Deconvolution of Smectite Hydration Isotherms

Sorption
isotherm models have traditionally served as an invaluable
tool to characterize synthesized and natural mineral particles. However,
for particles susceptible to substantial hydration, such as the swelling
smectite clay minerals and other layered minerals displaying intercalation
of discrete water monolayers, traditional isotherm models inadequately
describe the total water uptake as a result of the change in available
surface sites and area during the hydration process. With the goal
of deconvoluting the water uptake behavior of swelling smectite minerals,
this research presents a novel composite isotherm model that describes
water uptake by surface adsorption, condensation, and stepwise intercalation.
A set of eight montmorillonite samples ion-exchanged with different
countercations (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, and Cu2+) were used to develop this model, which was based on gravimetric
uptake measurements and X-ray diffraction data of basal spacings obtained
from relative humidity conditions up to 98% relative humidity.