Alkali metal ion exchange by the framework titanium silicate M2Ti2O3SiO4 center dot nH(2)O (M = H, Na)

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 a nd the pH of the solution. It was found that the accessability of three dif ferent ion-exchange sites in the titanium silicate framework controls the u ptake 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 alk ali metal ions were determined and the corrected selectivity coefficients a s a function of metal loading were analyzed. Sodium titanium silicate exhib its 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 tit anium silicate was found to be an efficient Cs+ ion exchanger in acid, neut ral and alkaline media, which makes it promising for treatment of different types of nuclear waste and contaminated environmental and biological Liquo rs. (C) 2000 Elsevier Science B.V. All rights reserved.