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Roberto Moretti
Seconda Università di Napoli Dip. Ingegneria Civile
Via Roma 29 - 81031 Aversa (I)
INGV - Osservatorio Vesuviano Via Diocleziano 328 - 80124 Napoli (I)
Redox in melts and glasses… an introduction ?
Gaillard & Behrens, 2006
Mysen and Richet 2005
!???!
Mysen and Richet 2005
……..
Empirical efforts….
S2- + 2O2 SO42-
44 BaSO
glass
FeSBaSO
FeSglass24
SKSK
SKSKSKSK
nStotnSO
αλΔ
αλΔ=
αλ−αλ
αλ−αλ=
−
[ ][ ]
log . log /S
SOfO T
2
42 2
1 02 25410 10−
−= − − +
Locus of points from Wallace and Carmichael (1994)
Dealing with redox couples: an example from lte literature
Log K = -1.97 logfO2R2 = 0.98
0
5
10
15
20
25
30
35
40
-20 -15 -10 -5 0log fO2 (bars)
Ther
mod
ynam
ic e
quili
briu
m K
12
(log 1
0, ad
imen
sion
al)
Log K = 35078/T - 7.6021
R2 = 0.67
5
15
25
35
0.0005 0.00075 0.001
1/T (K-1)
log
K12
K = [SO42-]/[S2-]fO22
Moretti and Ottonello (2003), J. Non-Cryst. Sol.
X
=> Good compatibility between different techniques!
0
0.2
0.4
0.6
0.8
1
MössbauerXANESRaman
0 0.2 0.4 0.6 0.8 1
Fe3+
/ !Fe
Fe3+/ !Fe (wet chemical analyses)
Magnien V., Neuville D.R., Cormier L., Mysen B.O. and Richet P. (2004) Kinetics of iron oxidation in silicate melts: A preliminary XANES study. Chem. Geol., 213, 253-263.
Galoisy 2006
The questions…
-How do we write chemical reactions for silicate melts
to account for COMPOSITIONAL dependences?
-Which ‘syntax’ do we use?
-Is the chemical syntax for describing chemical
exchanges directly available from structural studies?
Or is just an (useful) approximation of some major
features?
Intact solvation shells Partial disruption of solvation shells
Disruption of solvation shells
Outer sphere ion pair Inner sphere ion pair
(complex)
Mysen and Richet, 2005
Depolymerization of Silicate Melts to accommodate volatiles (e.g. water)
Some observations…
We usually do not perceive the problem of the chemical
syntax as long as:
-we interpret our own data and a few more
Thus we tend to adopt the detected structural
scenario and turn it into the chemical syntax
Some observations…
- But what happens if we want to find the general chemical mechanism and set models? (….the problem of many data from many compositions…)
- How “convert“ structural findings into speciation hypotheses for general chemical mechanisms?
Acid-base exchanges The dividing line between the Lewis acids and bases is not sharp a one, and its theoretical interpretation is obscure Strong role of the molecular structure (hence, bulk composition) Hard and soft categories…(atomic structures associated with hard acids and bases are rigid and impenetrable, whereas those associated with soft acids and bases are more readily deformable)
...it is not practical if we deal with chemical reactions
For example…
This acid-base and redox exchange synthesizes many (combined) reactions:
SO2(g) + 1/2O2(g) + CaO(m) CaSO4(m) + SO2(g) + 1/2O2(g) + H2O(m) H2SO4(m) +
SO2(g) + 1/2O2(g) + 1/2SiO2(m) 1/2Si(SO4)2(m) +
… … +
… … +
… … …
Marini, Moretti ,Accornero 2011
So we need ions… • “The formation of ions sensu stricto in liquid water is due to
the high dielectric constant of aqueous medium (efficient shielding of charge) as also manifested by the formation of hydration spheres.
• In contrast, none of these concepts is applicable to silicate melts. The dielectric properties are different, no volumetric electrostriction is known, electrostatic bond valences are generally greater to allow for such effects.
• The only and apparent similarity arises from adoption of analogous symbolic notation for melt species that uses negative charge, therefore, the thermodynamic identities look like ions”
• the connectivity of the silicate structure is such that cations and anions have actual charges lower than formal ones, and the residual charge distribution from bonding of bridging oxygen to silicon allows oxygen bonding with other cations.
