Extraction of alumina from industrial waste pollutants for the preparation of blue spinel ceramic materials: Processing and characterization

Abstract The present work aims to fabricate colored pigment materials (spinels) from recycling fly ash pollutants. Using a chemical treatment method, alpha alumina was extracted from fly ash and characterized using differential thermal analysis, thermogravimetry, X-ray diffraction analysis, transmission electron microscopy, and Fourier-transform infrared spectroscopy. Different transition metals, Cr3+, Mg2+, and Zn2+, were used to prepare the metal cobalt aluminate spinel structures, CrCoAlO4, Mg0.8Co0.2Al2O4, and Co0.5Zn0.5Al2O4, respectively. The influence of the sintering temperature on the structure and surface morphology of the obtained spinels was investigated. Porosity, density, diffuse reflectance spectroscopy, scanning electron microscopy, and electrical and magnetic properties were determined. The results show that at 1500 °C, the spinels physic-mechanical, magnetic and electrical properties improve. The addition of transition metal ions (Cr3+, Mg2+, and Zn2+) to the tetrahedral or octahedral sites of the CoAl2O4 structure is responsible for the characteristics of the produced spinels.