The absorption of dyestuffs by montmorillonite can be attributed to two
different processes, namely (1) base exchange and (2) van der Waals
adsorption. There are some mixed cases, but usually one of the two effects
is predominant and can be easily distinguished by several of the following
features (see table 1.).
This paper deals with the base exchange type of adsorption only and in
particular with the quantitative relations between the adsorbed dye and the
released exchangeable cations. The simplest assumption, which is very often
taken for granted, is that the two quantities are equivalent and correspond
to the base exchange capacity of the montmorillonite.