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1.
The use of metallic iron filters (Fe0 filters) has been discussed as a promising low‐cost option for safe drinking water production at household level. Filter clogging due to the volumetric expansive nature of iron corrosion has been identified as the major problem of Fe0 filters. Mixing Fe0 and sand (yielding Fe0/sand filters) has been proposed as a tool to extent filter service life. However, no systematic discussion rationalizing Fe0/sand mixtures is yet available. This communication theoretically discussed suitable Fe0/sand proportions for efficient filters. Results suggested that Fe0/sand filters should not contain more that 50 vol% Fe0 (25 wt% when Fe0 is mixed with quartz). The actual Fe0 percentage in a filter will depend on its intrinsic reactivity.  相似文献   

2.
Water treatment with metallic iron (Fe0) is still based on the premise that Fe0 is a reducing agent. An alternative concept stipulates that contaminants are removed by adsorption, co‐precipitation, and size‐exclusion in a reactive filtration process. This article underlines the universal validity of the alternative concept. It is shown that admixing non‐expansive material to Fe0 as a pre‐requisite for sustainable Fe0‐based filtration systems. Fe0‐based filters are demonstrated an affordable, appropriate, and efficient decentralized water treatment technology.  相似文献   

3.
Filtration systems containing metallic iron as reactive medium (Fe0 beds) have been intensively used for water treatment during the last two decades. The sustainability of Fe0 beds is severely confined by two major factors: (i) reactivity loss as result of the formation of an oxide scale on Fe0 and (ii) permeability loss due to pore filling by generated iron corrosion products. Both factors are inherent to iron corrosion at pH > 4.5 and are common during the lifespan of a Fe0 bed. It is of great practical significance to improve the performance of Fe0 beds by properly addressing these key factors. Recent studies have shown that both reactivity loss and permeability loss could be addressed by mixing Fe0 and inert materials. For a non‐porous additive like quartz, the threshold value for the Fe0 volumetric proportion is 51%. Using the Fe0/quartz system as reference, this study theoretically discusses the possibility of (i) replacing Fe0 by bimetallic systems (e.g., Fe0/Cu0), or (ii) partially replacing quartz by a reactive metal oxide (MnO2 or TiO2) to improve the efficiency of Fe0 beds. Results confirmed the suitability of both tools for sustaining Fe0 bed performance. It is shown that using a Fe0:MnO2 system with the volumetric proportion 51:49 will yield a filter with 40% residual porosity at Fe0 depletion (MnO2 porosity 62%). This study improves Fe0 bed design and can be considered as a basis for further refinement and detailed research for efficient Fe0 filters.  相似文献   

4.
Current knowledge of the basic principles underlying the design of Fe0 beds is weak. The volumetric expansive nature of iron corrosion was identified as the major factor determining the sustainability of Fe0 beds. This work attempts to systematically verify developed concepts. Pumice and sand were admixed to 200 g of Fe0 in column studies (50:50 volumetric proportion). Reference systems containing 100% of each material have been also investigated. The mean grain size of the used materials (in mm) were 0.28 (sand), 0.30 (pumice), and 0.50 (Fe0). The five studied systems were characterized (i) by the time dependent evolution of their hydraulic conductivity (permeability) and (ii) for their efficiency for aqueous removal of CuII, NiII, and ZnII (about 0.3 mM of each). Results showed unequivocally that (i) quantitative contaminant removal was coupled to the presence of Fe0, (ii) additive admixture lengthened the service life of Fe0 beds, and (iii) pumice was the best admixing agent for sustaining permeability while the Fe0/sand column was the most efficient for contaminant removal. The evolution of the permeability was well‐fitted by the approach that the inflowing solution contained dissolved O2. The achieved results are regarded as starting point for a systematic research to optimize/support Fe0 filter design.  相似文献   