• This makes the relative contribution of nonbridging and bridging oxygens to the oxygen coordination of the other cations poorly known (Mysen and Richet, 2005) and highlights the impossibility to readily distinguish solute and solvent like in aqueous solutions.
• The anionic framework of silicate melts, in fact, makes solute and solvents so intimately related that one cannot identify a solvation shell and identify directly, from structural studies, the complexes needed to define acid-base reactions.
So, we need ions to write chemical reactions…but…
2O- O0 + O2- Vs. 2Qn Qn-1 + Qn+1
(Polymerization Vs. Connectivity)
…to understand what determines acid-base behavior and to write and inspect chemical reactions we have to assume an understanding of the bonding, structure, and properties of individual molecules also in melts (with its pros and cons…)
Nevertheless…
The “thermochemical knowledge” of a melt system does not seem to require the microstructural
“complexity” that can be revealed by many spectroscopic investigations: the structural
“characterization” exceeding that required for the description of acid-base properties (e.g, in the
Lux-Flood notation) may be not useful.
How deep need we to go with connections between structure and chemical thermodynamics ?
In (essentially aprotic) silicate melts acid-base properties are expressed in terms of Lux-Flood formalism: Acid + O2- Base (1) “Reaction” 1 recalls the Bronsted-Lowry formalism for aqueous solutions: Acid Base + H+ (2)
Which acid-base ‘syntax’ to describe reactivity in melts?
Which redox ‘syntax’ to describe reactivity in melts?
In aqueous solutions the electrode of reference is the “normal hydrogen electrode”, whereas in silicate melts
the reference electrode is the “normal oxygen electrode” ,i.e.:
1/2O2 + 2e- O2- (3)
Even if the main redox couple in oxide melts is given by iron, reaction (3) follows the syntax based on the O2-
exchange
O2- ? Virtual or real ?
Calculated from data in Park and Rhee (2001)
Nesbitt et al. (2011)
Free-oxygen = oxide ion…attached to some metal cation
Polymeric nature of anion matrix: Toop-Samis and Masson models
In polymeric models for silicate melts, it is postulated that, at each composition, for given P-T values, the melt is characterized by an equilibrium distribution of several ionic species of oxygen, metal cations and ionic polymers of monomeric units SiO44-.
−− +⇔ 2m0
mm OO2O
−−−− +⇔+ 267244
44 OOSiSiOSiO
2
2
58 )(O))(O(OK
−
−°
=
polymmixing )/2]RTlnK[(OΔG−=
( ) ( )2ON4
O 2SiO0−−
=
( ) ( ) ( )2ON1O
2SiO2
−− −−=
( ) ( ) ( )( ) ( ) 01NN8N22O1K4O222 SiOSiOSiO2
2=−+++− −−
Kp=(O°)(O2-)/(O-)2
On the basis of simple mass balances we can link the three oxygen species to the melt composition and therefore to the melt compositions
Theory: the polymeric model
⎥⎥⎦
⎤
⎢⎢⎣
⎡−⎟⎟⎠
⎞⎜⎜⎝
⎛γ−γ×= +η+η+ν+ν ∑∑ 1445.1XX662.4expK
jjìi TjTM
iMpolym
Modifiers - Formers KP= exp(4.662Δγ-1.1445)-8
-7
-6
-5
-4
-3
-2
-1
0
0.5 1 1.5 2 2.5γΜν+
ln K
P,M
O-S
iO2
[16]
[17,18]
[24]
[25]
[26]
This study
( )polym.RTlnK2
OΔG mixing−
=
Ottonello et al., Chem. Geol. (2001)
Even simple interaction parameters along limiting binaries cannot be reduced to fitting coefficients of mathematical minimization routines, but must be formally linked to the intrinsic atomistic properties of the interacting ions and molecules
depolymerizing role of water has been overrated with respect to its actual acid-based properties in melts.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.2 0.4 0.6 0.8 1
X SiO2
(O- );
(O°)
; (O
2-)
(frac
tions
)
fO-
fO2-
fO°
T=1600°C ; P=1 barKP=0.0003 CaO-SiO2
Ottonello et al., 2001
Back to basics: amphoteric behavior of trivalent iron
melt2,2melt
-2melt
3melt
melt2,-2melt
2melt
-3melt
O41FeO
21Fe
_______________________________
O41O
21
FeFe
+⇔+
=+⇔
+⇔+
++
−
++
e
e
melt2,-2
melt2meltmelt2,
melt2,melt2,
-2melt
2meltmelt2,
O41 O
23 FeFeO
_________________________________
O41 O
21
2O FeFeO
++⇔
=+⇔
++⇔+
+−
−−
+−−
e
e
That’s the way electron transfer operates. It is not evident from the equilibrium involving macroscopic components: to get that you must adopt the ionic notation.
