An Analysis of the Evolution of Reactive Species in Fe0/H2O Systems 1 
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Noubactep C. 
Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, D - 37077 Göttingen, Germany. 
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e-mail: cnoubac@gwdg.de; Tel. +49 551 39 3191, Fax: +49 551 399379 
 
Abstract 
Aqueous contaminant removal in the presence of metallic iron (e.g. in Fe0/H2O systems) is 
characterized by the large diversity of removing agents. This paper analyses the synergistic 
effect of adsorption, co-precipitation and reduction on the process contaminant removal in 
Fe0/H2O systems on the basis of simple theoretical calculations. The system evolution is 
characterized by the percent Fe0 consumption. The results showed that contaminant reduction 
by Fe0 is likely to significantly contribute to the removal process only in the earliest stage of 
Fe0 immersion. With increasing reaction time, contaminant removal is a complex interplay of 
adsorption onto iron corrosion products, co-precipitation or sequestration in the matrix of iron 
corrosion products and reduction by Fe0, FeII or H2/H. The results also suggested that in real 
world Fe0/H2O systems, any inflowing contaminant can be regarded as foreign species in a 
domain of precipitating iron hydroxides. Therefore, current experimental protocols with high 
contaminant to Fe0 ratios should be revisited. Possible optimising of experimental conditions 
is suggested. 
Keywords: Adsorption; Co-precipitation; Iron Reactivity; Reduction; Zerovalent iron. 
Capsule: A Fe0/H2O system should be regarded as a domain of precipitating iron oxides. 
Introduction 
Widespread groundwater contamination has prompted intensive efforts to find efficient and 
affordable remediation technologies. Recently, the introduction of in situ permeable reactive 
barriers for groundwater remediation [1,2] has attracted the attention of environmental 
researchers. Permeable reactive barriers consist of a cost-effective material which functions as 
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a contaminant removing agent. The contaminated groundwater flows toward the barrier, 
which contains a removing agent. The groundwater passing through a reactive barrier is 
ideally completely freed from contaminants [3-5]. 
In the last two decades metallic iron (Fe0) has been extensively used in remediation schemes 
to effectively remove a wide variety of inorganic and organic contaminants in reactive 
barriers [3-6]. Ideally, Fe0 is oxidized only from the oxidized form of the contaminant (Ox) 
which reduction yields a corresponding reduced form (Red) (Eq. 1 - Tab. 1). Unfortunately, 
water is present in stoichiometric abundance (solvent), and is corrosive to Fe0 both under 
anoxic (Eq. 2) and oxic (Eq. 3) conditions ([7] and ref therein). FeII species resulting from Eq. 
1 to Eq. 3 may be oxidized to FeIII species by molecular O2 or other available oxidants (Ox1: 
contaminant, MnO2) (Eq. 4a,b). Under anoxic conditions, H2 from Eq. 2 may reduce the 
contaminant (Eq. 5). The process of H2O reduction by Fe0 obviously reduces the efficiency of 
the decontamination process (H2O as concurrent for contaminant) and also increases the pH 
of the system, promoting the formation of iron hydroxides (Eq. 6 and 7). Iron hydroxides are 
then transformed through dehydration and recrystallisation to various iron oxides depending 
on the geochemical conditions [3,8,9]. Iron (hydr)oxides are good adsorbent for several 
contaminants (Eq. 9). During their precipitation, iron hydroxides may sequestrate contaminant 
in their matrix (Eq. 10). 
The presence of iron hydroxides and other ferrous and ferric oxides (Eq. 6 to 8) causes 
passivation of the Fe0 surface [3,8-10]. As an oxide layer is formed on the Fe0 surface, a 
contaminant should migrate across the film to adsorb on the Fe0 surface and undergo 
reduction. Alternatively, the oxide layer should be electronic conductive to warrant electron 
transfer [11,12]. On the other hand FeII adsorbed on a mineral surface (structural FeII or FeII(s)) 
has been reported to be a very strong reducing agent, suggesting that beside Fe0 and H2, 
dissolved FeII and structural FeII are further contaminant reducing agents in Fe0/H2O systems 
(table 1). 
