Nano-scale Zero Valent Iron Research

1. Introduction

In the past, liquid wastes were frequently pumped directly into the ground or allowed to migrate into the ground from leaky storage ponds with no recognition of the likelihood that these wastes could persist in the subsurface for decades, potentially contaminating drinking water sources. Non-aqueous phase liquids (NAPLs) are one class of waste liquids that were commonly disposed of improperly and are the focus of this proposal. The origin of these contaminants is typically waste mixtures containing surfactants, chlorinated hydrocarbons and other compounds generated in various industrial processes. Chlorinated solvents, a particularly persistent NAPL contaminant, frequently contaminate water sources for decades and are one of the more common contaminants at brownfield and industrialized sites.

Synthesizing iron nano-particles

Although considerable advances in our understanding of the phenomena governing NAPL remediation have been made and a number of innovative remediation technologies have been developed, such as steam and brine flooding or density modified displacement, existing technologies are rarely able to achieve clean up goals in contaminated aquifers at the completion of remedial activities. The problem relates to the inability of existing remedial technologies to remove sufficient NAPL mass in the subsurface to significantly reduce aqueous phase concentrations. The decision to remediate contaminated aquifers is therefore still a source of considerable debate despite over two decades of active research and development. The development and pilot scale testing of new and innovative remediation technologies is, therefore, crucial to achieve clean up goals at contaminated sites and ensure an abundant source of safe water for future generations of Canadians.

Zero valent iron (ZVI) is a strong reductant for chlorinated solvents, and can transform chlorinated solvents into benign end products. The original applications of micron scale ZVI was in permeable reactive barriers for prevention of off-site migration of groundwater contaminated with chlorinated solvents and metals. Recently, with the growing interest in nanotechnologies, the potential for injection of nano-scale zero valent iron (nZVI) particles for in situ remediation of groundwater has been recognized. A number of priority source zone pollutants, including chlorinated ethanes, polychlorinated biphenyls, chlorinated methanes, heavy metals, arsenic, and perchlorate have all been successfully treated in laboratory studies using nZVI. The large reaction rates afforded by a higher surface area and small size allow nZVI to be utilized in difficult, deep aquifer remediation sites where there are limited remediation options. Field application of nZVI has the potential to be highly effective for treatment of groundwater contaminated by chlorinated compounds. The application could be alone or in combination with simultaneous or sequential stimulation of biodegradation. Pneumatic or hydraulic fracturing or electrokinetics may also be used to enhance movement of nZVI in low permeability soils to achieve effective treatment of groundwater contamination.

Brownfield site clean-up in Sarnia, Ontario