Thermodynamic Equilibria in Aqueous Suspensions of Synthetic and

Environ. Sci. Technol. 1998, 32, 1058-1068

Thermodynamic Equilibria in Aqueous Suspensions of Synthetic and Natural Fe(II)-Fe(III) Green Rusts: Occurrences of the Mineral in Hydromorphic Soils J E A N - M A R I E R . G EÄ N I N , * , † G U I L H E M B O U R R I EÄ , ‡ , § FABIENNE TROLARD,‡ MUSTAPHA ABDELMOULA,† ANNE JAFFREZIC,‡ PHILIPPE REFAIT,† V EÄ R O N I Q U E M A I T R E , ‡ BERNARD HUMBERT,† AND ADRIEN HERBILLON| Laboratoire de Chimie Physique pour l’Environnement, UMR 7564 CNRS, Universite´ Henri Poincare´, Nancy 1, and De´partement Science des Mate´riaux, ESSTIN, Universite´ H. Poincare´, 405 rue de Vandoeuvre, F-54600 Villers-le`s-Nancy, France, INRA, U.R. de Science du Sol et de Bioclimatologie, 65 rue de Saint Brieuc, F 35042 Rennes Cedex, France, Geósciences Rennes, UPR 4661 CNRS, Universite´ de Rennes, 1 Campus de Beaulieu, F 35042 Rennes Cedex, France, and Centre de Pe´dologie Biologique, UPR 6831 CNRS, Universite´ Henri Poincare´, 17 rue Notre-Dame des Pauvres, F 54501 Vandoeuvre-le`s-Nancy, France

Synthetic green rusts, GRs, are prepared by oxidation of Fe(OH)2 incorporating Cl-, SO42-, or CO32- ions. EhpH diagrams are drawn, and thermodynamic data are derived. A GR incorporating OH- ions, GR1(OH-), is suspected to exist like similar other M(II)-M(III) compounds. GRs form as corrosion products of steels, implying microbially induced corrosion. Mo¨ ssbauer and Raman spectroscopies allowed the identification of GR in samples extracted from hydromorphic soils scattered over Brittany, France. This mineral has a varying Fe(III)/Fe(II) ratio. At Fouge` res, it increases with depth till the occurrence of more oxidized ferric oxyhydroxide. In the same sites, soil solutions are collected and prevented from any oxidation and photoreduction. In large ranges of pH, pe, and Fe(II) concentration variations, soil solutions are in equilibrium with a Fe(II)-Fe(III) compound, a GR1 mineral with pyroaurite-like structure incorporating OH- ions and having the formula [FeII(1-x)FeIIIx(OH)2]+x‚[xOH]-x ≡ Fe(OH)(2+x). Computation of ionic activity products (IAP) of the equilibria between minerals and solutions leads to molar ratio x from 1/3 to 2/3, in agreement with the Fe(III)/Fe(II) ratios obtained from Mo¨ ssbauer spectroscopy. The GR mineral plays a key role for controlling iron in soil solutions, and equilibria between soil and suspension constrain the Fe(III)/Fe(II) ratios of the iron(II)-iron(III) hydroxide.

* Corresponding author e-mail address: [email protected]; telephone: +33 (0)3-83-91-63-00; fax: +33 (0)3-83-27-54-44. † UMR 7564 CNRS and ESSTIN. ‡ INRA. § UPR 4661 CNRS. | UPR 6831 CNRS. 1058

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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 32, NO. 8, 1998

Introduction Many minerals are made by the stacking of positively and negatively charged layers. Among them, the pyroauritesjo¨grenite group (1, 2) corresponds to the stacking of brucitelike layers carrying positive charges and layers constituted of anions and water molecules. In this paper, studies concerning major anions that are found in aquatic environments, i.e., Cl-, SO42-, and CO32-, are reported. The iron(II)iron(III) hydroxy salts of this group are generally known under the generic name of green rusts (GRs) since the original classification by Bernal et al. (3). From X-ray diffraction (XRD) characterization, it is admitted that there are two types of GRs: green rust one (GR1) with planar anions, e.g., Cl- and CO32-; and green rust two (GR2) with three-dimensional anions in the interlayers, e.g., SO42- (3). Synthetic GRs have been mainly studied for corrosion purposes because they are intermediate products during the process of oxidation of iron and steels in aqueous media. But the recent identification of a GR as a mineral, i.e., a compound forming in a natural environment (4, 5), raises questions about the conditions of occurrences and the environmental implications as well. For instance, since a synthetic material of similar crystal structure is likely able to reduce NO3- into NH4+ ions under abiotic conditions (6), potentialities for in situ denitrification due to such minerals are considered. In the first part of this paper, the preparation of synthetic GRs is described as devised mainly for corrosion studies. XRD and Mo¨ssbauer spectroscopy are used to characterize the products and to obtain information on their structure. Then by combining electrochemical data and structural information, the electrochemical potential and pH of the equilibria in aqueous solution under the form of Eh-pH diagrams are presented. In the second part, GRs are identified as corrosion products of steels, especially by microbially induced corrosion, and as a mineral in poorly drained redoxomorphic horizons, for which the name “fougerite” has been proposed to the International Mineralogical Association. Three occurrences in Brittany, France, are reported, and soil solutions are analyzed, showing that equilibria between soil and solution are likely to constrain the Fe(II)/Fe(III) ratios in such minerals.

Synthetic Green Rusts The crystal structure of GRs is still a matter of discussion, especially the exact positions of anions and water molecules in the intercalation layers. However, one can describe it qualitatively by considering the structure of the initial ferrous hydroxide Fe(OH)2. It is made of the stacks of hexagonal close-packed OH- ions with alternating Fe2+ layers and empty spaces as represented by the sequence AcB0A..., where A and B represent the planes of OH- ions, c is those of divalent cations, and 0 is the empty spaces. If some Fe2+ cations get oxidized into Fe3+, a hydroxide sheet AcB that was originally electrically neutral gains positive charges. Thus, negative charges provided by intercalated anions will restore neutrality. The resulting GR is constituted by hydroxide layers that alternate regularly with interlayers made of anions and water molecules. The anions intercalation induces structural rearrangements, which give various stacking sequences depending on the geometry of the anion. GR1 compounds, e.g., the iron(II)-iron(III) hydroxychloride or carbonate, have a crystal structure similar to that of pyroaurite, which follows the sequence AcBiBaCjCbAkA..., where A-C designate the OH- planes, a-c are the metal cation layers, and i-k are the S0013-936X(97)00547-6 CCC: $15.00

