Table 2

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)]


Boyd and Scott Geochemical Transactions 2001 2:45   doi:10.1186/1467-4866-2-45

Open Data