Adsorption behavior and mechanism of Cd (II) by modified coal-based humin

Abstract Shanxi coal-based humin (SCH) was extracted using sequential alkali extraction from Shanxi Lingshi coal, and obtained the modified coal-based humin (Ca-SCH) by Ca(OH)2. On the basis of the problem of SCH’s high alkalinity and low adsorption amount to heavy metals, SCH was modified by using Ca(OH)2 and characterized by a series of representation analysis, and studied by static adsorption experiments for the adsorption kinetic and thermodynamic characteristics of SCH and Ca-SCH to Cd (II). Results showed that scanning electron microscope (SEM), BET method and X-ray photoelectron spectroscopy (XPS) certificated that the Ca (II) was loaded onto Ca-SCH successfully. In addition, the surface of Ca-SCH became coarse, the pore diameter of Ca-SCH increased, and content of oxygen functional groups also increased which was beneficial to the adsorption of Cd (II). The adsorption equilibriums of SCH and Ca-SCH were reached within 120 min, which accord with the pseudo-second-order kinetic equation, and the adsorption isotherms were well depicted by the Langmuir and Freundlich models. The maximum adsorption capacity (Qm) of Cd (II) on Ca-SCH was 89.29 mg ⋅ g−1, and increased 23.23% compared with SCH. By chemical modification, the Ca (II) can be boned to Ca-SCH, and Ca (II) and Cd (II) by ion exchange can be used to improve the adsorption performance of SCH, which is valuable for deactivating of Cd (II) in soil.