¹³³Cs NMR and XPS investigation of cesium adsorbed on clay minerals and related phases

¹³³Cs MAS NMR and Cs XPS were used to study the adsorption of Cs on kaolinite, montmorillonite, corundum, and gibbsite from 0.1 N and 0.01 N CsCl solutions. XPS spectra for all samples except gibbsite contain strong signals associated with Cs 3d_3/2 and 3d_5/2 photopeaks. This result indicates that minerals without exchangeable cation sites have a tendency to sorb Cs on surfaces and along grain boundaries, although less than 1 mol% Cs is observed on these surfaces. Multiple surface or interlayer sites for Cs cannot be resolved from the individual Cs XPS peaks. The ¹³³Cs NMR data, combined with TEM/XRD data for kaolinite show the following: (1) For montmorillonite, most of the Cs is adsorbed in the interlayers and at room humidity is motionally averaged among two or more sites at room temperature. (2) The spectra for kaolinite are similar to those of montmorillonite, and the tightly bonded Cs in our sample appears to be in expandable interlayers which exist as mixed layers with kaolinite and not as discrete smectite. (3) The Cs environments in both montmorillonite and kaolinite are sensitive to humidity. (4) For kaolinite the ¹³³Cs chemical shift changes at low temperature and 100% humidity, indicating that the interlayer charge of its expandable layers is very small. (5) No ¹³³Cs NMR signal could be detected for gibbsite or corundum. ¹³³Cs NMR may be a useful probe of the presence and characteristics of expandable layers in kaolinite.