Azeotropic distillation-assisted preparation of nanoscale gamma-alumina powder from waste oil shale ash

A combined process was proposed for the utilization of waste oil shale ash (OSA) in the production of gamma-alumina nanoparticles. The process consisted of two stages, leaching and sintering. The ultrasonic technique followed by a heterogeneous azeotropic distillation process in the presence of polyethylene glycol (PEG) was carried to ensure complete elimination of the residual water in the precipitate. The structural and morphological properties of the calcined nanocrystalline powders were characterized by X-ray diffractometer (XRD), transmission electron microscope (TEM), Brunauer–Emmett–Teller nitrogen-gas adsorption method (BET). The as-prepared precursor hydroxides were analyzed using thermogravimetric–differential thermal analysis (TG–DTA), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The results indicated that the gamma-alumina powder with a uniform particle is well dispersed and the particle size is 20–40 nm; the waste OSA can be utilized to produce gamma-alumina nanoparticles.