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The ongoing discussion over the relative importance of adsorption and reduction on the 
process of contaminant removal in Fe
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0/H2O systems [3,9-14] illustrates the challenge in 
assessing the environmental relevance of laboratory results. The potential of Fe0/H2O systems 
for reductive transformation of various contaminants is well-established. However, the precise 
mechanism and the extent of reductive transformation remains controversial and has been 
recently kindled by considering the importance of contaminant co-precipitation [15,16]. 
The most important feature characterizing a Fe0/H2O system is that the weight fraction of iron 
corrosion products increases from zero at the beginning of the experiment to more or less 
higher proportions depending on the reaction progress (Fe0 consumption). The large changes 
in the solid composition during the reaction certainly influence the mass transfer of species to 
the Fe0/H2O interface and thereby play a significant role in the determination of reaction rates. 
However, as corrosion products are not inert, they actively participate to contaminant 
removal. The present communication aims at using theoretical calculations (computer-based 
analysis without numerical simulation) to better understand the reactivity of Fe0/H2O systems 
toward contaminant removal. Clearly, simulations for a well-thought-out experimental plan 
will be given. From the simulation results, a discussion of the suitability of experimental 
conditions will be given. The main goal is to purchase researchers with a solid guidance for 
purposeful experimental design for the investigation of Fe0/H2O systems. 
Background 
Contaminant removal in Fe0/H2O systems is neither a purely chemical/electrochemical 
reduction nor a purely physical adsorption process. Rather, it is the result of a complex 
interplay of processes (adsorption, co-precipitation, reduction) dependent on Fe0 type 
(intrinsic reactivity), temperature, water chemistry, hydrodynamic conditions, and microbial 
community. The literature is overwhelmingly dominated by studies considering Fe0 as the 
primary reductant for contaminants (direct reduction) [4-6,11,12,17]. It has been recently 
suggested that the chemical reactivity of Fe0 (iron corrosion) has not been properly considered 
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while using Fe0 as remediation medium [15,16]. In fact, as discussed above, the Fe0 reactivity 
yielding contaminant removal is not necessarily an intrinsic property (reduction by electrons 
from Fe
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0). Contaminant removal could be mostly associated with primary (FeII, H/H2) and 
secondary (iron oxyhydroxides) iron corrosion products. This suggests that the effectiveness 
of Fe0 for abiotic contaminant removal might be mostly related to the above-enumerated 
process-specific factors (temperature, water chemistry, and hydrodynamic conditions) [15]. 
Furthermore, the presence of other substances (“electron shuttles”), and impurities with 
catalytic effects might be important for the process of contaminant removal in Fe0/H2O 
systems [4,12]. The next section discusses the relative importance of the reactive species in 
Fe0/H2O systems. 
Evolution of reactive species in a Fe0/H2O system 
A Fe0/H2O system is primarily made up of elemental iron (Fe0) and an aqueous solution 
(H2O). Considering for simplification, that Fe0 is initially freed from atmospheric corrosion 
products (e.g. acid washed and vacuum dried), the initial system (t = 0) contains only Fe0 as 
reactant (adsorbent and/or reductant) for dissolved species (including contaminants). Aqueous 
iron oxidation (immersed corrosion) is known to be effective both under anoxic and oxic 
conditions [18,19], yielding at the term a layer of primarily non-protective oxide film on Fe0 
[20,21]. Therefore, from the early stage of iron immersion on, the impact of in situ generated 
reactants (FeII, H/H2, iron hydroxides and oxides) should be properly discussed. Moreover, 
once the oxide film is formed it constitutes a physical barrier shielding the Fe0 surface from 
dissolved species [15,22,23]. To reach the Fe0 surface any dissolved species has to move 
across the oxide film. With regard on the quantitative evolution of reactive species in Fe0/H2O 
systems, a purposeful system analysis has not been performed by the pioneers of the iron 
barrier technology. In fact, they mostly considered the low potential (-0.44 V) of the redox 
couple FeII/Fe0 to explain the observed contaminant reduction in Fe0/H2O systems [11,12]. 
