Role of iron surface oxidation layers in decomposition of azo-dye water pollutants in weak acidic solutions

Mielczarski, J.; Montes-Atenas, Gonzalo; Mielczarski, Ela

doi:10.1016/j.apcatb.2004.09.017

Cited by 159 publications

(104 citation statements)

References 34 publications

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“…The MTW concept is described in several recent works [5,14,15]. From the discussion above, the MTW concept suggests that Fe 0 serves as reducing agent for a contaminant (direct reduction) and the oxide film serves as catalyst for indirect reduction through adsorbed Fe II (structural Fe II or Fe II (s) ) or H 2 [2].…”

Section: The Mtw Concept and Its Limitationsmentioning

confidence: 99%

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

Noubactep¹

2008

TOENVIRSJ

110

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Abstract:The mechanism of aqueous contaminant removal by elemental iron (Fe 0 ) materials (e.g., in Fe 0 -H 2 O systems) has been largely discussed in the "iron technology" literature. Two major removal mechanisms are usually discussed: (i) contaminant adsorption onto Fe 0 oxidation products, and (ii) contaminant reduction by Fe 0 , Fe II or H/H 2 . However, a closer inspection of the chemistry of the Fe 0 -H 2 O system reveals that co-precipitation could be the primary removal mechanism. The plausibility of contaminant co-precipitation with iron corrosion products as independent contaminant removal mechanism is discussed here. It shows that the current concept does not take into account that the corrosion product generation is a dynamic process in the course of which contaminants are entrapped in the matrix of iron hydroxides. It is recalled that contaminant co-precipitation with iron hydroxides/oxides is an unspecific removal mechanism. Contaminant co-precipitation as primary removal mechanism is compatible with subsequent reduction and explains why redoxinsensitive species are quantitatively removed. Adsorption and co-precipitation precede reduction and abiotic reduction, when it takes place, occurs independently by a direct (electrons from Fe 0 ) or an indirect (electrons from Fe II /H 2 ) mechanism.

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Section: The Mtw Concept and Its Limitationsmentioning

confidence: 99%

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

Noubactep¹

2008

TOENVIRSJ

110

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“…It should be acknowledged that several studies have investigated the role of iron corrosion products on the process of contaminant removal in Fe 0 -H 2 O systems [35][36][37][38][39][40]. However, the objective of the investigators was mostly to explain the role of the film in mediating direct contaminant reduction in Fe 0 -H 2 O systems.…”

Section: Introductionmentioning

confidence: 99%

A CRITICAL REVIEW ON THE PROCESS OF CONTAMINANT REMOVAL IN FE⁰–H₂O SYSTEMS

Noubactep¹

2008

Environmental Technology

343

308

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A central aspect of the contaminant removal by elemental iron materials (Fe 0 or Fe 0 materials) is that reduction reactions are mediated by the iron surface (direct reduction). This premise was introduced by the pioneers of the reactive wall technology and is widely accepted by the scientific community. In the meantime enough evidence has been provided to suggest that contaminant reduction through primary corrosion products (secondary reductants) does indeed occur (indirect reduction). It was shown for decades that iron corrosion in the pH range of natural waters (4-9) inevitably yields an obstructive oxide film of corrosion products at the metal surface (oxide film). Therefore, contaminant adsorption on to corrosion products and contaminant co-precipitation with corrosion products inevitably occurs. For adsorbed and coprecipitated contaminants to be directly reduced the oxide film should be electronic conductive. This study argues through a literature review a series of points which ultimately lead to the conclusion that, if any quantitative contaminant reduction occurs in the presence of Fe 0 materials, it takes place within the matrix of corrosion products and is not necessarily a direct reduction. It is concluded that Fe 0 materials act both as source of corrosion products for contaminant adsorption/coprecipitation and as a generator of Fe II and H 2 (H) for possible catalytic contaminant reduction.

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“…This weakness is partly due to the failure of pioneers works of the iron technology to properly consider the available literature on: (i) iron corrosion, and (ii) the use of elemental iron in the synthetic organic chemistry. Nevertheless, the authors may have pay more attention to the work of Mielczarski et al [12] who discussed in some details the role of oxide-film on the removal of azo dyes by Fe 0 in weak acidic solutions. Clearly a different choice in experimental conditions may have increased the value of the interesting work of Hou et al [1].…”

Section: Discussionmentioning

confidence: 99%

“…Secondly, considering the large variation in the pK a values of the individual azo dyes, their impact in the interaction with iron surface and the surface of iron oxides/hydroxides should have been addressed, for example by determining the point of zero charge (pzc) of the used Fe 0 material and giving that of possible iron oxides and hydroxides relevant to the experimental conditions [12]. Figure 1 shows that from the six investigated initial pH values, only one (pH 2) was inferior to all pK a values whereas none was superior to the pK a of Orange I (pK a = 8.2).…”

Section: Rationale For Experimental Conditionsmentioning

confidence: 99%

Comments on “The effect of substituent groups on the reductive degradation of azo dyes by zerovalent iron” by M. Hou, et al. [J. Hazard. Mater. 145 (2007) 305]

Noubactep

2007

Journal of Hazardous Materials

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Role of iron surface oxidation layers in decomposition of azo-dye water pollutants in weak acidic solutions

Cited by 159 publications

References 34 publications

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

A CRITICAL REVIEW ON THE PROCESS OF CONTAMINANT REMOVAL IN FE⁰–H₂O SYSTEMS

Comments on “The effect of substituent groups on the reductive degradation of azo dyes by zerovalent iron” by M. Hou, et al. [J. Hazard. Mater. 145 (2007) 305]

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Role of iron surface oxidation layers in decomposition of azo-dye water pollutants in weak acidic solutions

Cited by 159 publications

References 34 publications

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

Processes of Contaminant Removal in “Fe0-H2O” Systems Revisited: The Importance of Co-Precipitation

A CRITICAL REVIEW ON THE PROCESS OF CONTAMINANT REMOVAL IN FE0–H2O SYSTEMS

Comments on “The effect of substituent groups on the reductive degradation of azo dyes by zerovalent iron” by M. Hou, et al. [J. Hazard. Mater. 145 (2007) 305]

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A CRITICAL REVIEW ON THE PROCESS OF CONTAMINANT REMOVAL IN FE⁰–H₂O SYSTEMS