Concept of a column experiment in PhreeqC

[Hydroman]

Hello together,

I like to model a more complex column experiment (closed system, pressure nearly 150 bar, circulation of the water phase). The sample only consists the silicates Quartz, Albite, Anorthie, K-Feldspar and K-mica. At The beginning I have a water with I=0.
Before I start with a 1-d model inclusive the Kinetic I like to understand the processes of the silicate weathering in general. So that I can get an idea what happens during the experiment (learning about the process).
My opinion is that the first step should be a simple model with a single silicate. So I can look what happens if this gets in contact with water.
So I need I need the Keyword "Solution" of course and the Keyword "Reaction" to put in the mineralphase. Then I need the "Equilibrium_phases" of SiO2(a) and Al(OH)3(a).

So for example for the mineralphase Albite I would write:



TITLE silicate weathering 1. step

SOLUTION 1

REACTION 1
 Albite 1
 1 millimoles in 1 step

EQUILIBRIUM_PHASES 1
SiO2(a) 0 10
Al(OH)3(a) 0 10

END

I think this should be the right inputfile to understand the processes of water-rock interaction in a column experiment, because nothing happens exapt the dissolution of the mineralphase Albite and the precipitation of SiO2 and Al(OH)3. With this simple code I can see for example that the ph-value increases due to the precipitation of SiO2(a) and Al(OH)3(a).


In the next step I would put in the other silicate phases into the "REACTION" part to see what happens with H4SiO4 an Al(OH)4- and the cations.

Do you think that this is a right concept to set up a model of an column experiment?

BR

Hydroman

[dlparkhurst]

There was a similar recent thread:

http://phreeqcusers.org/index.php/topic,1032.msg3024.html#msg3024

and Example 6 in the manual is similar and gives several approaches to the problem.

[dlparkhurst]

Also, the pH goes up because of dissolution of Albite (the REACTION). Precipitation of Al(OH)3 tends to decrease the pH.