Cr(VI) removal from water by synthesized Mg-Fe layered double hydroxides – Effect of calcination

Abstract

In the present study, Mg-Fe layered double hydroxides (Mg-Fe LDHs) have been synthesized by the co-precipitation method at pH 10 and at pH 12 and used for Cr(VI) removal from aqueous solutions. Their characterization by XRD analysis confirms the lamellar structure before calcination and shows the formation of spinel (Mg-Fe2O4) and magnesium oxide after calcination at 500°C. Batch experiments reveal that Cr(VI) removal by the prepared LDHs increases with the decrease of the solution pH. Whatever the prepared LDH used, Cr(VI) removal processes is spontaneous and exothermic. The kinetics is well described by the second-order model and the equilibrium data follow the Langmuir model. The lower removal equilibrium time (3 h) is obtained in the case of the uncalcined LDH prepared at pH 12. The calcination of the Mg-Fe LDHs prepared either at pH 10 or at pH 12 implies the decrease in Cr(VI) removal capacity.