ON THE SELECTIVITY REGULATION OF K2ZRSI3O9-CENTER-DOT-H2O-TYPE ION-EXCHANGERS

A series of mixed potassium zirconium-titanium silicates of the genera l formula K2MSi3O9. H2O (where M = Zr, Ti), containing different amoun ts of titanium and zirconium (from 0 to 100% at.) were synthesized hyd rothermally. All these compounds have a framework structure containing two types of channels the size of which smoothly changes, namely, dec reases with the increase of titanium content in the compound. Both cha nnels, small channels with a 22-membered ring opening and large ones w ith a 16-membered ring opening, run along the c-axis and they are conn ected to each other via a 14-membered ring opening in the perpendicula r direction. This creates three-dimensional openings for the total cha nnel system that enables easy cation migration. The ion exchange behav ior of K2MSi3O9. H2O and protonic forms of two end members of the fami ly, K0.3H1.7TiSi3O9. 2H(2)O and K0.5H15ZrSi3O9. 2H(2)O, towards alkali metal ions was studied and a distinct correlation between the exchang er composition (channels size) and selectivity to certain ions was fou nd. Zirconium-rich silicates with large channels exhibit affinity for rubidium and cesium ions, whereas titanium-rich compounds with much sm aller channels show a preference for potassium ion. (C) 1998 Elsevier Science B.V. All rights reserved.