In order to utilize the waste biomass resources efficiently, two raw materials of sawdust and apple branch were selected to produce biochars at 450℃ by oxygen-limited pyrolysis, and the adsorptions of Cu2+ in aqueous solutions were evaluated. The effects of initial Cu2+ concentration and contact time in batch sorption experiments were investigated by the four kinds of isothermal adsorption models (Langmuir, Freundlich, Temkim, D-R model) and the four kinds of adsorption kinetics models (Pseudo first-order, Pseudo second-order, Elovich model, Intraparticle diffusion model). The influencing factors of adsorption characteristics about sawdust biochar (JB) and apple branch biochar (PB) were discussed by characterizing their elemental composition, functional groups, surface area, surface morphology and scanning electron microscope. The results showed that:1The adsorption equilibrium of PB and JB was reached in three hours and six hours, respectively, and the maximum adsorption capacity of PB and JB reached 15.85 mg·g-1 and 17.44 mg·g-1, respectively. Compared with other studies, these biochars showed higher Cu2+ adsorption performance. 2The adsorption kinetics was best fitted by the pseudo-second order model, while the isothermal adsorption was best described by Langmuir isotherms. This indicated that the beneficial adsorption process via monolayer was affected by intraparticle diffusion, surface adsorption and liquid film diffusion. 3The adsorption mechanism for Cu2+ is a complex interaction of physical and chemical factors. Electrostatic interaction of physical adsorption is mainly adsorption mechanism, Chemical adsorption mechanism includes generally ligand exchange (phenolic hydroxyl)/ion exchange (H+) and cationic-π. It was demonstrated that JB and PB could be considered as promising materials to immobilize heavy metals in contaminated water or soil.
Keywords: adsorption characteristics; apple branch; biochar; copper; mechanism; sawdust.