Effect of Temperature on Microstructure and Cr(VI) Adsorption Capacity of MgAl Metal Oxides

The adsorption properties of Cr(VI) on the double oxides (LDO) from calcined MgAl hydrotalcites (LDH) were investigated. The effect of temperature on the adsorption performances of the LDO was studied, and the adsorption kinetics and thermodynamics were studied at different adsorption temperatures. The samples were characterized by XRD and FT-IR to clarify the adsorption mechanism.The results indicated that CrO4 2- had inter- calated into the interlayer structures of Mg-Al hydrotalcites. Moderately increasing temperature was beneficial for the reconstruction of LDH crystalline structure from LDO. In the temperature range of 20℃-60℃, adsorption capacity of the LDO was increased with temperature rising, it reached 91 mg/g in the temperature range from 50℃ to 60℃. The experimental data were well fit to the Langmuir equation. The negative values of ΔG o indicated that the adsorption process was spontaneous, and positive values of ΔH o and ΔS o showed the endothermic and entropy-increasing nature of the process. The adsorption was consistent with the pseudo-second order kinetic model. The active energy value was 20.04 kJ/mol, which implying that the internal diffusion was the rate-determining step in the chemical adsorption.