Effect and mechanism of cation species on the gel properties of montmorillonite

Using montmorillonite (Mt) as the raw material, six kinds of metal cations with different valences (monovalent, divalent and trivalent) are used to modify montmorillonite through interlayer cation exchange and octahedral and tetrahedral central ion (Al3+ and Si4+) substitution to obtain the corresponding modified montmorillonite. XRD, ICP, NMR and other methods are used to study the effects of the metal cations on the structure, electrical properties, morphology, dispersion and gel properties of montmorillonite. The XRD results show that the six metal cations that have different valences can fully exchange with the interlayer cations, and the ICP results show that the six cations undergo partial isomorphic substitution with central ions in the lattice, resulting in a change in the negative charge for the faces of the montmorillonite sheets. The degree of influence of the cation valence on the negative charge follows the order of trivalent > monovalent > divalent, and the contribution of metal cations of the same valence to the negative charge is positively related to the atomic number. The change in negative charge affects the zeta potential, and the influence law for the cations on the zeta potential is basically the same as that for the negative charge. SEM and microscope results show that the degree of lamellar peeling is negatively correlated with the valence of the cations, and the contribution of metal cations of the same valence to the dispersion of montmorillonite is negatively correlated with the atomic number. The viscosity results follow the order of Mt-Li > Mt-Na > Mt-Mg > Mt-Ca > Mt-Al > Mt-Fe. This result indicates that the zeta potential and the degree of peeling affect the gel properties at the same time. Therefore, the electrical properties and interlayer forces for the montmorillonite sheets are affected by the valence, electrostatic force and hydrated ion radius of the metal cations, so that the gel properties of the montmorillonite are affected.