Effect of Alumina Replacing Calcium Oxide on Vitrification of Molybdenum in Borosilicate Glass

Borosilicate glasses are the most potential matrices to vitrify high-level nuclear wastes. However, the low solubility of Mo, which is usually one of the main elements in HLWs coming from the nuclear power stations, is a main limitation for their application in vitrification. In this paper, the effect of the substitution of Al 2 O 3 for CaO on Mo solubility in a modified SiO 2 –B 2 O 3 –Na 2 O–CaO borosilicate glass is investigated in detail. The results show that the solubility of Mo can be increased up to 4 mol % at least in the borosilicate glasses. The mechanism of Al 2 O 3 substitution for CaO to improve the solubility of Mo has been explained in detail by analyzing the changes of the cations for compensating units and the depolymerized regions. It can be concluded that the borosilicate glasses with high substitution of Al 2 O 3 (15 or 20 mol %) are potential matrices to immobilize molybdenum-rich high-level nuclear wastes.