I am performing batch experiments to study specific adsorption of heavy metals in soil. For that why do I need to add any background electrolyte in that. I mean I have searched but the description given in some papers is that to maintain constant ionic strength. That seems little vague . I mean they are recommending to use say 0.01M NaNO3 as background electrolyte. How that will help?
Let's say I have to analyse the adsorption for chromium so can't I just perform the experiment with the k2cr2o7 solution in soil.
My best guess as to why they conducted the experiment in such a solution lies in the ionic strength. Changing the ionic strength of a solution has shown to affect the adsorption of other, analyte ions. There could be a variety of reasons given for the choice of ion-source. See papers below.
Article Effect of solution pH, ionic strength, and temperature on ad...
Article Ionic strength effects in aqueous phase adsorption of metal ...
Article Adsorption of microplastics on aquifer media: Effects of the...
Article Strong influence of surfactants on virgin hydrophobic microp...
Article Surfactant changes lead adsorption behaviors and mechanisms ...
Fully supporting the explanation given by Ryan G. Hoerr, I would add also another reason (perhaps mentioned in the provided papers): when it is about sorption from aqueous solutions on soils, clay minerals containing in the soil as well as soil organic matter undergo dispersion and dissolution. This makes multiple problems, such as preventing effective filtration, and forming complexes in aqueous phase which interferes with the further understanding olf sorption isotherms. The water-soluble organic matter forms complexes with heavy metals as well as dispersed clay particle are also interacting with solutes. Hence, in very many experiments, calcium chloride is used in order to keep clays and organic matter as flocculated as possible and prevent their dissolution. And, another common reason is that very often soils contain calcium carbonate. In this case, use of calcium chloride makes a typical natural environment expected in soil solutions.
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