mineral dissolution vs water-rock ratio

[Shiba7]

I want to create a plot, as given in the figure below (Hurowitz and McLennan, 2007), where the minerals will react with a known fluid composition in different water-to-rock ratios. However, I am unable to find the way through which such a reaction model can be performed. Any help in this regard would be highly appreciated. I have also attached a reaction file where a known acidic water is reacting with two minerals present in a system at 5:1 water-to-rock ratio (if I understand the system correctly). Surprisingly, no secondary minerals are forming in this reaction model. Except SiO2 (aq) all the other values of the initial fluid are known.

Mineral dissolution.rea

[Jia Wang]

Hello,

I took a quick look at the input file attached and so far what I see is that you have set up an initial fluid of about 1 kg of solution to react with albite and k-feldspar over a period of 1 year. The dissolution and precipitation of these two minerals are constrained using the built-in rate in the GWB. The pH is fixed throughout the simulation.

If you want to vary the water to fluid ratio, I see a couple of ways to approach this. Since you have set all the concentrations of your fluid in the basis pane in relative units, you can change the volume of H2O to the desired mass. Another option is to set the reactants times factor on the "Reactants" pane. The default value is 1, changing the factor will multiply the quantity of the reactants set on this pane. You can vary the ratio of rock to fluid and perform multiple runs as needed. There are a few options in The GWB to run a large batch of samples within the GWB,  including the Plugin feature and control scripts if you would like more control over what the program outputs and to store the results in specific files. For more information regarding Plugin and Control scripts, please refer to section 7 and 6 in the GWB Reference manual.

Please note that water to rock ratio is not a plottable variable in Gtplot. You can export the numerical data from the runs, mineral mass (set Variable type = Minerals) and mass solution (Variable type = chemical parameter), and make the calculation for a solution to mineral ratio in a spreadsheet. For more information on exporting numerical data from simulation, please see section 6.7 in the GWB Reaction Modeling Guide.

Are you expecting specific minerals to precipitate in your simulation? If you are trying to replicate the plots posted, I would suggest you check the equilibrium constants used in those simulations against the ones in the thermodynamic dataset you're using. The software considers all minerals in the database loaded for the simulation, for those that you are not expected to form in your system, you might consider suppressing them (Config menu -> suppress). In Gtplot, you can also investigate the mineral saturation indices to see which minerals the fluid is close to equilibrium to.

The caption in the plot also states that there are more details to how the curves are constructed. It would be good to check if the way you are setting up your problem matches that of the paper's.

Best regards,
Jia Wang
Aqueous Solutions LLC