Thermodynamic data on iron and solubility of Green Rusts
A consistent set of thermodynamic data on iron and revaluation of solubility of Green Rusts and fougerite Jihaine Ben Nacib1,2 , Guilhem Bourrié2 , Bechir Ben Thayer1 et Fabienne Trolard2 1 ESIER, 2 INRA,
Medjez-El-Bab, Tunisie.
[email protected] UMR 1114, Emmah, F-84914 Avignon, France.
19-21 mai 2016 — iCAGE, — Mahdia-Tunisia
Thermodynamic data on iron and solubility of Green Rusts Introduction
state of the art Basic and complex systems Iron is found in combinations and never in its native state, The main minerals containing iron are: hematite Fe2 O3 (s), magnetite Fe3 O4 (s), pyrite FeS2 (s) and siderite FeCO3 (s) In aqueous media, ferrous and ferric ions are most commonly observed, Ferrous and ferric ions can be complexed by many inorganic ligands such as chloride, sulfate, carbonate, ... Two sub systems are considered: basic systems (Fe2 O3 −FeO−H2 O) and more complex systems (FeO−H2 S−H2 O, FeO−Cl−H2 O, FeO−Fe2 O3 −CO2 −H2 O)
Thermodynamic data on iron and solubility of Green Rusts Green rusts: Origin and structures
Green rusts: Origin and structures
Origin of GRs Well characterized compounds iso-structural, This is a group of synthetic iron compounds inside the larger group of layered double hydroxides (LDHs), It consists of a simple octahedral layer of a compact stacking of OH – ions with divalent and trivalent cations in the octahedral sites.
Thermodynamic data on iron and solubility of Green Rusts Green rusts: Origin and structures
Green rusts: Origin and structures
Structures of GRs Two types of structures exist: GRs 1: A single water layer between the sheets GRs 2: Two water layers between the sheets
Thermodynamic data on iron and solubility of Green Rusts Green rusts: Origin and structures
Reevaluation thermodynamic data of GRs Structure of GRs
Thermodynamic data on iron and solubility of Green Rusts Thermodynamic data from 1952 to 2013
Thermodynamic data from 1952 to 2013
synthesis of Lemire-2013 The data evaluated resulted from the three classical methods: measurements of chemical equilibria, K , Ksp ; electrochemical measurements E ; calorimetry, ∆H , Cp .
Thermodynamic data on iron and solubility of Green Rusts Thermodynamic data from 1952 to 2013
Thermodynamic data from 1952 to 2013
synthesis of Lemire-2013 The data evaluated resulted from the three classical methods: measurements of chemical equilibria, K , Ksp ; electrochemical measurements E ; calorimetry, ∆H , Cp .
Thermodynamic data on iron and solubility of Green Rusts Thermodynamic data from 1952 to 2013
Thermodynamic data from 1952 to 2013
synthesis of Lemire-2013 The data evaluated resulted from the three classical methods: measurements of chemical equilibria, K , Ksp ; electrochemical measurements E ; calorimetry, ∆H , Cp .
Thermodynamic data on iron and solubility of Green Rusts Thermodynamic data from 1952 to 2013
Thermodynamic data from 1952 to 2013 The extrapolation to zero ionic strength
Extrapolation uses the SIT model (specific interaction theory) of Brønsted-Scatchard-Guggenheim: √ X A Im 2 √ + log γj = −zj (j, k, Im )mk , 1 + 1.5 Im k
Thermodynamic data on iron and solubility of Green Rusts Thermodynamic data from 1952 to 2013
Thermodynamic data from 1952 to 2013 The extrapolation to zero ionic strength
Extrapolation uses the SIT model (specific interaction theory) of Brønsted-Scatchard-Guggenheim: √ X A Im 2 √ + log γj = −zj (j, k, Im )mk , 1 + 1.5 Im k
Thermodynamic data on iron and solubility of Green Rusts Selection of thermodynamics data
Selection of thermodynamics data
Reaction of formation Fe2+ + Cl – −FeCl+ Fe2+ + SO42 – −FeSO4 Fe2+ + HSO4 – −FeHSO4+ Fe2+ + CO32 – −Fe(CO3 )
phreeqc.dat 0,14 2,25 1,08 4,38
log K (T 0 ) sit.dat Lemire-2013 0,14 2,2 1,082 5,69
−1,000 2,440 5,266
Some chemical species, considered doubtful, are excluded from the base: Fe(OH)42 – , FeHSO4+ , FeCO3 OH – , FeHCO3+ . . . The selected data are incorporated into a base sit_mod_2015.dat, including the values of the specific interaction coefficient .
