Adsorption Characteristics of Cd2+ Ions in Aqueous Solution on Modified Straw Biochar

Abstract

Rice straw and corn straw were selected as raw materials to prepare biocharby anoxic carbonization and the biochar was loaded on the surface with FeCl3, MnCl2 and Fe(NO3)3 & KMnO4, respectively, and then two types of straw biochar and six types of modified biochar were prepared. FT-IR, SEM, and XRD were used to characterize and analyze the physical and chemical properties of the biochar. The adsorption kinetics and adsorption isothermal tests of Cd2+ ions in aqueous solution were carried out. The results showed that modified biochars attached more active sites and surface group, especially iron-manganese-modified biochar (FMBC1, FMBC2). The kinetic adsorption tests showed that the adsorption process of eight kinds of biochar all conformed to the quasi-second-order kinetic equation, and chemisorption maybe dominated the adsorption process. The adsorption isothermal test showed that the adsorption process of Cd2+ ions by FeCl3-modified biochar (FBC1, FBC2) and Fe(NO3)3 & KMnO4-modified biochar (FMBC1, FMBC2) conforms to the Freundlich model, and the adsorption process of Cd2+ ions by MnCl2-modified biochar (MBC1, MBC2) conforms to Langmuir model. Compared with other kinds of biochar, the KF value of Fe(NO3)3 & KMnO4-modified biochar of rice straw biochar (FMBC1) was the largest, reached 18.602 L·mg−1, and its 1/n value was the smallest, it reached 0.474, indicating that the adsorption effect on Cd2+ of FMBC1 was the best.