Sedimentent as SiO2

[Aksenova]

Hello!
I want to simulate and see what state a system containing 5% Na2CO3 (aqueous solution) and SiO2 will be in.
Please look at my code.
To simulate dissolution, do I need to use the "reactions" function?

Code: [Select]

SOLUTION 1
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    C(4)      28300
    Na        21700
    -water    1 # kg
END   
SOLUTION 2
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    Si        600
    -water    1 # kg
END
MIX
1 0.5
2 0.5

SAVE SOLUTION 3
     
REACTION_PRESSURE 1
    7
REACTION_TEMPERATURE 1
100  160  180 200 220


SELECTED_OUTPUT
    -simulation false
    -state false
    -solution false
    -distance false
    -time false
    -step false
    -pH false
    -pe false
    -temperature true           
    -si SiO2               
END



[dlparkhurst]

I can't tell what it is you want to simulate. You can calculate saturation indices with your script. If you want minerals to dissolve or precipitate, you need to add EQUILIBRIUM_PHASES.

[Aksenova]

Thank you very much for your answer!
I want to simulate the dissolution of solid amorphous silica using solutions of different compositions.
With this code I checked whether amorphous silica precipitates.
Should I use the SOLID SOLUTIONS block?


SOLID SOLUTIONS requires two components to be selected.

[dlparkhurst]

I expect that you should use EQUILIBRIUM_PHASES. However, you may be looking at a kinetic process where silica precipitates, but evolves to more stable phases with time. To model that process, you should use KINETICS.

[Aksenova]

Thank you
Is it possible to put a substance in a solid state of aggregation into a SOLUTION?

[dlparkhurst]

REACTION adds specified amounts of minerals or elements, regardless of saturation state. KINETICS is another option to add minerals or elements to solution.

[Aksenova]

Thank you very much for your ansver
Please see my code.
Is it similar to simulating the SiO2 dissolution reaction using a Na2CO3 solution?
 

Code: [Select]

SOLUTION 1
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    C(4)      28300
    Na        21700
    -water    1 # kg
REACTION 1
    SiO2(a)    1
    1 moles in 1 steps

REACTION_PRESSURE 1
 7

REACTION_TEMPERATURE 1
100  160  180 200 220

END

[dlparkhurst]

You will have to decide how and what you want to simulate.

[Aksenova]

I want to simulate the dissolution of amorphous silica using a soda solution at different temperatures. And see how much amorphous silica will remain undissolved.

[Aksenova]

Code: [Select]

SOLUTION 1
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    C(4)      28300
    Na        21700
    -water    1 # kg
REACTION 1
    SiO2(a)    10
    1 moles in 1 steps

REACTION_PRESSURE 1
 7

REACTION_TEMPERATURE 1
100 

EQUILIBRIUM_PHASES 1
SiO2(a) 0 10  dissolve only

END

[dlparkhurst]

Okay, okay.

First look at your initial solution. There is a 44 percent charge imbalance. I think you should charge balance, which would produce a pH of 12.

Why don't you start with calculating equilibrium with SiO2(a) under different conditions.

Code: [Select]

SOLUTION 1
    -pH 7 charge
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    C(4)      28300
    Na        21700
    -water    1 # kg

REACTION_PRESSURE 1
 7

REACTION_TEMPERATURE 1
0 100 in 11 steps

EQUILIBRIUM_PHASES 1
SiO2(a) 0 10  #dissolve only

USER_GRAPH 1
    -headings               TC Si
    -axis_titles            "T, Celsius" "Molality" ""
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X TC
20 GRAPH_Y TOT("Si")
  -end
    -active                 true
END

[Aksenova]

Thank you very much for your answer

[Aksenova]

Thank you very much for your answer

Hello!
Tell me, please, how to set OH-ions in solution?
I want to specify an alkali solution.

[dlparkhurst]

Specify the pH in the SOLUTION definiton.

For reaction calculations, you can add NaOH with REACTION.

[Aksenova]

Thank you

Hello!
Please check my code. I decided to set the amount of sodium ions in a 10% mass solution of sodium hydroxide.
And I decided to see how much would dissolve SiO2 (a).

Code: [Select]

  ph 7 charge
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    Na        57500
    water    1 # kg
REACTION_TEMPERATURE 1
    90
EQUILIBRIUM_PHASES 1
    SiO2(a)   0 0.08
END


Is it possible to simulate the dissolution of amorphous silica by alkali in this way?

[dlparkhurst]

Code: [Select]

SOLUTION
 ph 7 charge
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    water    1 # kg
REACTION_TEMPERATURE 1
    90
REACTION
NaOH 1
1e-7 1e-6 1e-5 1e-4 1e-3 1e-2 1e-1 1

EQUILIBRIUM_PHASES 1
    SiO2(a)   0 1
USER_GRAPH 1
    -headings               pH Si
    -axis_titles            "pH" "Si, mol/kgw" ""
    -axis_scale y_axis      auto auto auto auto log
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X -LA("H+")
20 GRAPH_Y TOT("Si")
  -end
    -active                 true
END


[Aksenova]

Hello! Thank you very much for your code.
Please help me interpret the results. I took your code and changed it a little.

I want to simulate the reaction 2NaOH + SiO2 = Na2SiO3 + H2O
Mass of SiO2 = 3 grams
So, 0.08 mol
I took 50 g of a solution of 10% mass of NaOH
What does it mean, the amount of NaOH is 0.125 mol
Judging by the reaction, I do not have enough alkali, which means that not all of the SiO2 should dissolve.
Correct?

However, according to the simulation results, it turns out that the saturation index is 0 (amorphous phase of SiO2).

Are my thoughts correct?

