Reactions of Cu2+ and Pb2+ with Mg/Al layered double hydroxide

The adsorption mechanisms of metal cations on the surfaces of clay minerals and other minerals are important for understanding their fate in contaminated soils and in waste water treatment. The reactions of Cu2+ and Pb2+ heavy metal cations with layered double hydroxide (LDH), has been investigated in aqueous solutions to elucidate their removal behaviors by LDH. The reaction of aqueous CuCl2 solution with Mg/Al-LDH resulted in precipitation of Cu hydroxide chloride (Cu7Cl4(OH)10·H2O) along with slight decomposition of Mg/AI-LDH. On the other hand, the reaction of aqueous PbCl2 solution led to steady decomposition of Mg/Al-LDH structure along with the formation of various Pb precipitates such as carbonate chloride (PbCO3PbCl2) and hydroxide chloride (Pb(OH)Cl). Experimental techniques such as X-ray diffraction, X-ray photoelectron spectroscopy and cation removal isotherms were used to decipher the mechanism of uptake. This study indicates that LDH removes Cu2+ and Pb2+ transition metal cations from aqueous solution mainly by surface adsorption and precipitation.