Sorption of chromate ions on a calcined synthetic hydrotalcite

We examined the way that chromate ions arc held by a synthetic hydrotalcite (Mg-Al-CO3) and its calcination product at 550 degrees C. We used several physico-chemical methods of analysis (X-ray powder diffraction, thermal analysis and chemical composition) to determine the chemical formula of the starting material and to clarify its property of being able to regenerate itself after calcination and formation of mixed oxides. The sorption of chromate ions by the synthetized material and its calcination product were studied. Our results show that the kinetics of sorption are fast (equilibrium is reached after 20 min of contact) and that the phenomenon is pH dependent. The treatment of solutions containing 15 to 300 mg/L of Cr(VI) was successful. Comparison of the sorption capacity for Cr(VI) ions of calcined hydrotalcite with that of other LDHMg, (Al) phases confirms the superior sorptive properties of calcined hydrotalcites and hence their usefulness in the area of wastewater treatment.