Recycling of Al-rich industrial sludge in refractory ceramic pressed bodies

Processing of mullite-based refractory ceramic bodies by unidirectional dry pressing, from different formulations that include Al-rich sludge, as single or main component is described. The sludge is produced from anodising or surface coating processes and is generated in the wastewater treatment unit of an industrial plant. After a detailed characterisation study, involving determinations of chemical, thermal and granulometric parameters, as-received, and previously dried (110 °C) or calcined (1400 °C) sludge was used alone or combined with common ceramic raw materials, such as diatomite, kaolin or ball clay. Green bodies were consolidated by dry pressing and fired at temperatures in the range 1400–1650 °C, and the mechanical, thermal and electrical properties of the fired products were evaluated. Promising refractory materials based on mullite, mullite+alumina, or alumina were obtained.