<p>Removing heavy metal ions from the wastewater before discharge in an environment is an essential issue, because of their toxicity, carcinogenicity, and mutagenicity. Herein, NiFe₂O₄ grafted chitosan Schiff base with malic acid (NiFe-CSSB-MA) was synthesized, characterized, and applied as a new adsorbent to remove Pb(II) and Hg(II) metal ions from aqueous solutions. The results indicated that the NiFe-CSSB-MA has different functional groups, rough surfaces, good thermal stability, and magnetic properties. The removal efficiency of Pb(II), and Hg(II) ions was studied using the batch experiments at different initial pH solutions, contact times, initial metal ions concentration, adsorbent dose, and temperature. The adsorption results indicated that the as-prepared NiFe-CSSB-MA showed the maximum adsorption capacity of 147.75&#xa0;mg/g for Pb(II) and 140.25&#xa0;mg/g for Hg(II) at optimum conditions. The adsorption kinetic and isotherm models indicate the monolayer adsorption of Pb(II) and Hg(II) ions with the pseudo-second-order (PSO) and Langmuir models, respectively. The results confirmed that the Pb(II) and Hg(II) adsorption was dependent on the coordination of surface functional groups of NiFe-CSSB-MA with the Pb(II) and Hg(II) ions. Additionally, the ions adsorption was identified as an endothermic and spontaneous process. Finally, according to these results, the nanocomposite NiFe-CSSB-MA is a potential adsorbent for the removal of typical metal ions from an aqueous solution.</p>