Calculating Saturation Concentration of Ca(OH)2 in the Presence of HCl using PHR

[anaamine]

Hello everyone,

I am new to using PHREEQC and I am currently trying to model a scenario involving the dissolution of calcium hydroxide (Ca(OH)2) in water, with varying amounts of hydrochloric acid (HCl) at different temperatures.

The main goal of my simulation is to calculate the saturation concentration of Ca(OH)2 in the solution as a function of the moles of HCl present. However, I've been running into difficulties because I can't seem to find Ca(OH)2 or HCl in the database.

I understand that this might be a simple equilibrium calculation, and I could potentially solve it using charge balance equations, but I want to learn how to model this system using PHREEQC as part of my learning process, and also to cross-validate my results.

I've attempted to consult the help section of the software, but I am still facing difficulties in resolving this issue. Can anyone guide me on how to proceed with this, or point me in the direction of resources that might be helpful for this type of problem?

Any help is appreciated, and I thank you in advance for your time and assistance.

Best regards,

[dlparkhurst]

This should get you started. You will need to repeat the final set of USE and REACTION_TEMPERATURE statemetns for each additional temperature. (If you use multiple temperatures, the first temperature will be used in the first REACTION increment, the second in the second REACTION increment, etc, which is probably not what you want.)

Code: [Select]

PHASES
Portlandite # from llnl.dat
        Ca(OH)2 +2.0000 H+  =  + 1.0000 Ca++ + 2.0000 H2O
        log_k           22.5552
-delta_H -128.686 kJ/mol # Calculated enthalpy of reaction Portlandite
# Enthalpy of formation: -986.074 kJ/mol
        -analytic -8.3848e+001 -1.8373e-002 9.3154e+003 3.2584e+001 1.4538e+002
#       -Range:  0-300
END
SOLUTION 1
END
EQUILIBRIUM_PHASES
Portlandite 0 10
END
REACTION 1
HCl 1
1 in 10 steps
END
USE solution 1
USE reaction 1
USE equilibrium_phases 1
REACTION_TEMPERATURE 1
30
END


[anaamine]

Thank you for your helpful answer.

Could you provide me with some resources where I can read more about this topic and learn how to use it to calculate solution equilibrium?

Regards.

[dlparkhurst]

https://water.usgs.gov/water-resources/software/PHREEQC/documentation/phreeqc3-html/phreeqc3.htm.

Geochemistry, Groundwater and Pollution by Appelo and Postma.

https://water.usgs.gov/water-resources/software/PHREEQC/Geochem2011.tgz

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