Solar Assisted Production of MgAl2O4 from Bayer Process Electrofilter Fines as Source of Al2O3

Compared with conventional high-temperature methods based on electricity and fossil fuels, concentrated solar energy route offers distinct advantages in terms of mitigating emissions of contaminants and shortening processing times. Nevertheless, solar-based route also encounters challenges in producing significant quantities of materials, although the deployment of this technology is still conditioned by the limited investigation in the field. This study presents a novel high-temperature process based on solar energy to produce MgAl 2 O 4 spinel, which employs as source of Al 2 O 3 a waste from the aluminum industry: waste alumina fines from the Bayer process. First, mixtures were prepared by mechanical mixing in a molar ratio 1:1 in agreement with the MgO–Al 2 O 3 binary phase diagram. Then, synthesis of the MgAl 2 O 4 spinel was conducted by static experiments (5 min) with direct application of concentrated solar energy (1150 W/cm 2 ) at temperatures greatly exceeding 1800 °C as reported by ANSYS software. Wastes from three Bayer process factories were studied, which exhibited after the synthesis process a good crystallinity. The carbon dioxide emissions avoidance would range from the 200 to 500 tons of CO 2 /year in the case of a small plant producing 1000 tons/year to 5000 to 12,000 tons of CO 2 /year in the case of a commercial plant producing 25,000 tons/year, thus contributing to mitigate climate change. The proposed process might lead to smaller volume of wastes in the aluminum industry, while the MgAl 2 O 4 may be used as raw material in the numerous fields based on the chemical, thermal, dielectric, mechanical and optical properties. Graphical Abstract