ION-EXCHANGE PROPERTIES OF A CESIUM ION-SELECTIVE TITANOSILICATE

The ion exchange properties of crystalline and amorphous phases of a s odium titanosilicate towards alkali and alkaline earth cations has bee n examined. Potentiometric titration of the crystalline phase in the p roton form, H2Ti2O3(SiO4), showed that 80% of the sodium ion sites cou ld be occupied to pH=12 and only 25% of the exchange sites could be fi lled by Cs+. However, when an equal concentration of Na+ was present i n the Cs+ solution, the cesium loading was reduced to 5.6% (0.47 meq/g ) of the theoretical IEC. This loading is further reduced to less than 0.1 meq/g in solutions approximating the sodium content of nuclear wa ste solutions, i.e. 5-6M NaNO3, 1-3 M NaOH. This low capacity limits t he usefulness of this exchanger to waste solutions less than 10(-5)-10 (-6) M in Cs+. The amorphous phase exhibits a very high affinity for S r2+ but also for Ba2+ and Ca2+ in alkaline solution. These ions could serve as interferences for selective Sr2+ removal from nuclear waste s olutions. Sodium titanium silicate has a tunnel structure. The low cap acity of the exchanger for Cs+ stems from the fact that only a few of the exchange sites can be filled with Cs+ in the presence of Na+ and s till maintain charge balance.