However, a survey of the electrode potentials of the redox couples of iron (-0.44 V for 
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FeII/Fe0 and -0.35 to -0.65 V for FeIII(s)/FeII(s) [24]) suggests that, from a pure thermodynamic 
perspective, in some circumstances (E < -0.44 V), contaminant reduction by Fe
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II
(s) might be 
more favourable than reduction by electrons from Fe0. From a pure qualitative perspective it 
can be concluded that investigations of contaminant reduction by Fe0 (direct reduction) have 
to be performed under conditions where the interferences of all other removal processes 
(adsorption, co-precipitation and indirect reduction) are absent or minimal. This premise 
implies, that the formation of Fe corrosion products should be kept as low as possible. 
Therefore, (i) too large Fe0 loadings should be avoided and for a given Fe0 loading, (ii) too 
intensive mixing operations should be avoided. The next section will illustrate this on a 
quantitative perspective. 
Quantification of Reactive Species in a Fe0/H2O System 
To demonstrate the importance of in situ generated reactants on the process of contaminant 
removal in Fe0/H2O systems, lets consider contaminant removal experiments with 0 to 50 g L-
1 of an iron-based alloy (Fe0 material) containing 92 % Fe. The experiments are performed at 
pH > 4 in 20 mL of an aqueous solution containing a reducible contaminant (Ox) which 
reduced form (Red) is harmless or low soluble. Whether Red remains in solution or not, is it 
operationally considered in this work as removed. The aqueous speciation of Ox and Red and 
thus their affinity to adsorptive surfaces is necessarily pH dependant. At pH > 4 the iron 
surface is covered by insoluble oxide layers [18,22]. Whether the contaminant is reduced or 
not, it might be removed from the aqueous phase by adsorption and/or co-precipitation 
[15,25-27]. Therefore, “contaminant removal” and “contaminant reduction” should never be 
interchanged randomly. Moreover, when a contaminant is effectively reduced the exact 
reduction mechanism (direct or indirect) is difficult to access. In the field the situation is 
exacerbated by microbial mediated reduction. The question arises whether it is possible to 
distinguish between adsorption, co-precipitation, and reduction in laboratory experiments. 
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Adsorption, Co-precipitation, or Reduction? 130 
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Figure 1 depicts the results of the simulation of contaminant removal by: (i) direct reduction 
(Fig. 1a), (ii) physical adsorption (Fig. 1b), and (iii) co-precipitation (Fig. 1c) when 1 to 10 % 
of the initial amount of iron has reacted (n0/100 to n0/10). Reduction by FeII(aq), FeII(s), H2/H 
(indirect reduction) is not considered for simplification. For comparison, a reference system 
without Fe0 addition (blank) is presented. It is assumed that the contaminant is reduced by Fe0 
in a 1:1 ratio (assumption 1), that each mole of contaminant is adsorbed by two moles of 
FeOOH (assumption 2), and that each mole of contaminant is co-precipitated with four moles 
of Fe(OH)2 or Fe(OH)3 (assumption 3), FeOOH and Fe(OH)2 resulting from Fe0 oxidation. 
Assumption 2 is made to account for large molecules while assumption 3 is somewhat 
arbitrary but intends to considered the non-specific nature of co-precipitation (simple 
sequestration or entrapment, physical process). The simulated systems contains 100 μmoles of 
contaminant in 20 mL (5 mmol L-1). This corresponds for instance to 260 mg L-1 CrVI, 1.190 
mg L-1 UVI, 562.5 mg L-1 chlorophenol, or 1.596 mg L-1 methylene blue. This initial 
concentration is roughly one order of magnitude higher than those currently used in removal 
experiments for natural waters and wastewaters. Such a large initial concentration was 
nevertheless used to evidence the abundance of corrosion products relative to available 
amounts of contaminant. 
