Residues from Sewage Sludge Incineration for Ceramic Products with Potential for Zinc Stabilization

Serious environmental pollution has been frequently caused by the release of heavy metals from wastes generated from industrial activities. Although some of the heavy metals can be stabilized in ceramic matrix, the replacement of traditional ceramic precursors is needed due to adverse effects caused by clay mining. With abundant contents of aluminum, iron and silicon, the beneficial use of residues from sewage sludge incineration processes has attracted much attention. In this study, ZnO was simulated as zinc-bearing industrial waste, and the stabilization of zinc was achieved in aluminum- and iron-rich ceramic matrix provided by the residues of sewage sludge incineration. Through a 3-h sintering procedure at temperatures ranging from 650 to 1350 °C, zinc was found to be incorporated into a ZnAl_xFe_2-xO₄ spinel solid solution and the incorporation was greatly enhanced by the elevated temperature. The leachability of zinc was found to decline substantially with the continuous formation of the spinel when the samples were extracted in acidic, neutral and basic environments. Besides the effective stabilization of zinc, aluminum and iron can also be well immobilized in the sintered ceramic products. The temperature range of 950-1250 °C was found to be promising to reach the most satisfactory zinc stabilization without extra energy consumption, and to fabricate ceramic products with a variety of microstructures for future application. Therefore, the residues from the sewage sludge incineration can be blended into the existing ceramic sintering processes for making marketable products, which will further alleviate the environmental burden caused by heavy metal release from industrial wastes.