Study on the Characteristics of Red Mud-Lime Solidified Cadmium and Lead Heavy Metal Contaminated Soil

In order to realize the reuse of solid waste red mud and solve the problem of high lime emission, it is proposed to use red mud and lime to solidify/stabilize heavy metals, cadmium, and lead-polluted soil. The unconfined compressive strength, toxic leaching, scanning electron microscopy, and X-ray diffraction tests were carried out on cadmium and lead cured contaminated soil to explore the effects of different types of stabilizers, pollutant concentrations, and curing ages on the compressive strength and heavy metal leaching concentration in stabilized soil. The changes of microstructure and mineral composition were analyzed. The results show that: The addition of red mud-lime could significantly improve the compressive strength of contaminated soil and reduce the leaching rate of cadmium and lead. Under non-polluted conditions, the red mud-lime ratio of 4:6 with a curing period of 28d resulted in the highest strength. The strength of solidified soil increased first and then decreased with the concentration of pollutants, and the addition of a small amount of pollutants could increase the strength. Brittle failure was more likely to occur after adding lime. The leaching concentration of cadmium decreased while that for lead initially decreased, then increased with an increase in lime content. The pH value of contaminated soil increased with the increase of the proportion of lime in the curing agent. The main product of red mud-lime solidification contaminated soil was C-S-H, which filled the soil pores to form a dense spatial structure. With the increase of lime content, the products increased significantly. The reaction was inhibited at high pollutant concentration, leading to fewer products being formed.