The calcination process used for sodium nitrate could be the most important part of the liquid-waste calcination process used in high-level-waste (HLW) disposal. A French process that involves conversion of the solution of nitrate fission products into a solid mixture of oxides and undecomposed nitrates. These products are then mixed with a glass-making mixture (called a frit) in an induction melting pot.
In 1984, Utake et.al., (1) suggested the use of the Sol-Gel technique to decrease the calcination temperature of NaNO3.
In this work, we used the thermal-analysis technique to study the catalytic effect of some glass network formers like SiO2, B2O3 and of some network modifiers like A12O3, Fe2O3, MgO, TiO2 ZnO. The best effect was achieved by adding 20% diatomaceous earth (Kieselguhr) and 20% B2O3 In that case, the calcination temperature onset decreased from 780°C to 565°C.
The advantages of this process are as follows:
1. The proposed additives (Kieselguhr and B2O3) are glass network formers that have to be added anyway in the next piocess step.
2. In the proposed process, no sodium is added, and the only process change suggested is that the glass formers (or part of them) should added at the calcination step, rather than at the glass-melting step.
3. The proposed modification is easily achieved and is expected to improve the homogenization of the final product.