A comparative study on thermal behavior and oxygen solubility properties of eutectic 52/48 lithium/sodium carbonate salt containing minor additions of magnesium up to 10 mol% has been made in order to determine whether a general correlation between these two properties can be found or not. Consecutive TG/DSC heating/cooling thermal cycles carried out under alternating CO2 and N-2 gas flows allowed to assign thermal events observed in the premelting region to a partial decarbonation process of the magnesium-alkali mixed carbonates. The observed decarbonation process at 460 degrees C is believed to come from initial stage of thermal decomposition of magnesium carbonate resulting in the metastable formation of magnesium oxycarbonate-like phases MgO center dot 2MgCO(3), in a similar manner as previously reported for lanthanum. Reversible formation and decomposition of the magnesium carbonate phase has been observed under a CO2 gas atmosphere. The intensity of the decomposition process shows a maximum for a 3 mol% MgO addition that gives also the highest oxygen solubility, suggesting therefore that instability thermal analysis in the premelting region can be considered as providing an effective measure of the basicity/oxidizing properties of alkali carbonate melts with magnesium or, in more general terms, with cations that are strong modifiers of the carbonate melt basicity through formation of soluble oxycarbonate phases. (C) 2013 Elsevier B.V. All rights reserved.