webmaster Posted December 26, 2004 Share Posted December 26, 2004 From: Ian Hutcheon Subject: Activity of solids in act2 I am trying to figure out how to assign more than one activity for a solid species in ACT2. For the system: show system Diagram speciation of Paragonite on Na+/H+ vs SiO2(aq) Temperature is 25 C, Pressure is 1.013 bars Thermo dataset: .gtdatathermo.dat Working directory: c:program filesgwb Basis is: Paragonite (swapped for Al+++) Activity = 10^-2.57 (main species) H2O Activity = 10^0 (solvent) Na+/H+ (swapped for Na+) Y-axis variable SiO2(aq) X-axis variable The components that appear on a Paragonite, Na+/H+ vs SiO2(aq) diagram are as follows. Gibbsite Kaolinite Pyrophyllite Analcime Paragonite Albite low Clinoptil-Na Using the Aagaard and Helgeson approach to defining activities of these components in smectite requires assigning an activity for each of the components Paragonite and Pyrophyllite. However, we seem to only be able to define one activity? From: Craig Bethke Subject: Re: Activity of solids in act2 I think the following should work for you. The reactions for Paragonite and Pyrophyllite (like all the minerals) are written in the database as destruction reactions for a single stoichiometric unit of mineral. If you change the log K for these two reactions to log K + log a, where a is the desired mineral activity, therefore, this activity will be carried implicitly throughout your calculations. The easiest way to change the log K values is to use the â€œalterâ€? command -- there's no need in this case to edit the thermo database. Quote Link to comment Share on other sites More sharing options...
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