Value-added aluminium sulphate from multiple recycled aluminium utensils: Kinetic optimization and application as coagulant and paper filler

For preparing daily utensils, aluminium is repeatedly recycled globally by physical methods. However, after multiple recycling cycles, it often becomes contaminated by unwanted metallic parts, which are persistent. This contaminated aluminium is a threat to food safety. Herein, we chemically extracted aluminium in the purest form as sulphate from multiply recycled aluminium utensils. The synthesized coagulant was used as a potential water purifier and paper filler. The synthesis process was optimized, with the highest yield (85.6%) achieved using 12 M H₂SO₄ at pH 2, and 55°C temperature. The prepared sample was characterized using surface morphology, energy dispersive X-ray spectroscopy analysis and Fourier transform infrared spectroscopy (FTIR) spectra. In case of water treatment, 0.8 mg of synthesized Al₂(SO₄)₃ achieved the highest mud deposition (46 mg/10 mL), exceeding the commercial alum by approximately 4.5%. Statistical analysis by means of <i>t</i>-test confirmed the repeatability and significance of this improvement (<i>p</i> = 0.03). In case of application as paper filler, the ink absorptivity was found to be reduced, whereas the sheet strength was increased significantly. These findings demonstrate that synthesized Al₂(SO₄)₃ can serve as a safe and effective alternative to commercial alum, contributing to waste valorization, food safety and sustainable materials development.