cr(VI) removal via a comprehensive process including adsorption/coprecipitation and reduction. The results will help to guide the selection for nZVI nanocomposites aged under different conditions for environmental decontamination.

Synergistic roles of Fe(II) on simultaneous removal of hexavalent chromium and trichloroethylene by attapulgite-supported nanoscale zero-valent iron/persulfate system

Synthesized attapulgite-supported nanoscale zero-valent iron (AT-nZVI) composite/persulfate (PS) systems were utilized to simultaneously remove hexavalent chromium (Cr(VI)) and trichloroethylene (TCE) from aqueous solutions. The structures of AT-nZVI before and after the reaction with Cr(VI)-TCE were characterized by TEM-EDS-Mapping, HR-TEM and HR-XPS with ion sputtering. The effects of initial Cr(VI), TCE and PS concentrations, and PS addition time intervals on Cr(VI)-TCE removal efficiencies were evaluated. Experimental results revealed that the AT-nZVI composites with 1 mM PS can effectively and simultaneously remove Cr(VI) and TCE with the removal efficiencies of Cr(VI) and TCE reaching 90.02% and 90.40% respectively. It is thought that PS promoted TCE oxidation and the reduction of Cr(VI), which was predominately controlled by Fe(II). TCE was mainly degraded by free radical oxidation resulting from the PS activation of AT-nZVI. The enhanced Cr(VI) removal was attributed to the exposed areas and available active sites of nZVI, and Fe(II) in the solution increased by PS-mediated processes of rapid corrosion and dissolution of nZVI. The dual roles of AT-nZVI as a activator for PS activation and reductant for Cr(VI) reduction in Cr(VI)-TCE removal were identified. This implies that AT-nZVI/PS can be utilized as potential remediation reagents for simultaneous removal of heavy metal and chlorinated solvents in groundwater frequently encountered in contaminated sites.

Adsorption of Sb(III) from Aqueous Solution by nZVI/AC: A Magnetic Fixed-Bed Column Study.

The effectiveness of nanoscale zero-valent iron(nZVI) immobilized on activated carbon (nZVI/AC) in removing antimonite (Sb(III)) from simulated contaminated water was investigated with and without a magnetic fix-bed column reactor. The experiments were all conducted in fixed-bed columns. A weak magnetic field (WMF) was proposed to increase the exclusion of paramagnetic Sb(III) ions by nZVI/AC. The Sb(III) adsorption to the nZVI and AC surfaces, as well as the transformation of Sb(III) to Sb(V) by them, were both increased by using a WMF in nZVI/AC. The increased sequestration of Sb(III) by nZVI/AC in the presence of WMF was followed by faster nZVI corrosion and dissolution. Experiments were conducted as a function of the pH of the feed solution (pH 5.0–9.0), liquid flow rate (5–15 mL·min−1), starting Sb(III) concentration (0.5–1.5 mg·L−1), bed height nZVI/AC (10–40 cm), and starting Sb(III) concentration (0.5–1.5 mg·L−1). By analyzing the breakthrough curves generated by different flow rates, different pH values, different inlet Sb(III) concentrations, and different bed heights, the adsorbed amounts, equilibrium nZVI uptakes, and total Sb(III) removal percentage were calculated in relation to effluent volumes. At pH 5.0, the longest nZVI breakthrough time and maximal Sb(III) adsorption were achieved. The findings revealed that the column performed effectively at the lowest flow rate. With increasing bed height, column bed capacity and exhaustion time increased as well. Increasing the Sb(III) initial concentration from 0.5 to 1.5 mg·L−1 resulted in the rise of adsorption bed capacity from 3.45 to 6.33 mg·g−1.

Degradation of tetrachloroethylene by zero valent iron nanoparticles in the presence of a natural groundwater bacterial biofilm in a sandy porous media

Biofilms are naturally present in aquifers and can interact with zero valent iron nanoparticles (nZVI) used as remediation agents in contaminated groundwater; thereby they may alter nZVI reactivity towards targeted contaminants in porous media. Laboratory scale experiments using columns filled with sand (50 cm long and 5.2 cm in diameter) were performed to investigate the impact of natural biofilms on nZVI reactivity towards tetrachloroethylene (PCE) in conditions simulating an unconsolidated sandy aquifer. Solutions containing PCE were injected through the sand columns in the presence or absence of biofilm and nZVI. Concentrations in PCE and its metabolites were monitored during 45 days in dissolved and gas phases. PCE concentrations decreased at the column outlets due both to its reductive dechlorination by nZVI (~30% of injected PCE) and its sorption or deposition (as PCE-DNAPL) on sand (~35% of injected PCE). No significant differences in PCE concentrations were found in presence or absence of biofilm. However, biofilm presence affected the nature of PCE metabolites. A higher release of ethene in the column containing biofilm was observed, whereas ethane was dominant in the absence of biofilm. Microbes consumed H2 released by the corrosion of nZVI limiting the hydrogenation of ethene to ethane. The consequences of biofilm development in porous media should be taken into account when considering treatment with nZVI, as it may affect the nature of produced metabolites.