Formation of nickel and copper ferrites in ceramics: a potential reaction in the reuse of iron-rich sludge incineration ash

Abstract

This study investigates potential solid-state reactions for the stabilization of hazardous metals when reusing the incineration ash from chemically enhanced primary treatment (CEPT) sludge to fabricate ceramic products. Nickel and copper were used as examples of hazardous metals, and the iron content in the reaction system was found to play a major role in incorporating these hazardous metals into their ferrite phases (NiFe ₂O ₄ and CuFe ₂O ₄). The results from three-hour sintering experiments on NiO+Fe ₂O ₃ and CuO+Fe ₂O ₃ systems clearly demonstrate the potential for initiating metal incorporation mechanisms using an iron-containing precursor at attainable ceramic sintering temperatures (above 750°C ). Both ferrite phases were examined using a prolonged leaching experiment modified from the widely used toxicity characteristic leaching procedure (TCLP) to evaluate their long-term metal leachability. The leaching results indicate that both the NiFe ₂O ₄ and the CuFe ₂O ₄ products were significantly superior to their oxide forms in immobilizing hazardous metals.

Keywords:

• sludge
• incineration ash
• spinel
• ceramic
• hazardous metal

Acknowledgements

This work was supported by the Research Grants Council of Hong Kong (HKU 716310E, HKU 716809E) and the University Grants Council of Hong Kong (SEG_HKU10). The author thanks Mr Changzhong Liao for his assistance with the XRD data collection.