The role of foreign cations in enhancing the oxygen solubility properties of alkali molten carbonate systems: Brief survey of existing data and new research results

• Role of foreign cations on oxygen solubility of alkali molten carbonates is reported.
• La and Mg are the most effective in promoting oxygen solubility properties.
• Strong basic/oxidizing melts can be obtained by adding rare earth cations.
• La/Mg simultaneous additions to alkali molten carbonates boost oxygen solubility.

This work presents a summary of experimental data on the oxygen solubility-speciation properties of alkali molten carbonates that have been obtained by the authors through the development of a highly sensitive analysis method. The purpose of this summary is to show in particular the effect of foreign cation additions on both oxygen solubility and dissolution mechanisms at 650 °C. Our findings may be used to clearly indicate that rare earth and magnesium cations are the most effective in enabling oxygen solubility and basicity/oxidizing melt properties. The second part of this work reports new experimental results concerning the effect of simultaneous additions of La and Mg cations to an eutectic Li/Na carbonate system. A dramatic increase in oxygen solubility and active peroxide oxygen species has been found, thus revealing a strong synergistic effect of rare earth and alkaline earth cations on the molten carbonate oxygen chemistry. The results of this investigation suggest therefore that foreign cation addition is a potentially attractive option to design alkali molten carbonate salts with a high oxidizing power.