Conceptual Models > Database selection and modification

Modelling Water-CO2-Rock Interaction

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Fadeji01:
Hi everyone,

It's my first time asking questions on this platform. I apologize if my question has been attended to in another forum. I am trying to model a lot of things in a single code:

1. How much CO2 (mole) is sequestered in a 2-hour reaction
2. How much rock (ultramafic) mineral (all of the minerals in the rocks, including chrysotile and carbonates) (in moles) is dissolved in the 2-hour reaction
3. How much carbonates in (moles) is precipitating after the reaction

Here are my questions:

1. I am using the PHREEQC.DAT database and I am unable to add some of the phases in my rock, e.g., forsterite, diopside, magnesite and chrome-magnetite, looks like this database does not have them. How do I add them? or do I have to look for another database?
2. Apart from the fact that all of the mineral phases are not represented, are there modifications needed for this code below to meet the three objectives of this simulation?



--- Code: ---SOLUTION 1
    temp      25
    pH        7
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    -water    0.4 # kg

REACTION_TEMPERATURE 1
    25 25 in 1 steps
EQUILIBRIUM_PHASES 1
    CO2(g)    0 0.000143
    Calcite   0 0.0099
    Chrysotile 0 1.0122
# Output settings for carbonate formation
SELECTED_OUTPUT
    -file      output.txt
    -reset     false
    -pH        true
    -alkalinity true
    -si        Calcite Magnesite Dolomite # Saturation indices for carbonate minerals
    -totals    C        # Track CO2 and Mg species
    -equilibrium_phases CO2(g) Chrysotile   # Monitor chrysotile calcite and CO2 changes


--- End code ---

dlparkhurst:
You can add phases to a database with the PHASES data block. You can take PHASES definitions from other databases and include them in your input file or in a file that is included with INCLUDE$ (see the manual). There is at least one provision; you must consider the master species for Si. llnl.dat uses SiO2(aq), whereas most of the other databases use H4SiO4(aq). To use phases from one to the other, you must rewrite the chemical reactions to be consistent with the master species of the target database. You can rewrite the reactions using the relation H4SiO4 = SiO2 + 2H2O, and assume there is no affect on the log K of the reactions.

You can search this forum for lots of examples of CO2 reactions, including kinetic dissolution of CO2 (https://phreeqcusers.org/index.php/topic,2584.msg9711.html#msg9711).

You will have to decide if a script meets your objectives.

Fadeji01:
Dear Dr. David. Thanks for taking the time to reply

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