Syntheses of Titanate-Based Hosts for the Immobilization of Pu(III) and Am(III)

Abstract

ABSTRACTSyntheses of novel titanate-based waste forms, potentially suitable for immobilizing Pu(III) and Am(III), have been performed. The dititanate compounds An2Ti2O7 (An=Pu or Am) were found to have a monoclinic structure. A series of pyrochlore-type solid solutions between An2Ti2O7 and the cubic pyrochlore Ln2Ti2O7 (Ln=Gd, Er, or Lu) has been established, and limits of solid solubility for An2Ti2O7 were determined. These limits were found to increase as the ionic radius of the lanthanide in the host decreased. Strontium-containing titanate compounds SrAn2Ti4O12 were also prepared and were characterized as exhibiting a perovskite-type structure. Such compounds could serve as waste hosts for the immobilization of not only the actinide but also 90 Sr. A 2 month leaching study of Er1.78Pu0.22Ti2O7 and SrPu2Ti4O12 by WIPP “A” brine was performed. Very low amounts (< 1 ppm) of Pu(III) were leached. Although the ionic radius of Np(III) is similar to that of Pu(III) and Am(III), analogous Np compounds could not be prepared in any of the titanate systems investigated.