Thermoanalytical investigation of huntite

Abstract

This work investigates the thermal decomposition of huntite, CaMg₃(CO₃)₄, comparing it to that of dolomite. A small amount of the sample (5.0 mg) is used under atmospheres of various CO₂ partial pressures. In the CO₂ atmosphere, huntite decomposes in two steps CaMg₃(CO₃)₄ → CaCO₃·nMgCO₃ + (3 − n)MgO + (3 − n)CO₂ (i) (Mg—calcite) (n gradually changes with increasing temperature from 0.2 to 0.05). CaCO₃·nMgCO₃ → n MgO + CaO + (1 + n)CO₂ (ii) (n ⩽ 0.05) It has been clarified that both decompositions are straightforward dissociations similar to those of magnesite and calcite, and that their decomposition temperatures shift towards the higher temperature side with increasing CO₂ partial pressure. Therefore, it may be concluded that the mechanism of the first decomposition of huntite is quite different to that of dolomite.