Radioactive cesium-137 removal from contaminated wastewater using bio-based activated carbon from cassava rhizomes enhanced with copper hexacyanoferrate

Abstract

The presence of radioactive cesium-137 (Cs-137) contaminated in wastewater poses serious environmental and health concerns. This study presents the synthesis and characterization of activated carbon derived from cassava rhizomes (CRAC), further composited with copper hexacyanoferrate (CuHCF), for the removal of Cs-137 from actual wastewater. The cassava rhizome was treated with potassium permanganate (KMnO₄) via a hydrothermal carbonization process (HTC) before being pyrolyzed to produce high-surface-area activated carbon, which served as a support matrix for CuHCF nanoparticles known for their high selectivity toward cesium ions. The synthesis of copper hexacyanoferrate and cassava rhizome (CuHCF/CRAC) composites was achieved through the hydrothermal method. Batch adsorption tests were performed to assess the removal effectiveness of Cs-137 at a concentration of 10 000 Bq L⁻¹ from real wastewater. The incorporation of 5% w/w of KMnO₄ into the CuHCF/CRAC composites resulted in optimal Cs-137 removal efficiency, exceeding 99%. The improved adsorption capability was mainly attributed to the oxidative modification introduced by KMnO₄, which generated aromatic (CC), hydroxyl (–OH), and carboxylate (–COO⁻) groups, which improved electrostatic interactions with positively charged Cs ions. Adsorption isotherm and kinetic analyses revealed that the Freundlich isotherm and pseudo-second-order kinetic models provided the best fit for Cs-137 uptake across all tested adsorbents. The CuHCF/CRAC(5) composite demonstrated excellent reusability, maintaining high Cs ion removal efficiencies (>97%) over five consecutive adsorption–regeneration cycles following acid washing with 0.1 M HCl. Furthermore, adsorption efficiency was notably enhanced under neutral to alkaline pH conditions. These results highlight the strong potential of CuHCF-based activated carbon composites for practical applications in radioactive wastewater treatment.