Adsorption mechanisms of cadmium onto reed-derived biochar

In order to solve the problem of heavy metal-contaminated wastewater and to find a novel application for reeds, reed-derived biochar(RBC) was synthesized at different pyrolysis temperatures under limited oxygen conditions. Elemental analysis, adsorption kinetics, and isothermal models were used to explore the adsorption mechanism. The effects of different pyrolysis temperatures on the adsorption of Cd2+ onto RBC were investigated by SEM-EDS, FTIR, and XRD. The results showed that the adsorption of Cd2+ fitted a pseudo-second-order model, but could be better described by Langmuir models. RBC synthesized at 500℃ had a high yield and the largest theoretical Cd2+ adsorption capacity, which was as high as 39.05 mg·g-1. SEM images showed a granular structure on the surface of RBC after adsorption and, according to the XRD spectra, peaks of CdCO3 and CdSiO3 crystalline forms appeared. It was, therefore, inferred that Cd2+ could precipitate with CO32- and SiO32- respectively. In this study, the adsorption mechanism of Cd2+ onto reed biochar was systematically described as the common result of cation exchange, precipitation adsorption, complexation, and Cd-π metal bonding interaction.