Adsorption of cadmium and lead from aqueous solution using modified biochar: A review

Cadmium (Cd) and lead (Pb) contaminations are disturbing environmental issues, which cause serious harm to aqueous systems and human health. Therefore, removing them from aqueous solution is essential to prevent their damage to the environment. Environmental adsorption research as one solution is promising and has been getting a lot of attention in the recent years. Using modified biochar has proved to be more suitable for the adsorption of cadmium and lead. In this review, the sources of cadmium and lead in the environment and their hazards have been elucidated. In addition, the preparation methods of modified biochar to remove Cd and Pb have been discussed. This review also presents the adsorption kinetics and isotherms results for the adsorption of Cd and Pb from aqueous solution using modified biochar. The effect of experimental parameters and adsorption mechanisms are also discussed in order to understand the adsorption performances of modified biochar in great detail. The adsorption mechanisms were surface precipitation, surface complexation, ion exchange, chelation, electrostatic attraction, inner sphere complexation, redox and physical adsorption. The adsorption was mainly endothermic and spontaneous. Additionally, the results on the regeneration of modified biochar are presented to provide a direction for sustainable improvement. Finally, this review article also provides the challenges, prospects and future perspectives of adsorption of cadmium and lead from aqueous solutions using the modified biochar.