Saturation index and DOC

[m.gamrani]

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.

[dlparkhurst]

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.

[m.gamrani]

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.