(From the Fraser’s approach to Europium)
FeO + 1/4O2 FeO1.5
In the above reaction the redox potential is expressed by the oxygen fugacity . But how does the electron transfer take place?
5.12 FeOO41FeO ⇔+ 1)
−− ⇔+)melt()melt()melt( 2
232 FeO2OOFe 2)
Fe O Fe Omelt melt melt
2 33 22 3
( ) ( ) ( )⇔ ++ − 3)
FeO Fe Omelt melt melt( ) ( ) ( )
⇔ ++ −2 2 4)
Adopting The ionic model of Fused Salts after Temkin (1945):
[ ][ ] [ ]∑ ∑
∑+−
+
+==⎟⎟
⎠
⎞⎜⎜⎝
⎛
cationsFeanionsFeOcationsFe
nn
FeFe
32
2
Fe
FeIII
II
III
I1
∑ ∑∑+
×=⎟⎟⎠
⎞⎜⎜⎝
⎛
−
−
cationsKanionsaKcationsKa
KFeFe
O
O
OIII
II
213
2212
421
411 2
2
2f1
Ratio of activities (aFeO/aFeO1.5)
Ratio of activity coefficients (γFeO1.5/γFeO)
Iron redox model
The message:
1. Silicate melts are polymerized liquids 2. Polymeric units are highly reactive
Polymerization and redox state are intimately interrelated. This melt affects properties, including oxidation state, volatile solubility et cetera.
Fig. 4.12: Computed versus measured activity of ferrous oxide components in melts equilibrated with metallic iron at various T anf fO2 conditions and 1 bar pressure.
Fig. 4.10: Thermodybamic activity of stoichiometric ferrous oxide FeO in equilibrium with pure iron metal at T=1600K and various aO2.
Ottonello et al., 2001
ο This work eqn 4.61
Fig. 4.14: fO2 estimates based on thermochemical model (eqn. 4.61) (4.13) and those based on Sack equation 4.86 (b). The dataset is the same used for model calibration, in both cases.
Ottonello et al., 2001
Fig. 4.15: Comparison between fO2 estimates based on thermochemical model and estimates of the Kilinc equation. Dataset is the same adopted in constraining iron equilibria in molten systems.
Ottonello et al., 2001
Fig. 4.13: Iron redox ratio in quenched melts and glasses equilibrated with a fO2 buffered atmosphere at various T conditions.
Ottonello et al., 2001
Fig. 4.20: Quantile-quantile representation of the observed Vs calculated FeO and Fe2O3 wt% amounts in the two subsets.
calc
ulat
ed
measured
Fig. 4.19: Statistics of residuals for the Mossbauer and wet chemistry data subsets. The distribution of residuals for wet chemistry subset (444 samples) is normal, centered on x= 0.0003. The distribution of residuals for the Mossbauer dataset (100 samples) is non-normal, centered on x = -0.2254.
Ottonello et al., 2001
Let us introduce the amphoteric behavior of water, i.e. an acidic dissociation: H2O + O2- 2OH-
Which can be coupled to the basic dissociation (see Fraser): 2H+ + O2- H2O
By subtracting: H+ + O2- OH-
∑−+
−
− −⋅=
cationsnn
nn
K OHTOTH
OH
O2OHOH
INH 2n2nn ⋅=+ −+
Moretti (2005, AoG)
At parity of water content, high free hydroxyl concentration is expected in more basic melts, in
agreement with Xue and Kanzaki (2004), Behrens et al. (2004) for water diffusivities etc…
Iron redox ratio in hydrous silicate melts is also origin of controversies. Current hypotheses about the role of water on the FeIII/FeII value are:
-Water does not affect ferric to ferrous ratio. -Water causes a decrease of the ferric to ferrous ratio. -Water causes an increase of the ferric to ferrous ratio.
