Abstract: Divalent tin has been intercalated into montmorillonite by reacting partially hydrolyzed solutions of SnCl2 under aerobic conditions at pH = 2.8 with aqueous dispersions of the smectite mineral. The precursor tin solution contains mainly the cationic trimeric ion Sn3(OH)42+, which is shown to take part in the exchange reactions with the surface cations of the mineral. Variable temperature Mössbauer spectroscopy was used in order to: 1) directly probe changes in the oxidation state and coordination environment of Sn2+ in the process of intercalation; 2) examine the nature of tin atoms on the external surfaces and in the interlayer space of the clay platelets; and 3) study the dynamics of motion of tin atoms on the clay surfaces.
The main conclusion from these studies is that about 75% of the Sn2+ ions undergo extensive oxidation to the +4 state with concomitant hydrolysis and condensation that lead to the precipitation of SnO2 on the external surfaces of the clay. The rest of the Sn2+ ions are introduced into the lamellar zone, as evidenced by the detailed Mössbauer analysis of the dynamics of motion of tin atoms on the clay surfaces.