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°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°C. Furthermore, Zn3O(SO4)2 decomposed into ZnO, SO2 and O2 above 700°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.