 1998 American Chemical Society Published on Web 03/12/1998

intercalated anion layers. In contrast, GR2 compounds, e.g., the iron(II)-iron(III) hydroxysulfate, conserve the initial stacking sequence of Fe(OH)2 (7). Preparation. GRs can be synthesized using various procedures, and it seems that the method has no influence on the properties of the obtained GR. For example, Hansen (8) and Drissi et al. (9), using different methods, gave similar conclusions about GR1(CO32-), whereas Detournay et al. (10) and Schwertmann and Fechter (11) did the same for GR1(Cl-). Typically, GRs can be prepared by oxidation, in the presence of air, of ferrous hydroxide precipitates obtained by mixing ferrous salt and caustic soda solutions of various concentrations (9, 10, 12-20). They are commonly obtained where an excess of ferrous salt is permitted and are chosen for providing the appropriate anions. FeCl2‚4H2O and FeSO4‚7H2O are used to study GR1(Cl-) (14, 15) and GR2(SO42-) (16, 17), respectively. When the corresponding ferrous salt is insoluble, e.g., FeCO3, a slightly different methodology must be used. For instance, in order to prepare GR1(CO32-), carbonate ions are added as a Na2CO3 solution after precipitation from FeSO4‚7H2O and NaOH. The details concerning this case can be found elsewhere (9). The suspensions are aerated, and a magnetic stirring ensures a progressive homogeneous oxidation. A thermostat controls the temperature, which is kept at 25 ( 0.5 °C. A direct and continuous measurement of the redox potential Eh and pH of the suspension with time is made using a recorder. The resulting curves are found to be very useful in the evaluation of several thermodynamic parameters and in the synthesis of pure GR samples. Figure 1 illustrates the Eh and pH vs time curves obtained in the case of Cl- ions (15). The overall trend for Eh is to increase whereas that of pH is to decrease. Both curves present several domains; two plateaus A and B are distinguished and two inflection points Tg and Tf designate the end of a first and second stage, respectively. Tg corresponds to the formation of 100% GR, and Tf corresponds to that of the oxidation final products, in this case the γ-FeOOH lepidocrocite. The plateaus A and B where the pH and the redox potential do not vary are assumed to be close to the equilibrium conditions between the various present solid phases, i.e., Fe(OH)2 and GR at plateau A and GR and γ-FeOOH at plateau B. The validity of this assumption was recently fully established (18, 19). Stoichiometries. It was generally observed that the various GRs obey to a specific chemical composition, a stoichiometry, even though off-stoichiometric compounds may be obtained in peculiar conditions. This last point has been carefully studied by replacing Fe(II) ions by Ni(II) ions in GR1(Cl-) (20). These stoichiometries are for

GR1(Cl-)

[FeII3FeIII(OH)8]+‚[Cl‚nH2O](10, 11, 15)

2-

II

III

2+

2-

‚[SO4‚nH2O] (17, 21)

GR2(SO4 )

[Fe 4Fe

GR1(CO32-)

[FeII4FeIII2(OH)12]2+‚[CO3‚nH2O]2(8, 9)

2(OH)12]

Thus, the general formula of a GR is [FeII(1-x)FeIIIx(OH)2]+x‚ [x/nA-n‚m/nH2O]-x if one departs from stoichiometry, where hydroxide layers with positive charges alternate with interlayers constituted of anions A-n and water molecules. One direct consequence of the stoichiometries lies in the average degree of oxidation of iron for the various GRs: 2.25 for GR1(Cl-) and 2.33 for GR2(SO42-) and GR1(CO32-). It is also possible to obtain synthetically GRs off stoichiometry.

FIGURE 1. Eh and pH vs time curves obtained during the oxidation of Fe(OH)2 in an aqueous solution with an excess of Cl- ions at 25 °C. Eh is referred to standard hydrogen electrode (15).

FIGURE 2. X-ray diffraction patterns of two synthetic green rusts (GRs): (a) GR1(CO32-) and (b) GR2(SO42-). CoKr radiation (λ ) 0.17902 nm). The samples are left unprotected during the experiments and oxidize superficially, but only very small lines of ferric oxyhydroxides are detected. R ) [Fe2+]/[OH-]. In particular, because of the difficulty for stopping the oxidation once in the air, Fe(III) ions are likely to become more numerous as the system evolves. Many authors noticed that the GR structure can tolerate much higher proportions of Fe(III) than those of stoichiometry (10-12, 22-24). In oxidizing conditions, it is often a mixture of GR and ferric oxyhydroxide that is obtained.

Characterization of Green Rusts Three main methods have been used for characterizing green rust compounds (GRs): X-ray diffraction (XRD), Mo¨ssbauer spectroscopy, and Raman spectroscopy. X-ray Diffraction (XRD). As pointed out, there exist traditionally two types of XRD patterns that correspond to the nomenclature GR1 and GR2 (Figure 2). If most of GRs are of the first type, only the hydroxysulfate and selenate are, at least up till now, of the second type (7). There are no major differences among GR1s, and XRD does not indicate which counteranions lie in the interlayers. Some slight changes in lattice parameters, e.g., the c axis, can be detected from Cl- to CO32- ions, but departures from stoichiometry can also change lattice parameters, and consequently this cannot be reliable enough. Unfortunately, the small amount of GR in natural samples makes XRD useless for its identification even though the method is very convenient for synthetic materials. VOL. 32, NO. 8, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Mo1 ssbauer spectra measured at 78 K of GR2(SO42-) (17), GR1(CO32-) (9), and GR1(Cl-) (20). ratio of 2.95 measured by XPS matches a [Fe3+]/[Ni2+] ratio of 2.8 measured by ICP-AES for predicted values of 3 (20).

TABLE 1. Hyperfine Parameters Measured at 78 K of GR2(SO42-), GR1(CO32-), and GR1(Cl-)a GR2(SO42-) (17)

GR1(CO32-) (9)

site

δ

∆EQ

RA

δ

∆EQ

RA

δ

∆EQ

RA

D1 D2 D3

1.27

2.88

66

0.47

0.44

34

1.27 1.28 0.47

2.93 2.64 0.42

51 15 34

1.26 1.27 0.48

2.80 2.55 0.38

36 37 27

GR1(Cl) (20)

δ (mm s-1), isomer shift with respect to R-Fe; ∆EQ (mm s-1), quadrupole splitting; RA (%), relative abundance. Full widths at half maximum of Lorentzian-shape lines are constrained to be equal and found to be 0.28 mm s-1 for all lines. a

Mo1 ssbauer Spectroscopy. In contrast, 57Fe Mo¨ssbauer spectroscopy turns out to be very useful for the identification of natural GR occurrences in the field. Since it is only sensitive to iron atoms and even though data accumulation may take a long time for dilute mineral samples, a definite answer can be obtained. Moreover, by the use of low temperature measurements, it is possible to stop any oxidation. Mo¨ssbauer spectra of synthetic GRs, i.e., GR2(SO42-), GR1(CO32-), and GR1(Cl-), measured at 78 K are displayed in Figure 3 (9, 17, 20). Samples are precisely taken at the first inflection point Tg of the Eh or pH vs time curves (Figure 1). It has been checked by XRD that the sample is made of pure GR and that no lepidocrocite or goethite is mixed with it. At 78 K, hyperfine interactions are limited to isomer shift, δ, and quadrupole splitting, ∆EQ (Table 1). Lorentzian-shape lines are computer-fitted for all spectra with adjustable widths. The Mo¨ssbauer f factor is assumed to be the same for all iron sites, and peak positions allow us to determine each site in a given solid phase with its degree of oxidation. Spectra display three quadrupole doublets D1, D2, and D3 where D1 and D2 correspond to two ferrous ion sites (25) with δ and ∆EQ of about 1.3 and 2.8 mm s-1, respectively, and D3 corresponds to a ferric ion site with δ and ∆EQ of about 0.4 mm s-1. Line intensities are directly proportional to the site abundance and vary from a GR to another (Table 1). It is not possible to distinguish a GR from another one solely by the peak positions. Note that, at stoichiometry, D2 does not exist in the GR2(SO42-) spectrum, as previously observed by Cuttler et al. (21). From the Mo¨ssbauer spectra, some very useful structural information is deduced. First, it allows us to measure the Fe(II)/Fe(III) ratio, which leads to the chemical formula of each GR as due to the charge balance between anion interlayers and ferric ions. But, it has been carefully checked, e.g., in the case of a GR1(Cl-)-like compound where Fe2+ ions are exactly substituted by Ni2+ ions, that a [Cl-]/[Ni2+] 1060

