EQUILIBRIUM_PHASES understand

[robertaasa]

Good Morning!

I would like to inquire about the possibility of performing sequential precipitation reactions by incrementally increasing the pH. Specifically, my question is: how can the amount of a phase formed in a previous reaction be used as input for the subsequent reaction?

For example: 

Solution 3
pH 3
Al 0.007 mol/L

EQUILIBRIUM_PHASES
Al(OH)₃: 0 0 #(since no Al(OH)₃ has precipitated yet) 

After the reaction, as you know, the system outputs something like the following equilibrium data:

| Phase     | SI  | log IAP  | log K(T, P) | Initial  | Final | Delta | 
|-----------  |--- - |---- ------|--- ----------|---- -----|-- -----|------ -| 
| Al(OH)₃  | a    | b          | c              | 0         | Xf      | Xf     | 

For the next step, how could the equilibrium phases to be automatically updated as follows: 


EQUILIBRIUM_PHASES
Al(OH)₃ 0   Xf 

Would you be able to guide me about that?

[dlparkhurst]

Use the keywords SAVE and USE to keep results from one simulation to be used in a subsequent simulation.

Code: [Select]

Solution 3
-units mol/L
pH 7 charge
Al 0.007
END
USE solution 3
EQUILIBRIUM_PHASES
Gibbsite 0 0 #(since no Al(OH)₃ has precipitated yet)
SAVE solution 4
SAVE equilibrium_phases 4
END
USE solution 4
USE equilibrium_phases 4
REACTION
NaOH 1
1e-4
END

[robertaasa]

Unfortunately, it didn't work. I intended to set another equilibrium phase with the initial number of moles of precipitate equal to the final number of moles generated in the first step. In the example you provided, the command 'USE equilibrium_phases 4' does not achieve this. I apologize for bothering you again; I just want to ensure that it is possible.

I would also like to take this opportunity to ask another question: Is it possible to set the REACTION command to add an amount of, for example, NaOH until the pH reaches 5?

Thank you very much for your help; you are being very helpful!

[dlparkhurst]

I'm not sure exactly what you have in mind.

Here is a script that saves equilibrium phases 4, adds calcite from equilibrium phases 5 to make equilibrium phases 6, which has the original moles of equilibrium phases 4 and 5.

The calcite definition add NaOH to reach calcite saturation.

If this is not what you want, post your script and explain what else is needed.

Code: [Select]

Solution 3
-units mol/L
pH 7 charge
Al 0.007
Ca 0.001
C  0.010
END
USE solution 3
EQUILIBRIUM_PHASES
Gibbsite 0 0 #(since no Al(OH)₃ has precipitated yet)
SAVE solution 4
SAVE equilibrium_phases 4
END
EQUILIBRIUM_PHASES 5
Calcite 0 NaOH 0.1
END
EQUILIBRIUM_PHASES_MIX 6
4 1.0
5 1.0
END
USE solution 4
USE equilibrium_phases 6
REACTION
NaOH 1
1e-4
END