Characteristics of adsorption behavior of potentially toxic metals by biochar derived from fallen leaves (Platanus) and its mechanism

In this study, we aimed to evaluate the properties and mechanisms of heavy metal adsorption by biochar derived from fallen leaves (FLB). The optimum manufacturing temperature of FLB for heavy metal removal was 650 °C, which resulted in a high carbon content and specific surface area. The maximum adsorption capacities of Cd and Pb by FLB650 were 86.2 and 135.1 mg/g, respectively; their adsorption was achieved via chemisorption. The results from chemisorption agreed with the Langmuir isotherm and pseudo-second order models. We confirmed that the adsorption of Pb by FBL was dominantly affected by the surface boundary layer; however, the adsorption of Cd occurred in cooperation with the boundary layer and pore diffusion; which was accomplished by employing the intraparticle diffusion model. After heavy metal adsorption, the distribution characteristics and mechanisms of each heavy metal in the FLB were noticeably observed through SEM-EDS, FTIR, and XRD. In addition, the content of exchangeable cations released from the FLB during the heavy metal adsorption process corresponded to 52% for Cd and 34% for Pb of the total amount of adsorbed heavy metals. We determined that FLB exhibits high affinity for heavy metals and its adsorption occurs via an adsorption mechanism based on the properties of FLB.