NATURE OF EXCHANGE CENTERS OF MONTMORILLONITE FROM DATA ON ITS DIIONIC LI, NA-FORMS

We show that determination of the exchange capacity of heat-treated mi xed Li,Na-forms of montmorillonite with different Li/Na cation ratios allows us to estimate the number of exchange centers due to SiO- group s on the lateral faces of the crystals and isomorphic substitutions in the structure. The quantitative differentiation of the exchange cente rs connected with isomorphism in the octahedral and tetrahedral networ ks of the montmorillonite structure presents certain difficulties: it is possible only for a sufficiently pronounced level of isomorphic sub stitutions in the tetrahedra. We confirm that the exchange centers of layered silicates located on the lateral faces of their particles are characterized by a selectivity series Li+ > Na+ > K+ > Rh+ > Csf which is inverted compared with that for exchange centers due to isomorphis m in the structure Cs+ > Rb+ > Kf > Na+ > Li+.