Thermal decomposition of magnesian kutnahorite

This work investigates the thermal decomposition of magnesian kutnahorite, which belongs to the dolomite group.The DTA curve measured in static air using a small amount of sample (5.0 mg) is quite different from those published previously. This difference might be due to the effect of a self-generated CO₂ atmosphere.In a CO₂ flow of 100 ml min^?1, magnesian kutnahorite decomposes in four steps. Mg-kutnahorite → CaCO₃ + Mg₂MnO₄ + Mn₃O₄ + MgO → CaCO₃ + CaMnO₃ + MgO → CaCO₃ + CaMnO₃ + Ca₂MnO₄ + MgO → CaMnO₃ + Ca₂MnO₄ + MgO + CaO.However, in a mixed gas flow of CO₂ at 95 ml min^?1 and CO at 5 ml min^?1, it decomposes, like dolomite, in two steps. Mg-kutnahorite → CaCO₃ + (Mg,Mn)$\text{O}\text{-}$ → (Ca, Mn)O + (Mg,Mn)$\text{O}\text{-}$.It has been found that the equilibrium redistribution of Mn between (Ca, Mn)$\text{O}\text{-}$ and (Mg, Mn)$\text{O}\text{-}$ is achieved at the second decomposition step. This is supported by theoretical considerations.Consequently, when the O₂ partial pressure in the atmosphere is low enough to keep Mn in a bivalent state, the Mn bearing dolomite group mineral decomposes in a similar manner to dolomite itself.