SHS/QP Synthesis and Characterization of Ce‐Bearing Zirconolite‐Rich Waste Forms Using MoO₃ as the Oxidant

Abstract

In this study, zirconolite (CaZrTi 2 O 7 )/Mo composite was rapidly synthesized by self-propagating high-temperature plus quick pressing (SHS/QP) technique using MoO 3 as the oxidant. As the surrogate of tetravalent actinide nuclides, up to 50 at.% CeO 2 (about 17.5 wt% of the raw material) was introduced to substitute the Zr site of zirconolite. Perovskite (CaTiO 3 ) and rutile TiO 2 were inevitably produced after the incorporation of CeO 2 . The raw CeO 2 was partially reduced to trivalent state, which promotes the substitution of Ce into the Ca sites of perovskite and zirconolite. The aqueous durability of Ce-bearing waste form was investigated with normalized leaching rates (42 d) of Ce in moderate value of about 10 -2 g m -2 d -1 .

Two‐step synthesis of zirconolite‐rich ceramic waste matrice and its physicochemical properties

“…The 1 day LR Ca is 9.50×10 −2 g·m −2 ·d −1 , which declines to 3.96×10 −3 g·m −2 ·d −1 after 42 days leaching. Compared with our previously synthesized zirconolite‐rich waste forms using combustion synthesis, the LR Ca value is about one magnitude lower in this study. The sample after combustion synthesis is not under very stable state, which is harmful for the chemical stability.…”

“…Recently, we have prepared zirconolite‐rich waste forms using in‐situ combustion synthesis (CS), where Ca(NO 3 ) 2 , MoO 3 , and CuO were employed as the oxidants with Ti as the reductant . Zirconolite‐rich composites were rapidly synthesized within 3 minutes using this CS technique.…”

“…Recently, we have prepared zirconolite-rich waste forms using in-situ combustion synthesis (CS), where Ca(NO 3 ) 2 , MoO 3 , and CuO were employed as the oxidants with Ti as the reductant. [24][25][26][27] Zirconolite-rich composites were rapidly synthesized within 3 minutes using this CS technique. In this study, the synthesis of single-phase zirconolite was explored on the basis of CS preparation of zirconolite.…”