LAUSR

Abstract Ion-exchange properties of natural caryochroite (Na,Sr)3{(Fe,Mg)2+10(OH)6[TiO(Si6O17)(OH)0.5]2}·8H2O, a microporous heterophyllosilicate with a one-dimensional system of broad zeolytic channels, related to nafertisite Na3{Fe2+10(OH)6[TiO(Si6O17)F0.5]2}·2H2O, were studied in reactions with 1 N aqueous solutions of Rb, Cs, Ag, and Pb nitrates at 50 °C. In reactions with Rb+, Cs+, and Pb2+, sodium is partly replaced by nearly equivalent amounts of larger cations. In reactions with Pb2+ and Ag+, additional processes involving H2O molecules take place: replacement of two H2O molecules with Pb2+ + 2OH− and replacement of H2O molecule with Ag+ + OH−. The geometrical-topological analysis of ion migration pathways in the nafertisite-type structures carried out using an approach based on the Voronoi-Dirichlet partition has shown that only Na+ cations occurring at the centers of wide channels can take part in reactions with large alkaline cations proceeding in counter flows. In the reaction with Ag+, additional Na+ ions are involved. Li+ cations having a smaller radius can pass through the window between the channels, forming a 2D conducting layer.