Ball milling destroys PFAS in contaminated soil

It's a good candidate load for excess renewables that would otherwise be curtailed. Similar to how direct air carbon capture is sited where grid carbon intensity is low (Orca in Iceland, for example). Might need some Megapacks or other battery storage to arbitrage, but that can be built into the cost (capturing various incentives in the process). From a quick glance, everything can be shipped to processing sites in containers. Conveniently, brownfields are also ideal for redevelopment with renewables. Get enough solar and batteries on site to startup, and then continue deploying as you remediate and possibly build transmission to the closest substation.

Well considering that the US military has tried to incinerate the firefighting foam they have in stock with poor effects (massive air pollution and soil contamination in nearby areas), it seems to have some utility.

But yeah this whole PFAS cleanup project is going to be a long haul.

I take findings like this with a grain of salt. They're saying it's possible. Now we need further research to make the process viable at various scale.

Nobody sat there with the first combustion engine and said "well this is too much effort, nobody will ever make another one of these" with the same sort of thought process.

Throwaway idea: Maybe it can be an energy-storage flywheel at the same time?

Can they filter the target compound out first?

Ball milling exposes surfaces to fresh reactive radicals introduced through tribo-electric effects.

Ultrasonics just vibrates and could be combined with ball milling to improve mixing rates, but without physical friction, it probably won’t be as effected.

I'd speculate that ball milling transfers significantly higher force at higher intensity then ultrasound can.

I assume the ball milling stirs the material (and probably heats it up) exposing lots of surface area to interaction with the balls. I'd guess ultrasound would be blocked/absorbed by the material it hits first.

But I'm not a physicist, just my first thoughts.

Unless there remains some antisceptic by-product, the flora can quickly take back over if mixed with "healthy" soil.

I would be more concerned about effectively turning the soil into clay, that is reducing the particle size too small for many types of plants. I guess mixing it with an aggregate afterward could help.

Then again, the highly processed nanoscale dirt could be an ideal building product able to supplement concrete or enabling even more durable rammed earth houses. Not sure anyone would want to live inside a 99.9% PFAS-free dirt house though.

They refer to the byproduct as possible grinding compound or fill material so they aren't intending to use it as soil.

>The process left an inert powder suitable for being a grinding additive or non-hazardous fill

If you're breaking apart fluorine compounds, it's very likely nothing else survives.

Wayland, MA?

A fun little puzzle for those of us who don't already know this bit of trivia.

The journal article is open access and available through the DOI link. Short version, as I understand it (take with more than a grain of salt): the mechanical process does not degrade the C-F bonds at all, but when you grind quartz that is already sufficiently fine it produces some highly reactive species on fresh surfaces which chemically attack the PFAS. At least some of the C-F bonds are replaced with Si-F bonds, though I'm not sure exactly what the products are.

Fungi as well

It's an open access research article so you can see the full text of the original here:

"Mechanochemical destruction of per- and polyfluoroalkyl substances in aqueous film-forming foams and contaminated soil"

https://pubs.rsc.org/en/content/articlelanding/2023/VA/D3VA0...

This is the most relevant paragraph for understanding the mechanism:

We have recently studied the degradation of perfluorosulfonic acid (PFSA) standards under mechanochemical destruction (MCD) conditions on quartz sand, which highlighted the radical-mediated degradation pathway of these compounds ultimately resulting in the formation of stable Si–F bonds embedded in the silica matrix. Other studies have also established the effectiveness of MCD to destroy a variety of topical persistent PFASs under laboratory conditions. This degradative phenomenon can be explained by the mechanical activation of the matrix and the generation of highly reactive surface sites on freshly formed surfaces which initiate and propagate the mineralisation of organic substances, such as PFASs.

Naturally occurring minerals in sandy soil form very reactive surfaces in the instant after they are broken into fragments by milling. Normally those surfaces quickly react with other materials in the immediate environment (natural organic matter, moisture, other minerals). That's why you can't just grind up a bunch of silica and add it to PFAS afterward to get a decontamination effect. But if the contaminated soil is ground up, minerals and all, part of that reactive mineral surface reacts with PFAS contaminants. The organic fluorine chemicals get turned into thermodynamically stable mineralized fluorides, so a little change each second compounds into near-perfect PFAS removal with prolonged application.

Most cement (not all of concrete, just the cement part) passes through a ball mill during manufacture. Mining operations that are followed by chemical separation usually have a ball mill step. That gives a sense of the scale of the ball milling industry.

Replacing the steel or iron balls is easy. Replacing the drum liner plates is also required, maybe every six months. The plates un-bolt.

More than you wanted to know about ball mills [1]

[1] https://www.flsmidth.com/en-gb/products/milling-and-grinding...

Sifting generally. At the end of the process the largest thing in the mill will be the balls.

Presumably you perform chemical analysis rather than looking for globs of the stuff.

Analytical techniques are extremely sensitive and quite capable of determining their quantitative floor. A quick literate search shows PFAS LoQs of somewhere between 0.2-2.0 ng/L.

I don't know why you're getting downvoted just for asking a question, but my guess is that this process is actually damaging the chemical bonds or somehow breaking off any protective oxides so that all of the PFAs end up reacting with the other minerals in the soil so that they change their composition to something that is less dangerous, sort of how sodium and chloride, both potentially dangerous or deadly elements on their own, can combine into table salt which is an essential substance for life.

I would like to see a deeper analysis of what is found in the soils after the PFAs are broken up to make sure they haven't just changed one dangerous chemical for another one though. If they are being converted into a harmless salt, then great.

Presumably bonded to something other than carbon. In particular I'm guessing it gets pushed to ionic bonds, in the form of fluoride, which is much less scary than perfluoro-crap or (god forbid) elemental fluorine.

Lipitor and Xanax don't even have a fluoride atom, how can they be PFAS?

> Smart waste management is all that is required to minimize risk.

ok, but if you're the fire department and you want to put out a fire, are you going to stop and carefully seal up a catchment so that no firefighting chemicals get into the ground, or are you going to immediately put out the fire?

ignoring the impossibility of sealing the ground around a burning structure well enough to prevent soil contamination in the first place, you are going to extinguish the fire and deal with the contamination later, if at all; there may be another fire.