THE SPECTRAL INDUCED POLARIZATION (SIP) RESPONSE OF NANOPARTICLES IN PARTIALLY SATURATED ENVIRONMENT

Nano-materials are emerging in the global marketplace and the accidental introduction of these nano-materials to the environment may pose a potential risk and hazard to the environment and public health which demand the development of techniques to detect their presence and transport in the subsurface. Geophysical methods, specifically spectral induced polarization (SIP), have shown to be sensitive to the presence of subsurface contaminants. Laboratory experiments were conducted to investigate the SIP response of two common nanoparticles [silver (Ag) and zero valent iron (ZVI)] with particle diameters of 90-250 nm in a sand column under different nanoparticle concentrations and moisture content. A 0.2% agar solution and fine silica sand were used. SIP measurements were obtained between 0.1-10000 Hz using the dynamic signal analyzer (DSA) National Instruments (NI) – 4461. The impedance magnitude and the phase shift of the samples were measured and the real and imaginary parts of the sample complex conductivity were calculated. The first experiment was performed under fixed moisture content (15%) using the agar solution and variable concentration (0-10 mg/ml) of the nanoparticles. The agar solution-nanoparticle-sand mixture was packed into the sample holder and SIP measurements were obtained. The results show that the magnitude of the phase and imaginary conductivity component increases with increasing concentration of nanoparticles with ZVI being higher in magnitude than Ag by ~40%. However, insignificant changes were observed for the real conductivity component. The phase and complex conductivity spectra of the two nanoparticles show well-defined relaxation peaks that shift from 100 to 1000 Hz as nanoparticle concentrations increase. The second experiment was performed with a fixed concentration of the nanoparticles and different moisture content (5-20%). The background measurements without nanoparticles show that the SIP parameters increase linearly with increasing moisture content. Adding the nanoparticles elevated the magnitude of the SIP parameters with ZVI showing the highest values. Our results demonstrate that the SIP method is very sensitive to the presence of nanoparticles in the vadose zone which potentially could be used in guiding the remediation processes of such contaminants.