From Fig 1a it can be seen that under given experimental conditions, contaminant reduction 
(assumption 1) is quantitative for all tested extents of Fe0 consumption (1 to 10 %) for Fe0 
loadings equal or higher than 35 g L-1. At the same time, at least 57 % of the initial available 
contaminant could have been removed by pure adsorption (assumption 2) onto FeOOH (Fig 
1b) and 29 % by non-specific co-precipitation (assumption 3) with Fe(OH)2 (Fig 1c). As soon 
as corrosion products (Fe(OH)2, Fe(OH)3) start to precipitate they inevitably adsorb FeII from 
continuously corroding Fe0 yielding more reductive adsorbed FeII (so-called structural FeII) 
for contaminant reduction. Figure 1b clearly shows that for 10 % Fe0 consumption (n0/10) 
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more than 80 % of the initial amount of contaminant could be removed from the aqueous 
solution by pure physical adsorption for all tested Fe
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0 loadings (5 ≥ g L-1). From Fig. 1c it can 
be seen that at least 42 % could be removed by co-precipitation with in-situ formed corrosion 
products. These results suggest that when a 5 mmol L-1 contaminant solution is treated by 5 g 
L-1 Fe0 (containing 92 % Fe), and only 10 % of the used Fe0 reacts, contaminant removal by 
(i) direct reduction, or (ii) pure adsorption onto in situ generated corrosion products may be 
quantitative (> 80 % removal efficiency). In the same time the contribution of co-precipitation 
for contaminant removal could be more than 40 %. The minimal resulting percent molar ratio 
Fe/Ox is 60 %. This means that less than 40 % contaminant in a matrix of initially amorphous 
iron oxide matrix. Therefore, when a too high Fe0 loading is used in an experiment, 
distinguishing the mechanism responsible for contaminant removal is a very complex issue 
(see below). Furthermore, because contaminants (Ox) and reduction products (Red) might co-
precipitate with iron corrosion products, the extent of contaminant reduction is difficult to 
assess. Moreover, because removed Ox and Red are partly sequestrated in the matrix of iron 
corrosion products a purposeful mass balance can only be done if corrosion products are 
completely digested. Contrary to the simulated case of this work (5 g L-1 Fe0), studies using 
less than 20 g L-1 Fe0 are scarce. Furthermore, experiments are sometimes performed under 
high mixing conditions (up to 500 min-1) [28,29], possibly yielding a larger extent of Fe0 
consumption (> 10 %) for tested experimental durations and thus data that are more difficult 
to interpret as shown in the next section. 
Chemical transformation vs. physical processes 
To further evidence the importance of experimental conditions for the significance of 
expected results, the processes in a Fe0/H2O system can be abstractly considered independent 
and subdivided into chemical transformations (contaminant reduction, iron hydroxide 
precipitation) and physical processes (contaminant adsorption, contaminant co-precipitation). 
With respect to contaminant removal, all chemical transformations are called reduction and 
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physical processes are called fixation (Fig. 2). Fixation is thus the sum of adsorption and co-
precipitation while only direct reduction is considered. Figure 2 shows clearly that for 1 % 
material consumption (Fig. 2a) the extends for contaminant fixation and contaminant 
reduction are very closed for all Fe
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0 loadings. Therefore, if the studied contaminant is reduced 
to a low soluble species (e.g. UVI to UIV), contaminant removal is twice larger than 
contaminant reduction. For organic contaminant the result is quite the same as the processes 
are considered independent, the difference is that reduced species remain in the aqueous phase 
and the strength of contaminant fixation may be lower. For 10 % material consumption (Fig. 
2b), both contaminant reduction and contaminant fixation are quantitative (100 %). This result 
corroborates the statement that low Fe0 loadings should be used when reduction is to be 
investigated. This operation targets at avoiding large amounts of corrosion products. But 
which real world situation should be simulated by low Fe0 loadings or low amounts of iron 
(hydr)oxides? 
