rock-water interaction modeling

[jaehong]

Hello All. I want to analyze the interaction between rock and water especially saline water.
But, I have 2 questions.

1. I want to show the variation of total concentration(Salinity) with time when rock is exposed to saline water. I input the mineral composition of rock as equilibrium_phase and just ran a simulation. But, I couldn't see the variation of TOT with time.

Here is my code.

Title Salinity simulation_2 Nacl solution
Solution 1 Nacl solution
   units   mol/L
   pH   7.0
   temp   25.0
   Na   1.724
   Cl   1.724

Equilibrium_phase 1
   Quartz      0.0   0.084
   K-feldspar   0.0   8.5
   Manganite   0.0   14.1
   Albite      0.0   0.39

Selected_output
   -file   simple_NaCl1.sel
   -time   true
   -totals
   -si   quartz   K-feldspar Manganite Albite

User_graph 1   simple 1
   -headings _Time_ Totals Quartz K-feldspar Manganite Albite
   -chart_title "Variation of concentration with time"
   -axis_titles   "Time" "Concentration"
-start
10 graph_x TOTAL_Time / 3600 / 24
20 graph_y TOT("Quartz"), TOT("K-feldspar"), TOT("Manganite"), TOT("Albite")
-end
End

2. Rock is a material that assemblage of different minerals. Even if the composition of rock is known, the exposed area that contact with solution might be different depending on shape of rock and its porosity. Can PHREEQC consider this kind of actual situations? If it could, please let me know the keyword or the way.

Could you share your suggestion?

[dlparkhurst]

There are many possibilities. If you can conceptualize the system as partial equilibrium, where one reaction is proceeding irreversibly, whereas other minerals and gases are at equilibrium, you can define REACTION to introduce varying amounts of the irreversible reaction, while allowing the other minerals and gases to remain in equilibrium using EQUILIBRIUM_PHASES.

REACTION and EQUILIBRIUM_PHASES will not give you results directly in terms of time, but rather in terms of the extent of the irreversible reaction. You will need to use KINETICS to introduce the chemical evolution in terms of time. You will again need to separate reactions into those that occur kinetically (KINETICS) and those that occur at equilibrium (EQUILIBRIUM_PHASES). For those that occur kinetically, you will need rate expressions that give the rate of reaction as a function of chemical composition of the solution (RATES).

You should look at the various examples of the use of KINETICS in the Version 3 manual.

[jaehong]

I really appreciate for your reply. I will follow your suggestion and try to do my best.
Thank you very much!

[jaehong]

Now, I can represent the variation of concentration with time by using KINETICS.
Thank you very much for your teaching, Dr. David.

And could I ask you one more question?
I want to analyze the effects of salinity on mineral dissolution and precipitation, especially with different concentration of NaCl solution(0.5 - 1.5 M)
From what I understand in manual, If I want to represent that, do I have to find the rate equation and its constant, which have some terms of ionic strength or electrolyte. And extra chemical reaction thermodynamics data is required as well.

Such as
Chemical reaction between Quartz and Sodium( SiOH + Na+ = SiONa + H+)

Is that right?
I really appreciate your reply. Thank you. :)

[dlparkhurst]

You may not need to know the kinetics rate expression; you should probably start with equilibrium. The following shows the solubility of quartz as a function of ionic strength (NaCl). However, you will need PHASES definitions for the minerals that you want to consider.

SOLUTION
EQUILIBRIUM_PHASES
Quartz 0 10
REACTION
NaCl 1
1 mole in 10 steps
USER_GRAPH 1
    -axis_titles            "Ionic strength" "Si, mmol/kgw" ""
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 graph_x MU
20 graph_y TOT("Si")*1e3
  -end
    -active                 true
END

[jaehong]

I always thank you for your grateful teachings.
From your teaching, now I can simulate the amounts of dissolved elements with ionic strengths of solution.
Now I am learning every day for making reaction path from saline water-rock interaction and its quantitative analysis. There are still remains for achieving that but, I am learning it in patience for your teachings.
Thank you again and I will try my best and may be back soon with some questions.

[jaehong]

Hello again! :)
Now, I want to again simulate the rock-water interactions in order to investigate the amount of mineral variation because of dissolution and secondary precipitation depending on salinity of solution and time.
The rock is granite, which is consisted of four minerals(Quartz, Albite, K-feldspar, Muscovite).

The percentage of mineral composition is below.
Total Vol. of granite specimen = 110 cm^3
Quartz 35.4% 1.7 mole
Albite 28% 0.31 mole
K-feldspar 25.4% 0.26 mole
Muscovite 7.2% 0.06 mole

There is no flow during the experiment. Then, here is my code.

Code: [Select]

Title Simulation. Kinetic calculation of Albite, K-feldspar and K-mica
#Kinetic calculations when K-feldspar dissolved in solution and precipitable minerals are K-mica and Albite

Solution 1
-units mol/kgw
Al 1.e-13
K 1.e-13
Si 1.e-13
Na 1.e-13

# Composition of experimental solution
# Na 1.7
# Cl 1.7

Equilibrium_phases 1
# Minerals in granite
K-mica 0.0 0.06
Quartz 0.0 1.7
K-feldspar 0.0 0.26
# Albite 0.0 0.31

# Secondary minerals which are not included in minerals
Gibbsite 0.0 0.0
Kaolinite 0.0 0.0


Kinetics 1
Albite
-parms 2.85e-8
-m0 0.31
-m 0.31
        -steps    0 1 2 3 4 5 6 7 8 9 10 100 200 300 day
INCREMENTAL_REACTIONS true
RATES
Albite
-start
10 SR_Albite = SR("Albite")
20 moles = parm(1)*(1-SR_Albite)*Time
30 If ABS(SI("Albite")) < 1e-3 then goto 100
100 SAVE moles
-end


USER_GRAPH
-headings Time Na Si K
-axis_titles "Time, in days", "Concentration"
# -axis_titles "Log[H4SiO4]", "Log([Na+]/[H+])"

-start
10 GRAPH_X TOTAL_TIME /3600 /24
# 20 GRAPH_Y SI("K-mica"), SI("Quartz"), SI("K-feldspar"), SI("Albite")
# 30 GRAPH_Y SI("K-feldspar")
40 GRAPH_Y TOT("Na"), TOT("Si"), TOT("K")
# 50 PLOT_XY LA("H4SiO4"),(LA("Na+")-LA("H+")), color = Blue, line_w = 2, symbol = None
-end

END


I assumed albite is a dominant mineral for chemical reaction in this solution. Then I used only albite kinetics and other minerals are in equilibrium state but they have initial amounts.
Is that a reasonable concept? Could you let me know if there is better way for this?

And I have a one more question. The chemical reaction area between rock and solution may be the exterior and pore space of rock. Then, could I input the surface area calculated from the percentage of Albite composition?

I always really thank you for your advising and this forum.
If you don't mind, please let me know about your opinion.

[dlparkhurst]

Consider example 5 in the manual.