Synthesis of high-performance magnetic biochar for adsorption of Ni2+ and Co2+from spent lithium-ion battery effluent

The recovery of heavy metal ion pollutants, particularly Ni²⁺ and Co²⁺, from lithium-ion battery effluent represents a pivotal focus in contemporary environmental research. In this study, the magnetic biochar (ISBC_x-y) was synthesized co-hydrothermal method using aloe vera skin (AL) as raw material and Fe₂(SO₄)₃ as and Fe and sulfur source, respectively. The structural and chemical properties of the as-prepared ISBC_x-y was characterized by BET, SEM, FTIR, and Zeta analysis, and its adsorption performance for Ni²⁺and Co²⁺ in waste water was also evaluated. The results show that ISBC_5-1 exhibited a lamellar-like surface with many small flakes, demonstrating a specific surface area of 38 m²/g and a total pore volume of 0.06 cm³/g, featuring a hierarchical porous structure. The surface chemistry of ISBC_5-1 is enriched with active functional groups, such as O, S, and Fe, facilitating efficient interactions with Ni²⁺ and Co²⁺ via mechanisms including ion exchange, electrostatic adsorption, complexation, and co-precipitation. Adsorption studies revealed that ISBC_5-1′s interaction with these metal ions conformed to the Langmuir adsorption isotherm and pseudo-second-order kinetic model, highlighting predominantly chemical adsorption characteristics. Theoretical maximum adsorption capacities calculated from the Langmuir model indicate impressive values of 153.14 mg/g for Ni²⁺ and 163.67 mg/g for Co²⁺. In addition, at pH 10, ISBC_5-1 achieves a removal efficiency of nearly 100% for Ni²⁺ and Co²⁺, underscoring the significant potential of ISBC_5-1 for effective wastewater treatment applications.