varying inputs

[lltierney]

I am trying to equilibrate "pure" water with basaltic rock that is also in equilibrium with a martian atmosphere. I have attached a script that converges fine, but when I try to vary the CO2 log fugacity (from -.28 to .022) the file won't converge and I am not sure why. Also, I would like to add a fixed fugacity of SO2(g) to my model and understand that the "thermo" database doesn't include SO2(g). Would you reccommend that I copy the values for SO2 from the "v8.r6+" database?

Shergotty_purewater.rea

[Tom Meuzelaar]

I am trying to equilibrate "pure" water with basaltic rock that is also in equilibrium with a martian atmosphere. I have attached a script that converges fine, but when I try to vary the CO2 log fugacity (from -.28 to .022) the file won't converge and I am not sure why. Also, I would like to add a fixed fugacity of SO2(g) to my model and understand that the "thermo" database doesn't include SO2(g). Would you reccommend that I copy the values for SO2 from the "v8.r6+" database?

Hi,

I think your model is a bit too ambitious. You are titrating a highly alkaline solid into an acidic solute concentration, high CO2 concentration, neutral pH, and no provision for charge balance. Putting this many extremes into a single reaction path model is likely to lead to numerous convergence issues and frustration!

I recommend breaking the model into smaller models. Trying reacting less solid, take smaller reaction steps, using small but numerically tenable concentrations (but not e-14), and set pH by charge balance so it's consistent with CO2 fugacity.

Regarding the SO2(g) species, the simplest solution would be to use the v8.r6+ database for this simulation.

I hope that helps.

Regards,

Tom Meuzelaar

RockWare, Inc.