Copper aluminate spinel in the stabilization and detoxification of simulated copper-laden sludge

This study aims to evaluate the feasibility of stabilizing copper-laden sludge by the application of alumina-based ceramic products. The processing temperature, material leaching behaviour, and the effect of detoxification were investigated in detail. CuO was used to simulate the copper-laden sludge and X-ray Diffraction was performed to monitor the incorporation of copper into the copper aluminate spinel (CuAl2O4) phase in ceramic products. It was found that the development of CuAl2O4 increased with elevating temperatures up to and including 1000 °C in the 3 h short-sintering scheme. When the sintering temperature went above 1000 °C, the CuAl2O4 phase began to decompose due to the high temperature transformation to CuAlO2. The leachability and leaching behaviour of CuO and CuAl2O4 were compared by usage of a prolonged leaching test modified from US EPA’s toxicity characteristic leaching procedure. The leaching results show that CuAl2O4 is superior to CuO for the purpose of copper immobilization over longer leaching periods. Furthermore, the detoxification effect of CuAl2O4 was tested through bacterial adhesion with Escherichia coli K12, and the comparison of bacterial adhesion on CuO and CuAl2O4 surfaces shows the beneficial detoxification effect in connection with the formation of the CuAl2O4 spinel. This study demonstrates the feasibility of transforming copper-laden sludge into the spinel phase by using readily available and inexpensive ceramic materials, and achieving a successful reduction of metal mobility and toxicity.