Dehydration of the montmorillonite minerals

Abstract

Studies of the effect of dehydration at temperatures greater than 150° on sorption by montmorillonites have shown that small interlayer cations such as lithium and magnesium promote an irreversible decrease in the amount of interlamellar sorption and a consequent marked fall in the cation exchange capacity as measured by conventional methods (1, 2, 3, 4). The other minerals of the group do not show this property (4), which is quite distinct from the supposed 'potassium fixation' reported in these minerals (5). This latter effect, which is small for montmorillonite, refers to the decreased rate of exchange of potassium as compared with smaller exchange cations especially after the potassium-saturated mineral has been dried at ]00° C., and has been shown to be much more marked in mica-like minerals with silicate layers of higher charge density (e.g. illites and vermiculites (6)). The amount of water sorbed by potassium-saturated montmorillonite is not significantly affected by drying at temperatures below 400° C. although it is less than that of most other montmorilIonites (3), due probably to the low hydration energy of the potassium ion (7).