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

Abstract Cadmium (Cd) and lead (Pb) contaminations are disturbing environmental issues, which causes serious harm to aqueous systems and human health. Therefore, removing them from aqueous solution is essential to prevent its damage to the environment. Environmental adsorption research as one solution has seen a boom over the past decade. Using modified biochar has proved to be more suitable for the adsorption of cadmium and lead. Most of the studies apply a routine method such as kinetic and isotherm modelling to demonstrate the macroscopic trend of adsorption, often without elaborative evaluation of the effectiveness and characteristics of the models. This review compiles different adsorption kinetics and isotherms models and also presents their origins, modified versions, and their applicability in the liquid adsorption situation. The effect of experimental parameters and adsorption mechanisms are discussed to study the adsorption performances of modified biochar. The adsorption mechanism was majorly by surface precipitation, ion exchange, electrostatic attraction, complexation and physical adsorption. The adsorption was majorly endothermic and spontaneous. Additionally, preparation and regeneration of modified biochar are also presented to provide a direction for sustainable improvement. This paper summarizes with a note on challenges, prospects and future perspectives of adsorption of cadmium and lead pollutions.