Charge transport in diatomaceous earth studied by broadband dielectric spectroscopy

In the present work, broadband dielectric spectroscopy measurements in the frequency range of 10 mHz to 1 MHz and at elevated temperatures (room temperature up to 950 °C) were carried out in industrial diatomaceous earth samples, in order to study charge transport phenomena which play a key role to the transport of both organic and inorganic contaminants in this kind of minerals. Cole–Cole plots of complex impedance measurements may serve to distinguish the contributions of grain interior, grain boundaries and electrode polarization to the overall electrical behavior of diatomite. Complex electrical conductivity and electric modulus representations have been combined under the fulfillment of the BNN relationship over a wide temperature range, in order to investigate the temperature dependence of diffusion coefficients and concentration of charge carriers in thermally modified diatomite. Both diffusivity and mobility follow the same Arrhenius-type behavior at two distinct temperature regions as DC-conductivity does. The related activation energies were estimated and ascribed to proton conduction (Ea ≈ 1.00 eV) at low temperatures (T < 650 °C) and hopping conduction of small polarons (Ea ≈ 1.67 eV) at higher temperatures, due to the presence of transition metals in diatomite sample. The thermal treatment of diatomite at 950 °C enhances the available charge carriers and increases the diffusivity which might improve its adsorption capacity.