Effect of Heavy Metal Contamination on the Compressibility and Strength Characteristics of Chemically Modified Semiarid Soils

Abstract

Rapid industrialization in developed countries has led to a continuous release of heavy metals into the environment. When these effluents are discharged directly into natural surrounding soils, not only is the geotechnical behavior altered but the natural surface and subsurface waters become contaminated. In this study, experiments are conducted to examine the unconfined compressive strength (UCS) and compressibility behavior for two semiarid soils exhibiting different mineralogy spiked with selected heavy metals (As3+, Cr6+, Cu2+, Hg2+, Pb2+, and Zn2+) and their relative immobilization levels in the presence of a binder. Removal efficiencies of selected metal ions were estimated by performing desorption tests using different extractants [acetic acid (H3COOH), nitric acid (HNO3), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA)]. Analytical grade lime was used as a binder and the concentrations of spiked metal ions were maintained at 50 and 100 ppm respectively. The variations in electrical conductivity and pH for both soils spiked with selected metal ions were evaluated for the control case (absence of lime) and lime treated case and have been related to the compression behavior. Results from this study reveal that the UCS values of both soils increased for the control and lime treated cases. The compression behavior of the selected soils exhibited contrasting behavior with an increase in compression index (Cc) values for soil A and a decrement for soil B when spiked with selected metal ions. The desorption studies revealed higher removal efficiencies for EDTA compared with other extractants.