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Zero-valent iron (ZVI) and modified ZVI have been investigated extensively for groundwater remediation. However, ZVI based powder was difficult to be applied directly as permeable reactive barrier (PRB) materials due to their low water permeability and usage rate. In this study, sulfide iron-copper bimetal was prepared by ball milling, which is environment-friendly without second contamination. The optimal preparation parameters of sulfide iron-copper bimetal for Cr(VI) removal were determined (Cu/Fe ratio (w/w), 0.018; FeS/Fe ratio (w/w), 0.1213; ball milling speed, 450 rpm; ball milling time, 5 h). A composite permeable material was prepared by sintering a mixture of sulfide iron-copper bimetal, sludge, and kaolin. The parameters for composite permeable material preparation including sludge content and particle size, and sintering time were optimized, which were 60%, 60-75 mesh, and 4 h, respectively. The optimal composite permeable material was characterized by SEM-EDS, XRD, and FTIR. The results demonstrated preparation parameters can affect the hydraulic conductivity and hardness of composite permeable material. High sludge content, small particles size, and moderate sintering time resulted in high permeability of composite permeable material and were beneficial for Cr(VI) removal. The dominant Cr(VI) removal mechanism was reduction, and the reaction followed pseudo-first order kinetics. Conversely, low sludge content and large particle size, and long sintering time lead to low permeability of composite permeable material. Chromate removal was mainly by chemisorption following pseudo-second order kinetics. The hydraulic conductivity and hardness of the optimal composite permeable material achieved 1.732 cm/s and 50, respectively. The results of column experiments indicated that its Cr(VI) removal capacity was 0.54 mg/g, 0.39 mg/g and 0.29 mg/g at pH 5, 7 and 9, respectively. The ratio of Cr(VI) to Cr(III) on composite permeable material surface was similar under acidic and alkaline conditions. This study will provide an effective reactive material of PRB for field application., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationship that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Heavy metal removal using nano zero-valent iron (NZVI) has drawn growing attention due to the ease of application and high removal efficiency. However, uncertainties regarding its fate and transport in subsurface environments have raised concerns that require further exploration. In this study, aggregation, sedimentation, and Cr/As desorption of three types of NZVIs were investigated under various conditions. It was found that the aggregation behavior of the NZVIs differed from one another in regard to reaction time and ionic strength, associated with the respective critical size for sedimentation. Sedimentation of NZVIs was positively related to the concentrations and average particle sizes. The sedimentation kinetics of NZVI followed two concomitant processes, i.e., (1) direct sedimentation of larger particles, and (2) initial aggregation and then sedimentation of smaller particles. When loaded with Cr/As, NZVIs tended to deposit faster, possibly due to the precipitation of Cr/As onto the nanoparticle surfaces resulting in larger particle sizes. Moreover, desorption of Cr/As from Cr/As loaded NZVIs was detected in the presence of typical groundwater ions, as well as natural organic matter, and poses a potential risk to the subsurface environment. The desorption of Cr was linearly related to the release of iron ions, while As desorption was mitigated when the immobilization of Cr increased., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The effects of hardness (Ca(2+)) and alkalinity (HCO(3)(-)) on arsenic(V) removal from humic acid (HA)-deficient and HA-rich groundwater by zero-valent iron (Fe(0)) were investigated using batch experiments. Arsenic, in general, is removed from groundwater possibly by adsorption and co-precipitation with the iron corrosion products. However, in the co-presence of HCO(3)(-) and Ca(2+), the removal rate of arsenic increased with increasing concentrations of either Ca(2+) or HCO(3)(-). It was observed that the removal of arsenic was significantly enhanced by the formation of CaCO(3) as a nucleation seed for the growth of large iron (hydr)oxide particles. In the co-existence of Ca(2+), HCO(3)(-) and HA, the presence of HA diminished the positive role of Ca(2+) due to the formation of Fe-humate complexes in solution and delaying of the formation of CaCO(3). As a result, the formation of the large iron (hydr)oxide particles was inhibited in the earlier stage which, in turn, affected the removal of arsenic. However, after the formation of CaCO(3) and the subsequent growth of such particles, the presence of large iron (hydr)oxide particles resulted in the rapid removing of arsenic and Fe-humate by adsorption and/or co-precipitation.

The influences of various geochemical constituents, such as humic acid, HCO(3)(-), and Ca(2+), on Cr(VI) removal by zero-valent iron (Fe(0)) were investigated in a batch setting. The collective impacts of humic acid, HCO(3)(-), and Ca(2+) on the Cr(VI) reduction process by Fe(0) appeared to significantly differ from their individual impacts. Humic acid introduced a marginal influence on Fe(0) reactivity toward Cr(VI) reduction, whereas HCO(3)(-) greatly enhanced Cr(VI) removal by maintaining the solution pH near neutral. The Cr(VI) reduction rate constants (k(obs)) were increased by 37.8% and 78.3%, respectively, with 2 mM and 6 mM HCO(3)(-) in solutions where humic acid and Ca(2+) were absent. Singly present Ca(2+) did not show a significant impact to Cr(VI) reduction. However, probably due to the formation of passivating CaCO(3), further addition of Ca(2+) to HCO(3)(-) containing solutions resulted in a decrease of k(obs) compared to solutions containing HCO(3)(-) alone. Ca(2+) enhanced humic acid adsorption led to a minor decrease of Cr(VI) reduction rates. In Ca(2+)-free solutions, humic acid increased the amount of total dissolved iron to 25 mg/l due to the formation of soluble Fe-humate complexes and stably dispersed fine Fe (oxy)hydroxide colloids, which appeared to suppress iron precipitation. In contrast, the coexistence of humic acid and Ca(2+) significantly promoted the aggregation of Fe (oxy)hydroxides, with which humic acid co-aggregated and co-precipitated. These aggregates would progressively be deposited on Fe(0) surfaces and impose long-term impacts on the permeability of PRBs.

