Abstract: Red mud is a solid waste residue from the production of alumina, which is highly alkaline and produced with huge amount. In this study, red mud was used as an alkaline activator combined with fly ash and ground granulated blast-furnace slag (GGBS) to solidify/stabilize cadmium contaminated soil. The unconfined compressive strength, shear characteristics, heavy metal leachability and microstructure of the samples cured for 7, 14 and 28 days were studied. The results show that: Cadmium ions in soil reduce the strength of soil, and the strength of soil increases after the addition of red mud, GGBS and fly ash; the initial concentration of cadmium ions affects the strength of red mud-based solidified soil. When the initial value is higher than the critical concentration value, the soil strength begins to decrease gradually; the increase of cadmium concentration in soil reduces the shear strength and cohesion of soil and increase the friction angle. Compared to red mud-fly ash, red mud-GGBS has higher unconfined compressive strength and lower heavy metal leaching concentration.

Key words: red mud, contaminated soil, solidifying/stabilizing, unconfined compressive strength, shear strength, leaching