Cation exchange, interlayer spacing, and thermal analysis of Na/Ca-montmorillonite modified with alkaline and alkaline earth metal ions

Na-montmorillonites were exchanged with Li+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, and Ba2+, while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra2+ and Ca2+. Montmorillonites with interlayer cations Li+ or Na+ have remarkable swelling capacity and keep excellent stability. It is shown that metal ions represent different exchange ability as follows: Cs+ > Rb+ > K+ > Na+ > Li+ and Ba2+ > Sr2+ > Ca2+ > Mg2+. The cation exchange capacity with single ion exchange capacity illustrates that Mg2+ and Ca2+ do not only take part in cation exchange but also produce physical adsorption on the montmorillonite. Although interlayer spacing d (001) depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d (001) value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36-84 A degrees C), the dehydration of interlayer water and the chemical-adsorption water (47-189 A degrees C) and dehydration of bound water of interlayer metal cation (108-268 A degrees C). Data show that the quantity and hydration energy of ions adsorbed on montmorillonite influence the water content in montmorillonite. Mg2+-modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.