==> Parameterization of the ferric to ferrous ratio should consider the “impact” of water on melt acid-base properties and then polymerization together with the effect of pressure on the previous reactions.
New experimental evidences
Botcharnikov et al. (GCA, 2005)
QFM + const redox buffer holding on each line
Model comparison
Botcharnikov et al. (2005)
Fe/ F
eII
I II
H O (wt
%)
2
0.2
0.6
1
1.41.8
2.22.63
About the effect of water on the iron oxidation state of melts…
Redox models simply relating Fe2+/Fe3+ to fO2 are not applicable !
Moretti (in prep.)
Iron redox model: unexpected features
We can explain, for example, the increase of oxidation with decreasing T. This depends on oxygen fugacity, that is, on how fO2 varies with T. We propose that under constant fO2 , or more precisely for
a decrease of T can cause iron oxidation. 22000
12 −≈>
⎟⎠
⎞⎜⎝
⎛∂
∂
T
fO(depending on composition…)
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
400 600 800 1000 1200 1400 1600 1800
T (K)
log fO2= -8
P = 2000 barH2O = 2.5 wt%
log fO2= -17000/T + 2
NNO
QFM
Log F
eIII/F
eII
Métrich et al., 2006
S as sulphide S as sulphate
Sulfide equilibrium: (L)S(G)O
21(G)S
21(L)O 222
-2 −+⇔+
Sulfate equilibrium:
(L)SO(G)O23(G)S
21(L)O 2422
-2 −⇔++
S as sulphide S as sulphate
S solubility: the Conjugated-Toop-Samis (CTSFG) model (Moretti and Ottonello, 2005)
0
0.5
1
1.5
2
2.5
3
-4 -3 -2 -1 0 1 2 3 4ΔQFM
log
S(pp
m)
Model calculation
Katsura andNagashima (1974)
Katsura and Nagashima (1974), Tholeiite, 1250°C
SO2 (i) = 0.21%
Slope = -1.5
Slope = 0.5
for QFM > -1
Moretti and Ottonello (2005 GCA)
Sulfide equilibrium: (L)S(G)O
21(G)S
21(L)O 222
-2 −+⇔+
Sulfate equilibrium:
(L)SO(G)O23(G)S
21(L)O 2422
-2 −⇔++
CaO-SiO2
-7
-6
-5
-4
-3
-2
-1
0 0.2 0.4 0.6 0.8 1CaO (molar fraction)
log
Cs
(wt%
)
1650 °C
1500 °C
MnO - SiO2
-6
-5
-4
-3
-2
-1
0
0 0.2 0.4 0.6 0.8 1MnO (molar fraction)
log
Cs
(wt.
%)
1500 °C
1650°C °C
MnO - Al2O3
-2.5
-2
-1.5
-1
-0.5
0
0 0.2 0.4 0.6 0.8 1MnO (molar fraction)
log
Cs
(wt.%
)
1650 °C
Moretti and Ottonello, 2003
(L)MSO(G)O23)(
21MO(L) 422 ⇔++ GS
⎟⎟⎠
⎞⎜⎜⎝
⎛−
Δ−+==
−− )1(exp''
''21
23
22
4
4P
RTv
Tbaff
aa
k LiiSOOM
SOMSOO-MM
i
i
ii
Sulfate-metal oxide reactions:
(G)O21MS(L))(
21MO(L) 22 +⇔+ GS
⎟⎟⎠
⎞⎜⎜⎝
⎛−
Δ−+=⎟
⎟⎠
⎞⎜⎜⎝
⎛= )1(exp
''
21
2
2 PRTv
Tba
ff
aa
k LiiS
O
OM
SMSO-MM
i
i
ii
Sulfide-metal oxide reactions:
iSOSMOanneal
N
iiSOS kCNk
OX
),,(1
, 2422
42 lnln −−
+
−− −=∑=
ν
Gas-liquid reactions: Flood and Grjotheim (1952) thermochemical cycle:
∑=
+
++ =
OXN
iii
iii
n
nN
1ν
νν
where Niν+ represent electrically equivalent fractions, and ni are mole fractions computed over the appropriate matrix, either cationic or anionic (Temkin model of fused salts)
Theory of the S solubility model (CTSFG)
−− +⇔ 20 OO2OFincham and Richardson (1954):
O- are singly bonded (or non-bridging) oxygens
• O0 are doubly bonded (or bridging) oxygens
• O2- are free oxygens The Toop-Samis (extended) model is applied
[ ]21
%2
22 ⎟
⎟⎠
⎞⎜⎜⎝
⎛=−
S
OwtS f
fSC
[ ] 21S23
O%wtSO 2224ffSC
−−=−
The model computes Canneal. (entropies of annealing). kMO-(S2-,SO42-) constants are from independent thermodynamic compilations when available.
