Effect of Lead, Copper, and Zinc on Mechanical Properties of Compacted Bentonites

Abstract

The present research investigated the impact of heavy metals such as lead (Pb2+), copper (Cu2+), and zinc (Zn2+) on different bentonite’s characterization. Two types of bentonites, possessing a difference in physiognomies, were adopted for this objective. Interesting observations were extracted from the study; first, a decrement in the values of liquid limit (LL), swelling pressure (SPr), and swelling potential (SPo) was observed in both the bentonites. Also, a higher variability in the LL (36.3, 39.2, and 38.1% decrease), free swell (FS) (73.8%, 77.2%, and 80.0% decrease), and SPr (48.4%, 50.4%, and 54.4% decrease) was observed in presence of Pb, Cu and Zn for the bentonite with a higher LL, swelling capacity, specific surface area (SSA), cation exchange capacity (CEC), and montmorillonite content. Likewise, the time–swelling test confirmed a decline in the time consumed for primary swelling with a rise in heavy metal concentration. The void ratio–pressure study revealed lower void ratio values for samples with heavy metals than deionised (DI) water under any assigned pressure. On the other hand, this shrinkage in the void ratio was predominantly evident for Zn2+ and Cu2+ solutions, compared to Pb2+ solution. Furthermore, the compression index and time required for 90% of consolidation were found to vary inversely, whereas the coefficient of consolidation varied directly with the heavy metal concentrations. Finally, the unconfined compressive strength study at multiple concentration ranges (from 0 to 2,000 mg L−1) revealed a value higher than 200 kN/m2, the mandatory criteria for a liner material for application in landfills. The results obtained will aid in understanding the dynamics of heavy metals on the bentonites’ characterization.