Date of Award

5-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Environmental Engineering and Science

Committee Member

Dr. Stephen Moysey, Committee Chair

Committee Member

Dr. Brian A. Powell

Committee Member

Dr. Kevin T. Finneran

Committee Member

Dr. Delphine Dean

Abstract

Spectral induced polarization (SIP) has become a popular and useful tool for minimally-invasive monitoring of subsurface bio/geochemical processes due to its high sensitivity to the surface chemical properties of rocks and soils. However, it is not clear what mechanisms affecting the electrical properties of a porous medium, especially those leading to alteration of the pore space and mineral surfaces are responsible for the observed polarization in electrical signatures. A general objective of this work, therefore, is to test grain polarization mechanism as one of the controversial theories explaining the polarization observed in SIP measurements. In this dissertation I post several hypotheses around this issue related to physical versus chemical and biological modifications of mineral surfaces within a porous media and setup a series of experiments to address these questions. The first part of this dissertation investigates the effect of fundamental physical changes to the surface properties of porous media on SIP signals, including coating the surfaces with iron oxide and calcium carbonate (induced by abiotic and biotic processes), and etching the grain surfaces. The changes have the potential to alter the area, roughness and ion density of surfaces. And the SIP measurement has successfully detected distinct different electrical signals for heterogeneities present on grain surfaces. The second part of this dissertation is focused on testing how SIP signals respond to changes in the chemical state of a mineral surface, specifically to the surface ion adsorption on charged grain surfaces. Grain polarization is one of controversial mechanisms describing the stern layer ions polarization phenomena when grain is under electrical filed, which is therefore closely related to the electrical double layer theory, i.e., migration of ions distributed within both the tightly-bound Stern layer and loosely-bound diffuse layer may contribute to the complex conductivity signals. Modifying surface adsorption processes, e.g., by changing the dominant ion in solution or modifying the pore water pH, provides a means to investigate the role of surface chemistry on the SIP measurement in detail. The third part of this dissertation investigates a novel approach for evaluating the surface polarization at the scale of a single grain by using AFM measurement. A charged AFM tip is made closely to surface of grain particle which is applied by an AC current in an electrolyte solution, the deflection response of the tip is evaluated which could provide direct information about charge polarization of the surfaces. And initial promising results show us consistent response on AFM tip deflection force on sample and control samples. Further investigation and efforts will be needed to experimental methodology and data interpretation. Through investigation of the mechanisms and applications of SIP measurement in this dissertation, we have learned the main mechanism controlling electrical responses during surface ion adsorption process is stern layer polarization, and also found SIP may be capable to monitor the mass transfer process between mobile and immobile domains. In summary, the overall objectives for understanding SIP mechanisms are successfully achieved, but the SIP signals associated with biological activities need to be further investigated in future study.

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