Adsorption ability for several harmful anions and thermal behavior of Zn-Fe layered double hydroxide

A zinc-iron layered double hydroxide (Zn-Fe LDH) with sulfate as the interlayer ainon has been prepared by the coprecipitation method. The LDH was dehydrated in three steps below 300 degrees C and transformed to the amorphous phase. The recrystallization from the amorphous phase to ZnO (zincite), ZnFe2O4 (spinel) and Zn3O (SO4)2 occurred at approximately 450 degrees C. Furthermore, Zn3O (SO4)2 decomposed into ZnO, SO2 and O-2 above 700 degrees C. The adsorption ability of the Zn-Fe LDH was studied for several harmful anions (phosphate, chromate, borate, fluoride, selenate and arsenate) in aqueous solution, and it showed high selectivity for phosphate, chromate and selenate ions. The Zn-Fe LDH was found to be stable over a wide pH range (pH 2-12). The adsorption ability for phosphate ions depends on the initial pH and it increases with decreasing pH.