Removal of antimonate ions from an aqueous solution by anion exchange with magnesium-aluminum layered double hydroxide and the formation of a brandholzite-like structure.

A magnesium-aluminum layered double hydroxide intercalated with NO(3)(-) (NO(3)•Mg-Al LDH) removed Sb(V) in solution. The antimony (Sb) removal increased with time and with an increasing molar ratio of Al/Sb, i.e., the quantity of NO(3)•Mg-Al LDH. The removal of Sb(V) in solution by NO(3)•Mg-Al LDH was not due to the reaction of Sb(V) with dissolved Mg(2+) but was rather caused by anion exchange between Sb(V), i.e., Sb(OH)(6)(-), in an aqueous solution and NO(3)(-) in the interlayer of the Mg-Al LDH. The intercalation of Sb(OH)(6)(-) in the interlayer of Mg-Al LDH is thought to result in the formation of a brandholzite-like structure. Some Sb(OH)(6) (-) was likely adsorbed on the surface of the NO(3)•Mg-Al LDH. The efficiency of the Sb removal decreased in the following order, irrespective of the reaction time: NO(3)•Mg-Al LDH ≈ Cl•Mg-Al LDH > SO(4)•Mg-Al LDH > CO(3)•Mg-Al LDH. The removal of Sb by SO(4)•Mg-Al LDH and Cl•Mg-Al LDH was also caused by anion exchange between Sb(V), i.e., Sb(OH)(6) (-), in an aqueous solution and SO(4)(2-) and Cl(-) in the interlayer of Mg-Al LDH, which formed a brandholzite-like structure due to the intercalation of Sb(OH)(6)(-) into the interlayer. In the case of SO(4)•Mg-Al LDH, hydrogen bonds between the Mg-Al LDH-positive host layer and Sb(OH)(6)(-) were probably stronger than the electrostatic force of attraction between the Mg-Al LDH-positive host layer and SO(4)(2-). The results suggested that Cl•Mg-Al LDH was as effective as NO(3)•Mg-Al LDH for the treatment of Sb(V) in aqueous solutions.