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1D reactive transport in a column


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I am using GWB X1t to simulate fluoride transport in a soil column.

First, the column is contaminated with fluoride for a certain period of time and then

the column was flushed with deionized water.

In the simulation, first, I want to simulate the transport process during sorption,

where fluoride sorption was described by surface complexation.

For surface complexation, I used the general composite approach (I added a new basis

species (X) with 1g/mol molecular weight, defined a new element and a mineral with the basis species).

For the surface dataset, I defined the reactions in terms of a new surface species (>XOH).

For the mineral,if I use the exact density (e.g., 3591 g/l, that I used for my column with 39% porosity) and a site density of 2.6e-5moles/g, the program ends with the message that the porosity is too small.

Since the porosity at each grid block is calculated with each run, I decreased the mineral site density (e.g., 1g/l or 0.1 g/l) and accordingly increased the site density.

Then the program doesn't converge.

However, if I keep both site density and mineral density small, the program runs but the results are not satisfactory (fluoride appears in the outlet just after 1 pore volume because the sorption is small).

I appreciate any suggestion on how to keep the desired site density?

P.S.: My PHREEQC simulation gives good results with the same site density, mineral conc. and surface reactions.


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Hi Padhi,


Rather than setting mineral abundance at each nodal block relative to fluid volume, have you tried setting it as a percentage of the nodal block volume? Assuming your only mineral in the simulation is the general composite that accounts for sorption, you could set its abundance in the initial system (Initial pane) to 61 free volume %. Without setting porosity explicitly on the Medium, the program will calculate 39% for the porosity. Please let me know if that helps. If not, could you attach your X1t script along with your custom thermo and surface datasets?


Brian Farrell

Aqueous Solutions LLC

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