DECARBONATION BEHAVIOR OF MG-AL-CO-3 HYDROTALCITE-LIKE COMPOUNDS DURING HEAT-TREATMENT

Historically, the decarbonation of Mg-Al-CO3 hydrotalcite-like compounds (HTlc) has been thought to occur between 400 degrees and 500 degrees C. The present work demonstrates that when HTlcs having the maximum Al content, Al/(A + Mg) = 0.33, are heated to 500 degrees C, 20-30% of the carbonates remain. The evolution of the remaining carbonates was observed as two maxima, at 600 and 900 degrees C. At these temperatures, Al ions go into MgO, and spinel (MgAI(2)O(4)) forms. Therefore, the carbonates are released as the Al ions migrate. At a lower Al content, Al/(Al + Mg) = 0.25, CO2 evolution is almost complete at 500 degrees C. This HTlc has no maximum of CO2 evolution above 500 degrees C. Lower charge densities, due to lower Al contents, lead to lower amounts of remaining carbonate anions.