SiO2 Al2O3
CaO
25
50
75
25 50 75
25
50
75
-5.18-5.15
-3.52-3.84
-4.81-4.98
-4.21
-5-5.5-4.5-4-3.5-3-2.5
-2.5-3.83
-4.1-4.33-4.58
-4.60
-3.7
-3.71
-4.04
-4.17-4.38-4.64 -4.12
-3.98-4.2
-2
b)
SiO2-Al2O3-CaO, T = 1500°C
SiO2 Al2O3
CaO
25
50
75
25 50 75
25
50
75
-4.43
-5.5-4.5-4-3.5-3-2.5
-2.5
a)
-2
-5
-2.28
-4.30-4.22
-4.10
-3.62-3.60
■
Moretti and Ottonello (2003), Metall. Mat. Trans. B
The S solubility (CTSFG) model: verification and check of the simplex and its features
Moretti and Ottonello (2005)
Simple metallurgical slags (log Cs contouring)
Natural-like melts (sulfur content)
0500
1000150020002500300035004000
-10 -9 -8 -7 -6 -5 -4logfO2 - logfS2
O'Neill and Mavrogenes(2002) - measured
Cape Vogel Andesite
d)present model
0
5001000
150020002500
30003500
4000
-10 -9 -8 -7 -6 -5 -4logfO2 - logfS2
O'Neill andMavrogenes (2002)- measured
MORB
b)present model
0
2000
4000
6000
8000
10000
12000
14000
-12 -11 -10 -9 -8 -7 -6 -5 -4logfO2 - logfS2
S (p
pm)
Buchanan and Nolan (1983)
present model
a)
0500
1000150020002500300035004000
-10 -9 -8 -7 -6 -5 -4logfO2 - logfS2
S (p
pm)
O'Neill andMavrogenes(2002) - measured
Olivin Tholeiite
c)present model
S solubility at P: considering volumes for systems in which they have never been determined !
( )∫ +−+=ʹ′ −−−−P
1gm
'MS,O
'MS,O
TPMS,O dPΔVΔVRT
1TBAKln
1-bar lnK
Our value for the (partial) molar volume of VSO3 is 57.71 cm3/mol at 1673K… must be checked
experimentally (no data at present) 3
υ24
υ2 SOOMSOM VVV +=
++
/mol)(cm41VVΔV 3SMSOMS-SOυ24
υ224
=−=++
Moretti and Ottonello (2005)
The CTSFG solubility model: features of the sulfide and sulfate capacity surfaces
Kilauean Tholeite
-6.5-6.25
-6-5.75-5.5
-5.25-5
-4.75-4.5
-4.25-4
-3.75
0 1 2 3 4 5 6 7 8 9 10H2O (wt%)
log
CS
1050°C
1100°C
1150°C1200°C
5 kbar
4 kbar
3 kbar
2 kbar
1 kbar
0.5 kbar
1 bar
0.1kbar
a)
Arc Basalt
-7
-6.5
-6
-5.5
-5
-4.5
-4
0 1 2 3 4 5 6 7 8 9 10 11H2O (wt%)
log
CS
1000°C
1050°C
1150°C1100°C
1 bar
0.5 kbar2 kbar
1 kbar
3 kbar
4 kbar
5 kbar0.1 kbar
b)
Andesite
-9
-8.5
-8
-7.5
-7
-6.5
-6
-5.5
-5
0 1 2 3 4 5 6 7 8 9 10H2O (wt%)
log
CS
850°C900°C
1000°C
950°C
1 bar
0.5 kbar
1 kbar
2 kbar
3 kbar
4 kbar
5 kbar
0.1 kbar
c)
Rhyolite
-14
-13
-12
-11
-10
-9
-8
-7
-6
0 1 2 3 4 5 6 7 8 9 10H2O (wt%)
log
CS
800°C850°C
900°C
1 bar
0.5 kbar 1 kbar
2 kbar 3 kbar