The effects of humic acid (HA) on As(V) removal by zero-valent iron (Fe(0)) from groundwater, associated with corrosion products analyses, were investigated using batch experiments. It was found that arsenic was rapidly removed from groundwater possibly due to its adsorption and co-precipitation with the corrosion products of Fe(0). The removal rate of arsenic by Fe(0) was inhibited in the presence of HA probably because of the formation of soluble Fe-humate in groundwater which hindered the production of iron precipitates. A longer reaction time was then required for arsenic removal. Such an influence of HA on arsenic removal increased with increasing HA concentration from 5 to 25mgL(-1). The binding capacity of HA for dissolved Fe was estimated to be about 0.75mg Femg(-1) HA. When the complexation of HA with dissolved Fe was saturated, further corrosion of Fe(0) would produce precipitates, which significantly accelerated the removal of arsenic from groundwater via adsorption and co-precipitation with the corrosion products. Iron (hydr)oxides such as maghemite, lepidocrocite, and magnetite were characterized by XRD analyses as the corrosion products, while As(V) was found on the surface of these corrosion products as detected by fourier transform infrared spectrometry and X-ray photoelectron spectroscopy.

The combination of zero-valent iron (Fe0) and iron oxide-coated sand (IOCS) was used to remove Cr(VI) and As(V) from groundwater in this study. The efficiency and the removal mechanism of Cr(VI) and As(V) by using this combination, with the influence of humic acid (HA), were investigated using batch experiments. Results showed that, compared to using Fe0 or IOCS alone, the Fe0–IOCS can perform better on the removal of both Cr(VI) and As(V). Metal extraction studies showed that As(V) was mainly removed by IOCS and iron corrosion products while Cr(VI) was mainly removed by Fe0 and its corrosion products. Competition was found between Cr(VI) and As(V) for the adsorption sites on the iron corrosion products. HA had shown insignificant effects on Cr(VI) removal but some effects on As(V) removal kinetics. As(V) was adsorbed on IOCS at the earlier stage, but adsorbed/coprecipitated with the iron corrosion products at the later stage. [Copyright &y& Elsevier]

[Display omitted] • The MoS 2 @PANI/PMS with trace Fe(II) system degraded nearly 100 % of TAP in 15 min. • The cycle of Fe(III)/Fe(II) was greatly accelerated by MoS 2 @PANI. • The degradation of TAP was effective in a wide pH range of 3 to 9. • SO 4 · - , H O · , O 2 · - and 1O 2 were identified in the Fe(II)/MoS 2 @PANI/PMS system. • Possible degradation pathways and product toxicity of TAP were proposed. Fe(II) displayed a great potential in peroxymonosulfate (PMS) activation to remove pollutants but was limited by the cycle of Fe(III)/Fe(II) in the process. To solve this problem, different percentages of flower-like MoS 2 nanosheets were successfully coated on the surface of polyaniline (PANI) nanotubes named as MoS 2 @PANI-X(1, 2, 3) activating PMS efficiently with trace Fe(II) to remove thiamphenicol (TAP), in which MoS 2 @PANI-2 with 92.6% of MoS 2 was the best by removing 99% TAP within 15 min. Notably, the used trace Fe(II) concentration (2 μM) was environmentally friendly because it was far lower than the allowable limit (0.3 mg/L) in standard for drinking water by WHO. With the increase of PMS concentration (0.1–2.0 mM), k PMS increased from 0.083 to 0.118 min−1 and then decreased to 0.098 min−1.When MoS 2 @PANI-2 dosage increased from 10 to 50 mg/L, k M o S 2 @ P A N I - 2 increased from 0.068 to 0.558 min−1. However, N O 3 - , C l - , H P O 4 2 - , H C O 3 - , H 2 P O 4 - and natural organic matter inhibited the degradation of TAP in varying degrees. The special structure of MoS 2 @PANI increased many activity sites of Mo(IV) to promote the cycle of Fe(III)/Fe(II) for sustainable and effective activating PMS which generated SO 4 · - , H O · , O 2 · - and 1O 2 to achieve high removal rate of TAP in a wide range of pH (3–9) (>93%). Twenty-two degradation intermediates were identified and three possible degradation paths of TAP were proposed. Overall, this study provided a novel strategy to remove antibiotics by overcoming the limiting cycle of Fe(III)/Fe(II) in the peroxymonosulfate activation process, which had a great application in water treatment. [ABSTRACT FROM AUTHOR]