Maybe I am missing something, but I don’t see how this is feasible at all.
Running a mill filled with tons of earth for a day at 450 RPM seems to be an enormous amount of energy expenditure relative to the PFAS you’d be able to destroy at the concentrations in the US.
For their context, in which it was firefighting material in a small training zone, it seems like a great fit, but for widespread deployment this seems like a stretch.
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.
Using the excess energy to produce hydrogen will depress the value of hydrogen until it's no longer profitable to produce hydrogen at those rates and then you have room for ball milling in the economics again.
Or until there's not enough excess energy to continue producing hydrogen; I don't see a reason why we'd expect the hydrogen to become unprofitable (water to become too expensive?) first.
Oil price changes disrupt oil operations all the time. The hydrogen energy economy will have times where it's not profitable for an individual actor to generate hydrogen too.
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.
I get your point, but check out the history of the steam engine. The first one was invented in ~30 BC. Additional attempts were made in the 1500s and 1600s. It took until 1712 before it was commercially viable.
Sure, check the rest of human history though. Things moved at a fairly glacial pace until the industrial revolution. Since computers we've accelerated that even more. Things move very fast these days compared to 2000 years ago.
The nature of ball milling makes it a very inefficient flywheel:
The energy of the wheel is going into repeatedly lifting the material. That energy is lost: it's not transferring that energy back into the rotational energy of the wheel every time it falls, but into breaking up the material against the bottom of the wheel, more or less perpendicularly to the direction of the wheel's travel at that point.
If ball milling works, why wouldn't ultrasound (Knock the PFAS into components using ultrasound)? Both are in essence physical methods (as opposed to chemical methods).
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.
In the process described they're using metal balls - so there won't be any electric effects. The metal balls immediately conduct electrons to negate any charge imbalance.
You're thinking of non-metal balls, used for other processes, e.g.
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.
Does this kill everything else in the soil? Microbes, fungus, nutrients, etc. A bunch of sterilized dirt may be better than poisoned soil, but even if it's possible to sanitize soil over millions of acres I wonder what the impacts would be to the plants and animals that we expect to live there. Saving the dirt by making it lifeless and infertile won't save the forests.
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.
My town (named after a window system protocol back in 1835) has implemented activated carbon filtration to remove PFAS from municipal well water. After the carbon filter medium has been saturated it will need to be safely disposed of, including its PFAS load.
Being able to dispose of those filters in-situ by ball milling might make sense if the cost of the machine is less than the ongoing disposal costs for the filters. edit: EPA rulemaking for disposal of spent carbon filters is in process.
>>In some ways, "ball milling" is not all that different from the grinding of a mortar and pestle, but at an extremely high intensity, with the balls moving at incredible speeds to degrade the PFAS at a molecular level
That's the key point of the article, and it's astonishing that such a mechanical-scale process can degrade the chemical C-F bonds at a sufficiently useful rate. I'd really like to know more about how that actually works at a chemical level, and what is the remaining/resulting "safe by-product"?
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.
I wonder if it might not be possible to evolve and/or design bacteria to break PFAS down? There are bacteria that eat things as diverse as metals and plastic, so why not ?
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.
We're going to need one big centrifuge to ball mill all the thousands of tonnes of soil that needs to be cleaned up. I wonder how long the steel balls will last?
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.
What are the chances that this grinding just makes so much surface area for the pfas to stick to that it falls below the detection threshold of the measurement technique (which measures in a solution)?
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.
> 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.
I'd like that as well; it was weird that no single mention of the sub-products was made.
I wonder why they weren't able to perform a quick powder X-Ray Diffractometry analysis to verify that the formation of fluorine minerals was occurring.
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.
“Forever chemicals” is intellectually lazy nomenclature.
Flonase, Lipitor, Xanax are all PFAS.
The range of half-life for untouched PFAS ranges over many orders of magnitude in hours. For long half-life components, energy (like this anrticle) and catalysis can break them down in seconds.
Smart waste management is all that is required to minimize risk. Fear of manufacturing will just move the tech to China where the environment will be worse off.
> 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.
Running a mill filled with tons of earth for a day at 450 RPM seems to be an enormous amount of energy expenditure relative to the PFAS you’d be able to destroy at the concentrations in the US.
For their context, in which it was firefighting material in a small training zone, it seems like a great fit, but for widespread deployment this seems like a stretch.