4 kbar
5 kbar
0.1 kbar
750°C
700°Cd)
Kilauean Tholeite
88.5
99.510
10.511
11.512
12.513
13.514
14.5
0 1 2 3 4 5 6 7 8 9 10H2O (wt%)
log
CSO
4
1050°C
1100°C
1150°C
1200°C
3 kbar2 kbar
4 kbar
1 kbar
0.5 kbar1 bar
5 kbar
a)
0.1 kbarArc Basalt
8
9
10
11
12
13
14
15
16
0 1 2 3 4 5 6 7 8 9 10 11H2O (wt%)
log
CSO
4
1150°C
1100°C
1050°C
1000°C
1 bar 0.5 kbar
1 kbar
2 kbar3 kbar
4 kbar5 kbarb)
0.1 kbar
Andesite
11
12
13
14
15
16
17
18
19
0 1 2 3 4 5 6 7 8 9 10H2O (wt%)
log
CSO
4
850°C
900°C
950°C
1000°C
1 bar
0.5 kbar
1 kbar
2 kbar
3 kbar
4 kbar
5 kbar
0.1 kbar
c)
Rhyolite
11
13
15
17
19
21
23
0 1 2 3 4 5 6 7 8 9 10H2O (wt%)
log
CSO
4
800°C
850°C
900°C
1 bar
0.5 kbar1 kbar
2 kbar3 kbar
4 kbar
5 kbar
d)
0.1 kbar
750°C
700°C
[ ] [ ] [ ]21
2
21
2S
21
223
2Ssulfatewt%,sulfidewt%,totwt%, fOfSCfSfOCSSS 26 −+ +=+=
Lesne, 2008
The CTSFG model for sulfur: bulk performance and suggestions for experimentalists
Limits - Most data are at 1 bar ! => more data at pressure are needed
- Few data for sulfate solubility (high fO2) even at 1 bar !
- Lack of experimental data on partial molar volumes of sulfide and sulfate liquid species - Need of fS2 probes for high-P pressure vessel experiments
-12
-10
-8
-6
-4
-2
0
-12 -10 -8 -6 -4 -2 0
log Csulfide (experimental)
log
Csu
lfide
(cal
cula
ted)
Anhydrous dataset (P = 1 bar)1081 compositions
Hydrous dataset (via Papalemodel) 60 compositions
-20%
+20%
a)
R2 = 0.946 (1141 data)σy,x= 0.205
Annealing volumetric terms added2.5
5
7.5
10
12.5
15
17.5
20
2.5 5 7.5 10 12.5 15 17.5 20
log Csulfate (experimental)
log
Csu
lfate
(cal
cula
ted)
Anhydrous dataset (P = 1 bar)172 data
Hydrous dataset (via Papalemodel) 49 compositions
e)
-10%
+10%
R2 = 0.990 (221 data)σy,x= 0.278
Moretti and Ottonello (2005)
Lehmann and Nadif, 2011
Are complex approaches really needed for data interpretation?
Scaillet and Pichavant (2003) Geol. Soc. Spec. Publ. 213 Moretti et al. (2003) Geol. Soc. Spec. Publ. 213
Mass partitioning in Nature is non-linear. The expected linearity required by theory (stoichiometry in this case) is embodied, not
cancelled. “Complex” models may reveal it.
Tholeite, 1400K . H2Otot=3%wt; CO2tot=1%wt; Stot=0.5%wt
Moretti et al. (2003)
Baker & Moretti (2011)
Baker & Moretti (2008)
STRONG ROLE OF COMPOSITION (e.g. H2O content) ON SULFUR SPECIATION !
