Removal of chromate from aqueous solution by reduction with nanoscale Fe-Al layered double hydroxide

摘要

Nanoscale layered double hydroxides of Fe-II and Al-III (Fe-Al LDH) have been applied for removal of chromate (Cr-VI) from aqueous solution. Given the reaction stoichiometry, Cr-VI was completely reduced to Cr-III and coprecipitated with Fe-III and Al-III oxyhydroxides. The extent of Cr-VI removal decreased with increasing initial pH and decreasing molar ratio of Cr-VI/structural Fe-II in the LDH. The chromate reduction rate at different initial concentrations of Cr-VI was well described by the pseudo-second-order model with reaction rate constant ranging from 197.4 to 13.53 (mmol min)(-1). Initial pH and substitution of various amounts of Fe-III in the LDH structure had little effect on the reaction rate. Backtransformation of Cr-III to Cr-VI by birnessite Mn oxide (delta-MnO2) after 40 days of reaction was less than 1% of the initial Cr (as Cr-III solid), indicating high stability of the final reaction products and high efficiency of nanoscale Fe-Al LDHs for removal of chromate from aqueous solution.