Cadmium Remediation from Water Using Low-Cost Modified Biochar: An Approach Towards Sustainable Remediation

Biochar is increasingly recognized as an effective adsorbent for the removal of Cadmium (Cd²⁺), a prevalent contaminant in industrial wastewater. This study utilizes rice husk biochar to target aqueous Cd²⁺. The biochar was synthesized through rapid pyrolysis at 450°C. To enhance its Cd²⁺ removal efficiency, the biochar was modified with chitosan, using a treatment with a 2% aqueous acetic acid chitosan solution followed by sodium hydroxide (NaOH) processing. Both the chitosan-modified biochar (CMBC) and the non-modified biochar (NMBC) underwent comprehensive characterization via proximate and ultimate analysis, Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). At pH 5, the Langmuir maximum adsorption capacity of CMBC was 134 mg/g, compared to 48.2 mg/g for NMBC at 318 K. CMBC exhibited a significantly higher Cd²⁺ removal efficiency, attributed to the introduction of amine groups from chitosan modification that enhance Cd²⁺ adsorption. The adsorption mechanisms on CMBC were further explored through FT-IR and SEM comparisons before and after Cd²⁺ uptake. The chitosan modification notably improved the Cd²⁺ adsorption capacity, which was also influenced by pyrolysis temperature; higher temperatures led to reduced biochar yield but increased porosity, surface area, and adsorption capacity. The adsorption process was pH-dependent, with a peak capacity of 161 mg/g observed at pH 5. The Freundlich model effectively described the adsorption equilibrium, suggesting contributions from both chemisorption and physisorption on the heterogeneous biochar surface. In summary, rice husk biochar, especially when modified with chitosan, proves to be a cost-effective, sustainable material for Cd²⁺ removal from aqueous solutions, enhancing water treatment efficiency through improved adsorption capabilities.