9


It is possible to follow the Fe(II)/Fe(III) ratio by Mo ¨ ssbauer spectroscopy if GRs are off stoichiometry. This has first been done for GR1(CO32-) (22) and more recently for GR1(Cl-) (20). Generally speaking, it seems that GRs are formed in situ from the initial Fe(OH)2 by oxidation, which in fact corresponds to a gradual intercalation of anions in the initially empty spaces of ferrous hydroxide. This proceeds up to saturation, which means that the stoichiometry of GRs corresponds to the saturation of all interlayers by the anions and water molecules. An extra oxidation may further be accompanied by deprotonation of OH- ions. All these mechanisms are fully demonstrated in the case of GR1(Cl-) (20). Consequently, except in the case where stoichiometry is carefully controlled, GRs do not present peak intensity ratios at the predicted value. Since it is very likely that the natural GRs are off stoichiometry, it is hazardous to characterize a specific GR from its sole Mo¨ssbauer spectrum. There is no ambiguity that a Fe(II)-Fe(III) GR is obtained, but one cannot know yet which type of anions is responsible for its formation. Raman Spectroscopy. This method was first used by Thierry et al. (26) to characterize GRs formed as corrosion products on steel. A special cell used for Raman experiments allows us to keep the sample in an argon atmosphere in the absence of oxygen. The sample is set under an argon flow in a glovebox, and the cell is tightly closed by a glass window through which a laser beam is focused and the Raman backscattering is collected. The cell is mounted in the focal plane of an Olympus B.H. microscope in a Jobin-Yvon/ Instrument S.A. T64000 Raman microprobe, which allows us to analyze a surface of about 2 × 2 µm. The resolution is about 3 cm-1, and the precision on the wave number is 1 cm-1. The GRs spectra are characterized by two bands at about 420 and 510 cm-1 (5, 18, 27, 28), whatever the anions found in the interlayer. Note that (i) none of the common iron oxides or oxyhydroxides gives rise simultaneously to similar bands and (ii) their more intense band does not correspond to these wavenumbers (29). Therefore, the presence of these two lines characterize a GR, but again, it is not possible to ascertain which type of anions it is incorporated to.

Eh-pH Diagrams Thermodynamic data can be used to determine the iron species and the activity of ions in the surrounding equilibrium solution. Eh and pH values for the various equilibria are obtained from curves as those of Figure 1. As already noted,

a

b

the values of the first plateau A describe the equilibrium conditions between ferrous hydroxide and GR whereas those of the second plateau B correspond to that between GR and the final ferric oxyhydroxide. By varying the initial concentrations of reactants, the excess of anions, e.g., Cl-, SO42-, or CO32-, changes and the Eh vs pH variation corresponds to a straight line according to Nernst’s law. Detailed explanation can be found in the original papers (9, 15, 17, 30), and resulting Eh-pH diagrams known as Pourbaix diagrams are drawn accordingly. Such diagrams are concisely compiled here for the three synthetic stoichiometric GRs already quoted (Figure 4) and drawn according to the most recent estimation of the free enthalpy of formation of GRs (19). Some relevant iron minerals were not reported on these diagrams, such as Fe3O4 or FeCO3. It must be noted that GRs are metastable with respect to them, and other diagrams including these compounds instead of GRs could be considered alternatively. The domains of existence of GRs correspond to “triangles” between metallic Fe, Fe(OH)2, and ferric oxyhydroxide. The allotropic form of FeOOH, which is chosen in the diagram, depends upon the form that is actually obtained experimentally, e.g., γ-lepidocrocite for GR1(Cl-) and GR2(SO42-) or R-goethite for GR1(CO32-). Several dissolved Fe species concentrations are displayed, and number -n on the lines means a molar activity of 10-n. All diagrams have been drawn for an anion activity of 0.1. This implies that cations, such as Na+ or K+, are present in solution to restore electroneutrality, e.g., when [Fe2+] ) 10-6, but do not intervene. Each line in the Eh-pH diagrams corresponds to a chemical reaction as reported in Table 2. From the reactions, the lines in the Eh-pH diagrams are computed by using the standard chemical potentials of the various compounds. They are compiled in Table 3. Note that the values of µ° or ∆G°f are given for anhydrous GRs since the number of intercalated water molecules is not ascertained. Anyhow, as explained elsewhere (34), this does not matter since the water molecules do not intervene in the oxidation reactions. In contrast, the values are computed for GRs at stoichiometry.

Occurrences of Green Rust as Corrosion Product of Manmade Materials c

GRs can be found in natural environments as the corrosion product of iron and steel in special conditions. Some years ago, Stampfl (35) reported to have detected GR1(CO32-) in iron pipes. Later, GRs were assumed to be the product of corrosion of iron in seawater. A first experiment was done by using an iron coupon dipped in sediments in the sea. The Mo¨ssbauer and XRD spectra of this sample were that of GR2(SO42-) (36). More recently, GR2(SO42-) was reported to form under the fouling crust covering steel sheet piles at the lowest anoxic level of tide in the harbor of Boulogne sur Mer, France (37), and microbially induced corrosion was assumed to be responsible for it. The systematic study for obtaining GRs by corrosion of iron is not accomplished yet, but an approach has been recently tempted by Abdelmoula et al. (38) where GR1(CO32-) has been observed at the surface of an Armco R-iron coupon in agreement with the Pourbaix diagram drawn in Figure 4c (9). This approach will be developed.

Occurrences of Green Rust in Soils as Mineral GR1(Cl-)

FIGURE 4. (a) Eh vs pH diagram of drawn for an activity [Cl-] of 0.1 (-n means [Fe2+] ) 10-n). (b) Eh vs pH diagram of GR2(SO42-) drawn for an activity [SO42-] of 0.1 (-n means [Fe2+] ) 10-n). (c) Eh vs pH diagram of GR1(CO32-) drawn for an activity [CO32-] of 0.1 (-n means [Fe2+] ) 10-n).

