Physico-chemical properties of the molten NaCl-CaCl2-MgCl2 salt containing magnesium

NaCl-CaCl2-MgCl2 molten salt with the low melting point was developed through thermodynamic calculation and experimental characterization. A set of thermodynamic parameters for the NaCl-CaCl2-MgCl2 molten salt was obtained. The calculated melting point of 418.1oC is in good agreement with the experimental value of 418.5oC. The molten salt was purified by adding excess magnesium, and the content of magnesium in the molten salt system was 738.0 μg/g. Compared with the NaCl-CaCl2-MgCl2 salt, the weight loss of the NaCl-CaCl2-MgCl2 salt containing Mg is only 5.0 wt.% at 728.0oC. The average solid-phase and liquid-phase specific heat capacity of the NaCl-CaCl2-MgCl2 salt containing Mg are separately 0.89 J/g·oC and 1.44 J/g·oC. The thermal stability and specific heat capacity of the NaCl-CaCl2-MgCl2 salt containing Mg has been improved to a certain extent, while the difference of melting temperature and fusion enthalpy can be ignored between them. In addition, the ultrafast dynamic of NaCl-CaCl2-MgCl2 salt containing Mg was firstly determined through the polarization-selective mid-infrared pump-probe spectroscopy, where the dynamics of the Mg2+ (4.5 ps) peak are slower than the water peak (2.3 ps), and the dynamics of the water peak in the NaCl-CaCl2-MgCl2 salt show a similar behavior to that in pure water. This work not only enormously enriches the physico-chemical database of the molten salt, but also provides theoretical support and technical assistance for purifying the molten salt. It has the far-reaching implications for the comprehensive utilization of salt-lake resources with abundant reserves in China.