Memory Effect of Mg―Al Hydrotalcites and Its Chromium(VI) Adsorption Property

Mg―Al hydrotalcite (MAH) with high crystallinity was prepared using urea method. The memory effect and the chromium(VI) adsorption property of Mg―Al Hydrotalcites were studied. The MAH, reconstructed MAH (RMAH), calcined MAH (MAO) and calcined RMAH (RMAO) were characterized by XRD, FT―IR, SEM and DSC as well as self―deconvolution analyses. The results showed that the MAH and RMAH possessed a layered structure of hydrotalcites with high crystallinity, and there was little difference in crystal structures and charge density of brucite―like sheets between MAH and RMAH. The brucite―like sheets were still held in MAO, and a little remained in RMAO with more MgAl2O4. The adsorbility of Mg―A1 LDOs(MAO and RMAO) to Cr(VI) anions was substantially higher than that of Mg―A1 LDHs(MAH and RMAH), mainly because of the structure memory effect of hydrotalcites. The adsorbility of the MAO was higher than that of the RMAO. The adsorbility decrease of the RMAO might be due to the increase of the content of spinel MgAl2O4 phase and the decline of brucite―like sheets in RMAO that resulted in the descent of the memory effect reconstruction property. This newly discovery for anionic clays is useful for the decontamination of waste waters. The Mg―Al hydrotalcite can be considered as a potential material for sorption of anions in wastewater treatment systems.