Enhanced nickel (II) removal from aqueous media using magnesium-Punica granatum linn based adsorbent: Mechanism and performance

Abstract

The rapid expansion of urbanization and industrial activities has led to a substantial increase in the discharge of heavy metals into aquatic environments. This study employs the distinctive properties of MgO-BC_K to synthesize magnesium oxide embedded in biochar (Punica granatum linn)-modified KOH through a one-step precipitation method. The results offer significant insights into optimizing adsorbent design and operational conditions for efficient Ni(II) removal at low concentrations via batch adsorption from aqueous solutions. The biochar surface became rough and uniformly layered with MgO, increasing the specific surface area to 46.448 m²/g. Before modification, the specific surface area of the biochar was 30.685 m²/g, providing numerous adsorption sites for Ni(II) removal. The removal efficiency greater than 97.67 % was achieved for nickel ions from an aqueous solution with an initial concentration of 20 mg/L, using 22 mg of the adsorbent at 318 K under neutral pH conditions. The adsorption data fitted well to the pseudo-second-order kinetic and Langmuir isotherm models, indicating that the process involves homogeneous chemisorption. Co-existing anions (${Cl}^{-},$ ${SO}_4^{2-}$) and cations (Cd (II) and Mn (II)) had minimal impact, but 100 mg/L of NO₃⁻, HCO₃⁻, PO₄³⁻, Fe (III), Cr(VI) mixed anions/cations reduced adsorption capacities. Additionally, the nickel removal efficiency of MgO-BC_K was maintained at 81.80 % (40.80 mg/g) even after seven regeneration cycles. Electrostatic interaction, ion exchange, and physical and chemical adsorption were suggested as potential adsorption processes based on the findings of Ni(II) uptake tests, EDS, FTIR, and XPS investigations. This study suggests that MgO-BC_K is a promising material for removing Ni (II) from wastewater.