5.
Over the past 30 years the literature has burgeoned with in situ approaches for groundwater remediation. Of the methods currently available, the use of metallic iron (Fe0) in permeable reactive barrier (PRB) systems is one of the most commonly applied. Despite such interest, an increasing amount of experimental and field observations have reported inconsistent Fe0 barrier operation compared to contemporary theory. In the current work, a critical review of the physical chemistry of aqueous Fe0 corrosion in porous media is presented. Subsequent implications for the design of Fe0 filtration systems are modeled. The results suggest that: (i) for the pH range of natural waters (>4.5), the high volumetric expansion of Fe0 during oxidation and precipitation dictates that Fe0 should be mixed with a non‐expansive material; (ii) naturally occurring solute precipitates have a negligible impact on permeability loss compared to Fe0 expansive corrosion; and (iii) the proliferation of H2 metabolizing bacteria may contribute to alleviate permeability loss. As a consequence, it is suggested that more emphasis must be placed on future work with regard to considering the Fe0 PRB system as a physical (size‐exclusion) water filter device.  相似文献   

6.
Although intensive research on Fe(0) permeable reactive barriers (PRB) for in situ groundwater remediation has been conducted and multiple applications have been installed in the past two decades, some properties of reactive materials in use have not been fully considered and discussed yet. In the present investigation, a typical granular cast iron has been characterized with different techniques. The grain size distribution not only has an influence on the resulting pore geometry and the surface area but material properties significantly differ between fine and coarse grains. Metallographic analyses revealed large differences in both graphite inclusions and microstructures that likely influence the reactivity. Both graphite and cementite proved to be more resistant toward acidic dissolution compared to Fe0. The intrinsic material characteristics described here have not been covered in the existing PRB literature.  相似文献   

7.
A simple and rapid soft‐templating coupled with one‐pot solvent thermal method is developed to synthesize S‐doped magnetic mesoporous carbon (S‐doped MMC). In this method, phenolic resin is used as a carbon precursor and Pluronic copolymer P123 is used as a template and 2,5‐dimercapto‐1,3,4‐thiadiazole is used as sulfur source. Prepared S‐doped MMC processes a high specific surface area, the Fe3O4 particles are well embedded in the mesoporous carbon walls that exhibit a strong magnetic response, and the hydrated iron nitrate loading amount of 0.808 g is the best. Batch adsorption experiments are carried out at different pH, initial concentration, temperature, and contact time on the adsorption of methyl orange (MO) by S‐doped MMC. The kinetic data of the adsorption process are better fitted with pseudo‐second‐order model than the pseudo‐first‐order model. Langmuir model is more suitable for the equilibrium data than Freundlich model. The thermodynamic parameters including ΔG0, ΔH0, and ΔS0 indicate that the adsorption is a feasible, spontaneous, and endothermic process. Finally, it is found that the coexistence of PO43?, NO3?, SO42?, Cl?, and CO32? does not influence the adsorption process. These results illustrate S‐doped MMC can be an efficient adsorbent for the removal of MO from wastewater.  相似文献   

8.
Distinguishing Iron-Reducing from Sulfate-Reducing Conditions   总被引：2，自引：0，他引：2  
Ground water systems dominated by iron‐ or sulfate‐reducing conditions may be distinguished by observing concentrations of dissolved iron (Fe2+) and sulfide (sum of H2S, HS?, and S= species and denoted here as “H2S”). This approach is based on the observation that concentrations of Fe2+ and H2S in ground water systems tend to be inversely related according to a hyperbolic function. That is, when Fe2+ concentrations are high, H2S concentrations tend to be low and vice versa. This relation partly reflects the rapid reaction kinetics of Fe2+ with H2S to produce relatively insoluble ferrous sulfides (FeS). This relation also reflects competition for organic substrates between the iron‐ and the sulfate‐reducing microorganisms that catalyze the production of Fe2+ and H2S. These solubility and microbial constraints operate in tandem, resulting in the observed hyperbolic relation between Fe2+ and H2S concentrations. Concentrations of redox indicators, including dissolved hydrogen (H2) measured in a shallow aquifer in Hanahan, South Carolina, suggest that if the Fe2+/H2S mass ratio (units of mg/L) exceeded 10, the screened interval being tapped was consistently iron reducing (H2～0.2 to 0.8 nM). Conversely, if the Fe2+/H2S ratio was less than 0.30, consistent sulfate‐reducing (H2～1 to 5 nM) conditions were observed over time. Concomitantly high Fe2+ and H2S concentrations were associated with H2 concentrations that varied between 0.2 and 5.0 nM over time, suggesting mixing of water from adjacent iron‐ and sulfate‐reducing zones or concomitant iron and sulfate reduction under nonelectron donor–limited conditions. These observations suggest that Fe2+/H2S mass ratios may provide useful information concerning the occurrence and distribution of iron and sulfate reduction in ground water systems.  相似文献   