Thermodynamic data on iron and solubility of Green Rusts Selection of thermodynamics data
Selection of thermodynamics data
Reaction of formation Fe2+ + Cl – −FeCl+ Fe2+ + SO42 – −FeSO4 Fe2+ + HSO4 – −FeHSO4+ Fe2+ + CO32 – −Fe(CO3 )
phreeqc.dat 0,14 2,25 1,08 4,38
log K (T 0 ) sit.dat Lemire-2013 0,14 2,2 1,082 5,69
−1,000 2,440 5,266
Some chemical species, considered doubtful, are excluded from the base: Fe(OH)42 – , FeHSO4+ , FeCO3 OH – , FeHCO3+ . . . The selected data are incorporated into a base sit_mod_2015.dat, including the values of the specific interaction coefficient .
Thermodynamic data on iron and solubility of Green Rusts Selection of thermodynamics data
Data set Previous studies and this study Mineral
Fe(OH)2 GR2-SO4 GR1-Cl GR1-CO3 GR1-Ox
Previous studies * this study* ∆f Gm0 ∆f Gm0 /kJ mol−1 −489,0 −3790,0 −2131,0 −3569 −4672
-490.035 -3791.232 -2144.973 -3591.967 -4702.984 mineral.
Difference
1,0 1,2 14,0 23,0 31,0
*For anhydrous
The discrepancy increases with the complexing power of the anion vis-à-vis iron Fe(II): Cl – < CO32 – < Ox2 – when the iron complexation was not taken into account.
Thermodynamic data on iron and solubility of Green Rusts Selection of thermodynamics data
Data set Previous studies and this study Mineral
Fe(OH)2 GR2-SO4 GR1-Cl GR1-CO3 GR1-Ox
Previous studies * this study* ∆f Gm0 ∆f Gm0 /kJ mol−1 −489,0 −3790,0 −2131,0 −3569 −4672
-490.035 -3791.232 -2144.973 -3591.967 -4702.984 mineral.
Difference
1,0 1,2 14,0 23,0 31,0
*For anhydrous
The discrepancy increases with the complexing power of the anion vis-à-vis iron Fe(II): Cl – < CO32 – < Ox2 – when the iron complexation was not taken into account.
Thermodynamic data on iron and solubility of Green Rusts Relationship between free energy and electronegativity of the anion
Electronegativity of Allred-Rochow
Partial charges model of Jolivet (1994) P p ∗ χ + 1.36Z i , Pi 1
χ =
i
Element
H
C
χ∗i
2,10
2,50
–
Anion
Cl
χ
0,5421
OH
p ∗ χi
O
–
1,6005
S
Cl
3,50
2,48
2,83
2–
SO42 –
C2 O42 –
CO3
2,0007
2,2856
2,329
Thermodynamic data on iron and solubility of Green Rusts Relationship between free energy and electronegativity of the anion
Electronegativity of Allred-Rochow
Partial charges model of Jolivet (1994) P p ∗ χ + 1.36Z i , Pi 1
χ =
i
Element
H
C
χ∗i
2,10
2,50
–
Anion
Cl
χ
0,5421
OH
p ∗ χi
O
–
1,6005
S
Cl
3,50
2,48
2,83
2–
SO42 –
C2 O42 –
CO3
2,0007
2,2856
2,329
Thermodynamic data on iron and solubility of Green Rusts Relationship between free energy and electronegativity of the anion
Relation between ∆f Gm0 of GRs and electronegativities of the anions
Normalisation to 2 OH in the layer per mole formula The Gibbs free energy is normalized to 2 OH in the structure: for example 3+ 2– GR2 : [Fe2+ 4/6 Fe2/6 (OH)2 ][(SO4 )1/6 ], and logically the electronegativity of the anion is normalized in the same way.
Thermodynamic data on iron and solubility of Green Rusts Relationship between free energy and electronegativity of the anion
Relationship between free energy and electronegativity of the anion Previous studies
this study
y = −486.139 − 351.92 χn , R 2 = −0.990.
y = −488.354 − 353.11 χn , R 2 = −0.994.
Thermodynamic data on iron and solubility of Green Rusts Relationship between free energy and electronegativity of the anion
Dataset
Reevaluation of the free energy of fougerite Mineral
Previous studies* ∆f Gm0
this study* ∆f Gm0 /kJ mol−1
Difference
Fe(OH)2 GR2-SO4 GR1-Cl GR1-CO3 GR1-Ox
−489,0 −3790,0 −2131,0 −3569 −4672
-490.035 -3791.232 -2144.973 -3591.967 -4702.984
1,0 1,2 14,0 23,0 31,0
GR1-OH
−2034,57
-2030.220
4,4
* For anhydrous mineral.
Thermodynamic data on iron and solubility of Green Rusts Ferrous hydroxide: Conditions of preparation
Ferrous hydroxide: Conditions of preparation
Ferrous hydroxide: Conditions of preparation Under an inert atmosphere glove box, Mixture of ferrous chloride or ferrous sulfate and sodium hydroxide, Purity of the substances used, Quickly recover the precipitate before aging.
