Efficient removal of hexavalent chromium from wastewater using Fe-Cu impregnated char derived from coconut shell biowaste

The presence of hexavalent chromium [Cr( VI)] in industrial effluents is extremely detrimental to the environment and human health, and traditional treatment approaches are both expensive and ineffective at low levels, thus requiring sustainable solutions. This paper introduces a novel, low-cost green precursor-based, bimetallic Fe-Cu impregnated char, the first low-cost adsorbent to be used in the efficient removal of Cr(VI), an adsorption process involving both iron and copper in a single, low-cost green precursor. The adsorbent was synthesized via carbonization at 500°C, and bimetallic impregnation with FeSO₄ and CuSO₄, followed by calcination at 700°C. Characterization of the adsorbent was done through SEM, EDS, XRD, and FTIR to confirm successful incorporation of the Fe-Cu nanoparticles, a porous structure, and the presence of hydroxyl, carbonyl, and metal-oxygen functional groups, which are important in chromium binding. Experiments using batch adsorption showed that under optimal conditions of 0.06 g adsorbent dose, pH 3.84, and 60 min contact time, a maximum Cr(VI) removal efficiency of 97.2% was obtained. Equilibrium data were described better by the Freundlich (R 2 = 0.9897) than by the Langmuir model (R 2 = 0.9546), indicating uptake on an energetically heterogeneous surface rather than ideal monolayer coverage, while the Langmuir separation factor ( R L = 0.099) confirmed that adsorption is favorable. Kinetic studies revealed that the adsorption process followed a pseudo-second-order model, confirming chemisorption as the dominant mechanism. The adsorbent also retained over 80% of its original removal efficiency after five adsorption -regeneration cycles, indicating good reusability. The adsorbent developed provides a highly efficient, eco-friendly, and scalable solution to heavy metal removal in industrial effluents.