Reactive Transport modelling of CO2 with mining waste to form carbonate rocks

[evansmanu]

Dear All,

I am a newcomer to reactive transport modelling and seek expert guidance. I aim to employ reactive transport modelling to simulate CO2 removal using mining waste abundant in cations, specifically calcic-rich silicate minerals. Various approaches have successfully achieved CO2 sequestration through reactive transport modelling.

I am searching for an initial code that can effectively model this process, considering the weathering of mining waste as it reacts with atmospheric CO2.

Thank you for your assistance.

[dlparkhurst]

Because you have not tried anything, I am reluctant to give you too much help. Perhaps this will get you started.

Code: [Select]

SOLUTION
EQUILIBRIUM_PHASES
Anorthite 0 10
CO2(g)  -3.4 10
END


[evansmanu]

Thank you for responding promptly. If we consider that the initial composition of the solution in the mining waste is abundant in calcium (Ca) and magnesium (Mg), the interaction with CO2 will result in the formation of carbonate rocks. This is represented by Solution 1. Solution 0 corresponds to atmospheric CO2, presumed to be in equilibrium with the calcium-rich silicate mineral anorthite upon contact with the mining waste. The objective is to reduce CO2 levels by facilitating its reaction to produce carbonate rock in the presence of Ca and Mg in the mining waste.

How can we model this using reactive transport models to show the amount of CO2 consumed as against the Cation concentrations?

Find below my attempt to model what has been described above.

TITLE Reactive Transport Modelling for CO2 Removal

SOLUTION 0
    EQUILIBRIUM_PHASES
        Anorthite 0 10
        CO2(g)  -3.4 10
END

SOLUTION 1
    units mol/kgw
    pH 7.0
    Ca 1.0
    Mg 0.5
    C(4) 0.5
    -water 1.0
    EQUILIBRIUM_PHASES 1
        anorthite 0 10.0
        CO2(g) -3.5 10.0
END
 
#Defining reactive transport

TRANSPORT
   -cells 1
   -shifts 10

SELECTED_OUTPUT
    -file            CO2_Removal.sel
    -reset           false
    -step
    -pH true
    -totals         Ca Mg C(4)
    -high_precision true
END

[dlparkhurst]

And what did you find when you ran your script?

[evansmanu]

The positive saturation index (SI) values for carbonate minerals such as calcite, aragonite, and dolomite imply that they will precipitate when CO2 comes in contact with the mine waste which is assumed to be rich in calcium (Ca) and magnesium (Mg). This observation aligns with my initial hypothesis. However, I'm questioning the accuracy of my conceptual understanding and model framework.

I would like to know if the conceptual framework and the model configuration are in the right direction. Currently, the focus is solely on advective transport, and I aim to incorporate dispersion and diffusion once the model design is appropriately established.

Thanks very much.

[dlparkhurst]

You may not have noticed that you did not SAVE solution 0, so solution 0 is simply pure water in your transport calculation. SOLUTION 1 also was not SAVEd after equilibration with anorthite and CO2, so it remains the original definition of SOLUTION 1.

You also may not have noticed that all of your steps produced the same solution, which is the same as the calculation you intended for solution 1 and the calculation that I originally provided. So, the pertinent result is how much CO2 is consumed in dissolution of anorthite to equilibrium. If SIs or positive, you can also add the effects of precipitation of other minerals.

There is really no need for TRANSPORT if you are always calculating pure equilibrium with the same set of minerals and gases.