You are here:
Sensing the Presence and Transport of Engineered Nanoparticles in Saturated PorousMedia using Spectral Induced Polarization (SIP) Method
Citation:
Abdel, G. AND E. Atekwana. Sensing the Presence and Transport of Engineered Nanoparticles in Saturated PorousMedia using Spectral Induced Polarization (SIP) Method . To be Presented at Third International Conference on Engineering Geophysics (ICEG), Assiut, Egypt, EGYPT, November 15 - 18, 2015.
Impact/Purpose:
Laboratory column experiments were conducted to investigate the sensitivity of the spectral induced polarization (SIP) measurements to the presence and transport of Silver (Ag) and Zero Valent Iron (ZVI) nanoparticles with particle diameters of 90-250 nm in saturated quartz sand packed column. SIP measurements were obtained between 0.1 to 10000 Hz using the dynamic signal analyzer (DSA) National Instruments (NI) – 4461. The impedance magnitude |?| and the phase shift ? of the sample were measured relative to a high-quality resistor. The real (s¢) and imaginary (s²) parts of the sample complex conductivity were calculated. The first experiment measured the SIP response to the mixture of one pore volume of the nanoparticle suspension with the porous medium. The same procedure was repeated with the two nanoparticles using different nanoparticle concentrations (0-20 mg/ml). At frequencies above 1 Hz, the magnitudes of the phase and imaginary conductivity increased with increasing concentration of the nanoparticle concentration. The magnitudes of the phase and imaginary conductivity of the ZVI were two times the magnitude of the Ag. The transport experiment was conducted using a 12 mg/mL concentration nanoparticle suspension. A peristaltic pump with flow at 1 mL/minute was used to introduce the suspension into the sand columns. Effluent samples of the suspensions from the sand columns and SIP measurements were collected every five minutes for 180 minutes. The optical density of the nanoparticles in the effluent samples were determined at 430 nm wavelength using a spectrophotometer and then converted into concentrations using relationships determined from the linear correlation between concentrations of nanoparticle suspensions and their measured optical densities. A breakthrough curve (BTC) was obtained by plotting the normalized outlet nanoparticle concentration as a function of time. A similar procedure was followed for the SIP parameters. The BTC of normalized outlet Ag was higher in magnitude compared to the BTC of the normalized ZVI, suggesting retention of ZVI in the sand column was higher than Ag. Higher retention of ZVI was reflected in higher magnitudes for the normalized phase and imaginary conductivity component. Interestingly, the trend of the BTC of the normalized imaginary conductivity component was similar to the BTC trends of normalized outlet nanoparticle concentration. These results demonstrate the sensitivity of the SIP technique to nanoparticles and their transport in saturated porous media.
Description:
Nano-materials are emerging into the global marketplace. Engineered Nano-particles, and other throwaway nanodevices may constitute a whole new class of non-biodegradable pollutants of which scientists have very little understanding. Therefore, the production of significant quantities of nano-materials and their accidental introduction into the subsurface may pose a potential risk and hazard to the environment and public health which needs an urgent and exhaustive evaluation (Luque-Garcia et al. 2013). Nanoparticles are extensively used or tried for environmental remediation (Zhang et al. 2013), where information on their fate and impact is largely limited. Therefore, there is a demand to develop a technique that is sensitive to the presence and transport of these nanoparticles in the subsurface.Geophysical methods, specifically spectral induced polarization (SIP), have shown to be sensitive to the very small physiochemical changes that occur at the grain fluid interface and have been used to locate disseminated metallic mineral deposits (AbdelAal et al., 2014). The main objectives of the present study are to (1) investigate the sensitivity of SIP measurements to the presence of different concentrations of Ag and ZVI nanoparticles in saturated porous media and (2) assess the potential to use SIP measurements to monitor the transport of Ag and ZVI nanoparticles in the subsurface.