Production of titanate microspheres by sol-gel and spray-drying

Abstract

Synroc is a multi-component titanate ceramic, designed to immobilise High Level Waste (HLW) from nuclear fuel reprocessing plants [1]. The Synroc concept involves immobilising the elements present in HLW within an assemblage of mutually compatible, thermodynamically stable mineral phases, namely hollandite (BaAl2Ti6O16), zirconolite (CaZrTi2O7), perovskite (CaTiO3) and anatase (TiO2). These minerals are formed during calcination and hot-pressing of a precursor powder containing TiO2, ZrO2, Al2O3, BaO and CaO in relative mass abundances of 71.4, 6.6, 5.4, 5.6 and 11 percent, respectively. Synroc precursor powders have been previously produced by various methods, such as oxide and alkoxide-hydrolysis routes [2]. However, various technological aspects of HLW processing make the use of free-flowing, dust-free, highly sinterable precursor powders desirable. Such powders have been produced by spray-drying colloidal precursors, yielding microspherical particles with controlled morphology [3]. These particles were readily impregnated with 20 wt% simulated HLW solutions, calcined at 750°C and subsequently hot-pressed to produce dense Synroc monoliths. This paper discusses the preparation of the microspherical precursor particles by spray-drying and