Impact of Heavy Metal and Carbonate on Geotechnical Properties of Sand-Bentonite Mixtures

A Sand-Bentonite Mixture (SBM) modified with carbonate was studied with various lead concentrations to examine the influences of soil contamination and carbonate modification upon the geomechanical properties of the mixture. Different geotechnical parameters were studied to accomplish the stated objectives, including compaction characteristics, unconfined compressive strength, consolidation properties, permeability behavior, and microstructural investigation. Further, batch adsorption tests were conducted to evaluate the lead retention of SBM. The results indicate that carbonate caused an approximately 25% and 5% increase in the optimum moisture content and maximum dry density in heavy metal-contaminated SBM, respectively. However, the impact of the lead and carbonate had an adverse impact on the results of permeability and unconfined compressive strength. It is observed that the compression coefficient (C-C) and consolidation coefficient (C-V) decreased and increased with the addition of lead contaminants, respectively. However, adding carbonate to the lead-contaminated SBM resulted in an increase and a decrease in the C-C and C-V, respectively. Also, the scanning electron microscope (SEM) images illustrated that carbonate-treated contaminated mixtures exhibited less tighter aggregations of particles than contaminated mixtures. As a result, modified contaminated soils with carbonate exhibited a less flocculated structure than the unmodified ones. From a practical perspective, the results indicate that the proposed carbonate treatment for heavy metal-contaminated SBM can enhance the performance of buffer liners. However, the remediated soil may not be suitable as a load-bearing material.