Thermodynamic data on iron and solubility of Green Rusts Working in oxygen-free atmosphere
The glove box
Working in an inert atmosphere (pO2 < 5ppm) avoids any precipitation of ferric minerals (FeOOH) or ferrosoferric mineral (green rusts).
Thermodynamic data on iron and solubility of Green Rusts Working in oxygen-free atmosphere
The glove box
Working in an inert atmosphere (pO2 < 5ppm) avoids any precipitation of ferric minerals (FeOOH) or ferrosoferric mineral (green rusts).
Thermodynamic data on iron and solubility of Green Rusts The preliminary alkaline pH solubility curve
Dominant species Dominant species
Thermodynamic data on iron and solubility of Green Rusts The preliminary alkaline pH solubility curve
Solubility curve of Mg(OH)2
solubility curve of Mg(OH)2
Thermodynamic data on iron and solubility of Green Rusts XRD analyzes of the precipitate
Preparation of sample for analysis
Preparation of sample for analysis 1
2
3 4
Using a GTTP filter type 02500 in diameter and 0,5 µm, the precipitate is recovered; They were put into a desiccator for at least 2 hours in order to dehydrate; They were scraped thoroughly and ground in a mortar; They were put into a capillary type "Special Glass" and diameter 0,5 mm.
Thermodynamic data on iron and solubility of Green Rusts XRD analyzes of the precipitate
pattern typique of Mg(OH)2
pattern typique of Mg(OH)2
Thermodynamic data on iron and solubility of Green Rusts XRD analyzes of the precipitate
XRD patterns of Mg(OH)2 samples XRD patterns of Mg(OH)2 samples
Thermodynamic data on iron and solubility of Green Rusts Crystallite size and morphology of Mg(OH)2
Crystallite size The mean crystallite size can be estimated by applying Debye-Scherrer formula Lhkl =
k ∗λ β ∗ cos( 2θ 2 )
(1)
where: Lhkl is the mean size of the ordered (crystalline) domains, which may be smaller or equal to the grain size; K is a dimensionless shape factor, with a value close to unity. The shape factor has a typical value of about 0,9; λ is the X-raywavelength; β is the line broadening at half the maximum intensity (FWHM), after subtracting the instrumental line broadening, in radian; θ is the Bragg angle.
Thermodynamic data on iron and solubility of Green Rusts Crystallite size and morphology of Mg(OH)2
Morphology of Mg(OH)2 The XRD pattern of the products showed the presence of reflections characteristic of the hexagonal phase of the products; The powder XRD peaks are consistent with the data of the JCPDS file of Mg(OH)2 with hexagonal phase; The cell constants are calculated to be a = 3,1442 Å and c = 4,7770 Å which are in agreement with the reported values of a = 0,3147 Å and c = 0,4769 Å; the products size, calculated from DebyeScherrer formula based on the full width at half-maximum (FWHM) of different diffraction peaks, has different values, which indicates that Mg(OH)2 has a very small size. The morphology of crystalline particles obtained mainly varies depending on the salt concentration and base initially introduced into this solution
Thermodynamic data on iron and solubility of Green Rusts Conclusion
Conclusions Importance of choosing of the thermodynamic data basis and operating conditions The consideration of speciation in solution with SIT model and consistent database allow better identification of iron species and metal formed and may form; For isostructural compounds electronegativity Allred-Rochow and partial charge model of Jolivet (1994) predict thermodynamic datas; The width of the diffraction peaks and the crystallite size of Fe(OH)2 and Mg(OH)2 used to characterize the nature of the crystals contained in the powder samples analyzed
Thermodynamic data on iron and solubility of Green Rusts Conclusion
Conclusions Importance of choosing of the thermodynamic data basis and operating conditions The consideration of speciation in solution with SIT model and consistent database allow better identification of iron species and metal formed and may form; For isostructural compounds electronegativity Allred-Rochow and partial charge model of Jolivet (1994) predict thermodynamic datas; The width of the diffraction peaks and the crystallite size of Fe(OH)2 and Mg(OH)2 used to characterize the nature of the crystals contained in the powder samples analyzed
Thermodynamic data on iron and solubility of Green Rusts Conclusion
Conclusions Importance of choosing of the thermodynamic data basis and operating conditions The consideration of speciation in solution with SIT model and consistent database allow better identification of iron species and metal formed and may form; For isostructural compounds electronegativity Allred-Rochow and partial charge model of Jolivet (1994) predict thermodynamic datas; The width of the diffraction peaks and the crystallite size of Fe(OH)2 and Mg(OH)2 used to characterize the nature of the crystals contained in the powder samples analyzed
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