Insights into active and passive carbon sequestration and causticity reduction in hazardous red mud slurry

Batch experiments were conducted to collect data for obtaining insights into the chemical mechanisms and kinetics of red mud neutralization by both atmospheric (passive treatment) and injected CO 2 (active treatment) in the absence and presence of gypsum. Active treatments allowed effective sequestration of CO 2 within 1 h. A mixing ratio of gypsum to red mud at 0.04–0.06 enabled effective control of pH rebound, completely eliminating the causticity of the red mud by reducing the pH value of red mud to