Upcycling can seals into high-value boehmite-like for the synthesis of MnAl2O4: A circular economy approach

Boehmite is a mineral of aluminum oxyhydroxide widely used as a catalyst support, adsorbent for dyes, and a key component in producing advanced optical and electronic devices. This study focuses on the synthesis of boehmite using recycled metallic aluminum through acid digestion (HCl) and subsequent precipitation by pH correction (NaOH). The aluminum source used was can seals, which were characterized using various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). XRD analysis confirmed a boehmite-like phase of the recycled aluminum oxyhydroxide powder. SEM analysis revealed that the synthesized boehmite-like powder consisted of agglomerate plates, which influences its thermal and optical behavior, resulting in a lower dihydroxylation temperature and smaller band gap (∼3.7 eV) compared to the literature value (∼5.5 eV) for boehmite. The boehmite-like powder derived from recycling was used as a precursor for the synthesis of manganese aluminate (MnAl₂O₄). XRD analysis confirmed the formation of the MnAl₂O₄ galaxite phase, with XPS and absorbance spectroscopy in the visible region indicating the presence of mainly Mn²⁺ ions. The resulting brown manganese aluminate powder exhibited stability in harsh chemical environments, with a color change imperceptible to the human eye. Moreover, a near-infrared (NIR) reflectance of approximately 50% was achieved, superior to other brown pigments reported in the literature. These findings suggest that recycled aluminum can seals in aluminate have potential applications as pigments for coatings.