Intercalation of bentonite: Thermodynamics, kinetics, and practical applications

We have studied the thermodynamic and kinetic aspects of the intercalation of lithium, potassium, magnesium, and iodine ions in chemically modified natural bentonite. X-ray diffraction data and thermodynamic analysis indicate that the Li+ intercalation leads to the formation of a continuous series of nonstoichiometric phases, except for a phase transition in the range 0.15 < x < 0.45 (where x is the mole fraction of the guest) and the formation of a new, structurally ordered phase in an almost amorphous matrix at x = 0.6. The K+ intercalation leads to the formation of a continuous series of phases, and the Mg2+ intercalation carries the system to a two-phase state over the entire composition range studied. Iodine can only be intercalated in a narrow range (<0.1 V). The rate parameters of the intercalation process indicate that the lithium and iodine systems are close in resistance to charge transport, whereas the rate of iodine diffusion is an order of magnitude faster. The present results suggest that chemically modified natural bentonite is potentially attractive as an electrode material for lithium and magnesium batteries.