[Novel Insight into the Adsorption Mechanism of Fe-Mn Oxide-Microbe Combined Biochar for Cd(Ⅱ) and As(Ⅲ)].

A Fe-Mn oxide-microbe combined biochar (FM-DB) was prepared to simultaneously remove Cd(Ⅱ) and As(Ⅲ) contamination in an aqueous system. In the FM-DB, the best ratio of Fe-Mn oxide (FMBO) and carya cathayensis shell biochar (CCSB) was 3%+3%. The material had good acid resistance, mechanical strength, and mass transfer performance, and the maximum removal rates for Cd(Ⅱ) and As(Ⅲ) in the binary system were 77.29% and 99.94%, respectively. Characterization confirmed that the FM-DB was successfully prepared and had a rich functional group structure. The single-factor adsorption test results for Cd(Ⅱ) and As(Ⅲ) showed that the composite material had a certain adsorption capacity affected by initial pH, equilibration time, and initial concentration for Cd(Ⅱ) and As(Ⅲ) under different conditions. The adsorption isotherm and kinetic data indicated the adsorption equilibrium time for Cd(Ⅱ) and As(Ⅲ) was 3.5 h and 8 h, and the maximum capacity was 59.27 mg·gand 84.73 mg·g, respectively. The adsorption of Cd(Ⅱ) and As(Ⅲ) was mainly affected by the electron exchange, electron sharing, and complexation on the surface of the material. The whole adsorption process was a combination of single-layer adsorption and multi-layer adsorption on an uneven surface. The adsorption process was a multi-step process, including outer surface diffusion and inner particle diffusion. In addition, comparing the removal rate of composite materials in the single-component system and the binary system, a mutual promotion of adsorption between Cd(Ⅱ) and As(Ⅲ) was found under the binary system. In conclusion, oxide-microbe combined biochar could be an efficient adsorption material and was suitable for the remediation of aqueous system pollution caused by Cd(Ⅱ) and As(Ⅲ).