Preparation and characterisation of sodium nitrate/stone-sawing mud shape-stabilized phase change materials for medium-high temperature thermal energy storage

Stone-sawing mud (SSM) is a solid waste generated during stone processing, with a presently estimated global production of 30 million m 3 . SSM is usually disposed of in the stone yard, occupying a large area of land and causing serious dust and water pollution. In this study, a novel shape-stabilized composite phase change material (ss-CPCM) containing SSM loaded with NaNO 3 was prepared using the mixing and sintering method for medium-high temperature thermal energy-storage applications. The ss-CPCM retained 50 wt% NaNO 3 without leakage. X-ray diffraction analysis showed good chemical compatibility between the SSM and NaNO 3 , and microscopy analysis demonstrated that NaNO 3 was uniformly distributed within the SSM structure. The compressive strength of the ss-CPCM reached 23.14 MPa. The melting temperature and latent heat of the ss-CPCM are approximately 306.78 °C and 79.86 J·g −1 , respectively, and no significant variations are observed after thermal cycling. The energy storage density of the material is 444.86 J·g −1 in the range of 50–400 °C, and its thermal conductivity is 0.696 W (m·K) −1 . Furthermore, the thermal conductivity of the composites reached 2.421 W (m·K) −1 with the addition of 10 wt% of graphite. Hence, the NaNO 3 /SSM ss-CPCM is considered a promising material for waste heat recovery, thereby providing a valorisation method for the resource utilisation of SSM.