Unraveling sorption of Cr (VI) from aqueous solution by FeCl3 and ZnCl2-modified corn stalks biochar: Implicit mechanism and application

A novel functionalized biochar was prepared using corn stalks for efficiently removal and mobility control of Cr(VI). Compared to single modified biochar, iron/zinc biochar (Fe@Zn@HBC) displayed a better removal property and the maximum adsorption capacity of Fe@Zn@HBC reached 138.89 mg·g-1 at pH = 2 and 260 ± 10 Lux illumination. The positive charge on biochar might be the main reason promoting the rapid adsorption of Cr(VI) by electrostatic interaction. Reduction functional groups and photocatalysis (derived from ZnFe2O4 and B-H functional group) provided electrons for Cr(VI) reduction. And the SiO2 could enhance the reduction process by improving electrons transfer. Finally, FeCr2O4 and ZnFeCrO4 were formed by coprecipitation and ion exchange. Meanwhile, Fe@Zn@HBC showed a high solid-liquid magnetic separation potential due to the Fe3O4 and ZnFe2O4. In soil column experiment, Fe@Zn@HBC displayed a superior mobility control on biochar particles and Cr(VI) solution under the external magnetic field.