Although the iron wall technology is demonstrably efficient, the presentation above 
demonstrates that reported experiments are disconnected from reality. In fact, the main 
conclusion from the hitherto presentation is that in nature, contaminants flowing into a 
Fe0/H2O system are foreign species in a system of precipitating iron oxide (statement 1). This 
situation is illustrated by Fig. 3. Figure 3 shows the evolution of the molar ratio contaminant 
to Fe (Ox/Fe) in the simulated batch systems as function of the Fe0 loading. It can be seen that 
when the Fe0 consumption varies from 1 to 10 % the Ox/Fe-values vary from 86 to 6 %. 
Material consumption of 1 to 5 % can be attributed to the initial stage of the barrier 
installation, with increasing service life Fe0 consumption will increase to reach 100 % at 
depletion. Therefore, systems with high Ox/Fe-values (e.g. > 25 %) are not likely to be 
encountered in nature where diluted contaminated waters come in contact with an iron bed 
(Fe0 covered with an oxide layer). However, systems with high Ox/Fe-values are the most 
currently investigated in the laboratory, particularly in batch experiments. In long term 
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column experiments with significantly low initial contaminant concentrations on the contrary 
relevant results can be achieved. 
In conclusion, theoretical calculation demonstrates that contaminant removal in Fe0/H2O 
systems is necessarily a synergistic effect of adsorption, co-precipitation and reduction. The 
resulting removal extent is much more than that of their separate effects. While adsorption 
and reduction have been largely considered, co-precipitation has been mostly overseen (in 
particular for organic species). The theoretical calculation shows that to properly investigate 
contaminant reduction, investigations should be performed under conditions where corrosion 
products are minimal: e.g. early stage of Fe0 immersion and under experimental conditions 
avoiding rapid corrosion. Moreover, results from such investigations will only be of 
qualitative value because in field Fe0/H2O systems, corrosion products are abundantly present 
before contaminant inflow. 
Improved Experimental Conditions 
Typically, factors controlling Fe0 consumption (Fe0 reactivity) have been treated 
independently and with use of a variety of methodologies, for example: hydrogen production 
[30,31]; Fe0 oxidative dissolution in ethylenediaminetetraacetic acid - EDTA [32,33] or more 
commonly, the extend of contaminant removal [34,35]. Experimental measurements of 
aqueous contaminant removal coupled to Fe0 consumption are usually normalized to Fe0 
specific surface area [36]. However, the Fe0 area is only one of numerous reactivity factors. 
Therefore, it is difficult to compare published kinetic data. To circumvent this inherent 
difficulty, the analysis in this study has considered the percent Fe0 consumption. It is obvious 
that the kinetic of consumption depends on several factors [11,32,34,37] like Fe0 size (nm, 
μm, mm), Fe0 composition (C, Cr, Ni contents), water temperature, water chemistry, and 
hydrodynamic conditions. All these factors will influence the nature and crystallinity of 
formed corrosion products and possibly the strength of contaminant fixation. However, for the 
present discussion considers solely the abundance of Fe0 corrosion products. 
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To minimize the abundance of iron corrosion products in a Fe0/H2O system, the following 
operations can be undertaken: (i) use the lowest possible Fe
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0 loading (e.g. < 5 g L-1); (ii) work 
under non-disturbed conditions (mixing speed 0 min-1) or low mixing conditions (e.g. < 
critical value to be identified in preliminary studies); (iii) used a less reactive material; (iv) 
work at low temperature (e.g. 15 °C). From the discussion above, it is evident that the 
minimization of the abundance of iron corrosion products is a tool to investigate the role of 
Fe0 on the process of contaminant reduction. Because in a real world reactive wall corrosion 
products are available and abundant prior to contaminant inflow, a more purposeful approach 
is to characterize the process of contaminant removal in the Fe0/FexOy/H2O, FexOy 
representing the in situ generated oxide film on Fe0. For this purpose the systems could be 
preconditioned by several ways to obtain different amounts of FexOy in the starting systems. 
