In order to reuse red mud and bauxite tailings mud (two typical aluminum industrial wastes) to reduce the occupation of land resources and environmental damage, these two wastes were combined to develop subgrade materials for the first time. With different combinations, the effects of the amounts of red mud, tailings mud, and cementitious materials on the strength of tested subgrade materials were investigated. The mechanism of strength growth was analyzed by a micro-test. The test results showed that the material strength of three combinations met the requirements when the unconfined compression strength (UCS) of all combinations increased with age. The UCS of the A₁BC₂ combination (the mass ratio of red mud and tailings mud was 2:1, the mass ratio of cement and quicklime was 1:1, and the mass ratio of waste and cementitious materials was 1:0.2) was the best, with the UCS being 3.03 MPa in 7 days. Microscopic imaging showed that specimens with high red mud contents had compact structures without cracks. The strength of these materials is mainly due to hydration reactions and pozzolanic reactions; the cementitious products generated by the reactions solidify Na⁺ and inhibit the release of OH⁻, while the addition of tailings mud can reduce the content of Na₂O in the material, which makes the environmental compatibility of the A₃BC₂ combination the best (the mass ratio of red mud and tailings mud was 1:2, the mass ratio of cement and quicklime was 1:1, and the mass ratio of waste and cementitious materials was 1:0.2). Its pH value was 8.75. This experiment verifies the feasibility of the combined application of red mud and tailings mud in subgrade materials. To this end, a feasible scheme for the simultaneous consumption of these two kinds of aluminum industrial wastes has been proposed.

In order to effectively utilize aluminum industrial waste—red mud and bauxite tailings mud—and reduce the adverse impact of waste on the environment and occupation of land resources, a red mud–bauxite tailings mud foam lightweight soil was developed based on the existing research results. Experiments were conducted to investigate the mechanical properties and microscopic characteristics of the developed materials with different proportions of red mud and bauxite tailings mud. Results show that with the increase in red mud content, the wet density and fluidity of the synthetic sample was increased. With 16% red mud content, the water stability coefficient of the synthetic sample reached its maximum of 0.826, as well as the unconfined compressive strength (UCS) of the sample cured for 28 d (1.056 MPa). SEM images reveal that some wastes of the sample without red mud were agglomerated, the peripheral hydration products were less wrapped, and when the amount of red mud was 16%, the hydration products tightly wrapped the waste particles and increased the structural compactness. The final concentration of alkali leaching of samples increased with the addition of red mud. The maximum concentration of alkali leaching was 384 mg/L for the group with the addition of red mud of 16%. Based on the obtained mechanical strength and alkali release analysis, the sample B24R16 was selected as the optimum among all tested groups. This study explored a way to reuse aluminum industrial waste, and the results are expected to be applied to roadbed and mining filling.

In this study, the vertical migration and release characteristics of alkali and fluoride in Bayer red mud with different compaction degrees were investigated by conducting constant head vertical leaching tests. The experimental results showed that the breakthrough time of leaching liquid across the red mud column increased with the increase of compaction degree, the alkali and fluoride concentrations of the leaching outflow decreased fast as the compaction degree of red mud column increased, as well as the time required to reach the leaching equilibrium. Moreover, for all the leaching red mud columns, the cumulative release of alkali and fluorine from the increased with the increase of leaching durations. However, the total release of major pollutants decreased with the increase of red mud compactness. After leaching, the soluble alkali and water-soluble fluorine (Ws-F) residual in the red mud gradually increased from top to bottom along the leaching column, and at the identical depth, the higher the compactness of the leaching column, the greater the soluble alkali and water-soluble fluorine (Ws-F) remaining in the column after leaching. These phenomena indicated that improving the compactness can effectively slow down the release of main pollutants in the red mud. The results were expected to provide a scientific basis for the prevention and control of alkali and fluoride pollutants in red mud yard.