IMPROVED STRUCTURAL FORMULA METHOD FOR DETERMINING THE PERMANENT LAYER CHARGE FROM CHEMICAL ANALYSIS OF MONTMORILLONITE

抄録

The cations in the octahedral sheet of montmorillonite (usually composed of Al, Fe and Mg) occasionally exceed 2 mols of charge per mole of formula unit [mol/mol_FU] when analyzed by the conventional structural formula method (SFM) consisting of di-octahedral region from chemical analysis of refined clay samples exchanged with ions other than Mg. To correct this deviation, this paper proposes an improved structural formula method (iSFM) that places the excess amount of Mg (mMg) into the vacancy of the octahedral sheet to become m(Mg₂Al) in the tri-octahedral region. The iSFM is applied to five clay samples, and the results show that the clays, mainly containing montmorillonite, can be appropriately evaluated as bleaching earth or bentonite, regardless of their pH values or amorphous hydrated silica contents.