The ion-exchange properties of the titanium silicate, M2Ti2O3SiO4 . nH(2)O (M = H,Na), towards alkali ions has been examined. Potentiometric titration of the highly crystalline phase in the proton form: H2Ti2O3(SiO4) . 1.6H(2)O, showed a dependency of the exchange on the size and charge of the ion and the pH of the solution. It was found that the accessability of three different ion-exchange sites in the titanium silicate framework controls the uptake of ions: 100% of the total amount of the ion-exchange sites could be occupied at pH 12.5 by sodium and lithium ions, about 75% by potassium and rubidium ions and only 25% by cesium ion. The ion-exchange isotherms of alkali metal ions were determined and the corrected selectivity coefficients as a function of metal loading were analyzed. Sodium titanium silicate exhibits a high affinity for heavy alkali metals with the selectivity order Cs+ > Rb+ > K+. By studying the cesium and strontium uptake in the presence of NaNO3, CaCl2, NaOH, NaOH + KOH, and HNO3 (in the range of 0.01-6 M) the titanium silicate was found to be an efficient Cs+ ion exchanger in acid, neutral and alkaline media, which makes it promising for treatment of different types of nuclear waste and contaminated environmental and biological Liquors. (C) 2000 Elsevier Science B.V. All rights reserved.