Adsorption of Cd2+ in aqueous solutions using KMnO4-modified activated carbon derived from Astragalus residue
(1. School of Basic Medical Science, Ningxia Medical University, Yinchuan 750004, China;
2. School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: Activated carbon obtained from Astragalus residue was chemically activated by KOH and modified with KMnO4. The samples were characterized by N2 adsorption, Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy, and Boehm titration. Accordingly, the original and modified carbon materials were used for the removal of Cd2+ from aqueous solution by batch adsorption experiments. Results showed that the contents of oxygen-containing functional groups increased, and MnO2 was nearly uniformly deposited on the surface of activated carbon after modification by KMnO4. The adsorption kinetics was described by pseudo-second order model. Langmuir model fitted the adsorption-isotherm experimental data of Cd2+ better than the Freundlich model. The maximum adsorption capacities of the activated carbon before and after modification for Cd2+ were 116.96 and 217.00 mg/g, respectively. KMnO4 considerably changed the physicochemical properties and surface texture of activated carbon and enhanced the adsorption capacity of activated carbon for Cd2+.
Key words: Astragalus residue; activated carbon; modification; adsorption; Cd2+