The removal of heavy metals from industrial wastewater remains a major environmental challenge, demanding efficient, sustainable solutions. This study explores the combined use of Chlorella vulgaris and amine-functionalized magnesium ferrite (MgFe₂O₄-NH₂) nanoparticles to remove cobalt ions from battery effluents. The research aims to explore the capacity of C. vulgaris to adsorb heavy metals, followed by their separation using magnetic nanoparticles. Cobalt adsorption by C. vulgaris was facilitated through the interaction of metal ions on the cell wall, achieving a removal efficiency of 96.44% within 30 min, which increased to 98.78% over 10 h. Amine-functionalized MgFe₂O₄ nanoparticles, synthesized and characterized using HRTEM, FTIR, and VSM, displayed high surface reactivity due to the presence of -NH₂ and -OH groups. At neutral pH, zeta potential measurements revealed a slightly negative charge (−5.6 ± 4.3 mV), while protonation at lower pH levels enhanced electrostatic interactions with the negatively charged algal biomass. Magnetic separation of the cobalt-adsorbed biomass achieved efficiencies ranging from 94.9% to 99.2% within 60 s, significantly outperforming conventional sedimentation methods. SEM and FTIR analyses confirmed the binding of nanoparticles to algal cell walls. The even distribution of MgFe₂O₄ 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.

The removal of cadmium from contaminated water remains a critical challenge due to its high toxicity, persistence, and limited treatability at low concentrations. In this study, we propose a novel algal–nanoparticle system that integrates cadmium adsorption by Chlorella vulgaris with zinc ferrite (ZnFe₂O₄) nanoparticle-assisted sedimentation, with the aim of addressing a significant operational challenge in algal remediation. The microalgal biomass demonstrated the capacity to remove cadmium with efficiencies exceeding 90%, facilitated by adsorption through surface functional groups. The incorporation of ZnFe₂O₄ nanoparticles promoted the formation of dense, magnetically responsive aggregates, significantly accelerating biomass settling without the necessity for additional chemical flocculants. The strategy’s efficacy is evidenced by its enhancement of metal removal and solid–liquid separation processes, which renders it a potentially scalable and environmentally sustainable approach for the treatment of cadmium-contaminated wastewater. The strategy holds relevance for effluents derived from mining, electroplating, fertilizer production and battery manufacturing.

This study aimed to clarify the interactions between cobalt-adsorbed Chlorella vulgaris cells and amine-functionalized maghemite nanoparticles, focusing on nanoparticle adsorption to the algal surface and the subsequent magnetic sedimentation of the formed complexes. The combined process of cobalt uptake by algae and secondary binding of magnetic nanoparticles demonstrates a promising and sustainable strategy for heavy metal removal from industrial wastewater. The adsorption capacity of Chlorella vulgaris was assessed, achieving 96 ± 2% Co²⁺ removal, followed by magnetic separation using γ-Fe₂O₃ nanoparticles. The subsequent magnetic separation of the cobalt-adsorbed biomass achieved efficiencies ranging from 57.43% to 97.64% within a 60 s timeframe, demonstrating a significant enhancement over conventional sedimentation methodologies. Stable nanoparticle–biomass binding was facilitated by electrostatic interactions between protonated amine groups on the surface of amine-functionalized maghemite particles and the negatively charged functional groups of the algal cell wall, complemented by the contribution of hydroxyl and carboxyl groups. The even distribution of amine-functionalized maghemite nanoparticles on algal surfaces was further validated by Transmission Electron Microscopy (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 Chlorella vulgaris with amine-functionalized maghemite nanoparticles as a cost-effective, biocompatible, and environmentally sustainable approach for large-scale heavy metal removal from industrial wastewater.

Adsorption isotherm parameters are widely used to characterize biosorbent performance and are often interpreted as intrinsic properties of the adsorbent. However, the extent to which these parameters depend on biosorbent concentration remains insufficiently understood. Here, the adsorption of Ni²⁺ and Cd²⁺ by Chlorella vulgaris was systematically investigated over a broad range of biomass concentrations by determining complete adsorption isotherms independently at each biomass level. Increasing biomass concentration consistently decreased the specific adsorption capacity and shifted the adsorption isotherms toward lower apparent saturation capacities for both metal ions. Langmuir and Freundlich models were fitted using both linearized and nonlinear regression. Despite differences in the absolute parameter values obtained by the fitting approaches, all models revealed the same biomass-dependent trend. In particular, the Langmuir maximum adsorption capacity ( q _max ) and Freundlich adsorption coefficient ( K_F ) decreased systematically with increasing biomass concentration. These results demonstrate that biomass concentration influences the experimentally observed adsorption behaviour and the isotherm parameters derived from it. Consequently, q _max and K_F should not be interpreted as universal material constants without considering the biomass concentration at which they were determined. Biomass concentration should therefore be reported and considered when comparing biosorption isotherms across independent studies.

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.

The removal of heavy metals from industrial wastewater remains a major environmental challenge, demanding efficient, sustainable solutions. This study explores the combined use of Chlorella vulgaris and amine-functionalized magnesium ferrite (MgFe₂O₄-NH2) nanoparticles to remove cobalt ions from battery effluents. The research aims to explore the capacity of C. vulgaris to adsorb heavy metals, followed by their separation using magnetic nanoparticles. Cobalt adsorption by C. vulgaris was facilitated through the in-teraction of metal ions on the cell wall, achieving a removal efficiency of 96.44% within 30 minutes, which increased to 98.78% over 10 hours. Amine-functionalized MgFe₂O₄ nano-particles, synthesized and characterized using HRTEM, FTIR, and VSM, displayed high surface reactivity due to the presence of -NH₂ and -OH groups. At neutral pH, zeta poten-tial measurements revealed a slightly negative charge (-5.6 ± 4.3 mV), while protonation at lower pH levels enhanced electrostatic interactions with the negatively charged algal bi-omass. Magnetic separation of the cobalt-adsorbed biomass achieved efficiencies ranging from 94.9% to 99.2% within 60 seconds, significantly outperforming conventional sedi-mentation methods. SEM and FTIR analyses confirmed the binding of nanoparticles to algal cell walls. The even distribution of MgFe₂O₄ 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.