Ion Exchange Properties of a Cesium Ion Selective Titanosilicate

Abstract

The ion exchange properties of crystalline and amorphous phases of a sodium titanosilicate towards alkali and alkaline earth cations has been examined. Potensometric titration of the crystalline phase in the proton form, H₂Ti₂O₃(SiO₄), showed that 80% of the sodium ion sites could be occupied to pH=12 and only 25% of the exchange sites could be filled by Cs+. However, when an equal concentration of Na+ was present in 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 waste solutions, i.e. 5-6M NaNO₃, 1-3 M NaOH. This low capacity limits the 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 Sr²⁺ but also for Ba²⁺ and Ca²⁺ in alkaline solution. These ions could serve as interferences for selective Sr²⁺ removal from nuclear waste solutions. Sodium titanium silicate has a tunnel structure. The low capacity of the exchanger for Cs²⁺ stems from the fact that only a few of the exchange sites can be filled with Cs²⁺ in the presence of Na⁺ and still maintain charge balance.