For most of history, the world got along fine without the rare earth elements. We knew they existed, we knew they weren’t really all that rare, and we really didn’t have much use for them — until we discovered just how useful they are and made ourselves absolutely dependent on them, to the point where not having them would literally grind the world to a halt.
This dependency has spurred a search for caches of rare earth elements in the strangest of places, from muddy sediments on the sea floor to asteroids. But there’s one potential source that’s much closer to home: coal ash waste. According to a study from the University of Texas Austin, the 5 gigatonnes of coal ash produced in the United States between 1950 and 2021 might contain as much as $8.4 billion worth of REEYSc — that’s the 16 lanthanide rare earth elements plus yttrium and scandium, transition metals that aren’t strictly rare earths but are geologically associated with them and useful in many of the same ways.
The study finds that about 70% of this coal ash largesse could still be accessible in the landfills and ponds in which it was dumped after being used for electrical generation or other industrial processes; the remainder is locked away in materials like asphalt and concrete, where it was used as a filler. The concentration of REEYSc in ash waste depends on where the coal was mined and ranges from 264 mg/kg for Powder River coal to 431 mg/kg for coal from the Appalachian Basin. Oddly, they find that recovery rates are inversely proportional to the richness of the ash.
The study doesn’t discuss any specific methods for recovery of REEYSc from coal ash at the industrial scale, but it does reference an earlier paper that mentions possible methods we’ve seen before in our Mining and Refining series, including physical beneficiation, which separates the desired minerals from the waste material using properties such as shape, size, or density, and hydrometallurgical methods such as acid leaching or ion exchange. The paper also doesn’t mention how these elements accumulated in the coal ash in the first place, although we assume that Carboniferous-period plants bioaccumulated the minerals before they died and started turning into coal.
Of course, this is just preliminary research, and no attempt has yet been made to commercialize rare earth extraction from coal ash. There are probably serious technical and regulatory hurdles, not least of which would be valid concerns for the environmental impacts of disturbing long-ignored ash piles. On the other hand, the study mentions “mine-mouth” power plants, where mines and generating plants were colocated as possibly the ideal place to exploit since ash was used to backfill the mine works right on the same site.
If there is that much in the ash, I wonder how much is in the unburned coal?
Not very much of course. When coal is burned, the ashes left over are just a few percent of the total mass, so in the coal, the concentrations of these rare earths (which do not burn or evaporate) is about 100x lower.
A bit analog to this, consider burning wood.
During it’s life a tree collects a lot of solar energy, and captures CO2 from the air, and binds it with hydrogen from water (the oxygen is discarded). When the tree is burned, the solar energy is released as heat, and the CO2 is released into the air again. The ashes left is pretty much the fertilizer the tree took out of the ground, and can be used as fertilizer again to grow a new tree.
Production of coal ash and fly ash is a concentration process where the low-value element (carbon) is burnt off, leaving heavy metals and other oxides. Even after fly ash capture, with just 1% of the heavies escaping up the stack, it’s well documented that coal power plants release more radioactivity into the environment than nuclear power plants.
Which makes you think: Is processing of coal ash to extract uranium for fuel cost effective? Apparently, depending on the coal, it is: https://doi.org/10.1016/j.resourpol.2015.04.005
Since Germany isn’t using that stuff anymore, maybe we can take their ash and do something good with it.
Ash made by Germans 💀💀💀😂
Damn good question. It might make processing the coal to where it was as desirable as natural gas for fast start up generators economically viable. And allow pipeline transport with a large net increase in efficiency.
There are a lot of designs for coal powered generation which are not economic because of the processing cost preparing the coal. Another possibility is extracting the elements from the flue gas.
If there is that much in the ash, likely a lot more went up the smokestack as pollution instead of captured as product. There wasn’t the current demand for lithium, so very likely no one researched the subject.
At the end of the day, what matters is the overall economics. Can you do it at a price people can afford?
I’d find it quite hilarious if burning coal to generate electricity and extract lithium became the most economically efficient form of transport.
Rare earth metals arent actually rare. We have plenty of them available we’ve just exported the mining of them to other countries where they can exploit essentially slave labor to source the ore.
So, isn’t this saying that there is possibly $1.68 worth of rare earth elements per ton of coal ash.
5 gigatons == possibly $8.4 billion
$1.68 per ton processed seems very expensive to me but I don’t know extraction costs.
Considering there are literal mountains of coal ash it has to be among the cheapest way to extract these elements with a tracked excavator and dump trucks, when you compare the cost of operating a subterranian mine with wooden supports railways, elevators and all that entails.
Although the publication states “coal-derived ash is relatively free of radioactive substances compared to the radioactive elements (Th and U) released with the conventional REE ores utilization”, coal fly ash also contains radioactive potassium-40 and radioactive decay products (including radium) from uranium, and thorium isotopes. This was an issue raised 2-3 decades ago when fly ash was being used as a component in concrete used in the construction of apartment and office buildings, in which people would receive an additional radiation dose.
Furthermore, depending on the specific methods for recovery of REE/Yttrium/Scandium, there may be a concentration or precipitation of the radioactive materials in one or more of the separation steps (e.g., scale buildup in a container). If these concentrations exceeded certain regulated alpha/beta/gamma levels, such materials may be classified as low-level radioactive waste. If the material contains both hazardous (certain acid or organic) and radioactive components, it may have to be treated as “low-level mixed waste”.
Apparently not everyone got the Banana Memo.
Let’s be generous and say 1/2 gram of the money elements per 1,000 grams are recovered. As the article points out, it ain’t all lithium, and lithium isn’t even a rare earth.
What means “Oddly, they find that recovery rates are inversely proportional to the richness of the ash.” What is “the richness of the ash”? Can it be expressed with numbers?
I’m curious if there is something special about coal ash, or if this is just a case of big numbers. Extracting $8B out of 5 gigatonnes of material does not seem like a particularly rich source to me. By my naive math, that’s like 1/1000th the value you could create if you were able to just convert the ash into construction bricks.
I.E. if you have 5 gigatonnes of mass you will find many interesting atoms. Doesn’t mean it’s a good way to get them, or even a good way to use that mass.