9.
Abiotic degradation of chlorinated solvents by reactive iron minerals such as iron sulfides, magnetite, green rust, and other Fe(II)‐containing minerals has been observed in both laboratory and field studies. These reactive iron minerals form under iron‐ and sulfate‐reducing conditions which are commonly found in permeable reactive barriers (PRBs), enhanced reductive dechlorination (ERD) treatment locations, landfills, and aquifers that are chemically reducing. The objective of this review is to synthesize current understanding of abiotic degradation of chlorinated solvents by reactive iron minerals, with special focus on how abiotic processes relate to groundwater remediation. Degradation of chlorinated solvents by reactive minerals can proceed through reductive elimination, hydrogenolysis, dehydrohalogenation, and hydrolysis reactions. Degradation products of abiotic reactions depend on degradation pathways and parent compounds. Some degradation products (e.g., acetylene) have the potential to serve as a signature product for demonstrating abiotic reactions. Laboratory and field studies show that various minerals have a range of reactivity toward chlorinated solvents. A general trend of mineral reactivity for degradation of chlorinated solvents can be approximated as follows: disordered FeS > FeS > Fe(0) > FeS2 > sorbed Fe2+ > green rust = magnetite > biotite = vermiculite. Reaction kinetics are also influenced by factors such as pH, natural organic matter (NOM), coexisting metal ions, and sulfide concentration in the system. In practice, abiotic reactions can be engineered to stimulate reactive mineral formation for groundwater remediation. Under appropriate site geochemical conditions, abiotic reactions can occur naturally, and can be incorporated into remedial strategies such as monitored natural attenuation.  相似文献   

10.
Several methods were employed in the Ardennian rivers (Belgium) to determine the depth of the active layer mobilized during floods and to evaluate the bedload discharge associated with these events. The use of scour chains has shown that the depth of the active layer is systematically less than the b‐axis of the average particle size (D50) of the elements which compose the surface layer of the riffles. This indicates that only a partial transport exists during low magnitude floods. The bedload discharge has been evaluated by combining data obtained using the scour chains technique and the distance covered by tracers. Quantities of sediment transported during frequent floods are relatively low (0·02 t km–2) due to the armour layer which protects the subsurface material. These low values are also related to the fact that the distance calculated for mobilized bedload only applies to tracers fitted with PIT (passive integrated transponder)‐tags (diameter > 20 mm), whereas part of the bedload discharge is composed of sand and fine gravel transported over greater distances than the pebbles. The break‐up of the armour layer was observed only once, for a decennial discharge. During this event, the bedload discharge increased considerably (2 t km–2). The use of sediment traps, data from dredging and a Helley–Smith sampler confirm the low bedload transport in Ardennian rivers in comparison to the bedload transport in other geomorphological contexts. This difference is explained by the presence of an armoured layer but also by the imbricated structures of flat bed elements which increase the resistance to the flow. Finally, the use of the old iron industry wastes allowed to quantify the thickness of the bed reworked over the past centuries. In the Lembrée River, the river‐bed contains slag elements up to a depth of about 50 cm, indicating that exceptional floods may rework the bed to a considerable depth. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

11.
Sulfate in groundwater has been previously shown to change the reactivity of Fe0 in permeable reactive barriers for reducing chlorinated organics. To better understand the effect and mechanism of SO, the degradation of 1,1,1‐trichloroethane (TCA) by Fe0 in unbuffered aqueous solutions with and without SO was investigated. In a Fe0‐TCA‐H2O system with initial pH of 2.0 to 10.0, the maximum removal rate of TCA was achieved at the initial pH 6.0 with pseudo‐first‐order constant Kobs 9.0 × 10?3/min. But in a Fe0‐TCA‐Na2SO4‐H2O system, the removal rate of TCA decreased remarkably with a reduction in Kobs to 1.0 × 10?3/min, and the pH varied from 6.0 to 9.6, indicating an inhibition of TCA dehydrochlorination by SO. Sulfate remarkably inhibited TCA degradation via changing the route of Fe0 dissolution. It accelerated the dissolution of Fe0 and transformed the intermediate form Fe(OH)ads to Fe2(SO4)ads, which weakened the affinity between Fe and TCA, and thus depressed the degradation of TCA by Fe0.  相似文献   

