Removal of antimonate ions and simultaneous formation of a brandholzite-like compound from magnesium-aluminum oxide

Magnesium-aluminum oxide (Mg-Al oxide), obtained by thermal decomposition of a Mg-Al layered double hydroxide (Mg-Al LDH), was found to remove Sb(OH) ₆ (Sb(V)) in solution because of rehydration, and to combine with Sb(V) to form a brandholzite-like structure. Although the Sb concentration decreased with increasing amounts of Mg-Al oxide, differences in the Mg/Al molar ratio had little effect on this relationship. The removal of Sb(V) in solution by Mg-Al oxide was partially prevented by coexistent anions with high charge densities (SO₄^2- and CO₃^2-). In this case, Mg-Al oxide likely rehydrates and competitively combines with Sb(V) in solution to construct a brandholzite-like structure or with anions to reconstruct the LDH structure. However, in the case of coexistent anions with low charge densities (Cl and OH), Mg-Al oxide likely rehydrates and preferentially combines with Sb(V) in solution to construct the brandholzite-like structure. A high concentration of Cl and SO^2- ₄ had little effect on the decrease in Sb concentration, whereas a high concentration of CO^2-₃ had a large effect.