Efficient and low-cost removal of heavy metals from aqueous solution using eco-friendly adsorbent

Heavy metal contamination of water by ions such as Pb²⁺, Co²⁺, Cd²⁺, and Cu²⁺ poses significant environmental and public health risks. Adsorption is a widely accepted method for metal removal due to its efficiency, simplicity, and cost-effectiveness. This study investigates the adsorption potential of activated carbon derived from walnut (Juglans regia L.) shells, an agricultural waste material with high lignin and cellulose content. A novel, one-step activation method, developed at Ivane Javakhishvili Tbilisi State University was employed, to synthesize the sorbent using only water as the activating agent and without chemical additives. The process is energy-efficient and environmentally friendly, utilizing carbonization gases as an internal energy source. Physicochemical characterization showed a high surface area and well-developed porous structure suitable for adsorption. Batch adsorption experiments were conducted using model solutions of Pb²⁺, Co²⁺, Cd²⁺, and Cu²⁺ at various concentrations. Adsorption performance was evaluated in static conditions at 25 °C using atomic absorption spectroscopy. The results showed outstanding removal efficiency, especially at lower concentrations (0.0025 M), with metal uptake following both Langmuir and Freundlich isotherm models (R² > 0.90), indicative of monolayer and heterogeneous surface adsorption. The maximum sorption capacities and removal efficiencies confirmed the effectiveness of walnut shell–derived carbon as a means of treating heavy-metal-contaminated water. This biosorbent provides a low-cost, sustainable, and efficient alternative for water purification, with potential scalability for industrial applications.