So far, this paper has dealt with GRs that either were synthetic or occurred as corrosion products of steel. In this section, we shall document that GRs may occur as minerals in the soil environment and emphasize their role for controlling iron solubility in water. The samples for this part of the VOL. 32, NO. 8, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 2. Equilibrium Equations of Eh-pH Pourbaix Diagrams for Various Green Rusts: GR1(CO32-), GR1(Cl-), and GR2(SO42-) (a)

(A) (B)

(1) (2) (3) (4) (5) (6) (7)

(7) (7) (8) (8) (8) (9) (10)

(10) (10) (11) (12) (13) (14) (15) (16)

(16)

1062

9

H2 S 2H+ + 2eEh ) 0.000-0.0591pH

Water

Carbonate Species H2CO3 S HCO3- + H+ 6.37 ) log [H2CO3] - log [HCO3-] + pH HCO3- S CO32- + H+ 10.34 ) log [HCO3-] - log [CO32-] + pH Iron Species Fe2+ + H2O S FeOH+ + H+ 8.98 ) log [Fe2+] - log [FeOH+] + pH FeOH+ + H2O S FeOOH- + 2H+ 12.10 ) 0.5 log [FeOH+] - 0.5 log [FeOOH-] + pH Fe2+ + 2H2O S Fe(OH)2+ + 2H+ + eEh ) 1.324-0.0591 log [Fe2+] + 0.0591 log [Fe(OH)2+] - 0.1182pH FeOH+ + H2O S Fe(OH)2+ + H+ + eEh ) 0.79-0.0591 log [FeOH+] + 0.0591 log [Fe(OH)2+] - 0.0591pH FeOOH- + H+ S Fe(OH)2+ + eEh ) -0.638-0.0591 log [FeOOH-] + 0.0591pH + 0.0591 log [Fe(OH)2+] Fe + 2H2O S Fe(OH)2 + 2H+ + 2eEh ) -0.080-0.0591pH carbonate-containing media (a) 6Fe(OH)2 + CO32- S Fe6(OH)12CO3 + 2eEh ) -0.63-0.0296 log [CO32-] (b) 6Fe(OH)2 + HCO3- S Fe6(OH)12CO3 + H+ + 2eEh ) -0.33-0.0296 log [HCO3-] - 0.0296pH chloride-containing media 4Fe(OH)2 + Cl- S Fe4(OH)8Cl + eEh ) -0.55-0.0591 log [Cl-] sulfate-containing media 6Fe(OH)2 + SO42- S Fe6(OH)12SO4 + 2eEh ) -0.57-0.0296 log [SO42-] carbonate-containing media 6Fe + HCO3- + 12H2O S Fe6(OH)12CO3 + 13H+ + 14eEh ) -0.12-0.0042 log [HCO3-] - 0.0549pH chloride-containing media 4Fe + Cl- + 8H2O S Fe4(OH)8Cl + 8H+ + 9eEh ) -0.14-0.0066 log [Cl-] - 0.0525pH sulfate-containing media 6Fe + SO42- + 12H2O S Fe6(OH)12SO4 + 12H+ + 14eEh ) -0.15-0.0042 log [SO42-] - 0.0507pH Fe(OH)2 S FeOOH + H+ + eEh ) E0 - 0.0591pH, with E0 ) 0.097 and 0.197 V for R- and γ-FeOOH, respectively carbonate-containing media (a) Fe6(OH)12CO3 S 6R-FeOOH + CO32- + 6H+ + 4eEh ) 0.47 + 0.0148 log [CO32-] - 0.0887pH (b) Fe6(OH)12CO3 S 6R-FeOOH + HCO3- + 5H+ + 4eEh ) 0.31 + 0.0148 log [HCO3-] - 0.0739pH (c) Fe6(OH)12CO3 S 6R-FeOOH + H2CO3 + 4H+ + 4eEh ) 0.22-0.0148 log [H2CO3] - 0.0591pH chloride-containing media Fe4(OH)8Cl S 4γ-FeOOH + Cl- + 4H+ + 3eEh ) 0.46 + 0.0197 log [Cl-] - 0.0788pH sulfate-containing media Fe6(OH)12SO4 S 6γ-FeOOH + SO42- + 6H+ + 4eEh ) 0.59 + 0.0148 log [SO42-] - 0.0887pH Fe S Fe2+ + 2eEh ) -0.474 + 0.0296 log [Fe2+] Fe2+ + 2H2O S Fe(OH)2 + 2H+ 13.33 ) log [Fe2+] + 2pH FeOH+ + H2O S Fe(OH)2 + H+ 4.35 ) log [FeOH+] + pH Fe(OH)2 S FeOOH- + H+ 19.85 ) -log [FeOOH-] + pH FeOOH- S FeOOH + eEh ) E0 - 0.0591 log [FeOOH-], with E0 ) -1.08 and -0.98 V for R- and γ-FeOOH, respectively carbonate-containing media (a) 6Fe2+ + HCO3- + 12H2O S Fe6(OH)12CO3 + 13H+ + 2eEh ) 2.03-0.1773 log [Fe2+] - 0.0296 log [HCO3-] - 0.3842pH (b) 6Fe2+ + H2CO3 + 12H2O S Fe6(OH)12CO3 + 14H+ + 2eEh ) 2.22-0.1773 log [Fe2+] - 0.0296 log [H2CO3] - 0.4137pH chloride-containing media 4Fe2+ + Cl- + 8H2O S Fe4(OH)8Cl + 8H+ + eEh ) 2.57-0.2364 log [Fe2+] - 0.0591 log [Cl-] - 0.4728pH


TABLE 2 (Continued) (16) (17) (18) (19) (19) (19) (20)

sulfate-containing media 6Fe2+ + SO42- + 12H2O S Fe6(OH)12SO4 + 12H++ 2eEh ) 1.78-0.1773 log [Fe2+] - 0.0296 log [SO42-] - 0.3546pH Fe2+ + 2H2O S FeOOH + 3H+ + eEh ) E0 - 0.0591 log [Fe2+] - 0.1773pH, with E0 ) 0.89 and 0.99 V for R- and γ-FeOOH, respectively Fe + H2O S FeOH+ + H+ + 2eEh ) -0.21 + 0.0296 log [FeOH+] - 0.0296pH carbonate-containing media 6FeOH+ + HCO3- + 6H2O S Fe6(OH)12CO3 + 7H+ + 2eEh ) 0.44-0.1773 log [FeOH+] - 0.0296 log [HCO3-] - 0.2068pH chloride-containing media 4FeOH+ + Cl- + 4H2O S Fe4(OH)8Cl + 4H+ + eEh ) 0.45-0.2364 log [FeOH+] - 0.0591 log [Cl-] - 0.2364pH sulfate-containing media 6FeOH+ + SO42- + 6H2O S Fe6(OH)12SO4 + 6H+ + 2eEh ) 0.19-0.1773 log [FeOH+] - 0.0296 log [SO42-] - 0.1773pH FeOH+ + H2O S FeOOH + 2H+ + eEh ) E0 - 0.0591 log [FeOH+] - 0.1182pH, with E0 ) 0.35 and 0.45 V for R- and γ-FeOOH, respectively

TABLE 3. Thermodynamic Constants Used for Calculations species

av oxidation no. of Fe

∆G°f (kJ mol-1)

ref

R-Fe Fe(OH)2 FeII3FeIII(OH)8Cl FeII4FeIII2(OH)12CO3 FeII4FeIII2(OH)12SO4 γ-FeOOH R-FeOOH

