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 + , Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ , while Ca-montmorillonites were treated with alkaline and alkaline earth ions except for Ra 2+ and Ca 2+ . 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 Ba 2+ > Sr 2+ > Ca 2+ > Mg 2+ . The cation exchange capacity with single ion exchange capacity illustrates that Mg 2+ and Ca 2+ 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 °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. Mg 2+ -modified Na-montmorillonite which absorbs the most quantity of ions with the highest hydration energy has the maximum water content up to 8.84%.