[ClintFix]

I was an engineer at a company attempting to extract rare earth metals from fly ash using a solvent method (supercritical CO2). Similar to how caffeine is removed from coffee.

There aren’t a lot of rare earths in coal/fly ash but even modest coal plants produce tons of fly ash daily.

[John_KZ]

Also fly ash is a pain in the ass to get rid off. I've heard about companies re-using it in concrete products and other construction materials. Even if the value produced is low, any profit is better than dealing with the cost of safely disposing it.

[Symbiote]

Making cheap bricks with waste ash has been common for decades.

Most British houses have two layers of brick, the nice ones on the outside, and these ones on the inside, which will be covered. An air (or fibreglass) gap between them provides insulation.

https://en.wikipedia.org/wiki/Concrete_masonry_unit

https://en.wikipedia.org/wiki/Cavity_wall

[Erlangolem]

Wouldn’t that make the resulting concrete unusually radioactive?

[John_KZ]

No, the idea that fly-ash is highly radioactive is a faux created by the nuclear lobby. Some coal is more radioactive than other, but in general they're very safe from this perspective. The real problems are is it's corrosiveness, it's heavy metal content (if any), and the particle size.

[Erlangolem]

I live and learn, thanks. The particle size I assume is an issue for pulmonary reasons? So sequestered in concrete that wouldn’t be an issue, smart.