Impact of Nano-Clay on Consolidation and Permeability Behaviour of Bentonite in the Presence of Heavy Metal Contaminant

Recently، the study of nano materials in different fields of engineering science has been widely performed. In fact، the study on the behaviour of mixtures of nano material with other materials is among the new horizons in engineering research works. In this paper the impact of nanoclay on consolidation behaviour of bentonite in the presence of heavy metal contaminant is investigated. For this purpose، different percentages of nanoclay were mixed with bentonite and were additionally mixed with different concentrations of copper nitrate. Then، the odometer experiments performed on these prepared homogeneous samples in order to study the consolidation and permeability variations of samples. The results of this study show that the presence of industrial nanoclay causes an increase on the osmotic settlement of samples at the heavy metal concentrations up to 30 cmol/kg-soil of copper nitrate in comparison to the settlement of bentonite. Furthermore، the addition of industrial nano-clay to bentonite causes an increase in permeability of sample in comparison to the permeability of bentonite. This difference is more noticeable at high concentration of heavy metal. In addition، with an increase in external pressure، the permeability of bentonite sample and mixtures of bentonite/nanoclay gets closer to each others. This behaviour has been attributed to the presence of clay particles with nano dimensions in the mixtures of nanoclay-bentonite، the cation exchange capacity (CEC) and specific surface area (SSA) variations of samples due to the presence of nanoclay. In other words، according to the results of this study in the process of settlement of mixtures of bentonite and nano clay in the presence and absence of heavy metals the cation exchange capacity and specific surface area have the significant role. In this regard at the low concentration of heavy metals at the effective stress less than 100 kPa، cation exchange capacity governs the soil behaviour. However، at the effective stress more than 100 kPa، specific surface area is the governing factor which controls soil consolidation performance. Once the concentration of heavy metal increases in which it overcomes the soil buffering capacity، the heavy metals will neutralize negative charge of clay particles. Therefore، the cation exchange capacity of soil will have low effect on the settlement behaviour of soil. In such a case the specific surface area governs soil settlement process. For this reason due to the larger surface area of nano clays، the possibility for the secondary consolidation of soil increases.