Standard ferric–ferrous potential and stability of FeCl2+ to 90°C. Thermodynamic properties of Fe(aq)3+ and ferric-chloride species

Тагиров, Б. Р.; Diakonov, Igor I.; Devina, O.A.; Зотов, А. В.

doi:10.1016/s0009-2541(99)00150-3

Cited by 44 publications

(21 citation statements)

References 34 publications

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“…The presence of chlorine neighbors was not detected in the first and second Fe atomic shell in hydrolyzed 0.01-m FeCl 3 solution at pH 2.8. This is in agreement with equilibrium calculations carried out using the available stability constants for Fe(III) chloride species (taken from the compilation of Tagirov et al, 2000), suggesting that only 6% of total Fe should be complexed in the form of FeCl 2ϩ and FeCl 2 ϩ species in this solution. In strongly acid non-hydrolyzed solution (pH ϳ 1, 0.1-m Cl Ϫ , 0.01-m FeCl 3 ), less than 0.3 Cl atoms could be detected in the Fe first shell from analysis of its EXAFS spectrum.…”

Section: Iron-chloride Complexingsupporting

confidence: 89%

Iron (III)-silica interactions in aqueous solution: insights from X-ray absorption fine structure spectroscopy

Pokrovski

Schott

Farges

et al. 2003

Geochimica et Cosmochimica Acta

230

187

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The influence of aqueous silica on the hydrolysis of iron(III) nitrate and chloride salts in dilute aqueous solutions (m Fe ϳ 0.01 mol/kg) was studied at ambient temperature using X-ray absorption fine structure (XAFS) spectroscopy at the Fe K-edge. Results show that in Si-free iron nitrate and chloride solutions at acid pH (pH Ͻ 2.5), Fe is hexa-coordinated with 6 oxygens of H 2 O-and/or OH-groups in the first coordination sphere of the metal, at an Fe-O distance of 2.00 Ϯ 0.01 Å. With increasing pH (2.7 Ͻ pH Ͻ 13), these groups are rapidly replaced by bridging hydroxyls (-OH-) or oxygens (-O-), and polymerized Fe hydroxide complexes form via Fe-(O/OH)-Fe bonds. In these polymers, the first atomic shell of iron represents a distorted octahedron with six O/OH groups and Fe-O distances ranging from 1.92 to 2.07 Å. The Fe octahedra are linked together by their edges (Fe-Fe distance 2.92-3.12 Å) and corners (Fe-Fe distance ϳ3.47 Ϯ 0.03 Å). The Fe-Fe coordination numbers (N edge ϭ 1-2; N corner ϭ 0.5-0.7) are consistent with the dominant presence of iron dimers, trimers and tetramers at pH 2.5 to 2.9, and of higher-polymerized species at pH Ͼ 3. At pH Ͼ 2.5 in the presence of aqueous silica, important changes in Fe(III) hydrolysis are detected. In 0.05-m Si solutions (pH ϳ 2.7-3.0), the corner linkages between Fe octahedra in the polymeric complexes disappear, and the Fe-Fe distances corresponding to the edge linkages slightly increase (Fe-Fe edge ϳ 3.12-3.14 Å). The presence of 1 to 2 silicons at 3.18 Ϯ 0.03 Å is detected in the second atomic shell around iron. At basic pH (ϳ12.7), similar structural changes are observed for the iron second shell. The Fe-Si and Fe-Fe distances and coordination numbers derived in this study are consistent with (1) Fe-Si complex stoichiometries Fe 2 Si 1-2 and Fe 3 Si 2-3 at pH Ͻ 3; (2) structures composed of Fe-Fe dimers and trimers sharing one or two edges of FeO 6-octahedra; and (3) silicon tetrahedra linked to two neighboring Fe octahedra via corners. At higher Si concentration (0.16 m, polymerized silica solution) and pH ϳ 3, the signal of the Fe second shell vanishes indicating the destruction of the Fe-Fe bonds and the formation of different Fe-Si linkages. Moreover, ϳ20 mol.% of Fe is found to be tetrahedrally coordinated with oxygens in the first coordination shell (R Fe-O ϭ 1.84 Å). This new finding implies that Fe may partially substitute for Si in the tetrahedral network of the silica polymers in Si-rich solutions. The results of this study demonstrate that aqueous silica can significantly inhibit iron polymerization and solid-phase formation, and thus increase the stability and mobility of Fe(III) in natural waters. The silica "poisoning" of the free corner sites of iron-hydroxide colloids should reduce the adsorption and incorporation of trace elements by these colloids in Si-rich natural waters.

