Preparation sequences and pretreatment optimization of alkali-activated red mud and blast furnace slag-based materials

The preparation of alkali-activated materials from red mud for building materials is a promising way to solve the environmental pollution caused by red mud. However, the low compressive strength of alkali-activated red mud-based materials is the biggest obstacle to this solution. In this paper, we illustrate that the compressive strength of alkali-activated red mud and blast furnace slag-based materials is strongly influenced by the modulus of sodium silicate, preparation sequence, and calcination pretreatment. Thus, the best sodium silicate modulus (1.0) and optimized preparation sequence that involved using a cooled sodium hydroxide solution mixed with the red mud-blast furnace slag mixture before exposure to the sodium Csilicate were adopted. Then the calcination pretreatment of the red mud, gypsum, and lime was adopted to improve the compressive strength, and the optimal calcination temperature was selected to be 700 °C. The increase in the compressive strength (up to 71.82 MPa) resulted from a large number of active particles, which were generated by the fracture of numerous Si–O bonds and Al–O bonds after the calcination pretreatment. The results support the extensive utilization of red mud in building materials to prevent environmental pollution.