How adding silicic acid to the thermodynamic database of interest

[AliMahaqi]

Dear Jia,

I hope this message finds you great.

I am going to add clinopyroxene and Stapafell basaltic glass to my database as minerals to do reaction path modeling. Based on the formula, I could add every components, but I have serious issue with adding silicic acid (amin problem) as I could not find it as a species in "Species in reaction" and if I could not add it to the chemical reactions, I see charge and mass imbalance, could you please explain to me how can I solve this issue?

(I have also attached the files including formula - taken from papers that did reaction path modeling in PHREEQC if helps- and a screenshot of the database)

Thanks in advance

[Jia Wang]

Hello,

I think there are a couple of issues here. In the screenshot provided, you didn't enter a mole weight for the mineral, and therefore the Status line is indicating that you have a mismatch between the program calculated mole weight vs an empty value.

In cases where you are certain that the stoichiometry of your reaction is correct, you can hit the "Adjust mw" button and TEdit will calculate the mole weight of your mineral and you can choose to use that value. In this case though, as you have pointed out, the database doesn't contain silicic acid (H4SiO4) which is used in the clinopyroxene reaction. The species in reaction you have put in, by just using SiO2(aq), isn't stoichiometrically balanced. For example, you can see that the left side of your equation has 8 hydrogens and the right side has none. There is also a similar issue with oxygen. If you want to put in the reaction exactly as your paper, you will need to add a reaction for H4SiO4, which isn't typical to have both silica and silicic acid in a dataset. Assuming that H4SiO4(aq) and SiO2(aq) + 2 H2O can be used interchangeably, you can rebalance the reaction from literature and include the correct reaction coefficients for each species.

For more information on editing thermo datasets using TEdit, you can visit our tedit webpage and see section 9 in the GWB Essentials User's Guide.

Hope this helps,
Jia Wang
Aqueous Solutions LLC