Effect of heavy metal contamination on the plasticity of kaolin-bentonite clay mixtures and an illite-smectite rich natural clay

Abstract

The behaviour of soil is complex in a natural environment. Contamination of soil with organic and inorganic contaminants may change the properties of soil. Recent studies have shown that the heavy metal contaminants affect the plasticity and consolidation behaviours. However, little is known about the effects of heavy metals on the behaviour of different types of clay, especially how clay behaves when multiple heavy metals are present in clay. The paper will present results from tests on the effect of three different heavy metal ions used separately, and mixed together in combinations, on the liquid limit (wL), plastic limit (wP) and plasticity index (PI) of kaolin, bentonite, mixtures of kaolin and bentonite and reconstituted Lucera clay. It is found that plasticity index of bentonite is reduced significantly with the addition of heavy metals while PI increases slightly in kaolin. A 1:1 clay mixture of kaolin and bentonite showed significant reduction, while reconstituted Lucera clay has shown small reduction with the addition of heavy metals. It is found that at higher concentrations of copper and zinc cations, the effect takes reverse trend on the liquid limit of kaolin and similar behaviour was observed on the bentonite at higher concentrations of lead ion. Interestingly, lead ion exhibited a significant effect on the plasticity of bentonite when tested with NaCl solution as pore fluid.