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[OLD] Two tables for ionic activities in React


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From: Sadoon Morad

Subject: Two tables for ionic activities in React!

When I calculated the ionic activities and mineral saturation indices in react for a water sample I have, I faced two problem for which I have no explanation:

(1) I obtained two different tables, in both of which the ionic concentrations are different from my original water composition. It is mentioned for the first table that there are “no minerals in the system� and for the second table some minerals, which were calculated by the software to be in saturation with the water, were used. Which of these tables are correct and relevant to my task (i.e., obtaining free ionic activities and saturation indices)?

(2) why are there composite ions in the tables, e.g. NaSO4-, if I am concerned with calculating the free ionic activities and saturation indices?


From: Craig Bethke

Subject: Re: Two tables for ionic activities in React!

The two entries in React_output.txt correspond to the apparent equilibrium state of the supersaturated fluid, and the theoretical equilibrium state of the fluid, once minerals precipitate to saturation. If you don't care to see the second entry, set “precip = off�. To calculate the activity of a free ion (say Na+) from a total analytical concentration (Na), you must determine not only the ion's activity coefficient, but the fraction of the total concentration present as the free ion. In order to do the latter, you must calculate the concentrations of the complex species and subtract these from the total concentration.

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