Red mud-molten salt composites for medium-high temperature thermal energy storage and waste heat recovery...

Red mud (RM) is an industrial waste of the aluminum industry with presently estimated worldwide legacy-site stockpiles of 4 billion tones. RM is typically disposed in the sea, dams or dykes, posing a significant environmental hazard due to its high alkalinity and traces of heavy metals. Despite recent valorization efforts, only 15% of RM deposits are currently utilized. In this work, a novel use of RM to formulate composite phase change materials (CPCMs) is proposed. The CPCM is formulated by milling nitrate salts with RM, compressing and subsequent sintering of the two. Overall good performance over the temperature range of 25-400 ℃ is observed. Maximum latent heat of the CPCMs is 58 J/g, while average thermal conductivity and C_p are in the range of 0.77-0.83 W/mK and 1.03-1.31 J/g ℃, respectively. No variations in the melting point or latent heat are observed after 48 cycles. Energy storage density is calculated to be up to 1396 MJ/m³. The working temperature of this novel CPCM make it ideal for waste heat recovery of medium-high temperature waste heat streams providing a valorization pathway and valorization for RM as a by-product for energy-related applications.