Aqueous redox speciation

Step 1 - No redox equilibrium

Aqueous redox species are defined as primary species. They do not react at equilibrium.

TITLE Redox speciation - Step 1

RUNTIME
database ../../CrunchDatabase_ThermoChimie_v12a.dbs
speciate_only true
END

PRIMARY_SPECIES
H2O
H+
Na+
Cl-
Fe+2
O2
H2  
HS-
Fe+3
END

SECONDARY_SPECIES   
OH-  
FeCl+    
Fe(OH)+  
Fe(OH)2  
Fe(OH)3- 
Fe(OH)4-2
Fe(OH)2+    
Fe(OH)3   
Fe(OH)4-  
Fe(OH)+2  
FeCl+2    
FeCl2+    
Fe2(OH)2+4
FeCl3     
Fe3(OH)4+5
FeCl4-  
H2S
S-2                                          
END


GASES
O2(g)
END

Condition redox_example
units mmol/kg
temperature      25.0
pH       4.376
Cl-      charge
Na+      100
Fe+2     0.1
O2       O2(g) 1e-9
H2       1e-9
HS-      1e-6
Fe+3     1e-8
END

Step 2 - Fe\(^{2+}\) / Fe\(^{3+}\) redox equilibrium

Fe\(^{3+}\) is defined as a secondary species, but it is not enough: the reacting redox species that is responsible of equilibrium with the Fe\(^{2+}\) / Fe\(^{3+}\) redox couple must also be given. In this example, O\(_2\) is considered as the oxidant of Fe\(^{2+}\).

TITLE Redox speciation - Step 2

RUNTIME
database ../../CrunchDatabase_ThermoChimie_v12a.dbs
speciate_only true
END

PRIMARY_SPECIES
H2O
H+
Na+
Cl-
Fe+2
O2
H2  
HS-
END

SECONDARY_SPECIES   
OH-  
Fe+3 redox O2
FeCl+    
Fe(OH)+  
Fe(OH)2  
Fe(OH)3- 
Fe(OH)4-2
Fe(OH)2+    
Fe(OH)3   
Fe(OH)4-  
Fe(OH)+2  
FeCl+2    
FeCl2+    
Fe2(OH)2+4
FeCl3     
Fe3(OH)4+5
FeCl4-   
H2S
S-2                                         
END


GASES
O2(g)
END

Condition redox_example
units mmol/kg
temperature      25.0
pH       4.376
Cl-      charge
Na+      100
Fe+2     0.1
O2       O2(g) 1e-9
H2       1e-9
HS-      1e-6
END

Step 3 - Multi-species redox equilibria

TITLE Redox speciation - Step 3

RUNTIME
database ../../CrunchDatabase_ThermoChimie_v12a.dbs
speciate_only true
END

PRIMARY_SPECIES
H2O
H+
Na+
Cl-
Fe+2
O2
SO4-2
END

SECONDARY_SPECIES   
OH-  
Fe+3  redox O2
H2    redox O2
HS-   redox O2
FeCl+    
Fe(OH)+  
Fe(OH)2  
Fe(OH)3- 
Fe(OH)4-2
Fe(OH)2+    
Fe(OH)3   
Fe(OH)4-  
Fe(OH)+2  
FeCl+2    
FeCl2+    
Fe2(OH)2+4
FeCl3     
Fe3(OH)4+5
FeCl4-   
H2S
S-2                                         
END


GASES
O2(g)
H2(g) redox O2
END

Condition redox_example
units mmol/kg
temperature      25.0
pH       4.376
Cl-      charge
Na+      100
Fe+2     0.1
O2       O2(g) 1e-9
SO4-2      1e-6
END