Formatted Title

The Diversity of ZVI Formulations and Applications

Background/Objectives

The application of granular zerovalent iron (ZVI) to form permeable reactive barriers (PRBs) is a well-established remedy for groundwater sites contaminated with trichloroethylene (TCE) and other chlorinated solvents. However, during the ~30 years since this technology was developed there have been many efforts to diversify the technology to include other types of amendments, deployed in other configurations, and/or to target other types of contaminants. Most of these efforts have had modest impact, in part because it can be hard to assess the benefits compared with the cost vs. established remedies. However, when there are no established or even viable remedies, the incentives for innovative variations on ZVI/PRBs become more compelling.

Approach/Activities

We have been involved in many efforts to develop or evaluate innovative variations of ZVI/PRBs, including formulation of ZVI that is nano-sized, doped with catalytic metals, coated with organic polymers, supported by activated carbon, sulfidated and/or nitridated, etc. In order to make quantitative comparisons among the performance of these variations, we have developed several metrics, calculated and compiled them as data, and analyzed these results for significant differences or trends. In some cases, the benefits to innovative formulations arise not so much with increased rates of contaminant degradation, but via other enhancements such as decreased rates of water reduction and therefore increased longevity and overall efficiency of the process. However, it appears that the biggest innovations arise from the need to treat emerging contaminants where ZVI-based reductants are inadequate. Two examples of this will be featured: (i) zerovalent zinc (ZVZ) for dechlorination of polychlorinated alkanes like 1,2,3-trichloropropane (TCP), and (ii) zerovalent magnesium (ZVMg) for defluorination of perfluoroalkyl substances (PFAS). In both cases, the parent contaminants show little if any reactivity with most forms of ZVI, but fairly rapid and deep reduction can be achieved with these more strongly reducing metals.

Results/Lessons Learned

Early efforts to expand the range of zerovalent metals used in remediation from ZVI where relatively unsuccessful mainly because stronger reductants like ZVZ and ZVMg were not needed to treat chlorinate solvents. For more recalcitrant contaminants, such as TCP and PFAS, the incentives are more compelling for further innovation beyond ZVI/PRBs.