Experimental study on solidification of Cu(II)- contaminated soil using red mud with cement and Ca(OH)₂

Red mud is a waste product generated by the aluminum industry and its presence has significantly damaged the environment. Interestingly, red mud has some desirable adsorptive properties and can solidify heavy metal ions. Moreover, after processing, red mud has certain cementing properties that have a positive influence on the curing effect of red mud cement-treated soil. This study examined different ratios of red mud, cement and Ca(OH)2 by testing the electrical resistivity and unconfined compressive strength of various soils. The resistivity test indicates that the electrical current frequency has a great influence on the test results. It is recommended that a current frequency between 1 and 50 kHz is used in a resistivity test. The study also indicates that, with increasing Cu²⁺ content, conductive tunnel effect occurs. However, when the ratio of curing agent and content of Cu²⁺ are different, the time causing the conductive tunnel effect varies. The unconfined compressive strength of different cement-to-soil ratios decreases with increasing Cu²⁺ content and the reduction extent is related to that ratio. Lastly, the study results suggest a good linear relationship between unconfined compressive strength and electrical resistivity, which is dependent on the specific ratio of contaminating materials.