Never forget this!
... the S2- + 2O2 SO42- equilibrium computed by the CTSFG model is then applied to an independent set of data:
-8
-6
-4
-2
0
2
4
6
8
−8 −6 −4 −2 0 2 4 6 8
ΔQFM (experimental or estimated)
ΔQ
FM (c
alcu
late
d)
Model calculation
Wallace andCarmichael(1994) equation
Validity range of ΔλSKα technique
in melts.
a)
-8
-6
-4
-2
0
2
4
6
8
−8 −6 −4 −2 0 2 4 6 8
ΔQFM (experimental or estimated)
ΔQ
FM (c
alcu
late
d)
Model calculation
Wallace andCarmichael(1994) equation
Validity range of ΔλSKα technique
in melts.
Volumetric annealing terms
included
b)
Application to S speciation and fO2 determination
Moretti and Ottonello 2005
The H2O-CO2-H2S-SO2 saturation model
Morett i and Papale (2004) Chemical Geology
Gas phase H 2 O, CO 2 , SO 2 , H 2 S
homogeneous equilibrium ( chemical reactions )
(SUPERFLUID – Belonoshko et al., 1992 )
Liquid phase H 2 O + CO 2 saturation
( Papale, 1999 )
Liquid phase mass balance
reactive and/or dissolution effects
Redox conditions
Gas phase H 2 O, CO 2 , SO 2 , H 2 S
homogeneous equilibrium ( chemical reactions )
(SUPERFLUID – Belonoshko et al., 1992 )
Liquid phase H 2 O + CO 2 saturation
( Papale, 1999 )
Liquid phase mass balance
reactive and/or dissolution effects
Redox conditions
Gas phase H 2 O, CO 2 , SO 2 , H 2 S
homogeneous equilibrium ( chemical reactions )
(SUPERFLUID – Belonoshko et al., 1992 )
Liquid phase H 2 O + CO 2 saturation
( Papale, 1999 )
Liquid phase mass balance
reactive and/or dissolution effects
Redox conditions
Gas phase H 2 O, CO 2 , SO 2 , H 2 S
homogeneous equilibrium ( chemical reactions )
(SUPERFLUID – Belonoshko et al., 1992 )
Liquid phase H 2 O + CO 2 saturation
( Papale, 1999 )
Liquid phase S saturation S saturation S saturation S
mass balance
reactive and/or dissolution effects
Redox conditions
(Moretti et al., 2003) al., 2003)
FeII/FeIII model (Moretti, 2004)
Theory of the revised and extended H2O-CO2 saturation model (Papale et al., 2006)
• Fully non-ideal • Fluid phase of any composition in the system H2O+CO2
• Liquid phase of any composition from two/three components to natural (12 components)
Equilibrium equations
oLCOCOCOCOCO
LCO
GCO
oLOHOHOHOHOH
LOH
GOH
LG
LG
fxPyff
fxPyffTTTPPP
2222222
2222222
γφ
γφ
=⇒=
=⇒=
==
==
22
22
22
22
221
COCO
COTCO
OHOH
OHTOH
COOH
xyxx
xyxx
yy
−
−=
−
−
=+
Mass balance equations
The revised H2O-CO2 saturation model (Papale et al., 2006)
Excess Gibbs free energy of the liquid: ijjn
i
n
iji
E wxxNG ∑∑−
= +=
=1
1 1
Water:
Carbon dioxide:
)0(
1
'2
2
22222222)1)(1()1(ln OiH
n
COiiCOOHOHOCOHCOOHOH wxxxxwxxRT ∑
=≠
−−−+−=γ
⎥⎦
⎤⎢⎣
⎡+−−− ∑∑
=≠=≠
n
OHiiCOio
n
OHiiCOiCOOHCO wxP
Pwxxxx1
)1('
1
)0('
2
2
2
2222ln)1(
)22()1(1
1, 1,
''2
22 22
22 ∑ ∑−
=≠ +=≠
−−−n
COOHi
n
iCOOHjijjiCOOH wxxxx
)0(
1
'2
2
22222222)1()1(ln OiH
n
COiiCOOHOHOCOHOHCOCO wxxxxwxxRT ∑
=≠
−−−−=γ
⎥⎦
⎤⎢⎣
⎡+−−−+ ∑∑
=≠=≠
n
OHiiCOio
n
OHiiCOiCOOHCO wxP
Pwxxxx1
)1('
1
)0('
