Study On Incorporation Of Zinc And Copper Into Layered Double Hydroxide And Its Structure Evolution With Heating Treatment

Layered double hydroxide(LDH) has been becoming international focus in material and chemistry fields in recent 10 years for its special structure and properties. Application of LDH in environmental protection is an important and promising attempt.The possibility of Zn2+ or Cu2+ removal from synthetic wastewater by preparing LDH in situ was investigated experimently. In this process LDH was prepared by Mg2+, Al3+ and Zn2+ or Cu2+ coprecipitating with NaOH. The effects of pH, Mg/Zn molar ratio or Mg/Cu molar ratio, reaction time, reaction temperature, Zn2+ or Cu2+ initial concentration and anions existed in synthetic wastewater were studied when M2+/M3+ molar ratio is 2. The removal efficiency of Zn2+ is found to be different significantly under the 0.05 level at different pH values, the most efficiency occurs in the pH range of 9.0 to 11.0, removes more than 99% of Zn2+ from synthetic wastewater, other factors have no significant effects on Zn2+ removal efficiency. The removal efficiency of Cu2+ is different significantly under the 0.05 level at different pH values and Mg/Cu molar ratio. The most efficiency occurs in the pH range of 9.0 to 11.0, removes more than 99% of Cu2+ from wastewater, Cu2+ removal efficiency is decreasing with the increasing of Mg/Cu molar ratio, however, relatively high removal efficiency can also be remained. The products were characterized by X-ray diffraction, indicates that Zn2+ or Cu2+ are removed from wastewater mainly occurs in the crystal formation stage as Zn/Mg/Al-LDH or Cu/Mg/Al-LDH, with consideration of the characteristics of the in-situ method itself. The products can be used as functional material, that means contaminations can be recycled. Compared with sedimentation treatment with NaOH, in-situ method for removal of Zn2+ is more effective and suit for more wider pH range.Structure evolution and BET surface area changes of heating treated Mg/Al-LDH was evaluated by X-ray diffraction, transmission electronmicroscopy and N2 Brunauer-Emmett-Teller analyses. The results indicates that for Mg/Al-LDH with carbonate as interlayer anion, periclase-like oxide is formed at the temperature range of 400℃-800℃. At the same time, 2nm-3nm nanometer mesopores are formed during the decomposition of LDH. However, the heat treated samples still preserves the morphology of original LDH plates. Periclase-like oxide formed from LDH heating treatment may re-hydrolyze and recover the structure of LDH. However, crystallinity of the recovered LDH is lower than that of original LDH. Such a heating treatment will result in the formation of Mg-Al-oxide nano-crystals and nanopores among the nano-crystal. When the heating temperature exceeds 1000℃, the periclase-like Mg-Al-oxide is transformed into a composite with periclase (MgO) and spinel phases.the periclase can be re-hydrolyzed and dissolved in HCl solution. After acid treatment ,the sample with high surface area is composed of spinel nano-crystals and nanopores among them.