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Chloroform (CF) is a widely used chemical reagent and disinfectant and a probable human carcinogen. The extensive literature on halocarbon reduction with zerovalent iron (ZVI) shows that transformation of CF is slow, even with nano, bimetallic, sulfidated, and other modified forms of ZVI. In this study, an alternative method of ZVI modification─involving simultaneous sulfidation and nitridation through mechanochemical ball milling─was developed and shown to give improved degradation of CF (i.e., higher degradation rate and inhibited H 2 evolution reaction). The composite material (denoted as S-N(C)-ZVI) gave synergistic effects of nitridation and sulfidation on CF degradation. A complete chemical reaction network (CRN) analysis of CF degradation suggests that O-nucleophile-mediated transformation pathways may be the main route for the formation of the terminal nonchlorinated products (formate, CO, and glycolic polymers) that have been used to explain the undetected products needed for mass balance. Material characterizations of the ZVI recovered after batch experiments showed that sulfidation and nitridation promoted the formation of Fe 3 O 4 on the S-N(C)-ZVI particles, and the effect of aging on CF degradation rates was minor for S-N(C)-ZVI. The synergistic benefits of sulfidation and nitridation on CF degradation were also observed in experiments performed with groundwater.

Metal(loid) oxyanions in groundwater, surface water, and wastewater can have harmful effects on human or ecological health due to their high toxicity, mobility, and lack of degradation. In recent years, the removal of metal(loid) oxyanions using zerovalent iron (ZVI) has been the subject of many studies, but the full scope of this literature has not been systematically reviewed. The main elements that form metal(loid) oxyanions under environmental conditions are Cr(VI), As(V and III), Sb(V and III), Tc(VII), Re(VII), Mo(VI), V(V), etc. The removal mechanisms of metal(loid) oxyanions by ZVI may involve redox reactions, adsorption, precipitation, and coprecipitation, usually with one of these mechanisms being the main reaction pathway and the other playing auxiliary roles. However, the removal mechanisms are coupled to the reactions involved in corrosion of Fe(0) and reaction conditions. The layer of iron oxyhydroxides that forms on ZVI during corrosion mediates the sequestration of metal(loid) oxyanions. This review summarizes most of the currently available data on mechanisms and performance (e.g., kinetics) of removal of the most widely studies metal(loid) oxyanion contaminants (Cr, As, Sb) by different types of ZVI typically used in wastewater treatment, as well as ZVI that has been sulfidated or combination with catalytic bimetals., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

FeN X in Fe single-atom catalysts can be the active site for adsorption and activation of reactants. In addition, FeN X species have been shown to facilitate electron transfer between Fe and the carbon supports used in newly developed metal-air batteries. We hypothesized that the combination of FeN X species with granular zero-valent iron (ZVI) might result in catalyzed reductive decontamination of groundwater contaminants such as trichloroethylene (TCE). Here, such materials synthesized by ball milling microscale ZVI with melamine and the resulting N species were mainly in the form of pyridinic, pyrrolic, and graphitic N. This new material (abbreviated as N-C-mZVI bm ) dechlorinated TCE at higher rates than bare mZVI bm (about 3.5-fold) due to facilitated electron transfer through (or around) the surface layer of iron oxides by the newly formed Fe-N X (C). N-C-mZVI bm gave higher k TCE (0.4-1.14 day -1 ) than mZVI bm (0-0.4 day -1 ) over a wide range of pH values (4-11). Unlike most ZVI systems, k TCE for N-C-mZVI bm increased with increasing pH values. This is because the oxide layer that passivates Fe 0 at a high pH is disrupted by Fe-N X (C) formed on N-C-mZVI bm , thereby allowing TCE dechlorination and HER under basic conditions. Serial respike experiments gave no evidence of decreased performance of N-C-mZVI bm , showing that the advantages of this material might remain under field applications.

