Thermochemical heat storage and optical properties of red mud/Mn co-doped high alumina cement-stabilized carbide slag in CaO/CaCO3 cycles

CaO/CaCO3 thermochemical heat storage has been considered as a competitive technology in concentrated solar power plants. Carbide slag and red mud are solid wastes from the chlor-alkali industry and aluminum industry, respectively. In this work, the red mud/Mn co-doped high alumina cement-stabilized carbide slag was synthesized for CaO/CaCO3 heat storage. The effects of the addition of high alumina cement and red mud/Mn on the heat storage capacity, cyclic stability, and optical absorption of the modified carbide slag were investigated. The modified carbide slag exhibits excellent heat storage capacity and optical absorption. The Ca3Al2O6 and CaMnO3 inhibit the growth of CaO grains. FeMnO3 and Ca2Fe2O5 possess high optical absorption properties. The additions of Mn and red mud enhance the heat storage rate and basicity of the carbide slag. The effective conversion of the modified carbide slag is 0.62 after 30 cycles, which is 3.1 times as high as that of the untreated carbide slag. The modified carbide slag reaches the optical absorptance of similar to 58%, which is 6.5 times as high as that of the untreated one. Thus, the red mud/Mn co-doped high alumina cement-stabilized carbide slag is a potential candidate for the CaO/CaCO3 heat storage system.