Comparison of adsorption behavior studies of Cd by vermicompost biochar and KMnO-modified vermicompost biochar.

Cd pollution in aquatic environments can pose a serious threat to human health. Biochar can remove Cd from aquatic environments, but the Cdadsorption capacity of conventional biochar is low, therefore, we focused on exploring the Cd adsorption capacity of modified biochar. In this study, KMnO was used to modify vermicompost biochar (VBC), and static adsorption tests for Cd were carried out. The biochar properties and its adsorption efficiency toward Cd before and after modification were studied by kinetics and isotherm model fitting, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Additionally, an adsorption mechanism was discussed. The results showed that the KMnO-modification resulted in a successful loading of the vermicompost biochar with MnO, which greatly improved its adsorption capacity for Cd. The adsorption of Cd by VBC and MVBC was a spontaneous, endothermic, and monolayer chemical adsorption process. Mineral precipitation mechanism accounted for the largest proportion, and CdCO was the main precipitate. After modification the proportion of surface precipitation and other mechanisms (π-electron coordination and the inner/outer sphere surface coordination) increased，while adsorption via cation exchange, oxygen-containing functional groups, physical adsorption and electrostatic attraction reduced. Hence, KMnO modification has a significant effect on the Cd adsorption behavior of vermicompost biochar.