Thermal stability and oxidizing properties of mixed alkaline earth-alkali molten carbonates: A focus on the lithium-sodium carbonate eutectic system with magnesium additions

•TG/DSC analysis was conducted on magnesium-containing eutectic Li/Na eutectic carbonates.•Magnesium influence on the oxygen solubility properties of carbonate was also experimentally determined at 600°C and 650°C.•A reproducible partial decarbonation process in premelting region caused formation of magnesium oxycarbonate-like phases.•The acidobase buffering action of magnesium oxycarbonate species could explain the high basic/oxidizing properties of such carbonate melts.•A general correlation between thermal instability in premelting region and basic/oxidizing melt properties was established.