[Preparation of Magnetic Biomass Carbon by Thermal Decomposition of Siderite Driven by Wheat Straw and Its Adsorption on Cadmium].

C-FeO composite material [magnetic biomass char (MBC)] was prepared by pyrolysis of a mixture of wheat straw and siderite at 500℃. The MBC was characterized by XRF, FTIR, XRD, SEM, XPS, and a magnetic susceptibility device. The effect of contact time, pH value, initial Cd concentration, and ionic strength on the adsorption capacity of the MBC to Cd was investigated. The results showed that the BET surface areas of the MBC and biomass char (BC) were 23.38 m·g and 7.20 m·g, respectively, total pore volumes were 1.04×10 cm·g and 2.23×10 cm·g, and average pore diameters were 17.74 nm and 12.38 nm. The magnetic susceptibility of the MBC was 42900×10 m·kg. FTIR showed that phenolic hydroxyl and carboxyl functional groups bound metal ions on the surface of the MBC and BC. The kinetic data of the MBC were described well by the pseudo-second-order model. Isothermal adsorption of Cd by MBC and BC was fitted well by the Freundlich equation. The adsorption velocity increased with an increase of pH in the region 3-6 and then stabilized in the region 6-9. The adsorption capacity of Cd decreased slightly when ionic strength increased from 1 mmol·L to 100 mmol·L, whereas the desorption rate increased from 0.51% to 8.5%. The adsorption properties and characterization results illustrated that the removal mechanism of Cd likely was through adsorption and ion exchange on the surface of the MBC with a high amount of functional groups. In addition, magnetic adsorbents offered a significant advantage compared to other adsorbents in the aspect of separation from aqueous solution.