generally CaCl2 is added to maintain a constant ionic strength of soil (media) during the adsorption and column experiment, why this is important ?
I have read that you have to do that in batch scale experiments, but I have never seen the same necessity in column experiments... Could you, please, give some references? And how it is even possible, if the system is not "closed"?
@ Artis Robalds : definitely it is possible, just dissolve CaCl2 in the feed solution to the column. you can find it in the attached publication.
In the article you have given, they use CaCl2 to have similar composition of the solution to rain water. Sometimes researchers use tap water for the same reason.
And what do you mean by "to maintain a constant ionic strength of the media(soil)"? That the ionic strength in the effluent should be always the same? It is hard to imagine that you adjust the ionic strength of the feed solution, based of the concentration in the effluent.
you can find that in this article that CaCl2 is being used to maintain the ionic strength, even the OECD guidelines suggests to use the 0.01M CaCl2 solution for batch experiments.
In the last reference you have given, they used CaCl2 in batch studies, not in column studies!I know that in many studies devoted to biosorbents and heavy metals, researchers maintain constant pH during the experiment so to be sure that precipitation do not take place. I have not seen that they do the same for ionic strength...
Yes, you want to avoid mineral precipitation and dissolution. Also, changes in ionic strength can alter electrostatic charge of clays and some other minerals, which can cause changes in hydraulic conductivity of the soil during the soil column transport experiment.
In general, it is nice to change only 1 variable at a time so that you can observe the impact of that variable. For column experiments, you are injecting a tracer (e.g., pharmaceutical) at a constant concentration in the influent end and observing the tracer concentration at the effluent end of the column. I would try to not change any other variables. Attached is another paper that may be of use.
Hope this helps!
@ Kenneth C. Carroll : thanks a lot. This is exactly what I was thinking.
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