Reactivity evaluation of red mud as a raw material for cementitious materials: The dissolution characteristics and kinetics of Si and Al

• Three typical mineral phases in TARM was found using the BSE-IA method. • The dissolution process and dissolution kinetics of Si and Al in TARM were cleared. • The reactivity improvement of TARM by the alkali and sulfate system was verified. • The dissolution process of Si and Al was controlled by the internal diffusion. This work evaluated the reactivity of various phases in thermally activated red mud (TARM) in OH - solution, OH - and SO 4 2- complex solution based on BSE-IA-EDS, SEM-EDS and XRD, and provided the dissolution kinetics of Si and Al in TARM. The relationship between the physicochemical properties, dissolution behavior, and reactivity of the Si and Al structure in TARM were revealed. The results showed that TARM has three typical mineral phases, and the dissolution order is Ca-Al-Na-Si phase > Ca-Si-Al phase > Fe phase. The dissolution process of Si and Al in TARM is mainly controlled by internal diffusion process, which is most affected by temperature. The OH - and SO 4 2- complex solution have a significant synergistic effect on the dissolution of Si and Al from TARM. The SO 4 2- further dissolves TARM particles mainly by changing the gel property wrapped on the particle surface in OH - environment. This work found and verified that the OH - and SO 4 2- system can significantly improve the reactivity of TARM, which provides a reference for the investigate of TARM as a raw material for cementitious materials.