Evidence of the Formation of Crystalline Aluminosilicate Phases in Glass-Ceramics by Calcination of Alkali-Brick Aggregates, Enabling Cs+, Rb+, Co2+, and Sr2+ Encapsulation

The feasibility of using brick aggregates for the preparation of aluminosilicate “glass-ceramic” forms as a novel cementitious composite capable of immobilizing radioactive elements was examined. Raw brick was initially activated with sodium hydroxide. X-ray diffraction analysis (XRD) confirmed zeolites (Na-A and Na-P), illite, and sand (quartz) as major phases. Thermal analysis showed several successive events: dehydration/dehydroxylation of illite, followed by degradation of illite and zeolites. Upon heating to 1000 °C, scanning electron microscopy and XRD provided evidence of the presence of novel crystalline aluminosilicate forms (analcime and leucite in the form of solid solutions). Then, upon heating to 1150 °C, the thermal process led to the additional formation of mullite and an amorphous silica-rich phase. The latter resulted from silica melting taking place, owing to the involvement of low-melting-point components on sand grains. Alkali-brick particles were then doped with Cs+, Rb+, Ca2+, and Sr2+ ions (individually) and subsequently heated at different temperatures. The corrosion resistance of the heated materials was examined in a hydrochloride acid solution. The aim was to highlight (i) the enhanced cationic-immobilization capacity of crystalline aluminosilicate phases embedded inside amorphous silica, and (ii) the role of sand in the creation of brick-based glass ceramics.