TOF-SIMS study of Cs+ sorption on natural kaolinite

The sorption of Cs+ on natural kaolinite has been studied using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Depth profiling up to 70 Angstrom was performed to study the change in the amount of sorbed Cs+ as a function of depth in the kaolinite matrix. Quantitative determination of the amounts of primary cations in the kaolinite structure before and after sorption of Cs+ ions was carried out to identify which cations are possibly taking part in the sorption process. The experimental results showed that large amounts of Cs+ are sorbed onto the surface of kaolinite and that sorption decreases sharply over the first 10-Angstrom depth. The fact that kaolinite surface was negatively charged under the operating pH indicates that physisorption has an important contribution to the sorption process. The results also showed that Na+, K+, Li+, Ca2+, Mg2+ and Fe3+ were involved in the sorption process with Cs+ and that the total decrease in the amounts of these cations is close to the amount of sorbed Cs+, suggesting that ion exchange is the dominant sorption mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.