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The arc plasma vitrification of hospital wastes containing metals and inorganic oxides yields to a leach resistant glassy or vitreous slag, which can be environmentally safe for landfill disposal or could be transformed in glass-ceramic tiles with physical and mechanical properties similar to those showed by marketable products for building applications. Standard methods have been used for testing the leachability of elements from this new type of tiles. The water resistance was evaluated by the DIN 38414 S4 standard and the chemical durability of glass and glass ceramics by the weight losses per surface unit, employing NaOH and HCl (5%) aqueous solutions, at boiling temperature. Results show that although glass-ceramic tiles are most water leachable than original plasma vitreous glass, the concentration of toxic minor elements in their leaching solutions are lower than those allowed by the Normative. [ABSTRACT FROM AUTHOR]

Mullite precursors were prepared using kaolin waste, sericite clay containing kaolinite and industrial kaolin with addition of alumina in a wet medium to synthesize mullite (72 wt% Al 2 O 3 and 28 wt% SiO 2 ). Uniaxial pressed bars of the powdered mullite precursors were fired in the range 1400–1600 °C with soaking times 30–120 min. The resultant materials were studied by XRD and SEM-EDX. Bulk densities, apparent porosities and flexural strengths in four points were determined in the fired bars at 1500, 1550 and 1600 °C. It was concluded that the thermal behaviour of these mullite precursors was influenced by the presence of impurities in the raw materials. These impurities originate a liquid phase forming a glassy phase which produces a progressive and enhanced densification of the mullite materials by reaction sintering at 1500–1600 °C. The technical properties were also influenced by the relative proportion of vitreous phase. The microstructure of characteristic mullite crystals was revealed by SEM. It was emphasized the use of kaolin waste by-products of mining and sericite clays as valuable raw materials for mullite preparation. [ABSTRACT FROM AUTHOR]