Heterogeneity of cation-exchange sites for K-CA exchange in aluminosilicates

Differential and integral thermodynamic functions were evaluated from equilibrium isotherm and microcalorimetric measurements for KCa exchange in the <2-μm particles of 1:1 and 2:1 layer aluminosilicates. The heterogeneity of exchange sites for K sorption in each mineral was inferred qualitatively from changes, with K saturation, of the activity coefficient of adsorbed K+ and of the integral functions. However, the corresponding change in differential enthalpy, measured by microcalorimetry, was found to separate precisely groups of sites with constant exchange enthalpies in each mineral. The role of the enthalpic and entropic forces during exchange is discussed, emphasizing the differences between each “standard” mineral, and also the anomalous behavior of the kaolinite and montmorillonite minerals.

RESP-08171