Adsorption Mechanism and Structure-Performance Relationship of Chromium Ions by Biochar

Abstract

In order to further explore the adsorption mechanism of chromium ion by biochar, organic components (OCs) and inorganic components (ICs) of biochar (RC) were prepared, and adsorption experiments of chromium ions by these types of carbon (RC, OC, IC) were performed. The three types of carbon were characterized before and after adsorption of chromium ions, using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Boehm titration, and zero charge (pHpzc). Results showed that the adsorption efficiency of IC on trivalent chromium (Cr3+) was the strongest, ion exchange of Cr3+ with metal cations present on IC being the main adsorption mechanism, accounting for 61% of the total adsorption capacity. Among the metal ions, K+ accounted for about 51%. The REDOX between Cr3+ and carboxyl accounted for 20% of the total adsorption capacity. Other adsorption mechanisms, such as chelation between Cr3+ and carboxyl, and co-precipitation between Cr3+ and carbonate, occupied a small proportion. OC showed the largest adsorption capacity to hexavalent chromium (Cr6+). The adsorption mechanism of OC to Cr6+ was the result of combined actions, such as electrostatic attraction, and REDOX between Cr6+ with the aromatic π-conjugated system and reductive functional groups like hydroxyl. Among them, the REDOX accounted for 53% of the total adsorption of Cr6+ by OC.