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Saturation index and DOC
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Topic: Saturation index and DOC (Read 1019 times)
m.gamrani
Frequent Contributor
Posts: 12
Saturation index and DOC
«
on:
April 14, 2020, 01:27:39 PM »
I’m a French master's student in the field of Geoscience,
my objective is to create a Phreeq-C model corresponding to the main horizons encountered on the sequences of alkaline lakes with a pH>9. to explain the concentration by evaporation of the lakes. after I go looking explained the pH drop in other areas by natural desalkalination of the soils.
I have some problem firstly, is that I introduced elements to my data.base knowing that I work with data.base llnl. for example stevensite and vermiculite and before completing my model I need saturation indices, these two minerals, for the minerals present in the data the indices is calculated automatically.
I have another problem is that I’m trying to get the DOC into the model but I only have the % of DOC.
My third problem is that I find problems with balancing.
#TITLE calculates phase exchanges between an initial and final solution "evaporation"
SOLUTION_MASTER_SPECIES
Si H4SiO4 0 SiO2 28.0843
SOLUTION_SPECIES
H4SiO4 = H4SiO4
-dw 1.10e-9
-Vm 10.5 1.7 20 -2.7 0.1291 # supcrt + 2*H2O in a1
H4SiO4 = H3SiO4- + H+
-log_k -9.83; -delta_h 6.12 kcal
-analytic -302.3724 -0.050698 15669.69 108.18466 -1119669.0
-Vm 7.94 1.0881 5.3224 -2.8240 1.4767 # supcrt + H2O in a1
H4SiO4 = H2SiO4-2 + 2 H+
-log_k -23.0; -delta_h 17.6 kcal
-analytic -294.0184 -0.072650 11204.49 108.18466 -1119669.0
SOLUTION 1 #non-saline
Units mmol/L
Na 0.34
K 0.34
Mg 0.26
Ca 0.301
Cl 0.415
S(6) 0.09
Si 0.25
Fe 0.001
Al 0.001
P 0
pH 6
pe 0.325 #potentiel d'ox-red (volts)
SAVE Solution 1
END
SOLUTION 2 #saline
Units mmol/L
Na 59
K 10.02
Mg 0.5025
Ca 1.015
Cl 15.4
S(6) 2.0045
P 0.5045
pH 9.15
pe -0.025 #potentiel d'ox-red (volts)
SAVE Solution 2
END
INVERSE_MODELING
-solution 1 2
-phases
Dolomite
Talc
Illite
stevensite
saponite
-balances
Cl 0.05 #5% incertitude
Na 0.05 #5% incertitude
S(6) 0.05 #5% incertitude
P 0.05 #5% incertitude
Alkalinity 1 #100% incertitude
-uncertainty 1
-range true
PHASES
stevensite
Ca0.15Na0.33Mg2.8Fe0.2Si4O10(OH)2 + 4H2O + 6H+ =\
0.15Ca+2 + 0.33Na+ + 2.8Mg+2 + 0.2Fe+2 + 4H4SiO4
log_k 25.45
Water
H2O = H2O
log_K 0
END
I can’t turn this model.
Logged
dlparkhurst
Top Contributor
Posts: 2736
Re: Saturation index and DOC
«
Reply #1 on:
April 14, 2020, 05:05:32 PM »
If you are using llnl.dat, then you need to write the chemical reaction with SiO2. I have balanced your reaction with Mg and made the change using the reaction 2H2O + SiO2 = H4SiO2, log K 0.
PHASES
stevensite
Ca0.15Na0.33Mg2.485Fe0.2Si4O10(OH)2 + 6H+ =\
0.15Ca+2 + 0.33Na+ + 2.485Mg+2 + 0.2Fe+2 + 4SiO2 + 4H2O
log_k 25.45
For all other databases:
Ca0.15Na0.33Mg2.485Fe0.2Si4O10(OH)2 + 4H2O + 6H+ =\
0.15Ca+2 + 0.33Na+ + 2.485Mg+2 + 0.2Fe+2 + 4H4SiO4
You can use the phase H2O(g) in INVERSE_MODELING when you are investigating evaporation.
I would skip DOC for now.
Your solutions have more than 50% charge imbalances. For one thing, you have not defined Alkalinity or C (carbon) in either or your solutions. For inverse modeling, you will need solutions that balance within 5-10 percent.
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m.gamrani
Frequent Contributor
Posts: 12
Re: Saturation index and DOC
«
Reply #2 on:
April 15, 2020, 12:34:03 AM »
dlparkhurst
I want to thank you for your relevant remarks, I will try to correct these mistakes and I will look for the middle alkalinity and C.
to balance the loads I think it is necessary to look for the complete composition of the water (ions added) I thank you for the time and attention that you have devoted to me.
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