Influence of Potential Determining Ions on the Microstructural Performance and Contaminant Adsorption of a Homoionic Illitic Clay

Abstract

Contaminant adsorption properties of clays are markedly influenced by the type of clay minerals, the nature of the exchangeable ions, and the type of clay microstructure present. Clay soils, due to their high buffering capacity and low permeability, are very helpful materials as barriers in waste disposal projects. On the other hand, the different microstructures of clay soils, due to their different surface areas and the different quantity of these surfaces exposed to the water, cause different contaminant attenuation levels for clay minerals. Even though the dispersive structures of soils might cause some geotechnical problems, in geo-environmental projects they might be of use as an excellent contaminant absorbent due to the fact that their clay particles are well-exposed to the soil pore fluid. The present study investigates the role of various types and concentrations of pore fluid on the microstructure and contaminant adsorption of illite. A series of pH measurements, a turbidity experiment, an XRD analysis, batch equilibrium testing and soil adsorption evaluation were performed to achieve the aforementioned objective. Homo-ionic illite mineral was prepared and some experiments were performed on it to support the findings. The results of this study show that although the theoretical calculation of the double layer theory does not take into account the effect of different anion types on the variation of the thickness of double layer, the anion type has a major impact on the microstructure variations of clay minerals. In addition, the turbidity measurement and the monitoring of XRD peak intensity of the major basal spacings of illite are appropriate tools for evaluating its dispersivity behaviour. It is shown that the PDI treated illite has more capacity for adsorption of heavy metal contaminant than that of illite or Ca–illite. It is concluded that the observed geo-environmental behaviour is noticeably a function of changes in the microstructure of illite.