Characterization of interlayer Cs+ in clay samples using secondary ion mass spectrometry with laser sample...

Ultraviolet laser irradiation was used to greatly enhance the secondary ion mass spectrometry (SIMS) detection of Cs(+) adsorbed to soil consisting of clay and quartz. Imaging SIMS showed that the enhancement of the Cs(+) signal was spatially heterogeneous: the intensity of the Cs(+) peak was increased by factors up to 100 for some particles but not at all for others. Analysis of standard clay samples exposed to Cs(+) showed a variable response to laser irradiation depending on the type of clay analyzed. The Cs(+) abundance was significantly enhanced when Cs(+)-exposed montmorillonite was irradiated and then analyzed using SIMS, which contrasted with the behavior of Cs(+)-exposed kaolinite, which displayed no Cs(+) enhancement. Exposed illitic clays displayed modest enhancement of Cs(+) upon laser irradiation, intermediate between that of kaolinite and montmorillonite. The results for Cs(+) were rationalized in terms of adsorption to interlayer sites within the montmorillonite, which is an expandable phyllosilicate. In these locations, Cs(+) was not initially detectable using SIMS. Upon irradiation, Cs(+) was thermally redistributed, which enabled detection using SIMS. Since neither the illite nor the kaolinite is an expandable clay, adsorption to inner-layer sites does not occur, and either modest or no laser enhancement of the Cs(+) signal is observed. Laser irradiation also produced unexpected enhancement of Ti(+) from illite and kaolinite clays that contained small quantities of Ti, which indicates the presence of microscopic titanium oxide phases in the clay materials.