Sorption of oxyanions on nanocrystalline Mg/Al layered double hydroxides : sorption characteristics, mechanisms, and matrix interferences

Abstract

Nanocrystalline Mg/Al layered double hydroxide (LDH) with nitrate intercalation produced in this study exhibited excellent affinity for polyvalent oxyanions, but comparatively less affinity for monovalent oxyhalides. Nanocrystalline LDH was prepared by a fast coprecipitation with subsequent hydrothermal treatment method. The synthesized nanocrystalline LDH possessed mesoporous characteristic with a large surface area and comprised nanocrystalline grains. Interactions of oxyanions (i.e. arsenate, chromate, and vanadate) and oxyhalide (i.e. bromate) with nanocrystalline LDH were studied through stoichiometric calculations, nitrate displacement investigations, comprehensive sorption/desorption experiments, and analyses with several microscopic techniques such as XPS, EXAFS, XRD, FTIR, CHNS/O, and EDX. The influences of co-existing species on the sorption of oxyanions by nanocrystalline LDH were investigated by conducting experiment in the presence of natural organic matter (NOM) and common anions such as nitrate, silica, sulfate, carbonate, and phosphate. Arsenate sorption performances of LDHs prepared by various alternative synthetic routes were also explored and compared with those of LDHs prepared by conventional routes.