The efficiency and selectivity of zerovalent iron-based treatments for organohalide contaminated groundwater can be quantified by accounting for redistribution of electrons derived from oxidation of Fe 0 . Several types of efficiency are reviewed, including (i) the efficiency of Fe(0) utilization, ε Fe(0) , (ii) the electron efficiency of target contaminant reduction, ε e , and (iii) the electron efficiency of natural reductant demand (NRD) involving H 2 O, O 2 , and co-contaminants such as nitrate, ε NRD . Selectivity can then be calculated by using ε e /ε NRD . Of particular interest is ε e and the key to its determination is measuring the total quantity of electrons provided by Fe 0 oxidation, which can be based on either the loss of Fe(0), the formation of Fe(ii)/Fe(iii), or the composition of the total reaction products. Recently, many data have accumulated on ε e for the treatment of various chlorinated solvents (esp. trichloroethylene, TCE) by zerovalent iron (ZVI), and analysis of these data shows that ZVI particle properties (e.g., stabilization with polymers, bimetallic modification, sulfidation, etc.) and other operational factors have variable effects on ε e . Of particular interest is that pre-exposure of ZVI to reduced sulfur species (i.e., sulfidation) consistently improves the ε e of contaminant reduction, mainly by suppressing the reduction of water.

In situ chemical oxidation (ISC0) and in situ thermal remediation (ISTR) are applicable to treatment of groundwater contaminated with chlorinated ethenes. ISCO with persulfate (S2O82-) requires activation, and this can be achieved with the heat from ISTR, so there may be advantages to combining these technologies. To explore this possibility, we determined the kinetics and products of chlorinated ethene oxidation with heat-activated persulfate and compared them to the temperature dependence of other degradation pathways. The kinetics of chlorinated ethene disappearance were pseudo-first-order for 1–2 half-lives, and the resulting rate constants—measured from 30 to 70 °C—fit the Arrhenius equation, yielding apparent activation energies of 101 ± 4 kJ mol-1 for tetrachloroethene (PCE), 108 ± 3 kJ mol-1 for trichloroethene (TCE), 144 ± 5 kJ mol-1 for cis-1,2-dichloroethene (cis-DCE), and 141 ± 2 kJ mol-1 for trans-1,2-dichloroethene (trans-DCE). Chlorinated byproducts were observed, but most of the parent material was completely dechlorinated. Arrhenius parameters for hydrolysis and oxidation by persulfate or permanganate were used to calculate rates of chlorinated ethene degradation by these processes over the range of temperatures relevant to ISTR and the range of oxidant concentrations and pH relevant to ISCO. [ABSTRACT FROM AUTHOR]

The degradation of 2,4,6-trinitrotoluene (TNT) and other explosives by zero-valent iron (ZVI) is rapid and, as a result, potentially useful for both ex situ ground water "pump-and-treat" systems and in situ permeable reactive barriers. However, the usefulness of ZVI in either configuration may be limited by reaction-induced reduction in both hydraulic conductivity (K) and reactivity (as represented by the surface area-normalized rate constant, ksa). The impacts of dissolved oxygen and TNT on K and ksa are examined here using field and laboratory columns. The data suggest that K reduction in ZVI columns can be significant when dissolved oxygen is present. However, when TNT is present at approximately the same concentration (10 mg/L), it does not cause significant reduction in K. In contrast, TNT causes a significant reduction in ksa, while dissolved oxygen appears to have relatively little impact on the reactivity of the columns toward TNT. [ABSTRACT FROM AUTHOR]

Focuses on the use of discovery-based method experiment illustrating the application of iron metal in remediating contaminated groundwater. Details of the degradation process; Materials covered in the laboratory; Usability of the experiment as a vehicle to introduce more advanced topics in chemistry.

The emplacement of nano zerovalent iron (nZVI) for groundwater remediation is usually monitored by common measurements such as pH, total iron content, and oxidation–reduction potential (ORP) by potentiometry. However, the interpretation of such measurements can be misleading because of the complex interactions between the target materials (e.g., suspensions of highly reactive and variably aggregated nanoparticles) and aquifer materials (sediments and groundwater), and multiple complications related to sampling and detection methods. This paper reviews current practice for both direct and indirect characterizations of nZVI during groundwater remediation and explores prospects for improving these methods and/or refining the interpretation of these measurements. To support our recommendations, results are presented based on laboratory batch and column studies of nZVI detection using chemical, electrochemical, and geophysical methods. Chemical redox probes appear to be a promising new method for specifically detecting nZVI, based on laboratory tests. The potentiometric and voltammetric detections of iron nanoparticles, using traditional stationary disc electrodes, rotating disc electrodes, and flow-through cell disc electrodes, provide insight for interpreting ORP measurements, which are affected by solution chemistry conditions and the interactions between iron nanoparticles and the electrode surface. The geophysical methods used for characterizing ZVI during groundwater remediation are reviewed and its application for nZVI detection is assessed with results of laboratory column experiments. [ABSTRACT FROM AUTHOR]