Processes > Inverse modelling

Calculation of amount of precipitated minerals

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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
-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
-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 ---