Adsorptive Removal of Cd²⁺ from Aqueous Solution Using Arecanut Husk-Derived Biochar under Different Experimental Conditions

Abstract

Heavy metals occur naturally in soil due to the weathering of parent materials.  At trace levels, they are nontoxic. Cadmium is a heavy metal that is highly toxic at low levels.  This study investigates the potential of Arecanut husk-derived biochar as a low-cost and eco-friendly adsorbent for removing cadmium ions (Cd²⁺) from aqueous solutions. Biochar production was carried out using a pyrolysis process. The results demonstrated that adsorption capacity (qe) was strongly influenced by biochar dosage, contact time, solution pH, and temperature, on cadmium removal efficiency. Optimal performance was observed at a biochar dosage of 60–80 mg, contact time of 60 minutes, pH range of 6–8, and a temperature of 50°C.  Under these optimal conditions, the maximum adsorption capacity was found to be 1.73 mg/g and removal efficiency was achieved up to 89.8%. FTIR analysis revealed the involvement of functional groups, including C-H, –COOH, and C=O, in the adsorption process through coordination and complexation with cadmium ions. XRD analysis confirmed the successful immobilization of Cd²⁺ via the formation of cadmium-containing crystalline phases, without altering the biochar’s amorphous carbon structure. These findings indicate that chemisorption mechanisms, including surface complexation and mineral precipitation, primarily govern cadmium adsorption. To the best of our knowledge, this research study signifies a novel, acceptable, innovative method that is eco-friendly, cost-effective, and utilizes readily available materials, such as biochar derived from arecanut husk, which helps as a promising, sustainable, and efficient adsorbent for the remediation of cadmium-contaminated water.