Assessment of the influence of copper and zinc on the microstructural parameters and hydraulic conductivity of bentonites on the basis of SEM tests

The aim of this study was to determine the influence of potentially toxic metals, such as Cu(2+) and Zn(2+) ions, on the microstructural parameters of bentonites and their hydraulic conductivity (K), calculated based on the empirical formulas for clays according to Hazen-Tkaczukowa (formula 1 based on granulometric parameters) and Kozłowski et al., (2011) (formula 2 based on microstructural parameters). Metal ions influence the microstructure changes of bentonites, which can lead to changes in the geotechnical parameters that are used in empirical K formulas. The research was carried out on model clays (SWy-3, Stx-1b and Slovak bentonite), which were modified by introducing Cu(2+) or Zn(2+) ions into the structure. A significant dependence was observed between an increase in the Cu(2+) ion content in clay and an increase in the pore area. Therefore, the value of the hydraulic conductivity was estimated with the use of formula 2, which proved to be a useful tool for determining hydraulic conductivity in the case of bentonites contaminated with Cu(2+) ions. In contrast, the effect of Zn(2+) ions on the granulometric parameters was significant, and formula 1 proved to be useful tool for determining hydraulic conductivity in the case of bentonites contaminated with Zn(2+) ions. The results showed that the behavior of bentonites saturated with Cu(2+) and Zn(2+) ions differed. Therefore, the authors believe that the empirical formulas of the hydraulic conductivity of the clays saturated with potentially toxic metals should be based on the selected clay parameters dependent upon the nature of the ion.