| Calcined Mg/Al hydrotalcite (CH-Mg/Al), calcined Mg/Al vanadate hydrotalcite (CHV-Mg/Al) and modified hydrotalcites were prepared by thermal decomposition and characterized. Adsorption kinetics, effect of pH, equilibrium isotherms were assessed. The maximum absorption capacity of CH-Mg/Al, CHV-Mg/Al, Mg/Al-EDTA, Mg/Al-C6H1207, Mg/Al-C2O4with initial vanadium (V) concentrations50mg/L at25°C at the initial pH3.0were200,170,199,183and145mg/g, respectively. Calcined hydrotalcites is more suitable than modified hydrotalcites for application in practice. CH-Mg/Al and CHV-Mg/Al reached maximum adsorption at pH2.5while modified hydrotalcites at pH3.0. The data of all absorbent were best fitted to Sips model and could be best described by pseudo-second order equation which suggested that the nature of adsorption may be a chemical-controlling process. The removal mechanism was studied by XRD, XPS and FTIR. The results showed that there was no redox reaction during the adsorption process. The adsorption process of CH-Mg/Al was mainly anion exchange and adsorption on external surface of the layers. The adsorption capacity of CHV-Mg/Al was mainly caused by ion exchange. Using vanadate to synthesize hydrotalcite was unfavorable to removal of vanadium (V) from aqueous solution. CHV-Mg/Al had highly selectivity of vanadium (V) in the mixed solution of vanadate and dichromate which suggested that the structure memory effect and ion memory effect may exist at the same time in the process of adsorption. The calcined Mg/Al hydrotalcite showed wonderful vanadium (V) adsorption capacity. Calcined hydrotalcites material has potential application for the removal of vanadium (V) from aqueous solution and other field like sepration of V(V) and Cr (VI). |
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