Solid 0 +2 +2.25 +2.33 +2.33 +3 +3

0 -490 ( 1 -2146 ( 5 -3590 ( 10 -3795 ( 15 -470.7 -480.3

19 19 19 19 31 13

-237.13

32

-131.2 -527.9 -586.8 -623.2 -744.5 -91.5 -277.4 -376.4 -438.0

32 32 32 32 32 33 33 33 32

Liquid H2O ClCO32HCO3H2CO3 SO42Fe2+ FeOH+ FeOOHFe(OH)2+

Aqueous Medium

+2 +2 +2 +3

study originate from the subsurface B and C horizons of pedons affected by seasonal waterlogging. Accordingly, these horizons exhibit, when saturated by water, those bluegreenish or green-grayish colors recognized as diagnosis for some soil materials having the so-called “gleyic properties”. Three locations have been selected in Brittany, France, at (i) Fouge`res (Ille and Vilaine), (ii) Quintin (Coˆtes d’Armor), and (iii) Naizin (Morbihan). These locations design a triangle with two sides of about 160 km and a third one of 60 km in the middle of Brittany. (i) At Fouge`res, from top to bottom, the profile shows two major units: (1) (0-15 cm) a histic horizon; (2) a granitic saprolite displaying a gleyey horizon (15-70 cm) followed by an oxidized horizon with accumulation of iron(III) oxides. The waterlogged soil is located near a spring under the historical forest of Fouge`res. (ii) At Quintin, the profile shows a typical hydromorphic sequence occurring in a loamy cover overlying a granitic saprolite. The profile shows five major units from top to bottom: (1) (0-40 cm) an organomineral horizon; (2) (4050 cm) an albic horizon; (3) (50-100 cm) an illuvial mottled clayey horizon; (4) (100-120 cm) a structural redoxic horizon; (5) a granitic saprolite displaying large ochrous clayey pouches (120-140 cm) at the water level table and a grayish matrix that turns bluish with reductomorphic properties at

FIGURE 5. Mo1 ssbauer spectra measured at 78 K of the green rust mineral extracted (a) at Fouge` res and (b) at Quintin. about 180 cm. The soil is located at the middle of a slope in a field under intensive farming. (iii) At Naizin, the profile is developed in a loamy cover overlying a schistose saprolite. It displays four units: (1) (0-10 cm) an organomineral horizon; (2) (10-30 cm) an albic horizon; (3) (30-70 cm) a structural redoxic horizon; (4) a schistose saprolite with reductomorphic properties. The soil is located in a colluvio-alluvial system near a stream in an intensive farming area. Soil samples were taken from the gley horizon at a depth of 20 cm at Fouge`res, 150 cm at Quintin, and 50 cm at Naizin. Table 4 reports data concerning the location, the color, and the environmental conditions at the sites where the samples were collected. As it was already observed that the color of VOL. 32, NO. 8, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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TABLE 4. Brief Description of Soil Samples Selected for This Study horizon designation

depth (m)

Munsell color

remarks

Quintina Naizina

Cg Cg Cg 2Cg Bg

0.2 0.4 0.6 1.5 0.5

granitic saprolite id. id. granitic saprolite loessic cover on schists

Naizina

Bg

0.5

5BG6/1 5BG6/1 5GY6/1 5BG6/1 5GY5/1 + 7.5YR6/8 and 7.5YR5/8 spots id.

sample

location

F (20 cm) F (40 cm) F (60 cm) Quintin Naizin 1

Fouge` resa

Naizin 2b a

Brittany, France.

b

id.

Sampled in pits 20 m apart.

TABLE 5. Hyperfine Parameters of Soil Samples Measured at 78 or 16 Ka

Fouge` res F (20 cm) F (40 cm) F (60 cm) Quintin

Quintin Naizin 1 Naizin 2

δ

∆EQ

D1 D3 D1 D3 D1 D3 D1 D3 D'3 D1 D3

1.25 0.45 1.25 0.43 1.25 0.44 1.25 0.33 0.53 1.26 0.31

D1 D3 D1 D3 S1 D1 D3 S1 S2

1.3 0.42 1.31 0.26 0.47 1.31 0.27 0.46 0.40

H

W

RA (%)

78 K 2.87 0.54 2.81 0.72 2.81 0.61 2.88 0.58 0.55 2.71 0.42

0.41 0.51 0.36 0.51 0.36 0.46 0.41 0.41 0.41 0.62 0.62

51 49 56 44 60 40 45 25 30 36 64

16 K 2.74 0.41 2.82 0.33 -0.26 2.65 0.28 -0.26 0.05

0.7 0.7 0.5 0.5 0.6 0.67 0.67 0.67 1.6

36 64 13 14 73 21 33 36 10

503 491 441

a δ (mm s-1), isomer shift taking R iron as a reference. ∆E (mm s-1), Q quadrupole splitting. H (kOe), hyperfine field. W (mm s-1), full width at half maximum. RA (%), relative abundance.

such horizons rapidly turned from bluish-green to orange when exposed to the air (4, 5), the sampling procedure was designed to avoid any unwitting oxidation and therefore any change in color. Large decimetric blocks of soil materials were cut in freshly open soil pits and kept in a container filled up with the water solution collected in the sampling pit itself. Mo¨ssbauer spectra were then recorded on small subsamples cut in the core of the oversized blocks collected in the field. In order to confirm the identification of GR from Mo¨ssbauer spectroscopy, a Raman spectrum was also performed. Once exposed to the air, the color of a sample from Fouge`res changes, according to the Munsell soil color chart (39), from a homogeneous bluish-gray (5BG 6/1) to greenish-gray (5GY 6/1) after about 10 min, then to pale olive (5Y 6/4) after 1 h, and finally, gray with light olive brown scattered spots (2.5Y 5/6) after 1 day of exposure. The color for the sample from Quintin is greenish-gray (5BG 5/1). Those for the samples from Naizin are greenish-gray (5GY 6/1) with reddish yellow (7.5YR 6/8) and strong brown (7.5YR 5/8) spots. As for Fouge`res, Quintin’s and Naizin’s samples turn yellowish in the air with time. These color changes are consistent with those observed by Girard and Chaudron (40) during the transformation of GRs into lepidocrocite. Mo¨ssbauer spectra of the samples were measured at 78 or 16 K and compared with those obtained on synthetic GRs. In order to confirm the identification of a GR by Mo¨ssbauer spectroscopy, a Raman characterization was performed. Overall the Fe 1064

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FIGURE 6. Mo1 ssbauer spectra measured at 16 K of samples extracted from the soil (a) at Quintin and (b and c) at Naizin where the soil is inhomogeneous. content of samples by X-ray fluorescence yields from 2 to 3.9% Fe2O3. Thus, the small amount of GR and its dispersion in the mineral samples makes XRD unfortunately useless. Finally, it was ascertained for the samples of Fouge`res that

