Predictive model for the phase diagrams of ternary mixtures composed of calcium, lithium and sodium/potassium nitrates

The study and development of multi-component alkaline nitrates systems is of utmost interest to investigate low melting and low cost HTFs and HSMs, to be used in CSP plants. At this aim, several binary and ternary mixtures have been proposed as feasible and promising materials in the scientific literature. In order to evaluate the most feasible HTF and HSM, the simulation campaign proposed in this work was focused on economical and readily available compounds, ruling out rare and costly species. A semi-predictive model, based on the regular solution theory, was employed to draw the ternary phase diagrams of LiNO3/NaNO3/Ca(NO3)2 and LiNO3/KNO3/Ca(NO3)2, from which it was possible to select the lower melting zones and the compositions. The binary sub-systems were the starting point for the employed approach. The results showed a good agreement with literature experimental data, and new low melting compositions were simulated and experimentally validated. It is noteworthy that it was possible to identify in great detail the zones of the two ternaries presenting the lowest freezing points and this can allow the design of interesting and cost-effective low melting mixtures.