Processes > Inverse modelling
Calculation of amount of precipitated minerals
mukherjeeindrani09:
I have some physicochemical data of a borehole including cations, anions, EC/TDS, pH and temperature = 12°C and I want to calculate how much amount of the supersaturated minerals would be precipitated in mg/L when the borehole temperature changes from 12°C to 25°C.
Can someone help me here please.
I have below data -
--- Code: ---TITLE Borehole groundwater sample collected on 24/10/2023 at 10:30
SOLUTION 1
temp 12.0
pH 6.4
pe 4
redox pe
units mg/l
density 1
Alkalinity 125
Cl 94
S(6) 228
Ca 106
Mg 54
Ba 0
Na 32
K 8
Mn 0.8
B 0
N(-3) 0.3
Al 0.07
Si 0
Fe 6.41
-water 1 # kg
END
--- End code ---
dlparkhurst:
You will need to use EQUILIBRIUM_PHASES, which will react each mineral to equiilbrium.
You can then use the Basic function EQUI_DELTA in USER_PUNCH (SELECTED_OUTPUT must also be defined) to get the moles of mineral that reacted. GFW("Al(OH)3"), for example will calculate the molecular weight of Gibbsite.
REACTION_TEMPERATURE can be used to change the temperature.
Note that some minerals are supersaturated at 12 C, and in most cases, minerals become more soluble at higher temperature.
mukherjeeindrani09:
I have used the below model
--- Code: ---USER_PUNCH 1
-headings ABCD
-start
10 PUNCH EQUI_DELTA("Calcite")*GFW("CaCO3")*1000
-end
SELECTED_OUTPUT 1
-file selected_output_2.sel
-high_precision true
-simulation true
-step true
-active true
-user_punch true
EQUILIBRIUM_PHASES 1
REACTION_TEMPERATURE 1
17 22 27 32 37 42 47
52 55
TITLE
SOLUTION 1
temp 12.6
pH 6.4
pe 4
redox pe
units mg/l
density 1
Fe 6.4
Alkalinity 125
Cl 94
S(6) 228
Ca 106
Mg 54
Na 32
K 8
Mn 0.8
N(-3) 0.3
Al 0.07
-water 1 # kg
END
--- End code ---
The output of this -
--- Code: ---EQUI_DELTA SI
0.0000e+00 -1.15
0.0000e+00 -1.12
0.0000e+00 -1.08
0.0000e+00 -1.03
0.0000e+00 -0.979
0.0000e+00 -0.918
0.0000e+00 -0.850
0.0000e+00 -0.777
0.0000e+00 -0.698
0.0000e+00 -0.648
--- End code ---
It means the saturation index of calcite is increasing with temperature increase and the mineral is in an undersaturated condition but 0 mg of calcite in the equilibrium-phase assemblage that reacted during the current calculation. In other words, calcite did not react at all, which seems unreasonable.
dlparkhurst:
Check the description of EQUILIBRIUM_PHASES in the manual.
mukherjeeindrani09:
It seems I need to define the minerals in the equilibrium phase. I have added calcite -
--- Code: ---USER_PUNCH 1
-headings EQUI_DELTA SI
-start
10 PUNCH EQUI_DELTA("Calcite")*GFW("CaCO3")*1000, SI("Calcite")
-end
SELECTED_OUTPUT 1
-file selected_output_2.sel
-high_precision true
-simulation true
-step true
-active true
-user_punch true
EQUILIBRIUM_PHASES 1
Calcite 0 10
REACTION_TEMPERATURE 1
17 22 27 32 37 42 47
52 55
TITLE Sample
SOLUTION 1 Sample
temp 12.6
pH 6.4
pe 4
redox pe
units mg/l
density 1
Fe 6.4
Alkalinity 125
Cl 94
S(6) 228
Ca 106
Mg 54
Na 32
K 8
Mn 0.8
N(-3) 0.3
Al 0.07
-water 1 # kg
END
--- End code ---
Which resulted in below output - which is still unreasonable. I am not sure what I am missing. Could you please help me here.
--- Code: --- EQUI_DELTA SI
0.000000000000e+00 -1.151107278269e+00
-1.323817211872e+02 0.000000000000e+00
-1.277038058017e+02 0.000000000000e+00
-1.220108976500e+02 0.000000000000e+00
-1.153465859325e+02 0.000000000000e+00
-1.077660370659e+02 0.000000000000e+00
-9.933889065589e+01 0.000000000000e+00
-9.015048906007e+01 0.000000000000e+00
-8.030141521264e+01 0.000000000000e+00
-7.412173627486e+01 0.000000000000e+00
--- End code ---
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