Advances in biochar-based absorbents: Sustainable solutions for heavy metal removal from contaminated water

Abstract

Heavy metal contamination in water poses serious environmental and health risks, necessitating cost-effective and sustainable remediation methods. Biochar, a carbon-rich material produced through the pyrolysis of organic waste such as agricultural residues, sewage sludge, and marine algae, has emerged as an efficient adsorbent for removing heavy metals. This review examines recent advancements in biochar-based adsorption, focusing on key factors influencing its efficiency, including feedstock type, pyrolysis conditions, surface functionality, and porosity. The study explores the role of modified biochars, such as magnetic biochar, in enhancing metal recovery while maintaining high adsorption capacity. The adsorption mechanisms like cation exchange, electrostatic interactions, complexation, and precipitation are analysed to explain the effectiveness of biochar in capturing heavy metals such as Pb(II), Cd(II), Cu(II), and Zn(II). Additionally, the impact of parameters such as pH, contact time, and initial metal concentration on adsorption performance is discussed. While biochar presents a scalable and eco-friendly wastewater treatment solution, challenges such as competitive adsorption in multi-metal systems, regeneration efficiency, and production costs remain. Future research should focus on optimising biochar modifications, integrating it with existing treatment technologies, and enhancing its selectivity for specific contaminants.