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Reacting 1 kg water at 300 C with various minerals


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Hi all,

 

I'm trying to look at what happens when 1 Kg pure water at 300 C and 2000 kBars interacts with a large quantity of Granite, Slate, and pure quartz. I have the mineral assemblage percentages for both Granite and Slate, but I'm not quite sure what program in GWB to use. I would like to get measurements on the SI indexes of various minerals, pH, alkalinity, salinity, and of course the resultant fluid composition. I have a working thermo database for this T & P range.

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Hi,

 

I would start with React. It's best to start simple (single node, simple chemical system, equilibrium) and add in complexity as required (reactive transport, more complete fluid analysis, kinetics, etc.). The Getting Started with React section of the GWB Reaction Modeling Guide includes an example in which K-feldspar is reacted into a dilute fluid. I think that will be helpful.

 

Even though you want to react a "pure water" with a mineral or assemblage of minerals, you'll need to specify in the fluid very small amounts of the components that make up the mineral to be titrated in. This is a requirement of the thermodynamic model. For example, to react K-feldspar with pure water, you'll actually need to set the fluid's pH and add K+, Al+++, and SiO2(aq) in small, non-zero amounts to account for reaction between the fluid and the K-spar.

 

Hope this helps,

 

Brian Farrell

Geochemist

Aqueous Solutions LLC

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Thanks! I did as you say and it seems to work well with my expectations. I have another question though. Suppose I do the above, react a fluid with quartz, and then want to take that fluid composition and react it with the same mineral suite at a different pressure? I have two separate thermo datasets for the two pressures I want to work with, but I couldn't find anything on saving and importing a fluid composition for react. What would I do in this case?

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Hi,

 

One option is to "pick up" the results of your run, then load the new thermo dataset. It's not common to change thermo data in the middle of your calculations, however, so I would be a little careful. You'll probably want to make sure that when specifying the composition of your fluid on the Basis pane everything is in terms of components (bulk constraints). For example, you'll probably want total moles of Hydrogen, not the pH, since that could be different at different pressure. If your pickup results include free constraints (like pH) then you can just get the bulk composition of the fluid from React's output file on the line beginning "Original basis".

 

For more on the "pickup" feature, check out section 3.9 in the GWB Reaction Modeling Guide.

 

Regards,

Brian

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