ION-EXCHANGE OF ALKALI-METALS ON HYDROUS TITANIUM-DIOXIDE IN NEUTRAL AND ALKALINE-SOLUTIONS

Selectivity of hydrous titanium dioxide as an ion exchanger for alkali metal and tetraalkylammonium ions, has been studied using radioactive indicators: Na-22 and Cs-137. The equilibrium distribution of trace amounts of sodium and cesium ions between the exchanger and aqueous solutions containing macroamounts of other univalent cations was studied over the temperature range of 15 to 80-degrees-C. The selectivity sequence in slightly acidic and neutral solutions is as follows: (CH3)4N+ < Li+ < Na+ < K+ < Rb+ < Cs+, whilst in alkaline solutions it is partly reversed. From the values of selectivity coefficients and the calculated values of thermodynamic functions one can infer that whilst hydrated ions are exchanged from acidic and neutral solutions, from alkaline solutions partly dehydrated ions enter the exchanger phase. The existence of ion-sieve effects for the univalent cations studied was observed, and the presence of at least two kinds of hydroxyl functional groups of different acidities is postulated. Ion exchange reactions of alkali metal cations on hydrous titanium dioxide, as well as the selectivity sequences observed have been interpreted on the basis of EISENMAN theory.