Preparation of Mg-Al layered double hydroxide doped with Fe2+ and its application to Cr(VI) removal

Mg-Al layered double hydroxide (Mg-Al LDH) doped with Fe2+ was prepared by dropwise addition of a mixed solution of MgCl2, FeCl2, and AlCl3 to NaOH solution at a constant pH. The Fe2+-doped LDH was found to be able to remove Cr(VI) from an aqueous solution through the anion exchange of Cr2O72- with the intercalated Cl−, the production of Cr(OH)3, and the adsorption of Cr2O72- on the surface of the produced FeO(OH). The excellent performance of this LDH for Cr(VI) removal is caused by both the anion exchange properties of Mg-Al LDH and the reducing activity of the Fe2+ doped into the Mg-Al LDH. This process can be considered to occur through Langmuir-type adsorption, and the maximum adsorption amount and equilibrium adsorption constant are 12.5 mmol g−1 and 242.1, respectively.