Code: [Select]

SOLUTION
 ph 7 charge
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    water    1 # kg
REACTION_TEMPERATURE 1
    90
REACTION
NaOH 0.125
1e-1

EQUILIBRIUM_PHASES 1
    SiO2(a)   0 0.08
END

[dlparkhurst]

I think you are on the right track. Here is a script with my thinking, which creates the 10% wt/wt NaOH solution, and then reacts the specified amount of SiO2(a) with 50 mL of the solution. Using the phreeqc.dat database, all of the SiO2(a) dissolves to produce an SI of -0.1.

Code: [Select]

USER_PRINT
10 PRINT "NaOH, moles in 100 g: ", 100 / GFW("NaOH")
SOLUTION 1
 ph 7 charge
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    water    1 # kg
END
PRINT
-user_print false
END
USE solution 1  # 1 kg of water
REACTION
NaOH 1
2.5             # 100 g of NaOH
SAVE solution 2 # 10% solution
END
MIX
2 0.05 # ~50 mL of 10% NaOH solution
REACTION_TEMPERATURE 1
    90
EQUILIBRIUM_PHASES 1
    SiO2(a)   0 0.08
END


[Aksenova]

Thanks, but I can't understand your code.

Please tell me, what does MIX (2 0.05) NaOH mean?

Judging by the equation, it takes twice as much alkali to dissolve 1 mol of SiO2(a).
SiO2 (a) in excess.

[dlparkhurst]

Solution 2 is approximately 1 L. MIX takes a fraction of 0.05 of solution  2, which is about 50 mL. I understood that you wanted to react the SiO2(a) with 50 mL.

Code: [Select]

MIX
2 0.05 # ~50 mL of 10% NaOH solution


[Aksenova]

Yes, that's right, thank you very much. That's what I meant. Please tell me, is it possible to take into account the reaction time in this code?

[dlparkhurst]

Here is a kinetic calculation using the database kinec_v3.dat. See references in the database for more details.

Code: [Select]

SOLUTION
pH 9
Na 1 charge
#Four parameters are necessary when using rates from Kenec.dat:
# - The first parameter specifies if the specific surface area is entered as m2 per g of rock (0) or m2 per kg of water (1)
# - The second parameter specifies the specific surface area of the mineral (in m2/g or m2/kgw depending on the choice of the first parameter)
#  - The third parameters define how the surface area changes during dissolution and has three possible values. This option is only available when the first parameter is 0. If the first parameter is 1, the surface area is always constant.
#   0: The surface area changes linearly with the moles of the mineral present
#   1: The surface area changes according to the geometry of dissolving cubes or spheres
#- The fourth  parameter specifies the dissolution and precipitation option
# 0: allow dissolution and precipitation
# 1: allow precipitation only
# 2: allow dissolution only
KINETICS
Chalcedony
-m 1
-parm 0 1 0 0
-step   15*86400
INCREMENTAL_REACTIONS
USER_GRAPH 1
    -headings               time Si SI(Chalcedony)
    -axis_titles            "Days" "Molality" "Saturation Index"
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X TOTAL_TIME / 86400
20 GRAPH_Y TOT("Si")
30 GRAPH_SY SI("Chalcedony")
  -end
    -active                 true
END


[Aksenova]

Hello!
Thank you very much for your help.
Please can you see the two codes, I am trying to model the dissolution of amorphous silica with a solution of 3%mass soda (Na2CO3).
I am getting different results.

Code: [Select]

SOLUTION 1
    pH        7 charge
    temp      20
    pe        4
    redox     pe
    units     mg/kgw
    density   1
    C(4)      16981.13
    Na        13018.87
    -water    1 # kg


REACTION_TEMPERATURE 1
95

EQUILIBRIUM_PHASES 1
SiO2(a) 0 0.05

END

Code: [Select]

SOLUTION 1
 ph 7 charge
     temp      20
     pe        4
     redox     pe
     units     mg/kgw
     density   1
     water    1 # kg

END
USE solution 1  # 1 kg of water
REACTION
Na2CO3 1
0.283             # 30 g of Na2CO3
SAVE solution 2 # 3% solution
END
MIX
2 0.05 # ~50 mL of 3% Na2CO3 solution
REACTION_TEMPERATURE 1
     95
EQUILIBRIUM_PHASES 1
    SiO2(a)   0 0.05
END

[dlparkhurst]

Either use mol/kgw, or, if you use mg/kgw, use the correct gram formula weight for converting mg to moles.

Code: [Select]

SOLUTION 1
 ph 7 charge
     temp      20
     pe        4
     redox     pe
     units     mg/kgw
     density   1
     water    1 # kg

END
USE solution 1  # 1 kg of water
REACTION
Na2CO3 1
0.283             # 30 g of Na2CO3
SAVE solution 1 # 3% solution
END
USER_PRINT
10 PRINT "C(4), mg/kgw: ", STR_F$(0.283*GFW("CO3")*1000, 10, 2)
20 PRINT "Na, mg/kgw:   ", STR_F$(0.283*2*GFW("Na")*1000, 10, 2)
SOLUTION 2
    pH        7 charge
    -density  1 calc
    temp      20
    pe        4
    redox     pe
    units     mg/kgw # mol/kgw
    C(4)      16978.02 as CO3  # 0.283 # 16981.13
    Na        13012.23 # 0.566 # 13018.87
END


[Aksenova]

Thank you!
Please tell me what does SiO2 (am-gel) and SiO2 (am-ppt) mean in the minteq4v.date database?

[dlparkhurst]

Each represents measurement of the stability of a poorly defined amorphous silica phase.

Please start another thread. This one is too long.

[Aksenova]

Okay, thanks, I'll start another thread with the following question.
How do you decode am-ppt? ppt exactly?

[dlparkhurst]

Start another thread.