TABLE 6. Ionic Activity Product (IAP) Relationships and Corresponding Solubility Products at 25 °C Computed from Gibbs Free Energies of Formation Admitted in the Literature of Different Fe Compounds expression of ionic activity product (log IAP)

mineral hematite goethite lepidocrocite ferrihydrite ferrous hydroxide GR1(Cl-) GR1(CO32-) GR2(SO42-)

log K

ref

log [Fe2+] + 3pH + pe 12.2 log [Fe2+] + 3pH + pe 15 log [Fe2+] + 3pH + pe 16.7 log [Fe2+] + 3pH + pe [15.6; 18] log [Fe2+] + 2pH 13.3 4 log [Fe2+] + 8pH + 46 pe + log [Cl-] 6 log [Fe2+] + 12pH + 63 2pe + log [CO32-] 6 log [Fe2+]+ 12pH + 60.3 2pe + log [SO42-]

58 13 19, 31 59 19 15 9 17, 19

TABLE 7. Ionic Activity Products (IAP) of Soil Waters for GR1(OH-) Green Rustsa T location (°C)

FIGURE 7. Variability of the Mo1 ssbauer spectra measured at 78 K from Fouge` res with depth at 20, 40, and 60 cm. only a very minor part of the iron present in the soil did not come from the GR by use of the citrate-bicarbonate (CB) or citrate-bicarbonate-dithionate (CBD) reagent (4); 98% of the total iron dissolved rapidly in this reagent without previous reduction, which is characteristic of GRs (41), since ferric oxyhydroxides such as R- or γ-FeOOH do not dissolve (42). Similarly, structural Fe(III) substituted to Al(III) in clay minerals such as kaolinite is not extracted by CB or CBD treatment (43). Mo1 ssbauer and Raman Characterization of the Green Rust Mineral. The Mo¨ssbauer spectrum measured at 78 K of the soil sample from Fouge`res at a depth of 20 cm with the computed hyperfine interaction parameters (Figure 5a and Table 5) displays the same characteristic quadrupole ferrous (δ ) 1.3 mm s-1, ∆EQ ) 2.9 mm s-1) and ferric doublets (δ ) 0.5 mm s-1, ∆EQ ) 0.5 mm s-1) as the synthetic GRs (cf. Table 1). In order to ascertain that the Fe(III) doublet was not partially due to a ferric oxyhydroxide or oxide, analyses

pFe2+

pe

pH

F1 F2 F3 F4 F5 F6 F7 av SD

9.2 8.9 8.7 9.2 8.9 8.9 8.9

5.771 9.755 5.15 6.140 9.804 5.15 6.115 9.797 5.35 7.069 9.665 5.50 7.064 10.162 5.70 7.133 10.340 5.70 7.149 10.591 5.55

Q1 Q2 Q3 Q4 Q5 Q6 Q7 av SD

8.2 7.7 8.2 8.2 8.2 8.2 7.7

5.077 4.679 4.540 5.059 4.791 4.473 5.420

7.224 7.018 7.368 6.669 4.340 4.466 8.445

N1 N2 N3 N4 N5 N6 N7 N8 N9 av SD

13.9 10.8 10.2 7.4 8.7 7.6 5.5 11.8 10.8

5.542 5.363 4.306 4.648 4.472 4.436 4.835 4.699 5.146

7.723 7.281 6.860 6.467 6.183 6.870 7.077 7.013 6.606

Fe3(OH)7 Fe2(OH)5 Fe3(OH)8 (x ) 1/3) (x ) 1/2) (x ) 2/3) 9.497 9.144 9.634 8.986 9.624 9.614 9.331 9.404 0.258

11.981 11.637 12.158 11.514 12.267 12.287 12.022 11.981 0.301

14.466 14.129 14.683 14.042 14.911 14.961 14.712 14.557 0.362

5.60 5.45 5.60 5.85 6.25 6.35 5.50

10.397 10.377 10.983 10.814 11.239 11.832 10.228 10.839 0.570

12.535 12.455 13.144 12.901 13.004 13.635 12.553 12.889 0.421

14.672 14.533 15.306 14.987 14.769 15.438 14.877 14.940 0.330

5.78 6.10 5.50 6.03 6.36 5.95 5.90 6.01 5.95

10.519 11.297 10.814 11.578 12.429 11.737 11.291 11.662 10.940 11.363 0.572

12.770 13.527 12.874 13.661 14.520 13.874 13.454 13.832 13.032 13.505 0.555

15.020 15.757 14.934 15.744 16.610 16.011 15.616 16.003 15.125 15.647 0.546

a F, Fouge ` res; Q, Quintin; N, Naizin; av, average; SD, standard deviation; pFe2+ ) -log [Fe2+].

at 16 K were performed (Figure 6 and Table 5). The presence of a sextet reveals a ferric oxyhydroxide, since GR remains paramagnetic (7, 44). Similarly, these analyses demonstrate that none of the common ferrous minerals is present, e.g., siderite FeCO3 or vivianite Fe3(PO4)2‚8H2O give rise to a magnetically split sextet or a ferrous doublet with a large ∆EQ of 3.12 mm s-1 at 78 K, respectively (45). Since none of the studied synthetic GRs can be definitively identified and no Cl-, SO42-, or CO32- concentration is significantly detected in the mineral sample, it is assumed that the observed GR incorporates OH- ions. Such a solid phase was suggested once by Arden (46) or Ponnamperuma et al. (47) under the name of “ferrosoferric hydroxide”. It is rather GR1(OH-), i.e., an iron(II)-iron(III) hydroxide. Homologous Ni(II)Fe(III) compound was stabilized by means of Ni(II) ions and characterized as being a GR1 by XRD and Mo¨ssbauer VOL. 32, NO. 8, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 8. Diagrams of residuals for equilibrium of soil waters with GR1(OH-) (a) at Fouge` res, (b) at Quintin, and (c) at Naizin. spectroscopy (48). Similar compounds incorporating other divalent and trivalent ions are also observed, e.g., Mg(II)Al(III) (49, 50) or Zn(II)-Cr(III) (51). The general formula of the homologous GR1(OH-) is established as [FeII(1-x)FeIIIx(OH)2]+x‚[xOH]-x, i.e., FeII(1-x)FeIIIx(OH)(2+x). The ratio Fe(II)/ Fe(III) occurs to be here experimentally close to 1 (50.7/ 49.3); this allows us to propose as the most probable formula for this sample [FeIIFeIII(OH)4]+‚[OH]- or Fe2(OH)5, i.e., x ) 0.5. In contrast, the Mo¨ssbauer spectrum of the sample extracted in Quintin measured at 78 K (Figure 5b and Table 5) presents two quadrupole doublets with the same positions but with a completely different Fe(II)/Fe(III) ratio very close to 1/2. We propose to deal with the same GR1(OH-) phase but with the formula [FeIIFeIII2(OH)6]2+‚[2OH]2- or Fe3(OH)8, 1066