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Section: Iron-chloride Complexingsupporting

confidence: 89%

Iron (III)-silica interactions in aqueous solution: insights from X-ray absorption fine structure spectroscopy

Pokrovski

Schott

Farges

et al. 2003

Geochimica et Cosmochimica Acta

230

187

View full text Add to dashboard Cite

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“…This is in agreement with theoretical reasoning based on the thermodynamic stability diagrams of iron at high temperature [54], which indicate that at pH values of approximately 7 (fluid B) there is active corrosion at 100 • C, while at 200 • C, hematite is stable ( Figure 10). Thus, it can be reasoned that at 100 • C in fluid B, corrosion was rapidly occurring (considering also the supporting effect given by the lower pH and the presence of chlorides that may form soluble iron chloride complexes [56]). However, because of the massive precipitation of corrosion products, as evidenced by Figures 7 and 8, the electrochemical dissolution reactions became kinetically limited, which resulted in a decrease of the corrosion rate within a few days.…”

Section: Discussionmentioning

confidence: 99%

Corrosion Behaviour of L80 Steel Grade in Geothermal Power Plants in Switzerland

Vitaller

Angst

Elsener

2019

Metals

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In Switzerland, deep geothermal energy can give a promising contribution to the future energy scenario. However, the expertise in operational issues of deep geothermal power plants is limited, and technical challenges, such as corrosion, are a determining factor for their reliable and long-term operation. In this work, two representative fluids of optimal geothermal conditions in Switzerland were studied. The corrosiveness of the solutions was assessed using two experimental setups that allow investigating the range of temperatures and pressures that apply to the reservoir and power plant conditions. The corrosion behaviour of API L80 steel was analyzed by means of electrochemical measurements (at 100 and 200 • C) and of gravimetric tests (at 100 • C). After the tests, the morphologies and composition of the corrosion products were obtained by scanning electron microscopy (SEM) coupled with energy dispersive X-Ray (EDX) and X-Ray diffraction (XRD). Results show that corrosion rates are significantly high at 100 • C in environments with a chloride concentration of around 600 mg/L and pH around 7. The corrosion products deposited on the metal surface mainly consist of magnetite and/or hematite that might potentially form a protective layer. This study gives a first insight of the potential corrosiveness of geothermal fluids in Switzerland.

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“…The final state is a dilute solution of Fe III in 5 N HCl. At such a high concentration of HCl, the predominant Fe III species are FeCl 2 þ complexes (Tagirov et al, 2000). Since iron concentration in the acidic solution is very similar for the samples (LP77, LP90, LP103) and the reference phase (LP42), all FeCl 2 þ complexes cancel out in the thermochemical cycles.…”

Section: Calorimetric Measurementsmentioning

confidence: 99%

Enthalpy of water adsorption and surface enthalpy of lepidocrocite (γ-FeOOH)

Majzlan

Mazeina

Navrotsky

2007

Geochimica et Cosmochimica Acta

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Standard ferric–ferrous potential and stability of FeCl2+ to 90°C. Thermodynamic properties of Fe(aq)3+ and ferric-chloride species

Cited by 44 publications

References 34 publications

Iron (III)-silica interactions in aqueous solution: insights from X-ray absorption fine structure spectroscopy

Iron (III)-silica interactions in aqueous solution: insights from X-ray absorption fine structure spectroscopy

Corrosion Behaviour of L80 Steel Grade in Geothermal Power Plants in Switzerland

Enthalpy of water adsorption and surface enthalpy of lepidocrocite (γ-FeOOH)

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