Sedimetent as SiO2

[Aksenova]

Hello

Can you please tell me in which tab of this program the pressure can be specified?
Where in the ionic composition is arsenic?
How can I specify the aggregate state of a substance in which it is located?

Thank you for your help..

[dlparkhurst]

You don't state which program you are using. For PHREEQC the following is acceptable if you are using a database that contains definitions for the element arsenic. Wateq4f.dat contains As.

Code: [Select]

SOLUTION 1
    -temp      25
    -pressure  2
    pH        7
    -units     mmol/kgw
    As        0.01
    Cl        1
    Na        1
END

PhreeqcI is a graphical user interface for PHREEQC. It is a little out of date and does not have an entry for pressure on the main screen for SOLUTION, but it is possible to add the -pressure identifier in the main edit screen.

For reaction calculations, you can use the REACTION_PRESSURE data block to change pressure.

I am not sure what you mean by your last question. In SOLUTION, you can define the total dissolved concentration of As, or of redox states As(5) or As(3). If you include EQUILIBRIUM_PHASES with As minerals there will be a reaction calculation, and you will see in output file the concentration in solution, and the moles of As-bearing minerals after the reaction calculation.

[Aksenova]

Thank you for detailed answer.

I am using PHREEQC version 3. Thank you, I was able to enter the arsenic in code form.

If H+ is given in the ionic composition, is it reasonable to choose H2?

How do I specify in this code that the phase aggregate state is liquid?

Code: [Select]

[SOLUTION 2
    temp      120
    pH        8.88
    pe        4
    redox     pe
    units     mg/l
    density   0.993
    Cl        213.407
    S(6)      211.726
    Alkalinity 44.225
    C(4)      52.5
    Na        240.583
    K         45.53
    Ca        2.405
    Mg        0.425
    H(0)      1.318
    Si        521
    B         22.6
    As        4.38
    -water    1 # kg]

[dlparkhurst]

A few comments:

If you define both C(4) and Alkalinity, the program will adjust the pH to achieve the two specified concentrations. Usually, you do not want the pH adjusted, so enter just C(4) or Alkalinity, but not both.

The distribution of As between As(5) and As(3) will be determined by the pe that you enter. pe = 4 will produce predominantly As(5) in the distribution of species.

llnl.dat may be better than wateq4f.dat for higher temperatures. For temperature and pressure calculations, I prefer phreeqc.dat and pitzer.dat, but they have a more limited set of elements.

H+ is defined with pH. H(0) is the concentration of dissolved H2(aq). The iniital solution calculation produced by a SOLUTION definition allows redox disequilibrium. You can define As(5) and H(0) to be present in the solution. When a the solution is reacted with REACTION, EQUILIBRIUM_PHASES, KINETICS, EXCHANGE, or other reactants, redox equilibrium will be calculated such that the H(0) will reduce As(5) to As(3).

SOLUTION defines an aqueous solution. All definitions in SOLUTION are dissolved concentrations of constituents in liquid water. All PHREEQC calculations require an aqueous solution; it is not possible to use other solvents. Elements in other than the dissolved state are defined through other data blocks like EQUILIBRIUM_PHASES, EXCHANGE, SURFACE, GAS_PHASE, and SOLID_SOLUTIONS. Reactions between a SOLUTION and these reactants will change the water composition and the masses of the other reactants.

[Aksenova]

Thak you for your detailed answer.
I have changed the database to llnl.dat
Please see my code.

Code: [Select]

[/SOLUTION 1
    temp      200
    pressure  15
    pH        8,88
    pe        4
    redox     pe
    units     mg/l
    density   0.993
    Cl(-1)    213.407
    S(6)      211.726
    C(4)  44.225 as HCO3
    Na        240.583
    K         45.53
    Ca        2.405
    Mg        0.425
    H(0)      1.318
    Si        521
    As        4.38
    B         22.6
    -water    1 # kg
]
How can I specify the concentration of CO3 (2-)?
And if I have H+ and pH given in the composition, how do I display this in the code?


[dlparkhurst]

You have defined pH as 8,88. I think it is possible to set your system to recognize commas instead of decimal points, but if you have not, then the pH will be interpreted as 8.

