Solubility diagram

[bmuncy]

Hello,

 

I am trying to make a solubility diagram with temperature and pressure/CO2 fugacity as the axes. Is there a way to do this? What program should I use?

[Brian Farrell]

Hi,

 

You'll most likely want to use Tact for this. Tact is like Act2, which produces activity-activity diagrams, except that one axis is always temperature. To make a solubility diagram, you'll want to choose the main species to diagram, then choose that same species to appear on one of the axes (note that a solubility plot must diagram an aqueous species, not a gas). In your case, you would choose HCO3- to look at the carbonate system.

 

If you'd like to see how the CO2(g) fugacity affects the stability of some other species, just choose HCO3- for an axis, then swap in CO2(g). If you'd like to set the total pressure of your system in Act2 or Tact, you can do so at the bottom of the GUI. This will affect the position of the water stability limits and the fugacities assigned to gaseous species, but not mineral or species stability.

 

The GWB Essentials Guide contains more information on how to make various diagrams in Act2 (Section 5) and Tact (Section 6). You can also view galleries of pre-calculated diagrams (with input files) on our website.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

[bmuncy]

Thank you for your help, but every time I do this it tells me there is an error. I'm putting the HCO3- in the diagram species then pressing on x-axis. The error keeps telling me that the diagram must be on aqueous systems when I go to press run.

[Brian Farrell]

Hi,

 

If you can send me your Tact file, or a screenshot of the GUI, I'll take a look.

 

Thanks,

Brian

[bmuncy]

If I am looking at CO2 gas on the axis what should I put in the diagram species?

[Brian Farrell]

Like I mentioned above, a solubility plot (main species also appears as an axis variable) can diagram only aqueous species. So you can have HCO3- as both the main species and an axis, or you could do the same with CO2(aq), CO3--, etc. CO2(g) cannot be both the main species and an axis variable.

 

If you'd like a diagram with CO2(g) on an axis, it can only be with some non-carbonate species as the main species of the diagram. You might, for example, consider how the fugacity of CO2 affects the stability of various iron species, including Siderite.

 

You might also be interested in running reaction path models using React. A titration path, sliding temperature (polythermal) path, or sliding fugacity path might be interesting you.Try checking out the GWB Reaction Modeling Guide for more info.

 

Hope this helps,

Brian