Production of Al-rich sludge-containing ceramic bodies by different shaping techniques

The present work deals with the processing of refractory ceramic products by using different shaping technologies, namely, unidirectional dry pressing, extrusion, and slip casting. The formulations used include an Al-rich sludge collected in the wastewater treatment unit of an industrial plant dealing with anodizing or surface-coating processes, diatomite and kaolin or ball clay. The effects of a pre-treatment given to the Al-rich sludge and of composition and amount of added dispersant on theological behavior of suspensions were studied. The green bodies were sintered at different temperatures in the range 1400-1650 degreesC, and the ultimate material properties (firing shrinkage, water absorption, bending strength, SEM microstructure) were evaluated. The results obtained demonstrated that: (i) the flow behavior of the suspensions is strongly affected by the history of the Al-rich sludge and the composition, as well as by the added amount of deflocculant, (ii) the shaping process has a great influence on the final microstructures and material properties, which derive from different degrees of homogeneity and particle packing achieved in the green state. Soluble salts present in the Al-rich sludge create difficulties in achieving proper dispersion and make slip casting products less reliable compared with those consolidated by other shaping techniques. (C) 2004 Elsevier B.V. All rights reserved.