Industrial waste salt resource utilization: construction and performance optimization of molten salt-ceramic composite thermal storage materials

Based on the urgent requirements for medium- and high-temperature thermal energy storage materials of solar thermal power generation technology and resource utilization of industrial waste salts, this study presents an eco-friendly strategy for preparing a molten salt-ceramic composite thermal energy storage material. Industrial waste salts (MgCl₂·6H₂O, KCl) were used as raw materials, mixed with glass powder and pre-sintered at low temperature to remove organic impurities through eutectic melting. Subsequently, the derived material was mixed with MgO, pressed into tablets, and then subjected to secondary high-temperature sintering in diatomite to construct a composite phase change material with a silicon-containing surface (C/KMg-D). Characterization results show that the effective content of the binary chloride salt (KMg-Cl) in C/KMg-D reaches 50.21 wt%. The melting point and latent heat of the prepared material are 433.5 °C and 141.72 J/g. The silicon-containing surface formed during diatomite-embedded sintering significantly enhances hygroscopic stability. After 48 h under high-humidity conditions, the mass increase is only 12.64 wt%, representing a 69.7% reduction compared with that of the unembedded samples. After 50 cycles, the mass loss rate of C/KMg-D is only 4.09 wt%, and XRD analysis confirms the stability of the crystal structure. The total thermal energy storage density of C/KMg-D is calculated to be 649.97 J/g within the temperature range of 25 °C to 500 °C. While addressing the challenge of industrial waste salt treatment, C/KMg-D demonstrates excellent thermal energy storage capacity, cyclic stability, and environmental adaptability, providing a low-cost, high-performance solution for the utilization of industrial waste salts in solar energy storage systems.