Alumina-based materials obtained by sintering of sludge generated from aluminium anodizing and lacquering processes


The present invention relates to obtaining alumina-based powder or consolidated refractory bodies, processed from sludge generated in Wastewater Treatment Plants (WWTP) of surface treatment, anodizing and aluminum lacquering industries.
Proper operation and monitoring of WWTP ensures properties reasonable consistency, in terms of chemical composition and limited amounts of harmful elements (e.g., iron, chromium, etc.).
The sludge has a moisture content above 75%, which is almost entirely removed by drying.
The calcination above 1200 °C ensures compositional consistency and neutralizes the rheological effects of added flocculent organic agents.
The milling and subsequent screening allows a fine and pulverizable powder, suitable for use as refractory inert filler.
By filling or unidirectional pressing and subsequent sintering above 1500 ° C, fire-resistant and electrical insulating bodies are obtained, which composition involves α-alumina and sodium aluminate (β-alumina).

Innovative aspects & main advantages

The present invention relates to the use of sludge generated from the wastewater of industry Al-anodising and surface coating processes as secondary raw material for the production of alumina based powders or shaped bodies. The calcination at temperatures above 1200 °C generates a remarkably constant powder, containing more than 90 wt% alumina, so able to be use in the formulation of distinct ceramic products (e.g. porcelain, clinker) or to be shaped by common techniques (e.g. pressing or extrusion) to produce usable bodies. After proper sintering (> 1400 °C) remarkable electrical insulating or refractory properties can be obtained. Main phases detected are α- and β-alumina, also normally found in similar commercial products obtained from primary ores.


The main application of this invention (the potential commercial/industrial sectors) is focused on the producers of sludge (as an alternative to landfill) and to consumers of alumina (cement and ceramic producers), namely for technical applications (electrical insulators, refractories, inorganic pigments).


Batista, João; Boia, Cristina; Pereira, Maria;

Our Inventors


Universidade de Aveiro
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