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Amount of calcite dissolved


Christoph
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Hello to everybody,

 

i am doing some modelling with Geochemist's Workbench, but now i am wondering about the right amount of calcite dissolved. The system consists of a solution with 2.2 mmol Ca+2 and HCO3- is swapped to calcite (amount of 1 mol available). The fugacity of CO2 is swapped in for H+ and the values is fixed to 50 bars. This solution reacts with 4 mol of Na+ and Cl- and the fugacity of CO2 is fixed. For this problem I used thermo.dat.

The output-file shows in the category "Basis components" now a negative amount of Ca+2 and an amount of calcite, which is 1.14 mol, from which 0.14 moles are in solution. So is this values now the amount if calcite dissolved in the first step?

In the third step the amount of calcite is 1.00220 and the amount in the solution 0.00334767. Why is this changing? Which amount is the correct amount of calcite dissolved in each step?

I observed this phenomennon in various models.

I attached the react file and the output file and I hope you can help me!

 

Regards,

Christoph

thermo.txt

NaCl_thermo.rea

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Hi Christoph:

 

The actual amount of Calcite dissolved is listed under the heading "Minerals in system", not "Basis Components". In GWB there is a distinction between components, which are mathematical entities and can be negative, and actual minerals and dissolved species, which are physical entities and cannot be negative. This is detailed in Craig Bethke's Geochemical and Biogeochemical Reaction Modeling, Chapter 3.

 

I hope that helps,

 

Tom Meuzelaar

RockWare, Inc.

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