12.
The transport of reactive iron (i.e. colloidal and dissolved) by a glacier‐fed stream system draining a high relief periglacial landscape in the high Arctic archipelago of Svalbard is described. A negative, non‐linear relationship between discharge and iron concentration is found, indicative of increased iron acquisition along baseflow pathways. Because the glaciers are cold‐based and there are no intra‐ or sub‐permafrost groundwater springs, baseflow is principally supplied by the active layer and the colluvial and alluvial sediments in the lower valley. Collectively, these environments increase the flux of iron in the stream by 40% over a floodplain length of just 8 km, resulting in 6 kg Fe km?2a?1 of reactive iron export for a 20% glacierized watershed. We show that pyrite oxidation in shallow‐groundwater flowpaths of the floodplain is the most important source of reactive iron, although it is far less influential in the upper parts of the catchment where other sources are significant (including ironstone and secondary oxide coatings). Microbial catalysis of the pyrite oxidation occurs in the floodplain, enabling rapid, hyporheic water exchange to enhance the iron fluxes at high discharge and cause the non‐linear relationship between discharge and reactive iron concentrations. Furthermore, because the pyrite oxidation is tightly coupled to carbonate and silicate mineral weathering, other nutrients such as base cations and silica are also released to the stream system. Our work therefore shows that high Arctic floodplains should be regarded as critically important regulators of terrestrial nutrient fluxes to coastal ecosystems from glacial and periglacial sources. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

13.
Metallic iron (Fe0) is often reported as a reducing agent for environmental remediation. There is still controversy as to whether Fe0 plays any significant direct role in the process of contaminant reductive transformation. The view that Fe0 is mostly a generator of reducing agents (e.g. H, H2 and FeII) and Fe oxyhydroxides has been either severely refuted or just tolerated. The tolerance is based on the simplification that, without Fe0, no secondary reducing agents could be available. Accordingly, Fe0 serves as the original source of electron donors (including H, H2 and FeII). The objective of this communication is to refute the named simplification and establish that quantitative reduction results from secondary reducing agents. For this purpose, reports on aqueous contaminant removal by Al0, Fe0 and Zn0 are comparatively discussed. Results indicated that reduction may be quantitative in aqueous systems containing Fe0 and Zn0 while no significant reduction is observed in Al0/H2O systems. Given that Al0 is a stronger reducing agent than Fe0 and Zn0, it is concluded that contaminant reduction in Fe0/H2O systems results from synergic interactions between H/H2 and FeII within porous Fe oxyhydroxides. This conclusion corroborates the operating mode of Fe0 bimetallics as H/H2 producing systems for indirect contaminant reduction.  相似文献   

14.
Many of the commonly used analytical techniques for assessing the properties of fluvial suspended particulate matter (SPM) are neither cost effective nor time efficient, making them prohibitive to long‐term high‐resolution monitoring. We present an in‐depth methodology utilizing two types of spectroscopy which, when combined with automatic water samplers, can generate accurate, high‐temporal resolution SPM geochemistry data, inexpensively and semi‐destructively, directly from sediment covered filter papers. A combined X‐ray fluorescence spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy approach is developed to estimate concentrations for a range of elements (Al, Ca, Ce, Fe, K, Mg, Mn, Na, P, Si, Ti) and compounds (organic carbon, Aldithionate, Aloxalate, Fedithionate, and Feoxalate) within SPM trapped on quartz fibre filters at masses as low as 3 mg. Calibration models with small prediction errors are derived, along with mass correction factor models to account for variations in retained SPM mass. Spectral pre‐processing methods are shown to enhance the reproducibility of results for some compounds, and the importance of filter paper selection and homogeneous sample preparation in minimizing spectral interference is emphasized. The geochemical signal from sediment covered filter papers is demonstrated to be time stable enabling samples to be stored for several weeks prior to analysis. Example results obtained during a heavy precipitation event in October 2012 demonstrate the methodology presented here has considerable potential to be utilized for high‐resolution monitoring of SPM geochemistry under a range of in‐stream hydrological conditions. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

