Problem with dissolution

[Sergio913]

Hi community hope you are well
I am new in phreeqc. I am studying the behavior of different mixtures of water in contact with different minerals, and I have a question

I have a mixture of different waters (ions, salinity) and saturation indexes show to be supersaturated for some mineral phases, but if we put these waters in contact with the “rock” (equilibrium phase) they change and become sub-saturated, for example calcite. How can I explain this phenomenon?

Thanks

[dlparkhurst]

It is certainly possible to precipitate one mineral that causes another to go from supersaturated to undersaturated when they share a common ion.

Code: [Select]

SOLUTION
Ca 10
S(6) 10 Gypsum 0.1
C(4) 1 Calcite 0.05
EQUILIBRIUM_PHASES
Calcite 0 0
Gypsum 0 0
END


[John Mahoney]

When the solution is equilibrated does the pH change?  From your description, most likely it could decrease.  This might suggest some issues with the quality of the original solution.   What is the charge balance on the original solution?  Is CO2(g) part of your equilibrium_phases?  When that is included in the Equilibrium_phases it could lower pH also.