Low frequency electrical properties of zero valent iron: Implications for performance monitoring of permeable reactive barriers (PRBs).

摘要

The permeable reactive barrier is an in-situ remediation technology for groundwater contaminants. Long term performance monitoring of PRB is critical to the estimation of barrier efficiency.; Iron corrosion and mineral precipitation are recognized as the primary causes of barrier performance reduction and can serve as a proper indicator of barrier efficiency. Electrical signature is sensitive to iron corrosion processes. This thesis investigated the usage of geoelectrical methods to detect and/or monitor iron corrosion and mineral precipitation processes in barriers. This research revealed clear correlation between geoelectrical signatures and iron corrosion processes, and suggested the feasibility of using geoelectrical methods as a viable means for barrier performance monitoring.; In the first part of the research, electrical response of sand/iron mixtures under variable Fe0 concentrations and electrolyte chemistry was investigated. A linear relation between polarization and the surface area of Fe0 was revealed. This part also revealed the correlation between polarization, relaxation time and electrolyte activity, pH and valence.; The second part examined sensitivity of electrical signatures to iron corrosion and mineral precipitation induced with simple electrolytes. This research revealed an increase of complex conductivity in response to iron corrosion and mineral precipitation. This was attributed to the increase of complex interfacial conductivity and electronic conduction.; In the third part, I conducted electrical measurements on field cores. This investigation showed a significant increase in complex conductivity in reacted zones relative to non/minimally reacted zones within the cores. This experiment verified the sensitivity of electrical method to iron corrosion and mineral precipitation processes.; The last part of the research examines the control of precipitate mineralogy on electrical properties of laboratory columns. This experiment revealed contrasting electrical behaviors associated with iron oxides relative to carbonate precipitate, which was attributed to differences in mineral electrical properties. This result suggests that precipitate mineralogy is an important factor influencing electrical properties of corroded iron cores and must be considered when electrical methods are applied to monitor PRB barrier corrosion processes.