The simplest way is to allow oxide film formation in time series, for example 0 to 6 weeks 
before the beginning of the experiment (t = 0; time of contaminant addition) with an acid-
washed Fe0. After a given reaction time (t > 0; e.g. three weeks) the extent of contaminant 
removal and the strength of contaminant fixation can be purposefully discussed. In discussing 
the strength of contaminant fixation, it should be kept in mine that a co-precipitated 
compound can only be released when iron (hydr)oxide is dissolved. 
Conclusions 
This study has presented an analysis of the evolution of reactive species in Fe0/H2O systems 
with relative little attention on published results. The discussion is performed on a relevant 
case study for Fe0 conversion/consumption varying from 1 to 10 %. Although the commonly 
cited reaction for reducible contaminant removal in Fe0/H2O systems is given by Eq. 1 (also 
see table 1), the simulations of this study demonstrated that direct reduction by Fe0 is only one 
of three potential contaminant reducing mechanisms and is not always the more favourable on 
a pure thermodynamic perspective. Furthermore, contaminant adsorption and co-precipitation 
always occur (table 1) 
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Fe0 + Ox ⇒ FeII + Red    (1) 260 
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The oxidative dissolution of Fe0 (iron corrosion) yielding aqueous contaminant removal has 
been extensively studied by environmental scientists during the past two decades. However, 
previous studies have generally concentrated on systems with high contaminant abundance 
(relative to Fe corrosion products). Such systems are non-representative for field situations as 
a rule. Therefore, existing models for designing iron barriers and predicting their long-term 
performance are based on results from inappropriate experimental conditions. Consequently, 
these models should be revisited. When revisiting available models, the first key question to 
address is, what are the processes relevant at the interface Fe0/FexOy/H2O? Experimental work 
on this issue is required before geochemical remediation strategies with Fe0 be effectively 
revisited. 
This article has demonstrated the importance of appropriate system analysis as a scientific 
method [38] prior to cost-intensive experimentations. The presented geochemical system 
analysis clearly indicates that in a real world Fe0/H2O system, any contaminant can be 
regarded as foreign species in an “ocean” of iron oxides (statement 1). Statement 1 should be 
used as primary point of departure for the future investigations and/or for re-evaluation of the 
abundant literature on environmental remediation with metallic iron. 
Acknowledgments 
The manuscript was improved by the insightful comments of anonymous reviewers from 
Journal of Hazardous Materials. This work was supported by the Deutsche 
Forschungsgemeinschaft (DFG-No 626/2-2). 
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 15
Table 1: Survey of reactive species for contaminant removal in a Fe0/H2O system. Fe0, 
Fe
370 
371 
372 
373 
374 
375 
II
(aq), FeII(s), and H2 are possible reducing agents; iron hydroxides and oxides (Fe(OH)2, 
Fe(OH)3, FeOOH, Fe2O3, Fe3O4) are adsorbing agents. Additionally contaminants may be co-
precipitated by precipitating iron (hydr)oxides. Water is a concurrent for contaminants for Fe0 
oxidation. Ox the oxidized form of a contaminant yield Red upon reduction. Ox1/Red1 is 
another redox couple present in the system (e.g. O2/OH- or MnO2/MnII). 
 Reaction Eq. 
