Stabilization Mechanisms and Reaction Sequences for Sintering Simulated Copper-Laden Sludge with Alumina

Abstract

To stabilize copper-laden sludge using alumina-based ceramic raw materials, this study quantifies the copper transformation behavior during the sintering process. Results indicate crystallochemical incorporation of hazardous copper through the formation of copper aluminate spinel (CuAl2O4) and cuprous aluminate (CuAlO2). To quantify the copper transformation and reveal reaction sequences, CuO was mixed with γ-Al2O3 and α-Al2O3 precursors and fired at 1050–1150 °C for 15–180 min. The sintered products were examined using X-ray diffraction (XRD), and copper transformations into both aluminate phases were quantitatively determined through Rietveld refinement analysis of XRD data. When γ-Al2O3 was used, CuAlO2 was predominately generated from CuAl2O4 decomposition. However, CuAlO2 was largely generated by the interaction between CuO and α-Al2O3. This study also compared the sintering behavior of both precursor systems and observed the relatively slower decomposition of CuAl2O4 in the γ-Al2O3 system. The reoxidation of CuAlO2 into CuAl2O4 with an extended sintering time was detected in the α-Al2O3 system. The sample leachability analysis reveals that both CuAl2O4 and CuAlO2 structures were superior in copper stabilization compared to the oxide forms. Such results suggest reliable mechanisms of incorporating hazardous copper into a ceramic matrix and demonstrate the potential of using waste materials as part of ceramic raw materials to produce detoxified products.