Table 2 |
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|
Gibbs free energies of low temperature iron and silica oxyhydroxides in the system Fe–Si–O–H at 25°C and 1 bar |
|||||
|
Sadiq and Lindsay, 1979 (ref. 39) kcal mole-1 |
Ponamperuma et al., 1967 (ref 25) kcal mole -1 |
Langmuir, 1969 (ref. 360) kcal mole-1 |
Winters and Buckley, 1986 (ref. 43) kcal mole-1 |
SUPCRT92, Johnson et al., 1991 (ref. 19) kcal mole -1 |
|
|
|
|||||
|
Fe3+ (aq) |
-4.02 |
-- |
-4.02 |
-- |
-4.12 |
|
Fe2+ (aq) |
-21.80 |
-20.3 |
-21.8 |
-18.85 |
-21.87 |
|
Fe(OH)2 (s) |
-117.584 |
-115.6 |
-117.584 |
-116.3 |
|
|
Fe(OH)3 (s) soil amorphous ferric iron |
-170.250 |
-- |
-- |
-- |
-- |
|
Fe(OH)3 (s) aged amorphous ferric iron |
-170.163 |
-- |
-- |
-- |
-- |
|
Fe(OH)3 (s) 4 day old amorphous ferric iron |
-169.250 |
-- |
-169.040 |
-- |
-- |
|
Fe(OH)3 (s) freshly precipitated amorphous ferric iron |
Nature uncertain |
-166.0 |
-167.460 |
-166.5 |
-- |
|
Fe3(OH)8 (s) freshly precipitated amorphous mixed-valence iron |
-459.220 |
-451.2 (nature uncertain) |
-- |
-- |
-- |
|
H2O |
-56.687 |
-56.7 |
-56.688 |
-56.69 |
-56.688 |
|
OH- |
-37.594 |
-- |
-37.594 |
-- |
-37.595 |
|
SiO2 amorphous |
-203.02 |
-- |
-- |
-202.89 |
-202.89 (SiO2- nH20) |
|
Ferrosilite |
-257.6 |
-- |
-- |
-267.16 |
-267.16 |
|
Si(OH)4 (aq) |
-312.66 |
-- |
-- |
-- |
-312.6 (SiO2 [aq)] |
|
|
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|
Boyd and Scott Geochemical Transactions 2001 2:45 doi:10.1186/1467-4866-2-45 |
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