15.
High-temperature experiments on ferromagnesian compositions have been hampered by the rapid absorption of up to 95% of the original iron by platinum and 40% by silver-palladium capsules. Molybdenum or iron capsule materials can decrease or alleviate iron loss, but restrict oxygen fugacities to values near the iron-wustite buffer. Because Co2+ is stable at fO2 =HM and because the solubility of Co in platinum in this range of fO2 is ～0.05% at temperatures to 1350°C, its use as an analogue for Fe2+ is possible. In addition, experiments simulating various Fe2+ ratios can be easily performed by choosing appropriate Co2+/Fe3+ ratios. The cobalt phases produced possess brilliant and distinctive colors which are valuable aids in optical identification of minute phases. The cobalt analogue hypothesis was tested with atmospheric pressure experiments in air on the cobalt analogue of the 1921 Kilauea basalt at three simulated Fe2+/Fe3+ ratios. The results were compared with those of R.E.T. Hill (1969) for the natural 1921 basalt. The phase relations were the same, with the cobalt system stability fields systematically shifted by about +50°C. Microprobe analysis of olivines and the coexisting glasses indicate that the distribution of Co2+ between olivine and melt is independent of temperature and liquid composition. Although the analogue liquid composition differs from the equilibrium composition of the natural system, it may be corrected be employing distribution coefficients (KD = 0.61 for the Co system; KD = 0.33 for the Fe system) to closely approximate what the natural system would yield if iron loss did not occur.  相似文献   

16.
The effect of large roughness elements on sand transport efficiency was evaluated on a coastal sand sheet by measuring sand flux with two types of sand traps [Big Spring Number Eight (BSNE) and the Cox Sand Catcher (CSC)] at 30 positions through a 100 m‐long × 50 m‐wide roughness array comprised of 210 elements each with the dimensions 1·17 m long × 0·4 m high × 0·6 m wide. The 210 elements were used to create a roughness density (λ) of 0·022 (λ = n bh/S, where n is the number of elements, b the element breadth, h the element height, and S is the area of the surface that contains all the elements) in an area of 5000 m2. The mean normalized saltation flux (NSF) values (NSF = outgoing sand flux/incoming sand flux) at the furthest downwind distance for the two trap types were 0·44 and 0·41, respectively. This is in excellent agreement with an empirical model prediction of 0·5. The reduction in saltation flux is similar to an earlier separate study for an equivalent λ composed of elements of similar height (0·36 m), even though the roughness element forms were different (rectangular in this study as opposed to circular) as were the horizontal porosity of the arrays (49% versus 16%). This corroborates earlier results that roughness element height is a critical parameter that enhances reduction in sand transport by wind for similar λ configurations. The available data suggest the form of the relationship between transport reduction efficiency and height is likely a power relationship with two limiting conditions: (1) for elements ≤ 0·1 m high the effect is minimized, and (2) as element height matches and then exceeds the maximum height of the saltation layer (≥ 1 m), the effect will stabilize near a maximum of NSF ≈ 0·32. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

17.
A simple, low cost, highly effective, and useful Fenton oxidation treatment of synthetic dye bath waste with pickling liquor as a source of iron (Fe2+ catalyst) is reported. Optimizations of contact time, Fe2+ and H2O2 doses are carried out. Oxidative de‐colorization and degradation of Reactive Blue 4 and Reactive Orange 16 was measured in terms of decrease in absorbance at their wavelength of maximum absorption (RB4, 599 nm; and RO16, 493 nm) and also as reduction in chemical oxygen demand (COD). Approximately, 62% COD was removed in 2 h at optimized doses of Fe2+ (8.95 mM) and H2O2 (61.8 mM) by using pickling waste as a source of Fe2+ catalyst. Similar performance efficiency was observed when neat FeSO4 was used as a source of Fe2+, indicating that pickling liquor can be a low cost source of Fe2+ to treat synthetic dye bath waste by Fenton method.  相似文献   