 Fe0  +  Ox   ⇔ Fe2+  +  Red [1] 
 Fe0  +  2 H2O  ⇔ Fe2+  +  H2  +  2 OH- [2] 
 2 Fe0  +  O2  +  2 H2O ⇔ 2 Fe2+  +  4 OH- [3] 
 FeII(aq)  +  Ox1   ⇔ FeIII(aq)  +  Red1 [4a] 
 FeII(s)  +  Ox1   ⇔ FeIII(s)  +  Red1 [4b] 
 H2  +  Ox   ⇔ H+  +  Red [5] 
 Fe2+  +  2 OH-  ⇔ Fe(OH)2 [6] 
 Fe2+  +  3 OH-  ⇔ Fe(OH)3 [7] 
 Fe(OH)2, Fe(OH)3   ⇒ FeOOH, Fe2O3, Fe3O4 [8] 
 FexOy  +  Ox   ⇔ FexOy-Ox [9] 
 Ox + n Fex(OH)y(3x-y) ⇒ Ox[Fex(OH)y(3x-y)]n [10] 
376 
377 
378 
 
 
 16
Figure 1 378 
0 10 20 30 40 50
0
20
40
60
80
100
(a) reduction
 blanc
 n0/100
 n0/75
 n0/50
 n0/35
 n0/15
 n0/10
co
nt
am
in
an
t /
 [μ
m
ol
]
iron loading / [g L-1]
 379 
380  
0 10 20 30 40 50 60 70
0
20
40
60
80
100
(b ) adsorp tion
 b la n c
 n 0/1 0 0
 n 0/7 5
 n 0/5 0
 n 0/3 5
 n 0/1 5
 n 0/1 0
re
si
du
al
 O
x 
/ [
μm
ol
]
iron  load ing  / [g  L -1]
 381 
0 10 20 30 40 50 60 70
0
20
40
60
80
100
(c) co-precipitation
 blanc
 n0/100
 n0/75
 n0/50
 n0/35
 n0/15
 n0/10
re
si
du
al
 O
x 
/ [
μm
ol
]
iron loading / [g L-1]
 382 
383 
 17
Figure 2 383 
0 10 20 30 40 50
0
20
40
60
80
100
(a): n0/100
 reduction
 adsorption
 co-precipitation
 fixation
O
x 
re
m
ov
al
 / 
[%
]
Fe0 loading / [g L-1]
 384 
385  
0 10 20 30 40 50
0
20
40
60
80
100
(b): n0/10
 reduction
 adsorption
 co-precipitation
 fixation
O
x 
re
m
ov
al
 / 
[%
]
Fe0 loading / [g L-1]
 386 
387 
 18
Figure 3 387 
388  
0 10 20 30 40 50
0
10
20
30
40
50
60
70
80
90
 n0/100
 n0/75
 n0/50
 n0/35
 n0/15
 n0/10
O
x/
Fe
 / 
[%
]
iron loading / [g L-1]
 389 
390 
 19
Figure Captions 390 
391 
392 
393 
394 
395 
396 
397 
398 
399 
400 
401 
402 
403 
404 
405 
406 
407 
408 
409 
410 
411 
412 
 
Figure 1: Evolution of contaminant removal by direct reduction through elemental iron (a), 
and its corrosion products: adsorption (b) and co-precipitation (c) in a batch 
system as a function of Fe0 loading. Amorphous FeOOH is taken as the model 
corrosion product. It is assumed that each mole of the reducible contaminant 
adsorbs onto two moles of FeOOH and each mole of contaminant co-precipitates 
with four moles of FeOOH. The lines are not fitted functions, they simply 
connected points to facilitate visualization. 
 
Figure 2: Comparison of the extent of contaminant (Ox) removal by direct reductive 
transformation (reduction by Fe0) and physical processes (fixation = adsorption + 
co-precipitation) in the simulated system as function of Fe0 mass loading for 1 % 
(a) and 10 % (b) Fe0 consumption. It is assumed for simplifications that 
adsorption, co-precipitation, and reduction are independent contaminant removal 
processes. Indirect reduction (FeII, H2/H) is also not considered. 
 
Figure 3: Evolution of molar ratio contaminant to iron (Ox/Fe) in the simulated batch systems 
as a function of Fe0 loading. The simulation are performed for Fe0 consumption 
varying from 1 % (n0/100) to 10 % (n0/10) and a contaminant concentration 
yielding 100 μM substance in 20 mL solution. The lines are not fitted functions, 
they simply connected points to facilitate visualization. 
 
 20