The concentration of CO3-2 will be calculated from C(4) and pH. C(4) is the total dissolved inorganic carbon, including all carbonate aqueous species (CO2, HCO3-, CO3-2, and others). Alternatively, you can define Alkalinity, however, this value will include contributions to alkalinity from boron and silica as well as carbonate alkalinity. Alkalinity is the value you would get from an alkalinity titration of your sample. Again, CO3-2 would be a calculated value from Alkalinity and pH.

The calculated values for all species, including CO3-2 species, are in the output file under the section "Distribution of species".

You can only define pH in a SOLUTION definition; there is no other input for H+. The output file will show the activity and concentration of H+ in the "Distribution of Species".

Finally, I suggest you define

Code: [Select]

-redox H(0)/H(1)

At 15 atm and 200 C, pe of 4 is in the range of significant dissolved oxygen for llnl.dat. With phreeqc.dat, these conditions are outside the stability field of water. If you have significant H2(aq), it is best to use the H(0)/H(1) couple to calculate a pe that is consistent with the dissolved hydrogen concentration; you will not get any dissolved oxygen in the distribution of species.

Finally, the charge imbalance with pH 8.88 is about 33 percent. You should check your analysis to see why it is so far out of balance.

[Aksenova]

Thank you for your reply.
So I can summarize the concentration of HCO3 - and CO3 (2-) in C(4)?
I tried to specify the total concentration and in the "Species Distribution" section the values changed.

Unfortunately, I don't have the -redox H(0)/H(1) values. I don't understand what this indicates. The pe 4 value was set by default when I entered the ion concentration.

I only need the pH value and the H+ concentration in mg/L.

Also of interest is it possible to predict from the saturation index the amount of substance that will be deposited?

[dlparkhurst]

When you enter C(4) in SOLUTION, that represents the total concentration of CO2 species (CO2, HCO3-, CO3-2, NaCO3-, and all other dissolved carbonate pairs and complexes). If you change this number, the total concentration of C(4) and the distribution of species will change. If you change the pH, the total concentration of C(4) will remain the same, but the distribution of species will change.

You have defined H(0), which is sufficient information to calculate a pe from the H(0)/H(1) redox couple. The following equation is used:

Code: [Select]

2 H+ + 2 e- = H2
Look at the results for O(0) in the distribution of species when you use -redox H(0)/H(1) and when you do not. There is also a section of the output file that calculates pe from each redox couple available.

You can calculate the H+ concentration from the molality in the distribution of species. You can usually assume that molality is equal to mol/L, and for H, mol/L = g/L. Phreeqc.dat and pitzer.dat allow calculation of solution volume and a more accurate calculation of concentrations of per liter.

To calculate the amount of a mineral that will precipitate (or dissolve), you must use the EQUILIBRIUM_PHASES data block.

[Aksenova]

Thank you very much for your answer !
I understand about the C(4) species.
Can you please tell me where I can see or how to use the EQUILIBRIUM_PHASES data block?

[Aksenova]

Can you please tell me if the steam dryness data can be taken into account when calculating the saturation index in this program?

[Aksenova]

I had a problem calculating saturation indices.
I work in the llnl.dat and waterq4f.dat databases
When calculating for the temperature T =157.5 C and P = 6 atm, there is no calculation, or I change the position to a more rigid position, then an envelope appears
warning: The program failed to come up with a numerical solution.
Tell me, please, what could this be related to?

[dlparkhurst]

The EQUILIBRIUM_PHASES data block is described in the manual for version 3 and version 2.

Sorry, I don't know what you are asking about steam dryness. For temperatures greater than 100 C,  llnl.dat uses a pressure defined by liquid-vapor curve for water. phreeqc.dat and pitzer.dat calculate thermodynamic properties for the specified temperature and pressure.

Defining a pressure for llnl.dat and wateq4f.dat has no effect.

You will have to post your script for me to determine the problem.

