Phase-reconstructed iron-tailings skeletons for shape-stabilized Na2SO4-NaCl high-temperature thermal energy storage

A novel waste-based CPCMs was prepared for high-temperature (≥600 °C) LHTES； • Waste-modified iron tailings eliminate chemical incompatibility with salts； • CPCMs achieve 50 wt% salt loading and exceptional strength (105 MPa)； • Thermal conductivity boosted to 1.48 W/m K, ∼2.5 times that of pure salt； • Simulation reveals optimal flow velocity (0.1 m/s) for energy efficiency. The inherent chemical incompatibility between iron tailings and molten salts severely hinders the high-value application of iron tailings in high-temperature latent heat thermal energy storage (LHTES), as it triggers composite structural failure and performance degradation. This study develops an innovative strategy to fabricate modified iron tailings as supporting skeletons for shape-stabilized Na 2 SO 4 -NaCl composite phase change materials (CPCMs) working above 600 °C. This modification effectively suppresses undesirable phase transformations and eliminates chemical incompatibility, enabling 50 wt% salt loading without leakage. Benefiting from the densified microstructure, the as-prepared CPCMs manifest outstanding mechanical robustness, achieving exceptional compressive strengths of 105 MPa and 94 MPa for steel slag- and red mud-modified variants, respectively. Thermophysically, the CPCMs exhibit suitable melting points of 636–637 °C and latent heats of 81–83 J/g with enthalpy attenuation rigorously restricted within 5–10%. Notably, the interconnected modified iron tailings skeleton establishes continuous thermally conductive pathways, significantly boosting the thermal conductivity to 1.35–1.48 W/m·K (≈2.5 times that of the pure eutectic salt). Furthermore, the CPCMs demonstrate remarkable long-term cycling stability in terms of mass retention, structural integrity, and latent heat preservation. A packed bed LHTES device based on prepared CPCMs is also proposed, and numerical simulations reveal that an inlet flow velocity of 0.1 m/s optimally coordinates the system output power and steam production efficiency. This work thus provides a pioneering paradigm to synergistically resolve the compatibility and mechanical bottlenecks of solid waste-based CPCMs, advancing the sustainable and high-value utilization of iron tailings in high-temperature LHTES systems. Graphic abstract Download: Download high-res image (167KB) Download: Download full-size image