Adsorption of Ionic Contaminants

Chapter 2 mentioned that the adsorption of charged ionic compounds on the solid phase is a result of a combination of chemical binding forces and electric fields at the interface. Here, we extend the discussion on this topic, focusing mainly on aspects relevant to behavior of ionic contaminants in the subsurface environment. 

The Gouy-Chapman model assumes (1) the exchangeable cations exist as point charges, (2) colloid surfaces are planar and infinite in extent, and (3) surface charge is distributed uniformly over the entire colloid surface. Even though this assumption 

In the Stem model, the surface charge is balanced by the charge in solution, which is distributed between the Stem layer at a distance d from the surface and a diffuse layer having an ionic Boltzman-type distribution. The total charge a is therefore due to the charge in the two layers  

Cation exchange capacity and selectivity are among the most important processes that control the fate of charged (ionic) contaminants in the subsurface. These processes 

Early work by Boyd et al. (1947), performed on zeohtes, showed that the ion exchange process is diffusion controlled and the reaction rate is limited by mass transfer phenomena that are either film-diffusion (ED) or particle-diffusion (PD) dependent. Under natural conditions, the charge compensation cations are held on a representative subsurface solid phase as follows within crystals in interlayer 

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