Zero-valent iron for the in situ remediation of Antarctic contaminated sites

• Main Author: STATHAM, THOMAS
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: 2015
• Subjects: permeable reactive barrier; PRB; mass transfer; heavy metal; low temperature; contamination; Wilkes Station; ground water remediation; Antarctic; Casey Station; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/11343/51012

© 2015 Dr. Tom M. Statham To successfully remediate contaminated areas in Antarctica and other cold regions there is a requirement to develop suitable heavy metal containment and treatment technologies. Potential contaminant technologies for the remediation of Antarctic contaminated sites were assessed and the results indicate that a granular zero-valent iron (ZVI) permeable reactive barrier (PRB) is appropriate for the treatment of heavy metal contamination. This containment and ground/surface water treatment approach could complement either dig-and-haul or stabilisation/fixation remediation methods. A mass transport model was developed that accounts for (i) aqueous-phase dispersion processes, (ii) film diffusion of contaminant ions to the reacting surface and (iii) the reactive mechanism itself. Regression of a series of dynamic flow-kinetic experiments suggest that the removal of Cu2+ and Zn2+ ions would be controlled by mass transfer to a small reacting proportion of the iron oxyhydroxide surface area. Designing water treatment systems with contamination removal based on ZVI requires an understanding of the formation of a series of iron oxyhydroxides produced during corrosion of the thermodynamically unstable ZVI core. X-ray diffractometry (XRD) and geochemical modelling were used to investigate the mechanisms of copper and zinc removal and the formation of iron oxyhydroxides in batch experiments at 4 and 25 °C over 349 days. Copper removal was predominantly associated with a mineral product, which was unstable in an aerobic environment. Zinc and some copper were sequestered into the iron oxyhydroxide structure and did not redissolve when the pH was reduced. When located in a cold region exposed to freeze-thaw cycling, solution-media interactions may be detrimental to PRB performance. A laboratory based simulation of PRB performance was conducted within Darcy Boxes under freeze-thaw conditions. The reactive contaminants, Cu2+ and Zn2+ ions, were removed from the pore water during solution flow and freeze-thaw cycling. The retention time within the reactive media, assessed by a conservative tracer, decreased by 15–18% during the set first freeze-thaw cycling and remained constant then on during the set second freeze-thaw cycling. Agglomeration of particles was observed during an experimental freeze-thaw ZVI PRB simulation. However, there was no significant change in the hydraulic conductivity. The < 212 µm particles produced during the flow of solution and freeze-thaw cycling did not contain concentrated levels of the treated contaminant metals. Based on the laboratory results, a media sequence for the treatment of both hydrocarbon and heavy metal contamination was installed within an existing PRB at Casey Station, Antarctica. Results from two seasons of monitoring indicate that the media achieved a greater chemical phosphorus removal capacity when compared to previous Antarctic PRB designs. However, non-idea flow was observed during the second season. Geophysical studies and an excavator based subsurface site assessment were conducted to continue the development of a conceptual site model for the Wilkes Tip Site, a contaminated site in Antarctica. The potential remediation directions of this site were also discussed.