Following three reactions can show calcination process.
(i) CaCO3.MgCO3Δ−→CaO+MgO+CO2
(ii)CuCO3.Cu(OH)2Δ−→2CuO+H2O+CO2
(iii)Al2O3.2H2OΔ−→Al2O3+2H2O
Note: In calcination, the ores are heated below their melting points in absence of air to remove volatile impurities like carbon dioxide, water and organic matter.