Complex Dielectric Permittivity and Electrical Conductivity Measurements as a Diagnostic Tool for the Detection of Heavy Metals Adsorbed in Bentonite Samples

The adsorption of heavy metals (Pb and Ni) in raw Wyoming bentonite was investigated by means of broadband dielectric spectroscopy (BDS) in the frequency range 10 -2 Hz – 10 6 Hz and at elevated temperatures, up to 1000 o C. In order to reveal various aspects of data interpretation, different formalisms of analysis were investigated, namely, complex electrical conductivity, dielectric modulus and Cole-Cole diagrams of complex impedance. The presence of different states of bound water in pure and contaminated bentonite samples results to nonreproducible recorded spectra at room temperature and it is necessary to measure at higher temperatures in order to clarify their contribution to the overall dielectric response. The observed spectral differences between pure and contaminated samples in modulus formalism are attributed to the contribution of heavy metal ions to the conduction mechanisms, which are thermally activated. A non-Arrhenius behavior of dc-conductivity is observed during heating and subsequent cooling of pure and contaminated samples, suggesting different conduction mechanisms in each case.