2
2
2
2222ln)1)(1(
)23()1(1
1, 1,
''2
22 22
22 ∑ ∑−
=≠ +=≠
−−−n
COOHi
n
iCOOHjijjiCOOH wxxxx
Activity coefficients: inTPi
E
RTnG
ij
γln,,
=⎟⎟⎠
⎞⎜⎜⎝
⎛
∂
∂
≠
The model computes H2O(m)-oxides interaction parameters and CO2(m)-oxides interaction parameters. All other oxide-oxide interactions are from Ghiorso et al. (1983)
(Papale et al., 2006)
Tamic et al., 2001
Moretti et al. (2003) Geol. Soc. Spec. Publ. 213
Volatile mixed “solubility”
Papale and Moretti, work in progress
Single-step volatile separation
(applicable to glass inclusions) (applicable to the geochemical sensing of volcanoes)
40030020010000
1000
2000
3000
4000
5000
6000
pressure (MPa)
diss
olve
d S
(ppm
)
total S in the system (wTS) = 0.5 wt%
wTH2O = 2 wt%
wTH2O = 4 wt%
wTH2O = 6 wt%
wTH2O = 8 wt%
Tholeite 1400K
Moretti & Baker (2008)
STRONG ROLE OF COMPOSITION (e.g. H2O content) ON SULFUR SPECIATION !
Never forget this!
FeO(m) + ½ S2 FeS(m) + ½ O2 ; FeS(po/liq) FeS(m)
aFeO and aFeS from “built-in” polymeric modeling and Flood and Grjotheim thermochemical cycle
0
500
1000
1500
2000
2500
0 5000 10000 15000 20000P (bar)
SCSS
(ppm
)
Tholeiite, H2O = 0.5 wt% - Liquid FeS
1200°CNNO - 0.5
NNO -1
c)
NNO
Falcone et al. 2011
-2melt4,
2melt
-2melt
-2melt
3melt SOFe8O4S8Fe +⇔++
++
SO Fe O S FeOmelt melt melt melt melt42 2 2 2
28 12 8, ,− + − − −+ + ⇔ +
meltmeltmelt OFeSFeOSO ,3222
,4 48 +⇔+−−
If you write:
We can also study the mutual redox exchanges between more redox couples (when existing…) such as Fe, Ni, S and so on… But even when studying mutual interactions, O2- and therefore oxygen species via Toop-Samis equilibrium, intervene through the normal oxygen electrode (see Moretti and Ottonello, 2003 JNCS). For example, if you consider Fe and S redox equilibria you should write the following ionic equilibria:
so that O2- cancel out, you make a very huge mistake, since you are mixing different notations, confusing species with components and therefore mixing up standard states! Remind that the basis of redox reactions in melts is the “normal oxygen electrode”
Fe-S mutual interactions
-6-4-202468
1012
-2 -1.5 -1 -0.5 0 0.5
dry
2.5 H2O wt%
AndesiteP = 2 kbarT = 1050°C
NNO-3-2
-1
NNO
+1
+2
+3
Log FeIII/FeII
Log
SO42
- /S2-
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
-3 -2 -1 0 1 2 3ΔNNO
FeIII/Fetot DRY
FeIII/Fetot 2.5 wt%
H2O
S6+/Stot 2.5 wt%
S6+/Stot DRY
AndesiteP = 2 kbarT = 1050°C
0
0.2
0.4
0.6
0.8
1
1.2
600 800 1000 1200 1400 1600
T (K)
S6+/Stot dry
S6+/Stot 2.5 H2O wt%
AndesiteQFM bufferP = 2 kbar
FeIII/Fetot dry
FeIII/Fetot 2.5 H2O wt%
Fe-S mutual interactions
Remember, it is the following connection:
acid-base properties => polymerization
polymerization => redox state
redox state => solubilities
solubilities => acid-base properties, and so on…
That promotes our full understanding of the role of bulk composition on the partioning of
volatiles in magmatic systems