ABSTRACTSilicotitanate ion exchangers are potential materials for the removal of
radioactive Cs and Sr from tank wastes. In this paper the viability of
direct thermal conversion of Cs-loaded silicotitanates to an acceptable high
level waste form has been examined. Results show that in aqueous solutions,
the Cs leach rates of crystalline silicotitanates (heat treated at 800°C)
are 0.04, 0.18, 0.4 g/m2day for Cs loadings of 1, 5, and 20 wt%,
respectively. Heating the Cs-loaded (up to 20 wt %) silicotitanates at or
above 900 °C for 1 hour further reduces the Cs leach rates to approximately
zero (beyond the lppm detection limits). Moreover, Cs volatilization was
found to be < 0.8 wt% at temperatures as high as 1000 °C. These results
suggest that thermally converted silicotitanate ion exchangers exhibit
excellent chemical durability (comparable to or better than borosilicate
glass) and thus, have great potential as an alternative waste form.