Maghemite Nanoflowers as Excellent Adsorbents for the Magnetic Removal of Algae That Bind Heavy Metal

The presence of heavy metals in industrial wastewater poses a significant environmental concern, emphasising the necessity for effective and sustainable remediation strategies. This study evaluates the combined functionality of the freshwater microalga Chlorella vulgaris and maghemite nanoflowers for the removal of cobalt ions, a typical contaminant originating from battery manufacturing effluents. The adsorption capacity of C. vulgaris was assessed, achieving 96 ± 2% Co²⁺ removal, followed by magnetic separation using γ-Fe₂O₃ nanoparticles. Subsequent magnetic separation of the cobalt-adsorbed biomass achieved efficiencies ranging from 57.43 % to 97.64 % within a 60-second timeframe, demonstrating a significant enhancement over conventional sedimentation methodologies. The strong electrostatic interactions between functional groups (–NH₂, –OH, –COOH) on maghemite particles and the negatively charged algal surface, enhanced by protonation at low pH, facilitated stable nanoparticle–biomass binding. The even distribution of maghemite nanoparticles on algal surfaces was further validated by TEM imaging, and the strong magnetic properties of the nanoparticles enabled rapid and efficient separation under an external magnetic field. This study underscores the promise of integrating C. vulgaris with maghemite nanoparticles as a cost-effective, biocompatible, and environmentally sustainable approach for large-scale heavy metal removal from industrial wastewater.