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 m3. 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 NaNO3 was prepared using the mixing and sintering method for medium -high temperature thermal energy-storage applications. The ss-CPCM retained 50 wt% NaNO3 without leakage. X-ray diffraction analysis showed good chemical compatibility between the SSM and NaNO3, and microscopy analysis demonstrated that NaNO3 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 degrees 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 degrees 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 NaNO3/SSM ss-CPCM is considered a promising material for waste heat recovery, thereby providing a valorisation method for the resource utilisation of SSM.