Study on the wet carbonation characteristics and carbon sequestration mechanism of red mud within 0 mm to 0.45 mm

Red mud, as an alkaline solid waste, can achieve CO₂ mineralization and storage through carbonation reactions.To investigate the wet carbonation characteristics of Bayer process red mud under the three factors of liquid-solid ratio, temperature, and CO₂ flow rate, and to evaluate the carbon sequestration performance under various conditions, the loss on ignition and variation in pH value of the carbonated red mud were used as criteria to evaluate its carbon sequestration capacity.Kinetic fitting was applied to analyze the influence of different variables on the carbonation modification of red mud.The evolution patterns of carbonation products in red mud were investigated using techniques such as XRD, FT-IR, N 2 adsorption, and SEM, and the mechanism of wet carbonation in red mud was explored.The results show that under the optimal conditions of a liquid-solid ratio of 2.0∶1, a CO₂ flow rate of 100 mL/min, and a reaction temperature of 30 ℃, the carbon sequestration rate of red mud can reach 5.68%, while the pH value of the red mud slurry gradually decreases from 9 and stabilizes at 6.45.Kinetic fitting results indicated that the degree of influence of variables on carbonation modification followed the order: liquid-solid ratio > CO₂ flow rate > temperature.Characterization of carbonation products revealed an increase in the content of cancrinite and CaCO₃.This is attributed to the participation of hydrogennet and AlO(OH) in the red mud during the carbonation modification process, releasing Ca²⁺, Na⁺, and OH^-.Some Ca²⁺ reacted with CO₂ dissolved in water to form CaCO₃, while the remaining Ca²⁺, Al³⁺, and Na⁺ served as ion sources for the formation of cancrinite.Additionally, the carbonation reaction corrodes the alkaline minerals in red mud and generates carbonation products, resulting in an increased specific surface area of carbonated red mud compared to uncarbonated red mud.