Alkali metal ion exchange by the framework titanium silicate M2Ti2O3SiO4 center dot nH(2)O (M = H, Na)
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abstract
The ion-exchange properties of the titanium silicate, M2Ti2O3SiO4nH2O (M = H,Na), towards alkali ions has been examined. Potentiometric titration of the highly crystalline phase in the proton form, H2Ti2O3(SiO4)1.6H2O, 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.
