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redox modeling



Dear mr. Parkhurst,

first of all let me introduce myself: My name is Jeroen Hanssen and I am in my final year of the course 'environmental GeoChemistry' at the University of Utrecht (Holland). Currently I am busy with my thesis on Cd and Zn -sulphide precipitation. I am trying to model the relevant processes with PHREEQC (for windows). Via the website of the USGS I obtained your e-mail adres to ask you a question about redox modeling:

I would like to model the addition (by 'Mix') of acetate to lower the pe and to invoke sulphate reducing circumstances. The Acetate reactions from the minteq database do not change pe. Therefore I took a reaction given by Lindsay:
#taken from Lindsay, W.L., 'chemical equilibria in soils' 1979, p376
2 H2O + CH3COO- = 2 CO2 + 8 e- + 7 H+
log_k -9.64
delta_h 0 kcal


CH3COO- = 2 CO2 + 4 e- + 3 H+
	log_k		-16.66
	delta_h	0	kcal

This to involve pe in the reactions.
Also is replaced all 'Acetate-' from minteq.dat by 'CH3COO-'.
I am getting the following messages:

ERROR: Coefficient of first species on rhs is not equal to 1.0.
ERROR: Equation for species CO2 does not balance.
ERROR: Could not reduce equation to secondary master species, CO2.
ERROR: Calculations terminating due to input errors.
Stopping.
No memory leaks

maybe you can help me, I have attached the input-file to this message,

with kind regards,

Jeroen Hanssen




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title Solution+HFO+Ferrihydrite+CEC (change balanced by Ca2+, PCO2 = 10^-2),
reaction+selected output, Mixing sol1+2,acetate as substrate
#step one: definition of solution input
solution 1

temp		20
pe		4.78	#Eh/0.0592=0.283/0.0592
#redox		S(+6)/S(-2)
pH		3.7
units		ug/l
density	1.00		#???
Zn		10677
Pb		23
As		5
Cd		4873
Ni		1264		#Ni+2
Fe		1304675
Cu		14229
Ca		266000	#charge
S(+6)		5165330	#SO4-2
P		250		#PO4-3
N(+5)     	20700		#NO3-
S(-2)		40
Humate	1870		#10% van TOC Diels, 2002 according to Frimmel 1998
Fulvate	9350		#50% van TOC Diels, 2002 according to Frimmel 1998
O(0)		4060		#dissolved oxygen
Alkalinity	4700	as CO3-2


SOLUTION_MASTER_SPECIES Ni Ni+2 0.0 58.71 58.71 #wateq As H3AsO4 -1.0 74.9216 74.9216 #wateq As(+3) H3AsO3 0.0 74.9216 74.9216 #wateq As(+5) H3AsO4 -1.0 74.9216 #wateq Fulvate Fulvate-2 0.0 650. 650. #wateqf4 Humate Humate-2 0.0 2000. 2000. #wateqf4 Nta Nta-3 0 188.06 188.06 #minteq SOLUTION_SPECIES #Fulvate-2 primary master species Fulvate-2 = Fulvate-2 log_k 0.0

#Humate-2 primary master species
	Humate-2 = Humate-2
	log_k		0.0
#HFulvate            523
	H+ + Fulvate-2 = HFulvate-
	log_k		4.27

#HHumate             524
	H+ + Humate-2 = HHumate-
	log_k		4.27

#FeFulvate           525
	Fe+3 + Fulvate-2 = FeFulvate+
	log_k		9.4

#FeHumate            526
	Fe+3 + Humate-2 = FeHumate+
	log_k		9.4

#CuFulvate           527
	Cu+2 + Fulvate-2 = CuFulvate
	log_k		6.2

#CuHumate            528
	Cu+2 + Humate-2 = CuHumate
	log_k		6.2

#CdFulvate           529
	Cd+2 + Fulvate-2 = CdFulvate
	log_k		3.5

#CdHumate            530
	Cd+2 + Humate-2 = CdHumate
	log_k		3.5

#labile organic matter (minteq,?)Nitrolotriacetate
Nta-3 = Nta-3
       log_k   0
       delta_h 0       kcal
Pb+2 + Nta-3 = PbNta-
       log_k   11.6233
       delta_h 0       kcal
Pb+2 + Nta-3 + H+ = PbHNta
       log_k   3.795
       delta_h 0       kcal
Cu+2 + Nta-3 = CuNta-
       log_k   13.1
       delta_h 0       kcal
Cu+2 + 2Nta-3 = CuNta2-4
       log_k   17.5
       delta_h 0       kcal
H+ + Nta-3 = NtaH-2
       log_k   10.334
       delta_h 0       kcal
2H+ + Nta-3 = NtaH2-
       log_k   13.27
       delta_h 0       kcal
3H+ + Nta-3 = NtaH3
       log_k   14.12
       delta_h 0       kcal
4H+ + Nta-3 = NtaH4+
       log_k   16.224
       delta_h 0       kcal
Cd+2 + Nta-3 = CdNta-
       log_k   9.4
       delta_h 0       kcal
Cd+2 + 2Nta-3 = CdNta2-4
       log_k   14.3
       delta_h 0       kcal
#arseen species

