Geochemist's Workbench Support Forum Calculation of (maximum) mineral / metal solubility in a reaction path using REACT

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Hello GWB experts,

I am wondering if there is an easy way to calculate the (maximum possible) solubility of a mineral / metal in a fluid along a reaction path in the REACT program.

Assuming an reaction path of a cooling fluid (e.g. from 250 °C to 25 °C) with different dissolved metal species (e.g., Fe, Na, Ca ....). REACT show nicely the actual concentrations of the different aqueous species, as well the amount of minerals that precipiate once saturation is reached.  Is it possible to calculate and show the max. solubility of metal / mineral in this context (e.g. max solubilty of Fe at temperature)?

Many thanks in advance,

Sebastian

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Hi Sebastian,

There’s an example diagram in the React section of GWB.com/diagrams.php entitled Mineral solubility. You can click on the React icon to download the script. It sets a fluid in equilibrium with Kaolinite at pH 3, then scans all the way to pH 9. We’ve shown a plot of the species distribution in the fluid as a function of pH, but you could easily plot the Al+++ Component in the fluid (the sum of the dissolved Al+++ species) to see the total dissolved aluminum. It’ll look like a curve traced just above the highest concentration species at each pH. In this example, the mineral is least soluble at ~pH 5.4, and the solubility increases in either direction from there. You could easily make a similar diagram with a sliding temperature path to figure the effect of temperature on the solubility of an iron mineral.

Of course, there are many factors that can control the solubility of minerals, such as pH, oxidation state, ionic strength, the presence of various complexing ligands in different concentrations, and temperature. React (or SpecE8) can calculate the solubility of a mineral in any fluid you specify, but not every fluid, at least in a single calculation. In other words, you can’t determine from a single reaction path the maximum solubility of a mineral considering every possible fluid composition. You can only find the maximum solubility subject to the prescribed conditions. React lets you consider one variable at a time, and Phase2 lets you consider two at a time.

Hope this helps,

Brian Farrell
Aqueous Solutions

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