A novel biochar derived from sugar beet pulp (O,N-SBB) was created through an initial surface activation in an acidic medium, followed by the functionalization with 3-aminopropyltrimethoxysilane. The adsorption of Cu(II), Ni(II), and Cd(II) was studied in ternary metal system. Optimal conditions included a pH of 8.14, an initial metal ion concentration of 77.23 mg L− 1 , and a dosage of O,N-SBB at 1.40 g L− 1 . Kinetic studies indicated that the adsorption process is predominantly governed by chemisorption, as evidenced by the superior fit of the pseudo-second-order model to the experimental data. The calculated ΔH◦values, ranging from 48.91 to 54.42 kJ mol− 1 , further supported the occurrence of chemisorption of metal cations on the adsorbent surfaces. In a ternary mixed system, the adsorption isotherm studies indicated that the Sips model provided the best fit for the experimental data, confirming the heterogeneous nature of the O,N-SBB adsorbent, which exhibited notable maximum adsorption capacities of 158.31 mg g− 1 for Cu(II), 373.42 mg g− 1 for Ni(II), and 67.91 mg g− 1 for Cd(II). The observed preference of O,N-SBB for Ni over Cu and Cd can be attributed to the cation’s characteristics in solution, particularly the charge-to-radius ratio of the hydrated ion, which affects the strength of interaction between the adsorbent and the ions.
