Activated carbon from olive pomace for hexavalent chromium removal: synthesis, characterization, and adsorption mechanism analysis

Chromium contamination, particularly in industrial wastewater, poses significant environmental and health risks due to its toxicity, carcinogenicity, and persistence. Despite various treatment methods, developing cost-effective and sustainable adsorbents remains challenging. This study addresses this gap by investigating the potential of activated carbon derived from olive pomace for Cr(VI) removal from aqueous solutions. The activated carbon was synthesized via chemical activation with phosphoric acid (H₂PO₄) followed by calcination at 500 °C. The structural and chemical properties of the adsorbent were characterized using FT-IR, HRTEM, SEM, XRD, and Raman spectroscopy. Additionally, density functional theory (DFT) calculations were employed to optimize the activated carbon structure and gain molecular-level insights into its interactions with Cr(VI) species. The adsorption process was systematically evaluated through batch experiments by optimizing key parameters such as pH, contact time, adsorbent dose, and initial Cr(VI) concentration. Response Surface Methodology (RSM) with a Box-Behnken design was applied to identify the optimal conditions for Cr(VI) removal. The results demonstrated that adsorption capacity increased with Cr(VI) concentration, with a maximum removal efficiency of 96% at pH 2, an adsorbent dose of 0.2 g, and a contact time of 2 h. Kinetic studies confirmed that the adsorption followed a pseudo-second-order model, suggesting chemisorption as the dominant mechanism. The isothermal analysis showed that the Freundlich model best described the adsorption behavior, indicating multilayer adsorption on a heterogeneous surface. Thermodynamic parameters confirmed the endothermic and spontaneous nature of the adsorption process.