Treatment technology of Cr, Se, and As in wastewater by layered double oxide containig capability for uptake, reduction, and acid neutralization

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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). Similarly, the Fe2+-doped LDH could take up As(V) and Se(VI) from an aqueous solution. The excellent performance of this LDH for the 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 to obey pseudo-second order kinetics.