9


i.e., x ) 2/3. According to the spectrum at 16 K (Figure 6a and Table 5), every Fe atom comes from the GR, i.e., the sample is not a mixture of several phases. The third location where two samples are extracted from Naizin gives rise to different spectra measured at 16 K (Figure 6b,c). Hyperfine parameters are also reported in Table 5. The soil is obviously inhomogeneous. Thus, the two samples are taken at a distance of 20 m from each other. At 16 K, one recognizes the two doublets of a GR and magnetic sextuplets, which characterize goethite and lepidocrocite with respective hyperfine fields of about 500 and 440 kOe. The Fe(II)/Fe(III) ratio inside the GR is 1 and 0.64. Therefore, it is close to Fe2(OH)5 and FeII2FeIII3(OH)13, respectively. By microprobe Raman spectroscopy, a spectrum obtained on fine particles of about 5 µm showed the same characteristic

bands at 518 and 427 cm-1 as for the synthetic GR (5, 18, 27, 28), suggesting that the identification of a GR as a natural mineral is definitively established. Variability of the Green Rust Mineral with Depth at Fouge` res. The variability of the mineral with depth has been studied by Mo¨ssbauer spectroscopy at the location of Fouge`res where three samples have been extracted at the same place at a depth of 20, 40, and 60 cm 2 months later than the previous one. Mo¨ssbauer spectra are displayed in Figure 7 with corresponding hyperfine parameters in Table 5. The evolution of the spectra at 78 K according to the sampling depth can be followed. The two spectra of the upper and intermediate levels look very similar. They show two quadrupole doublets D1 and D3 corresponding to a ferrous and ferric ion, respectively. Values are close to those found for the previous mineral (Figure 5a), confirming the identification of a GR. The variation of ∆EQ for D3 is not large enough, 0.72 vs 0.61 mm s-1, to be significant as well as the variation of relative abundance, 44 vs 40%. However, the spectrum corresponding to the deeper level is quite different; three quadrupole doublets are necessary: one ferrous doublet D1 and two ferric doublets, D3 and D′3. The hyperfine parameters of D′3 are typical of a ferric oxyhydroxide, e.g., γ-FeOOH lepidocrocite or ferrihydrite (52, 53), and the mineral happens to be a mixture of 70% GR with 30% ferric oxyhydroxide. Inside the GR, there exist two sites: 64% Fe2+ state and the Fe2+/Fe3+ ratio is almost equal to 2. Thus, the global increase of Fe3+ ions with depth could be explained by the occurrence of ferric oxyhydroxide and not by a major change in the composition of the fougerite GR phase. This result is consistent with the aspect of the samples since those of the upper and intermediate levels are greenish blue whereas that of the lower level is a little more yellowish. Nature of the Mineral That Controls Iron in Soil Solutions. In the same site, soil water solutions are collected in situ at depths of 100 cm at Fouge`res, of 85 and 220 cm at Quintin, and of 50 cm at Naizin using a device that prevents the solution from any contact with air and light (54) and filtered at 0.2 µm. This avoids any oxidation or photoreduction of the sample. Eh, pH, and temperature are measured in the field. Anions, cations, and total metals (Fe, Al, Cu, Zn, Mn) were determined (4). Total aqueous Fe(II) fraction is analyzed by a colorimetric procedure after extraction of the 4:7-diphenyl-1:10-phenanthroline (i.e., bathophenanthroline)-Fe(II) complex in chloroform (55) or di-2-pyridyl ketone-benzoyl-hydrazine (DPKBH) (56). From total Fe(II), Eh, pH, and the concentrations of major cations and anions, the activity of Fe2+ is computed. The aqueous Fe(II) species considered are Fe2+ and the ion pairs Fe(OH)+, FeCO30, FeSO40, FeCl+, and FeC120. Organoferrous complexes are assumed negligible. From Eh and the activity of Fe2+, the activity of Fe3+ is thus computed. EQUIL(T) model (57) is used to calculate the activities of free ions and ion pairs and the activity coefficients, on the basis of extended DebyeHu ¨ ckel law. To check the equilibria between minerals and the solutions, the ionic activity products (IAP) are computed and compared to the solubility products K of different iron minerals by plotting log IAP vs the equilibrium factors, i.e., pH, pe (electron potential, i.e., Eh/0.05916) and [Fe2+], the Fe2+ activity. Tested minerals are hematite, goethite, lepidocrocite, ferrihydrite, ferric hydroxide, ferrous hydroxide, GR1(OH-), siderite, and the chloride, sulfate, and carbonate GRs. The expressions of IAP and the ranges of variation currently admitted for solubility products in the literature are summarized in Table 6. For all the sites, soil solutions are (i) oversaturated with respect to ferric oxides (ferric hydroxide, goethite, hematite, lepidocrocite, ferrihydrite), (ii) undersaturated with respect

to ferrous minerals (ferrous hydroxide, siderite), and (iii) undersaturated with respect to synthetic GRs (chloride, sulfate, carbonate GRs), (iv) it can be assumed that a GR1(OH-) controls iron in solution. To verify it, the general reaction can be considered:

FeII(1-x)FeIIIx(OH)(2+x) + xe- + (2 + x)H+ T Fe2+ + (2 + x)H2O (1) with

log IAP ) log [Fe2+] + xpe + (2 + x)pH

(2)

where IAP is K at equilibrium; x ) 0 is the limiting case corresponding to ferrous hydroxide, and x ) 1 to ferric hydroxide. Since thermodynamic data for GR1(OH-) are not available, log IAP is initially computed using all the experimental values of pH, pe, and log [Fe2+]. The average value obtained is then used as log K to compute the estimation of log [Fe2+], i.e., fest given by the function

fest ) -xpe - (2 + x)pH + log K

(3)

and the residuals by

fest - fobs ) -xpe - (2 + x)pH + log K - log [Fe2+] (4) The value x of FeII(1-x)FeIIIx(OH)(2+x), which gives the smallest residuals, is thus computed. Depending on the milieu, the best values for x range from 1/3 to 2/3. The calculation of the standard deviation and the plot of residuals (Figure 8 and Table 7) show that the smallest dispersion is obtained with x ) 1/3-1/2 at Fouge`res, x ) 2/3 at Quintin, and x ) 1/2-2/3 at Naizin. These values of x correspond respectively to the following GR formulas:

x ) 1/3 to Fe3(OH)7 ≡ [Fe3(OH)6]+‚[OH]x ) 1/2 to Fe2(OH)5 ≡ [Fe2(OH)4]+‚[OH]x ) 2/3 to Fe3(OH)8 ≡ [Fe3(OH)6]2+‚[(OH)2]2These results are completely consistent with the previous Mo¨ssbauer characterizations and imply that the GR1(OH-) minerals in hydromorphic soils control reversibly at equilibrium the activity of Fe2+ in soil solution.

Acknowledgments The authors would like to thank the reviewers for their most stimulating and constructive discussion in order to perform clarity and persuasiveness.

