Morphological and Microstructural Study of Heavy Metal Contaminant Retention in Dispersive Soils

Various adsorbents have been used for retention of heavy metal contaminants. However, natural dispersive soils and soil morphology have received little attention. The dispersive natural soil used in this study is a clayey soil with micro and nano-scale particles. Accordingly, the main objective of the present study is to investigate retention of heavy metal contaminants and the changes in the structure and morphology of dispersive soils exposed to environmental contaminants.
To achieve this objective, environmental and geotechnical tests were performed to investigate and to compare the interaction of natural dispersive soil, bentonite and kaolinite clay samples with lead and zinc. The retention of heavy metals by dispersive soil was investigated by X-ray diffraction, scanning electron microscope (SEM) images and energy dispersion spectroscopy (EDX) experiments.
According to the results, the retention capacity of natural dispersive soil is higher than that of bentonite and kaolinite, because of its morphology, dispersive structure and high percentage of carbonate. Although cation exchange capacity (CEC) of the natural dispersive soil is approximately 50% less than that of bentonite, retention of the heavy metal contaminant in this sample is more than 20% as compared with that of bentonite at high concentrations of heavy metals. Furthermore, the retention capacity of the natural dispersive soil is 2.3 times more than that of kaolinite sample. According to the results obtained in this paper, the orientation and structure of clay platelets strongly influence the retention of contaminant by clay samples.