Novel mullite-based ceramics manufactured from inorganic wastes: I. Densification behaviour

A method towards recycling of both slate sludge and aluminium-containing residues to produce high-mullite refractory bodies is proposed. The slate powders used resulted from the cutting and polishing operations performed in the quarries. The alumina source was obtained by treating spent baths generated in industrial plants dealing with manufacturing and finishing of aluminium-made architectural profiles. Samples with a composition close to Al4SiO8 (mullite 2:1) were produced using conventional powder technology and characterised throughout the entire manufacturing process. Optimum sintering temperatures were found to lie in the range of 1425–1450 °C. Based on both XRD and DTA/TG data, the sequence of phase transformations occurring upon heating were depicted.