Abstract
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 d001 depends on both radius and hydration radius of interlayer cations, the latter one plays a decisive role in changing d001 value. Three stages of temperature intervals of dehydration are observed from the TG/DSC curves: the release of surface water adsorbed (36–84 °C), the dehydration of interlayer water and the chemical-adsorption water (47–189 °C) and dehydration of bound water of interlayer metal cation (108–268 °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%.
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