Removal of Zn(II) from low concentration waters by adsorption method with activated carbon obtained from plant waste

Natural adsorbents derived from agricultural waste are considered sustainable and cost-effective solutions for removing heavy metals. This study investigated the adsorbent potential of grape seed waste-derived bioactive carbon (GSW-BAC) for removing zinc(II) ions from water. GSW-BAC was produced by pyrolyzing grape seed waste at 500°C for 3 h. The GSW-BAC was analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Varying solution pH (1–10), GSW-BAC doses (10–75 mg), initial Zn(II) concentration (2–25 mg/L), contact time (30–720 min), and temperature (298–318 K) were used in batch adsorption tests. A mixture of twelve metal ions (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Hg, Pb, Mg, and Sn) was used to assess the competitive adsorption of several metals at 5.5, 6.0, and 6.5 pH levels. Adsorption kinetics (pseudo-first order and pseudo-second order), isotherms (Langmuir and Freundlich), and thermodynamic parameters were evaluated. Optimal single-metal adsorption was recorded at pH 6 with 25 mg GSW-BAC and an initial Zn(II) concentration of 5 mg/L. The adsorption followed pseudo-second-order kinetics (R 2 > 0.991) and was characterized by the Langmuir isotherm, yielding adsorption capacities (q max ) of 3.797, 2.395, and 1.847 mg/g at 298, 308, and 318 K, respectively. The thermodynamic study demonstrated that the process is spontaneous (ΔG° < 0 at all temperatures). The GSW-BAC achieved >99% removal efficiency for all metals over the tested pH spectrum in the multi-metal system. It is concluded that GSW-BAC has significant Zn(II) removal capacity and superior multi-metal adsorption efficiency, making it a viable, economical, and sustainable adsorbent aligned with circular economy principles for heavy-metal remediation in aquatic environments.