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PHREEQC modeling



I am modeling cadmium transportation in consideration
of reactions-adsorption and precipitation/dissolution 
in a column packed with fly ash and bentonite mixture.

For this purpose, I performed batch experiments about
cadmium to know surface complexation properties 
and tracer experiments to know hydrogeological
parameters-seepage velocity and dispersion
coefficient- using lithium bromide. 
First to consider the adsorption properties of cadmium
on the mixture I used SURFACE_SPECIES and SURFACE. 
The column experiment of bromine was simulated using
TRANSPORT. 
And then, I combined two models of surface
complexatoin and conservative transport to simulate
non-conservative transport of cadmium. 
However, I found some problems about my results and
had questions about them.
1.       To define SURFACE, are SURFACE and their
total mass also divided by 10 if I divided column to
10 cells?
2.       In the case of my experiments, the removal
rate of cadmium was very low in a range of 5~200mg/L. 
    So I changed reaction constants (log_K) of
SURFACE_SPECIES to negative values. Is it caused any
problem?
3.       I performed breakthrough experiment for a
single ion of cadmium. But the BTC showed the shooting
result 
    that appears in multi-ion (I mean the
concentration near the breakthrough is over the
initial concentration). 
    I think that result was caused by the other ions
that were defined for PHASES. How can I remove such a
phenomenon?
4.       I included surface complexation to account
for the retardation of cadmium in a column. 
    So I expected that cadmium flowed out more slowly
in the low concentration. 
    Though I changed the initial concentrations from
50mg/L to 5mg/L, the breakthrough times are much the
same. 
    Why did the results appear?
 
I attach input files to e-mail. I know they may be
very clumsy and improper. I believe you will give me a
proper advice. 


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Attachment: Inputfiles.zip
Description: Inputfiles.zip



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