Zinc stabilization efficiency of aluminate spinel structure and its leaching behavior

The feasibility of immobilizing zinc in contaminated soil was investigated by observing the role of zinc reacting with aluminum-rich materials under thermal conditions. To observe the process of zinc incorporation, mixtures of ZnO with alumina precursors (γ-Al(2)O(3) and α-Al(2)O(3)) were fired at 750-1450 °C. Both precursors crystallochemically incorporated zinc into the ZnAl(2)O(4) spinel structure. The incorporation efficiencies of a 3 h sintering scheme were first quantitatively determined by Rietveld refinement analysis of X-ray diffraction data. Different zinc incorporation behavior by these two precursors was revealed, although both resulted in nearly 100% transformation at the highest temperature. Different product microstructures and thermal densification effects were found by observing the sintered products from these two precursors. The leaching performances of ZnO and ZnAl(2)O(4) were compared by a prolonged acid leaching test for 22 d. The leachability analysis pointed to superiority of the ZnAl(2)O(4) structure in stabilizing zinc, suggesting a promising technique for incorporating zinc into the aluminum-rich product. Finally, the sludge collected from water treatment works was calcined and used as an aluminum-rich material to test its ability to stabilize zinc. Successful formation of ZnAl(2)O(4) indicated good potential for employing waterworks sludge to thermally immobilize hazardous metals as a promising waste-to-resource strategy.