	H3AsO4 = H3AsO4
	log_k		0.0

	H3AsO4 + 2H+ + 2e- = H3AsO3 + H2O
	log_k		18.897
	delta_h	-30.015 kcal
#H2AsO3-             478
	H3AsO3 = H2AsO3- + H+
	log_k		-9.228
	delta_h	6.56 kcal
#HAsO3-2             479
	H3AsO3 = HAsO3-2 + 2H+
	log_k		-21.33
	delta_h	14.2 kcal

#AsO3-3              480
	H3AsO3 = AsO3-3 + 3H+
	log_k		-34.744
	delta_h	20.25 kcal

#H4AsO3+             481
	H3AsO3 + H+ = H4AsO3+
	log_k		-0.305

#H2AsO4-             482
	H3AsO4 = H2AsO4- + H+
	log_k		-2.243
	delta_h	-1.69 kcal

#HAsO4-2             483
	H3AsO4 = HAsO4-2 + 2H+
	log_k		-9.001
	delta_h	-0.92 kcal

#AsO4-3              484
	H3AsO4 = AsO4-3 + 3H+
	log_k		-20.597
	delta_h	3.43 kcal

#Nikkel species
#Ni+2 primary master species

	Ni+2 = Ni+2
	log_k		0.0
#NiCl2               518
	Ni+2 + 2Cl- = NiCl2
	log_k		0.96

#NiHCO3+             519
	Ni+2 + HCO3- = NiHCO3+
	log_k		2.14

#NiCO3               520
	Ni+2 + CO3-2 = NiCO3
	log_k		6.87

#Ni(CO3)2-2          521
	Ni+2 + 2CO3-2 = Ni(CO3)2-2
	log_k		10.11

#Ni(SO4)2-2          522
	Ni+2 + 2SO4-2 = Ni(SO4)2-2
	log_k		1.02

#Fe+3 secondary master species  0 wateq4f
	Fe+2 = Fe+3 + e-
	log_k		-13.020
	delta_h	9.680 kcal

#FeOH+2              1
	Fe+3 + H2O = FeOH+2 + H+
	log_k		-2.19
	delta_h	10.4 kcal

#FeOH+               2
	Fe+2 + H2O = FeOH+ + H+
	log_k		-9.5
	delta_h	13.2 kcal

#Fe(OH)3-            3
	Fe+2 + 3H2O = Fe(OH)3- + 3H+
	log_k		-31.0
	delta_h	30.3 kcal

#Fe(OH)2+            102
	Fe+3 + 2H2O = Fe(OH)2+ + 2H+
	log_k		-5.67
	delta_h	17.1 kcal

#Fe(OH)3             103
	Fe+3 + 3H2O = Fe(OH)3 + 3H+
	log_k		-12.56
	delta_h	24.8 kcal

#Fe(OH)4-            104
	Fe+3 + 4H2O = Fe(OH)4- + 4H+
	log_k		-21.6
	delta_h	31.9 kcal

#Fe(OH)2             105
	Fe+2 + 2H2O = Fe(OH)2 + 2H+
	log_k		-20.57
	delta_h	28.565 kcal
phases
Greenockite         #wateq4f.dat 332
	CdS + H+ = Cd+2 + HS-
	log_k		-15.930
	delta_h	16.360 kcal
end

equilibrium_phases
CO2(g)	-2.0
end

phases #define hfo as a solid phase

Hfo_wOH
Hfo_wOH = Hfo_wOH
	log_k	0.0
Hfo_sOH
Hfo_sOH = Hfo_sOH
	log_k	0.0



# Step 2b: solid link Hfo to ferrihydrite
equilibrium_phases	2
Fe(OH)3(a)	0.0	Hfo_wOH	4.18e-3
Fe(OH)3(a)	0.0	Hfo_sOH	1.05e-4

surface 2 HFO-surface in equilibrium with solution 1
-equilibrate with solution 1
Hfo_wOH	Fe(OH)3(a)	equilibrium_phase	0.2	5.34e4	#600 m2/g*89 g/mol D&M p92
Hfo_sOH	Fe(OH)3(a)	equilibrium_phase	0.005

