5 Things to Know About Zero-Valent Iron
Sep 1, 2020 -
Zero-valent iron (ZVI) is an accepted and widely used remedial amendment for in situ chemical reduction applications. But if you’ve never implemented a ZVI remedy, what do you need to know before using it as an alternative for your site? In this blog post, I will highlight a few key areas that need to be considered.
If you want to dive deeper into how ZVIs work, join me next week for my webinar, How Understanding a Site’s Conceptual Site Model Can Prolong the Life Expectancy of a ZVI PRB Remedy. I’ll walk you through a real-life project, and explain how we were able to overcome site challenges and ensure a long and effective lifespan for our ZVI PRB remedy.
1. TYPES OF COMMERCIALLY AVAILABLE ZVI
Several types of ZVI exist. The most common ZVI form is cast iron from recycled engine blocks. Other forms include atomized, CO reduced, water atomized, centrifugal atomized, hydrogen reduced, and electrolytic. The differences between these types include purity, size and, of course, cost.
2. SIZES OF ZVI
Size does matter when it comes to ZVI. Typical ZVI sizes are grouped as granular, powder, colloidal and nano. The larger particle sizes provide overall longevity, while nano ZVI is highly reactive and expended quickly. When choosing which size to use for your project, you’ll need to consider the ZVI surface area, geology, method of distribution, and remedy life expectancy. Range of particle size is also a large consideration based on site geology.
3. ZVI PASSIVATORS
While ZVI is a robust technology, geochemical factors in groundwater can affect the reactivity and longevity. We call these parameters “passivators.” They include sulfate, nitrate, oxygen, carbonate, silica, phosphate, chromate, and microbial activity. Before designing your ZVI remedy, you must have a robust understanding of the existing passivators in the subsurface. This is key to the success of your project, as it helps determine if you need to pre-treat the groundwater to reduce passivators.
4. ZVI APPLICATIONS
While ZVI has been predominantly used in permeable reactive barriers (PRBs) as far back as 1995 in Sunnyvale, CA, other ZVI methods of emplacement include injection, fracturing, trenched in, ZVI column installation, and shallow soil mixing using soil mixers or buckets and deep auger soil mixing. The trend for future usage reflects the wider range of acceptable methods to distribute ZVI.
5. COMBINED REMEDY OPTIONS
ZVI has advanced in this century as a combined alternative with biosubstrates and/or bioaugmentation as a biotic/abiotic approach. Some sites’ source areas have been successfully treated with in situ chemical oxidation using permanganate upgradient from downgradient installed ZVI PRBs.
There’s a lot to know and consider before using ZVI remedies.
If you’d like to learn more, register for next week’s webinar, How Understanding a Site’s Conceptual Site Model Can Prolong the Life Expectancy of a ZVI PRB Remedy. If you have questions, you can submit them during registration for me to answer during a Q&A.
You can also download the latest research about ZVI’s prevalence, differences, usage and trends.
ABOUT THE AUTHOR
VICE PRESIDENT, GEOSIERRA, A CASCADE COMPANY
Deborah Shaffer Schnell is the Vice President at GeoSierra Environmental, a Cascade Company. She is a leading national expert on permeable reactive barriers (PRBs), hydraulic and pneumatic fracturing, and in-situ technologies such as in situ chemical oxidation (ISCO) and in situ chemical reduction (ISCR), with a focus on amendment distribution. Deborah works with clients to select the best remedial technology for their sites, based on data presented in their conceptual site model (CSM), project timelines, and budget.
Deborah works with clients whose sites include military bases, industrial and retail facilities and residential areas as well as Superfund sites with contaminants ranging from chlorinated solvents, metals, and petroleums. After 25+ years in the industry—first as a consultant, then as a founder of her own remediation company—Deborah understands the challenges inherent to these projects. With this experience, she is able to forecast potential problems, and address them ahead of time with proper planning and technology selection.
Clients rely on Deborah for everything from project planning support education about the selected technology to overseeing the implementation of the remedy on site. They know her broad skillset and experience enable her to adapt and optimize in the field when the unexpected happens, and that she is still available for questions or reviews after project implementation. Deborah is a valuable resource for clients who need an experienced remediation expert who can work with, explain and manage the latest technologies and strategies.