Processes > Dissolution and precipitation

Evaporation simulation study

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Jay Chou:
Hello, researchers
I'm doing a simulation study of geothermal water evaporation.
I want to use PHREEQC to do evaporation Simulation Research on the existing ion data of Kau geothermal water in Tibet. Will you judge whether minerals are precipitated according to the mineral saturation index after evaporating water?
Is my evaporation simulation correct?
For example, evaporate 90% of the water, observe what minerals precipitate, and there is no mineral combination of lithium carbonate. Is it because there is no data in the database?

SOLUTION 1 kawu
temp      25
pH        7
pe        4
redox     pe
units     mg/l
density   1
Alkalinity 440.7
Ca        46.9
Cl        610.7
K         189.8
Mg        1.32
Na        408.4
S(6)      29.48 as SO4
Li        23.3
B         148
-water    1 # kg
REACTION 1
H2O(g)     -1
55.34347 moles in 1 steps

END

dlparkhurst:
You have taken out too much water if you want to remove 90%. There are about 55.5 moles of H2O per kilogram of water, so you need to remove about 50 moles of H2O to concentrate by a factor of 10.

It may be more straightforward to use MIX:

--- Code: ---SOLUTION 1 kawu
temp      25
pH        7
pe        4
redox     pe
units     mg/l
density   1
Alkalinity 440.7
Ca        46.9
Cl        610.7
K         189.8
Mg        1.32
Na        408.4
S(6)      29.48 as SO4
Li        23.3
B         148
-water    1 # kg
SOLUTION 2
END
MIX
1 1
2 -0.9
END

--- End code ---

Note that there will be some hydrolysis that consumes water (Mg+2 + H2O = MgOH+ + H+, for example), so the amount of water remaining in the solution will not be exact.

You can add EQUILIBRIUM_PHASES to allow minerals to precipitate as a result of the evaporation. You could add all of the minerals that have positive saturation indices and PHREEQC will determine the stable phase assemblage.

None of the databases have thermodynamic data for a Li2CO3 phase. At 90% water removal, the ionic strength is about 0.2, so you can compare results from the different databases. At higher ionic strengths, you probably want to use pitzer.dat.

Jay Chou:
I just learned this software recently。
1. I would like to ask again. After the evaporation simulation of the above data, the calcite and dolomite saturation index is greater than 0 after losing 90% water, indicating that it has been supersaturated. Can it be understood that it has been precipitated?
2. Suppose I want gypsum to precipitate, I'm in EQUILIBRIUM_PHASES module defines the saturation index of gypsum as 0, so as long as a little water is evaporated, the saturation index of gypsum will be displayed as positive.
In fact, I want to observe what minerals will precipitate after how much water is evaporated through evaporation simulation.
The following is the data I run：
SOLUTION 1 kawu
temp      25
pH        7
pe        4
redox     pe
units     mg/l
density   1
Alkalinity 440.7
Ca        46.9
Cl        610.7
K         189.8
Mg        1.32
Na        408.4
S(6)      29.48 as SO4
Li        23.3
B         148
-water    1 # kg
EQUILIBRIUM_PHASES 1
Gypsum    0 10
SAVE  SOLUTION 1
END
SOLUTION 2
END
MIX
1 1
2 -0.01
END

dlparkhurst:
(1) No. The calculation will not precipitate calcite or dolomite unless you include these minerals in an EQUILIBRIUM_PHASES data block that reacts with the solution.

(2) You should also include Gypsum in EQUILIBRIUM_PHASES, but you may want to set the initial moles of gypsum (and calcite and dolomite) to zero. You have specified 10 moles of Gypsum are available to dissolve, so gypsum will react to equilibrium whether it is undersaturated or supersaturated.

Here is a run that allows Calcite, Dolomite, and Gypsum to precipitate if they become supersaturated during evaporation. Only Calcite precipitates.

--- Code: ---SOLUTION 1 kawu
temp      25
pH        7
pe        4
redox     pe
units     mg/l
density   1
Alkalinity 440.7
Ca        46.9
Cl        610.7
K         189.8
Mg        1.32
Na        408.4
S(6)      29.48 as SO4
Li        23.3
B         148
-water    1 # kg
END
USE solution 1
EQUILIBRIUM_PHASES 1
Calcite 0 0
Dolomite 0 0
Gypsum 0 0
REACTION
H2O -1
50 moles in 10 steps
USER_GRAPH 1
-axis_titles            "Concentration factor" "Precipitation, moles" ""
-initial_solutions      false
-connect_simulations    true
-plot_concentration_vs  x
-start
10 GRAPH_X 1 / TOT("water")
20 GRAPH_Y EQUI("Calcite"), EQUI("Dolomite"), EQUI("Gypsum")
-end
-active                 true

--- End code ---

Jay Chou:
Thank you very much for your reply. Thank you very much. I wish you a happy New Year