[Aksenova]

Code: [Select]

SOLUTION 1
    temp      275.5
    pressure  85.5 atm
    pH        9.31
    pe        4
    redox     pe
    units     mg/l
    density   0.993
    Cl        215.2
    S(6)      223.9
    C(4)      5
    C(4)      5 as HCO3
    N(3)      0.003
    N(5)      0.1
    Na        259.8
    K         39.29
    Li        1.384
    Ca        0.5
    Mg        0.1
    Fe(2)     0.05
    Fe(3)     0.05
    N(-3)     0.849
    Si        521
    As        1.37
    B         18.87
    -water    1 # kg


Thank you
This is where I modelled in the phreeqc.dat database.
As is not accounted for. I have set the HCO3 - and CO3 2- ions as total C(4).
I get : The program has failed to converge to a numerical solution.
Can you please tell me what can be the reason for this?

[dlparkhurst]

At your temperature and pressure, the pe and pH values put you outside the stability limits for water.

The following calculates a pe that gives a P(O2(g)) of 10^-5. You can adjust the pe as you see fit, but you probably need a pe of zero or less.

Code: [Select]

SOLUTION 1
    temp      275.5
    pressure  85.5 atm
    pH        9.31
    pe        4 O2(g) -5
    redox     pe
    units     mg/l
    density   0.993
    Cl        215.2
    S(6)      223.9
    #C(4)      5
    C(4)      5 as HCO3
    N(3)      0.003
    N(5)      0.1
    Na        259.8
    K         39.29
    Li        1.384
    Ca        0.5
    Mg        0.1
    Fe(2)     0.05
    Fe(3)     0.05
    N(-3)     0.849
    Si        521
    As        1.37
    B         18.87
    -water    1 # kg

[Aksenova]

Thank you for your kind reply.
Could you please tell me what is the best database to use if the conditions are high temperature and pressure and the main precipitate is SiO2?

[dlparkhurst]

If you are modeling aluminosilicates, try llnl.dat and phreeqc.dat. You will have to compare results and make a decision.

If aluminum is not involved, you can also try pitzer.dat.

[Aksenova]

Thak you
I am modelling the precipitation of the amorphous phase of silica

[Aksenova]

The EQUILIBRIUM_PHASES data block is described in the manual for version 3 and version 2.

Sorry, I don't know what you are asking about steam dryness. For temperatures greater than 100 C,  llnl.dat uses a pressure defined by liquid-vapor curve for water. phreeqc.dat and pitzer.dat calculate thermodynamic properties for the specified temperature and pressure.

Defining a pressure for llnl.dat and wateq4f.dat has no effect.

You will have to post your script for me to determine the problem.

Hello! Please tell me, do I understand correctly that this is an example of calculating the amount of minerals precipitated using the saturation index?

Code: [Select]

EQUILIBRIUM_PHASES
Chalcedony 0.0
SiO2 (am)   -0.4


[dlparkhurst]

There are more than two fields on the line of a phase in EQUILIBRIUM_PHASES. The first is the name, the second field is the target saturation index and the third is the amount of mineral present. If you do not specify a value, there are 10 moles of mineral available. (In addition, you can require a mineral only to dissolve or only to precipitate.)

The name of the mineral should not contain spaces.

In your case, you are including two silica phases. PHREEQC will determine the most stable of the two phases. Quartz is more stable than SiO2(am), but in addition you have specified that SiO2(am) will have an SI of -0.4. It will depend on the equilibrium constants in the database that you use which of these conditions produces the smallest Si concentration. In any event, one will dissolve completely and the other will precipitate.

[Aksenova]

Thank you
The phreeqc 3 2013 manual has an example for the EQUILIBRIUM_PHASES block. But if I enter it as a code, there is no calculation.
I enter the code

Code: [Select]

EQUILIBRIUM_PHASES 1 Define amounts of phases in assemblage.
Chalcedony 0.0 0.0
CO2(g) -3.5 1.0
Gibbsite(c) 0.0 KAlSi3O8 1.0 dissolve_only
Calcite 0.0 Gypsum 1.0 precipitate_only
pH_Fix -5.0 HCl 10.0
-force_equality
Can you please tell me what this could be related to?

[dlparkhurst]

Every calculation needs a solution. You can use SOLUTION, SOLUTION_SPREAD, USE solution, or MIX.

I'm getting a little worn down by these questions. You need to think, study, and be willing to experiment with the program.

[Aksenova]

Ok, thank you.

[Aksenova]

 Hello.
I tried to understand the EQUILIBRIUM_PHASES block
I entered this code.  For the minerals I am interested in, I have entered the saturation indices. Below are the results, I can't interpret them.

