Mechanical behavior of copper-contaminated soil solidified/stabilized with carbide slag and metakaolin

Abstract

Different doses of carbide slag and metakaolin are used to solidify/stabilize copper-contaminated soil in accordance with its degree of contamination. This paper presents some experimental findings on the physical and chemical properties of the treated soil, including unconfined compressive strength, stress–strain state and pH, explained by series chemical and mineralogical reactions in the solidified/stabilized soil. Results showed that the unconfined compressive strength decreases and the failure strain increases with the copper ion concentration in the soil increasing. Additionally, the failure mode of the soil gradually changed from fragile failure to plastic failure. Increasing the amount of carbide slag favored improvements in unconfined compressive strength, yet decreased the failure strain. Furthermore, the pH of the soil decreased from 8.22 to 4.36 with the initial concentration of heavy metal in the contaminated soil increasing. High concentrations of Cu2+ react with OH− in pore solutions to form complexes like [Cu(OH)4]2– to decrease alkalinity in the soil. Additionally, under certain conditions, the reaction of carboxyl (–OH) and hydrated groups (–OH2) with Cu2+ release H+, which will also reduce the pH value in the soil. However, when the carbide slag content increased from 5 to 15%, the pH increased significantly, up to 10.5, demonstrating the beneficial effect of the industrial waste carbide slag in solidifying/stabilizing the copper-contaminated soil.