Valorization of Acacia-Derived Biochar for Nickel Remediation: Surface Morphology, Thermodynamics, and Regeneration Insights

Nickel (Ni) contamination in aquatic systems poses escalating global risks due to its industrial ubiquity and toxic persistence. This study explores the adsorption potential of biochar derived from Acacia auriculiformis waste wood, an underutilized biomass pyrolyzed at 600°C, for Ni(II) removal from aqueous media. The biochar exhibited a high surface area (144.899 m²/g) and a honeycomb-like porous architecture, enabling efficient Ni(II) uptake. Batch experiments optimized removal conditions at 0.5 g dosage, 240 min contact time, and ambient temperature, achieving a maximum efficiency of 94.75%. Adsorption kinetics followed a pseudo-second-order model, indicating chemisorption, while equilibrium data conformed to both Langmuir and Freundlich isotherms, suggesting mixed monolayer and heterogeneous surface interactions. Thermodynamic analysis confirmed the process as spontaneous and endothermic. Regeneration with HCl eluents revealed declining efficiency over three cycles due to structural fatigue. Compared to modified biochars and commercial adsorbents reported in recent international studies, the unmodified Acacia-based biochar offers a cost-effective and sustainable alternative for decentralized water treatment. By valorizing regionally abundant biomass and demonstrating competitive performance, this work contributes to global clean water initiatives and advances biochar-based remediation strategies with international relevance.