Code: [Select]

SOLUTION 1
    temp      157.5
    pressure  6 atm
    pH        7.25
    pe        3
    redox     pe
    units     mg/L
    density   1
    Cl        220.8
    S(6)      163.4
    C         116.6
    N(3)      0.003
    N(5)      1
    F         1.95
    Na        228.6
    K         33.02
    Li        0.03
    Ca        0.5
    Mg        0.135
    Fe(2)     0.05
    N(-3)     0
    Si        444
    B         18.9
    As        1.28
    -water    1 # kg

EQUILIBRIUM_PHASES

Chalcedony      0.34     
Chrysotile      0.51     
Cristobalite    0.12   
Quartz          0.65     
SiO2(am-gel)     -0.19   
SiO2(am-ppt)     -0.22

Code: [Select]

Phase               SI  log IAP  log K(T, P)   Initial       Final       Delta

Chalcedony        0.34    -2.15     -2.49    1.000e+01           0  -1.000e+01
Chrysotile        0.51    22.14     21.63    1.000e+01   1.000e+01  -7.852e-09
Cristobalite      0.12    -2.15     -2.27    1.000e+01   5.000e+01   4.000e+01
Quartz            0.64    -2.15     -2.79    1.000e+01           0  -1.000e+01
SiO2(am-gel)     -0.20    -2.15     -1.95    1.000e+01           0  -1.000e+01
SiO2(am-ppt)     -0.23    -2.15     -1.92    1.000e+01           0  -1.000e+01


Please, help me. I understand I didn't specify the number of moles. It is then automatically set to 10.

[dlparkhurst]

Here is one way to use EQUILIBRIUM_PHASES with your solution:

Code: [Select]

SOLUTION 1
    temp      157.5
    pressure  6 atm
    pH        7.25
    pe        3
    redox     pe
    units     mg/L
    density   1
    Cl        220.8
    S(6)      163.4
    C         116.6
    N(3)      0.003
    N(5)      1
    F         1.95
    Na        228.6
    K         33.02
    Li        0.03
    Ca        0.5
    Mg        0.135
    Fe(2)     0.05
    N(-3)     0
    Si        444
    B         18.9
    As        1.28
    -water    1 # kg

EQUILIBRIUM_PHASES

Chalcedony      0 0
Chrysotile      0 0
Cristobalite    0 0
Quartz          0 0
SiO2(am-gel)    0 0
SiO2(am-ppt)    0 0

The results indicate that chrysotile and quartz should precipitate from your solution. Quartz is the most stable SiO2 phase, and so, thermodynamically, it should form in preference to the other phases. The other SiO2 phases could form in a rapidly precipitating environment, by over time, they should recrystallize to more stable forms. If you include moles of some of the phases, then you will find that they will dissolve and quartz will precipitate.

[Aksenova]

Thank you
I understand about phase stability. I entered that code and got the following.

Code: [Select]

Phase               SI  log IAP  log K(T, P)   Initial       Final       Delta

Chalcedony       -0.31    -2.79     -2.49    0.000e+00           0   0.000e+00
Chrysotile        0.00    21.63     21.63    0.000e+00   1.552e-07   1.552e-07
Cristobalite     -0.52    -2.79     -2.27    0.000e+00           0   0.000e+00
Quartz            0.00    -2.79     -2.79    0.000e+00   5.706e-03   5.706e-03
SiO2(am-gel)     -0.84    -2.79     -1.95    0.000e+00           0   0.000e+00
SiO2(am-ppt)     -0.87    -2.79     -1.92    0.000e+00           0   0.000e+00

Do I understand correctly that we set 0 mol initially, assuming that these precipitates do not exist at all?
The results that we got after entering this code, how can we interpret it to calculate the amount of this phase?

[dlparkhurst]

Sorry. I look at my task as how to use PHREEQC. I am not willing to teach geochemistry. You will have to run scripts and look carefully at the output.

In the script I provided, two phases precipitated from the solution. You will have to consider whether this represents the conditions you are interested in, and if not how to change the script.

[Aksenova]

Thank you, yes, the findings are consistent with reality.
Could you please tell me, in the Phreeqc programme, in the column "Final", in which units is the obtained number?

[dlparkhurst]

Moles.

[Aksenova]

Thank you