Exchange Behaviour of Cation Pairs with Bentonite, Illite and Kaolinite

Relationship between quantity of cation on adsorbent (Q) and intensity in solution (I) was studied for K/Ca, Na/Co, K/Mg, and Na/Mg ion pairs with Ca- and Mg-saturated bentonite and illite suspensions (<2μm particle size) and air dried Ca- and Mg-saturated kaolinite. Q/I relationships in K/Ca as well as K/Mg systems exhibited curvature with all the three clay minerals whereas Na/Ca and Na/Mg pairs gave linear relationships with the kaolinite, but not with the other two clay minerals. The forms of relationships were discussed in terms of the ionic size and hydration energy. That K⁺ was held with more energy than Na⁺ was supported by the values of free energy changes.