Heavy metal ions removal from an aqueous solution using an adsorbent derived from walnut shell: Equilibrium, kinetic and thermodynamic studies
2025
Anna Ivanchenko | Olga Soroka | Dmytro Yelatontsev | Vladimir Panasenko
A modified adsorbent for the removal of heavy metal ions (HMI) Pb2+, Cd2+, Cu2+, Ni2+, and Co2+ was synthesized from carbonized walnut shells (Juglans regia L.) pretreated with sodium carbonate (Na2CO3). By selecting the optimal parameters for the chemical activation of the raw materials (temperature, time, and concentration of Na2CO3), a 19-fold increase in the specific surface area and a 14-fold increase in iodine number were achieved. The obtained adsorbent was characterized by an enhanced porous structure and doubled acidic surface functional group content, which provided high-efficiency HMI removal (>85 %). The maximum adsorption capacity of 95–98 mg g–1 was observed at pH 6.5, with a 60-minute contact time and an adsorbent dosage of 5 g dm–3. The adsorption process follows the Langmuir isotherm, is governed by pseudo-second-order kinetics, and is spontaneous, endothermic, and physical in nature. HMI removal comprised physical interactions between the acidic functional groups of the adsorbent and the adsorbate via the formation of hydrogen bonds, which was facilitated by the formation of hydroxides at the corresponding pH. When HNO3 is used for regeneration, the proposed adsorbent can be reused for up to five sorption/desorption cycles, maintaining a satisfactory removal efficiency more than (>80 %). The present findings highlight the prospects of the developed method of processing walnut shells into an effective HMI adsorbent and indicate directions for further research on eco-friendly processing of plant biomass into cost-effective materials for large-scale wastewater treatment.
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