Jump to content
Geochemist's Workbench Support Forum

CO2(aq) - brine solns, ion size params, salting effect


Recommended Posts

From: Biniam Zerai

Subject: Info on CO2(aq)

I am trying to model the possible reaction of CO2 gas, albite, annite, siderite, calcite and dolomite in 2 molal of brine solution. I made the correction for fugacity of the gas using Duan and Sun equation of state but I am not sure what is the right way as how to correct the salting-out effect using GWB. I have been told to change the the ionic size in the thermodynamic database that contains the aqueous species, CO2(aq) to -0.5 in order to correct the effect of salinity on CO2(g) solubility. Is this the right way to do it? I did it using the above advise and observe a large difference. Any info, input or comment is highly appreciated. I am using GWB 3.2.2.


From: Craig Bethke

Subject: Re: Info on CO2(aq)

The equations used to calculate activity coefficients for electrically neutral species are given in Chapter 7 of the "Geochemical Reaction Modeling" text. The special meaning of the ion size parameter for neutral species is described in the "Thermo Datasets" appendix to the GWB Reference Manual:

The ion size parameter (ao) has special meaning for neutrally charged aqueous species in the thermo dataset. For neutral species with ao = 0, the species' activity coefficient is set to one. When ao = 1/2, the activity coefficient is calculated from the "CO2" coefficients in the data table section, according to equation 7.6 in the "Geochemical Reaction Modeling" text. When ao = 1, the logarithm of the activity coefficient is set to the product B(dot)x I, where B(dot) is given by the data tables above, and I is true ionic strength.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...