Historically, the decarbonation of Mg-Al-CO3 hydrotalcite-like compounds (HTlc) has been thought to occur between 400° and 500°C. The present work demonstrates that when HTlcs having the maximum Al content, Al/(Al + Mg) = 0.33, are heated to 500°C, 20–30% of the carbonates remain. The evolution of the remaining carbonates was observed as two maxima, at 600 and 900°C At these temperatures, Al ions go into MgO, and spinel (MgAl2O4) 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°C. This HTlc has no maximum of CO2 evolution above 500°C. Lower charge densities, due to lower Al contents, lead to lower amounts of remaining carbonate anions.