Exchange 1 #calculated CEC (mostly contributed by clay)
X 0.005
-equilibrate with solution 1
selected_output
-file sol1mix6.xls
-selected_out true
#-user_punch true
#-reset true
-simulation true
-state true
-solution true
-step true
-reaction true
-ph true
-pe true
-molalities Fe+2 CaSO4 Ca+2 FeSO4 FeHCO3+ Fe(OH)2+ FeSO4+ FeOH+2 Fe(SO4)2- SO4-2 ZnX2 CdX2 Hfo_sOZn+ Hfo_wOZn+ Hfo_sOCd+ Hfo_wOCd+
-equilibrium_phases Fe(OH)3(a)
-saturation_indices Greenockite Gypsum Anhydrite Fe(OH)3(a) Goethite Hematite Pyrite Sphalerite Sulfur O2(g) CO2(g) N2(g)
end



solution_master_species Acetate CH3COO- 0 59.05 59.05 #minteq.dat #NaSO- NaSO- 0 0.70 0.70 #Lindsay p121 solution_species #minteq.dat CH3COO- = CH3COO- log_k 0 delta_h 0 kcal Cu+2 + CH3COO- = CuCH3COO+ log_k 2.22 delta_h 0 kcal Ni+2 + CH3COO- = NiCH3COO+ log_k 1.43 delta_h 0 kcal CH3COO- + H+ = HCH3COO log_k 4.76 delta_h 0 kcal -gamma 0 0.06 Cd+2 + CH3COO- = CdCH3COO+ log_k 1.93 delta_h 0 kcal -gamma 0 0.01 Pb+2 + CH3COO- = PbCH3COO+ log_k 2.87 delta_h 0 kcal Zn+2 + CH3COO- = ZnCH3COO+ log_k 1.57 delta_h 0 kcal Na+ + CH3COO- = NaCH3COO log_k -0.18 delta_h 0 kcal Mg+2 + CH3COO- = MgCH3COO+ log_k 1.27 delta_h 0 kcal Ca+2 + CH3COO- = CaCH3COO+ log_k 1.18 delta_h 0 kca Mn+2 + CH3COO- = MnCH3COO+ log_k 1.4 delta_h 0 kcal Fe+2 + CH3COO- = FeCH3COO+ log_k 1.4 delta_h 0 kcal Fe+3 + CH3COO- = FeCH3COO+2 log_k 3.21 delta_h 0 kcal Fe+3 + 2CH3COO- = Fe(CH3COO)2+ log_k 6.5 delta_h 0 kcal Fe+3 + 3CH3COO- = Fe(CH3COO)3 log_k 8.3 delta_h 0 kcal #Na+ + SO4-2 = NaSO4- # log_k 0.70 # delta_h 0 kcal #NaSO4- = NaSO4- # log_k 0 # delta_h 0 kcal

#taken from Lindsay, W.L., 'chemical equilibria in soils' 1979, p376
2 H2O + CH3COO- = 2 CO2 + 8 e- + 7 H+
	log_k		-9.64
	delta_h	0 	kcal

CH3COO- = 2 CO2 + 4 e- + 3 H+
	log_k		-16.66
	delta_h	0	kcal



solution 2
pH		7.0 #charge
pe		-4.0	charge
redox S(-2)/S(+6)
temp		25
density	1.00
units		mol/kgw
Ca		0.05	#charge
Acetate	0.05
#NaSO4-	0.05
Na		0.05
S(6)		0.05
S(-2)		0.25

selected_output
-file sol2mix6.xls
-selected_out true
#-user_punch true
#-reset true
-simulation true
-state true
-solution true
-step true
-reaction true
-ph true
-pe true
-molalities CH3COO- HCH3COO Fe(CH3COO)2+ CH3COO- Fe(CH3COO)3 FeCH3COO+2 CaCH3COO+ CuCH3COO+ ZnCH3COO+ CdCH3COO+ NiCH3COO+ PbCH3COO+ FeCH3COO+ Fe+2 CaSO4 Ca+2 FeSO4 FeHCO3+ Fe(OH)2+ FeSO4+ FeOH+2 Fe(SO4)2- SO4-2 ZnX2 CdX2 Hfo_sOZn+ Hfo_wOZn+ Hfo_sOCd+ Hfo_wOCd+
-equilibrium_phases Fe(OH)3(a)
-saturation_indices Greenockite Gypsum Anhydrite Fe(OH)3(a) Goethite Hematite Pyrite Sphalerite Sulfur O2(g) CO2(g) N2(g)
end
save solution 2
Mix
1 1.0
2 0.01


selected_output
-file sol3mix6.xls
-selected_out true
#-user_punch true
#-reset true
-simulation true
-state true
-solution true
-step true
-reaction true
-ph true
-pe true
-molalities CH3COO- HCH3COO Fe(CH3COO)2+ CH3COO- Fe(CH3COO)3 FeCH3COO+2 CaCH3COO+ CuCH3COO+ ZnCH3COO+ CdCH3COO+ NiCH3COO+ PbCH3COO+ FeCH3COO+ Fe+2 CaSO4 Ca+2 FeSO4 FeHCO3+ Fe(OH)2+ FeSO4+ FeOH+2 Fe(SO4)2- SO4-2 ZnX2 CdX2 Hfo_sOZn+ Hfo_wOZn+ Hfo_sOCd+ Hfo_wOCd+
-equilibrium_phases Fe(OH)3(a)
-saturation_indices Greenockite Gypsum Anhydrite Fe(OH)3(a) Goethite Hematite Pyrite Sphalerite Sulfur O2(g) CO2(g) N2(g)
save solution 3
end





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