Literature Cited (1) Allmann, R.; Lohse, H. H. Neues Jahrb. Mineral. Monatsh. 1966, 161. (2) Allmann, R. Acta Crystallogr. 1968, B24, 972. (3) Bernal, J. D.; Dasgupta, D. R.; Mackay, A. L. Clay Miner. Bull. 1959, 4, 15. (4) Trolard, F.; Abdelmoula, M.; Bourrie´, G.; Humbert, B.; Geńin, J.-M. R. Compt. Rend. Acad. Sci. 1996, 323, 1015. (5) Trolard, F.; Geńin, J.-M. R.; Abdelmoula, M.; Bourrie´, G.; Humbert, B.; Herbillon, A. Geochim. Cosmochim. Acta 1997, 61, 1107. (6) Hansen, H. C. B.; Koch, C. B.; Nancke-Krogh, H.; Borggaard, O. K.; Sørensen, J. Environ. Sci. Technol. 1996, 30, 2053. (7) Geńin, J.-M. R.; Abdelmoula, M.; Refait, Ph.; Simon, L. Hyperfine Interact. In press. (8) Hansen, H. C. B. Clay Miner. 1989, 24, 663. (9) Drissi, S. H.; Refait, Ph.; Abdelmoula, M.; Geńin, J.-M. R. Corros. Sci. 1995, 37, 2025. VOL. 32, NO. 8, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

9

1067

(10) Detournay, J.; De´rie´, R.; Ghodsi, M. Z. Anorg. Allg. Chem. 1976, 427, 265. (11) Schwertmann, U.; Fechter, H. Clay Miner. 1994, 29, 87. (12) Feitknecht, W.; Keller, G. Z. Anorg. Allg. Chem. 1950, 262, 61. (13) Detournay, J.; De Miranda, L.; De´rie´, R.; Ghodsi, M. Corros. Sci. 1975, 15, 295. (14) Geńin, J.-M. R.; Re´zel, D.; Bauer, Ph.; Olowe, A. A.; Be´ral, A. Mater. Sci. Forum 1986, 8, 477. (15) Refait, Ph.; Geńin, J.-M. R. Corros. Sci. 1993, 34, 797. (16) Olowe, A. A.; Geńin, J.-M. R. Corros. Sci. 1991, 32, 965. (17) Geńin, J.-M. R.; Olowe, A. A.; Refait, Ph.; Simon, L. Corros. Sci. 1996, 38, 1751. (18) Bon, C. Ph.D. Thesis, Universitat H. Poincare´, Nancy, France, 1997. (19) Refait, Ph.; Bon, C.; Simon, L.; Bourrie´, G.; Trolard, F.; Bessie`re, J.; Geńin, J.-M. R. Clay Miner. In press. (20) Refait, Ph.; Geńin, J.-M. R. Clay Miner. 1997, 32, 597. (21) Cuttler, A. H.; Man, V.; Cranshaw, T. E.; Longworth, G. Clay Miner. 1990, 25, 289. (22) Murad, E.; Taylor, R. M. In Industrial Applications of the Mo¨ssbauer Effect; Long, G. F., Stevens, J. G., Eds.; Plenum Press: New York, 1986; pp 585-593. (23) Vins, J.; Zapletal, V.; Hanousek, F. Collect. Czech. Chem. Commun. 1987, 52, 93. (24) Refait, Ph.; Geńin, J.-M. R. Corros. Sci. 1997, 39, 539. (25) Murad, E.; Taylor, R. M. Clay Miner. 1984, 19, 77. (26) Thierry, D.; Presson, D.; Leygraf, C.; Deliche`re, D.; Joiret, S.; Pallotta, C.; Hugot-Le Goff, A. J. Electrochem. Soc. 1988, 135, 305. (27) Boucherit, N.; Hugot-Le Goff, A.; Joiret, S. Corros. Sci. 1991, 32, 497. (28) Boucherit, N.; Hugot-Le Goff, A.; Joiret, S. Mater. Sci. Forum 1992, 111-112, 581. (29) de Faria, D. L. A.; Venanciao, S.; de Oliveira, M. T. J. Raman Spectrosc. 1997, 28, 873. (30) Olowe, A. A.; Geńin, J.-M. R. Proc. Int. Symp. Sci Eng. 1989, CEBELCOR RT297, 363. (31) Hashimoto, K.; Misawa, T. Corros. Sci. 1973, 13, 229. (32) Wagman, D. D.; Evans, W. H.; Parker, V. B.; Schumm, R. H.; Halow, I.; Bailey, S. M.; Churney, K. L.; Nutall, R. L. J. Phys. Chem. Ref. Data 1982, 11, 2-177-2-182. (33) Kelsall, G. H.; Williams, R. A. J. Electrochem. Soc. 1991, 138, 931. (34) Refait, Ph.; Geńin, J.-M. R. Corros. Sci. 1994, 36, 55. (35) Stampfl, P. P. Corros. Sci. 1969, 9, 185.

1068

9


(36) Olowe, A. A.; Bauer, Ph.; Geńin, J.-M. R.; Gue´zennec, J. Corrosion 1989, 45, 229. (37) Geńin, J.-M. R.; Olowe, A. A.; Re´siak, B.; Benbouzid-Rollet, N. D.; Confente, M.; Prieur, D. In Marine corrosion of stainless steels: chlorination, and microbial effects; European Federation Corrosion Series 10; The Institute of Materials: London, 1993; pp 162-166. (38) Abdelmoula, M.; Refait, Ph.; Drissi, S. H.; Mihe´, J.-P.; Geńin, J.-M. R. Corros. Sci. 1996, 38, 623. (39) Munsell Soil Color Chart; Macbeth: Baltimore, 1975. (40) Girard, A.; Chaudron, G. Compt. Rend. Acad. Sci. 1935, 200, 127. (41) Trolard, F. Me´m. Agre´g. Ens. Sup. 1997. (42) Soulier, A. Ph.D. Thesis, ENSA, Rennes, 1995. (43) Mitchell, B. D.; Smith, B. F. L.; De Endredy, A. S. Isr. J. Chem. 1971, 9, 45. (44) Geńin, J.-M. R.; Bauer, Ph.; Olowe, A. A.; Re´zel, D. Hyperfine Interact. 1986, 29, 1355. (45) Ono, K.; Ito, A. Rev. Mod. Phys. 1964, 36, 459. (46) Arden, T. V. J. Chem. Soc. 1950, 24, 882. (47) Ponnamperuma, F. N.; Tianco, E. M.; Loy, T. Soil Sci. 1967, 103, 374. (48) Refait, Ph.; Drissi, S. H.; Marie, Y.; Geńin, J.-M. R. Hyperfine Interact. 1994, 90, 389. (49) Miyata, S. Clays Clay Miner. 1983, 31, 305. (50) Mascolo, G.; Marino, O. Mineral. Mag. 1980, 43, 619. (51) De Roy, A.; Besse, J. P.; Bondot, P. Mater. Res. Bull. 1985, 20, 1091. (52) Murad, E.; Schwertmann, U. Mineral. Mag. 1984, 48, 507. (53) Murad, E.; Schwertmann, U. Am. Mineral. 1980, 65, 1044. (54) Maıˆtre, V. Science Sol 1991, 29, 71. (55) Maıˆtre, V. Ph.D. Thesis, Universite´ Paris VI, 1991. (56) Jaffrezic, A. Ph.D. Thesis, Universite´ Rennes, 1997. (57) Fritz, B. Me´m. Sci. Geól. 1981, 65, 197. (58) Bratsch, S. G. J. Phys. Chem. Ref. Data 1989, 18, 1. (59) Schwertmann, U.; Cornell, R. M. Iron oxides in the laboratory. Preparation and characterisation; VCH: Cambridge, 1991; 137 pp.

Received for review June 23, 1997. Revised manuscript received December 22, 1997. Accepted January 23, 1998. ES970547M

Thermodynamic Equilibria in Aqueous Suspensions of Synthetic and

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