Solubility > Dissolution/precipitation

Dissolution of Montmorillonite, only occuring 1 cell at a time

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ravreeland:
Hello, I am new to PHREEQc and been having trouble. I looked in the manual and the forum and couldn't find an answer to the problem I am having.

I am trying to model the affect of pH in a clay column in terms of the clay dissolving. What my problem is, my model is only dissolving the clay in cell 1, and won't start dissolving the clay in cell 2 until cell 1 has completely dissolved. The pH changes in the rest of the cells, but the amount of clay does not. I feel like its because I have not set up the code correctly. One thing that I can think of that is possibly happening is that the material dissolved in cell 1 is not allowing the rest of the cells to dissolve because of equilibrium balance.
My questions are if the dissolution should happen one cell at a time? If it is not, what can I do to fix it?

Thank you very much for your time.

TITLE pH Study
#This is a commit

SOLUTION 0  MgCl2 #solution to be flowed into the cells at cell 1
units mmol/kgw #molality
# default --> 1 kg of solution
temp 25.0
pH 1.0     charge      # need this pH to be around 0, 1 or 2.
pe 12.5    O2(g)   -0.68
H(1) 0.016              #0.016 should be the molility of 37% HCl solution
# need to add H(1) to it for solution to reach pH target.
Cl 10

SOLUTION 1-10  Initial solution for column
units mmol/kgw #molality
temp 25.0
pH 10.0     charge
pe 12.5    O2(g)   -0.68
#Cl 20 # helps with the other cells, but they are still not disolving. AKA just starts lower

EQUILIBRIUM_PHASES 1-10
Ca-Montmorillonite 0 0.1

#[name of mineral] [saturation index] [amount]
-force_equality false

TRANSPORT  # 1D simulation
-cells 10 #designates the number of cells in 1D
-lengths 10*0.01
-flow_direction forward
-shifts 100 #number of times solution is shifted to next higher cell
-time_step 1 #seconds
-initial_time 0
-punch_cells 1-10
-punch_frequency 1

SELECTED_OUTPUT
-file pH_precipTest_1.sel    #name of file where results are written
-reset false    # sets some options to false, see user manual
-step       # prints out the advection shift number of transport calculations
-distance true
-totals H(1) Cl Ca Si Al S #prints out concentration in molatity of list
-water true #prints mass of water, perhaps in Kg
-equilibrium_phases Ca-Montmorillonite #prints out two lines, moles of each phase, and moles transferred
-pH true

#this is to print out other custom stuff to output
USER_PUNCH