18.
Magnetic hydroxyapatite (HAP), which combined superparamagnetic Fe3O4 nanoparticles and HAP, composite materials were prepared by ultrasound method in this paper. It has also been found that these materials have the ability to adsorb phenol in wastewater. The magnetic materials were investigated by scanning electron microscope, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, thermal gravimetric analysis, vibrating sample magnetometer, and N2 adsorption in order to elucidate the morphology, structure, and other properties. When the prepared magnetic materials were calcined at 200°C, the prepared Fe3O4 was oxidized to Fe2O3, possessing loose‐shaped holes with a high specific area of 325.2 m2/g, a magnetization intensity of 12.5 emu/g, and the N2 adsorption isotherm belongs to porous adsorption type I. Moreover, the magnetic HAP can adsorb 90% phenol in wastewater. This means that it is an excellent recyclable phenol sorbent for sewage treatment. Experiments confirmed that the Freundlich adsorption isotherms model applies to lower phenol concentrations (0–50 mg/L), while for high phenol concentrations (50–500 mg/L) the Langmuir adsorption isotherms model fits. The magnetic sorbents have the capacity to regenerate after reaching adsorption saturation using ethanol as eluant and external magnetic field as separation unit. The efficiency of adsorption was reduced only by 10% over a six time use period.  相似文献   

19.
The removal of chemical oxygen demand (COD) and phenol from olive oil mill wastewaters (OOMW) was investigated experimentally by using conventional Fenton (CFP) and Fenton type processes (FTP) with zero valent iron (ZVI). Different operational parameters such as initial pH, Fe2+, Fe0, and H2O2 concentrations were examined. Kinetic studies in terms of COD and phenol removals for both CFP and FTP were performed. The original pH value (4.6) of OOMW for CFP was found as the optimum pH. The determined optimum conditions are [Fe2+] = 1500 mg L?1, [H2O2] = 1750 mg L?1, and pH = 4.6 for CFP; [Fe0] = 2000 mg L?1, [H2O2] = 2000 mg L?1, and pH = 3 for FTP. 82.4% COD and 62% phenol removals were performed under the optimum conditions by CFP, while 82% COD and 63.4% phenol were removed by FTP. According to the results of kinetic studies, it was observed that COD and phenol were removed by FTP more rapidly, compared to CFP. Consequently, it was determined that both CFP and FTP were effective processes for the pretreatment of OOMW.  相似文献   

20.
Simulated rainfall experiments were performed on bare, undecomposed litter layer and semi-decomposed litter layer slopes with litter biomasses of 0, 50, 100 and 150 g m−2, respectively, to evaluate the effect of the undecomposed layer and semi-decomposed layer of Quercus variabilis litter on the soil erosion process and the particle size distribution of eroded sediment. The undecomposed layer and semi-decomposed layer of litter reduced the runoff rate by 10.91–27.04% and 12.91–36.05%, respectively, and the erosion rate by 13.35–40.98% and 17.16–59.46%, respectively. The percentage of smaller particles (clay and fine silt particles) decreased and the percentage of larger particles (coarse silt and sand particles) increased with an increased rainfall duration on all treated slopes, while the extent of the eroded sediment particle content varied among the treated slopes with the rainfall duration, with bare slopes exhibiting the largest variability, followed by undecomposed litter layer slopes and finally semi-decomposed litter layer slopes. The clay and sand particles were transported as aggregates, and fine silt and coarse silt particles were transported as primary particles. Compared with the original soil, sediment eroded from all treated slopes was mainly enriched in smaller particles. Furthermore, the loss of the smaller particles from the undecomposed litter layer slopes was lower than that from the semi-decomposed litter layer slopes, indicating that the undecomposed litter layer alleviated soil coarsening to some extent. The findings from this study improve our understanding of how litter regulates slope erosion and provide a reference for effectively controlling soil erosion.  相似文献   

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