Low-Temperature Micro-Oxidation-Driven Synergistic Dealkalization and Soil Reconstruction of Red Mud with Coal
Red mud, a highly alkaline industrial solid waste from alumina production, poses severe environmental risks due to its high alkalinity, low organic matter content, and poor aggregation, which critically impede its soil reconstruction and ecological utilization. This study proposes a novel approach of low-temperature micro-oxidation to drive the synergistic soil reconstruction of red mud and coal. By constructing a low-temperature micro-oxidation atmosphere, the soil properties of the reaction products were investigated, the decomposition and reconstruction of alkaline minerals and alkali release were analyzed, and the oxidation of carbon-based minerals and organic matter transformation in coal were examined. The mechanism of the synergistic reaction between red mud and coal under low-temperature micro-oxidation was elucidated. Results showed that at 250 °C under micro-oxidation, the pH of the product decreased to 8.47, organic matter content increased to 12.98%, and the proportion of aggregates >0.250 mm increased. Alkaline minerals such as cancrinite and grossular in red mud underwent decomposition and reconstruction in the low-temperature hydrothermal environment, releasing substantial free alkali. The condensed aromatic rings of carbon-based minerals in coal were oxidized by free radicals, leading to ring-opening and bond cleavage, producing small-molecule organic acids and macromolecular humic acids. The continuous oxidation of carbon-based minerals in coal generated acids, which neutralized the alkali released from red mud, driving sustained dealkalization. The inorganic particles of red mud flocculated with macromolecular humic acids, forming micro-aggregates and significantly improving soil properties. This research provides technical support for the rapid ecological utilization of red mud at industrial scale.