ELECTRON MICROSCOPY INVESTIGATIONS OF SELECTED CS-EXCHANGED PHYLLOSILICATES AT LOW AND HIGH TEMPERATURES: IMPLICATIONS FOR REMEDIATION OF NUCLEAR ACCIDENTS.

¹³⁷Cs pollution is a major pollution problem associated with radiological disasters of numerous types. The Fukushima disaster in Japan in March of 2011, as reported by the Tokyo Electric Power Company (TEPCO), has released quadruple the amount of ¹³⁷Cs into the environment than the iconic Chernobyl disaster in Ukraine in 1986. Exploring ways to sequester radioactive ¹³⁷Cs is pertinent to the remediation of the environment as well as protecting the health of the surrounding population. In this investigation ¹³³Cs, a non-radioactive analog for ¹³⁷Cs, was exchanged with smectite group members nontronite, and montmorillonite as well as sepiolite using solutions of ¹³³CsCl . Samples were heated to 475 °C, 675 °C and 800 °C in ambient atmosphere using a small muffle furnace with a temperature error estimated to be +/- 3°C. Transmission electron microscopy (TEM) data on starting exchanged materials, collected using a JEOL JEM 2100, indicate that exchange with ¹³³Cs is extensive with the smectite minerals and minimal with sepiolite. Preliminary SEM investigations indicate an effective retention of ¹³³Cs has taken place with the Cs-nontronite and Cs-montmorillonite heated to 800 °C, as indicated by energy dispersive spectroscopy analyses. Exchange of ¹³³Cs with sepiolite was ineffective and this is interpreted as a function of the size and geometry of tunnels in the sepiolite structure. Current results indicate that short term heating of smectite minerals to temperatures up to 800 °C produces a phyllosilicate repository phase. Results of this study suggest that thermal treatment of soils, particularly those with high levels of contamination may be part of a clean-up strategy for future nuclear accidents. Heat treatment of soil may provide mechanical and chemical stability required for long term storage, analogous to high temperature repository phases such as zircon. Although palygorskite has been shown to be an effective media for sorbtion of Cs cations from aqueous solutions, sepiolite appears to be far less reactive and is a poor candidate for groundwater or surface water reactive media. The results suggest potential exists to investigate other high temperature derivative materials from other phyllosilcate minerals.