Spacings interlayer, salt concentration

Interlayer Spacing d as a Function of Salt Concentration c from Laboratory Experiments... 

Interlayer Spacing d as a Function of Salt Concentration c from Neutron Diffraction Measurements in the Sol Concentration Range r between 0.01 and 0.1... 

Recently, it was noted that the addition of poly(vinyl methyl ether) to a clay-salt-water system induced the contraction of the interlayer separation between the clay platelets [18], The K-butylammonium vermiculite used in those experiments provided an ideal structure of regularly spaced and parallel charged colloidal platelets in a salt solution [19,20], Swenson et al. [21-23] studied the effect of the addition of poly(ethylene oxide) (PEO) on the distance between the vermiculite layers and observed that, with increasing PEO concentration, the distance between the vermiculite layers decreased. They estimated that the bridging force per bridge was 1.4 pN. 

To summarize, calcium ions in the solution can be present as hydrated Ca2+ions, and CaHEDTA and CaEDTA2 complexes, of which only the positive calcium aqua complexes (Ca2+) participate in the ion-exchange reaction. In the process, calcium ions dissolve from montmorillonite to the solution, and mostly hydrogen ions get into the interlayer space of montmorillonite. In addition, sodium ions are also present in the system (EDTA is added as disodium salt H4EDTA is hardly soluble in water), which also affects the ion-exchange process. The ratio of cCa aCa can be plotted as a function of the concentration of Ca2+ (Figure 2.11). 

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