4 ms·

I wonder if there's a positive gain in drawing metals out with the plants, removing the metal content, and producing biochar with the waste. Then you'd be able

I wonder if there's a positive gain in drawing metals out with the plants, removing the metal content, and producing biochar with the waste. Then you'd be able to use the plants to remove CO2 from the air and metals from the ground simultaneously. Obviously, there's a finite amount of metal one could draw from any given location, and depending how deep root systems grow there's maybe not a lot of long term value in mining the surface this way. (Though with breeding/engineering programs, perhaps you could get deeper root systems.) It's the sort of stuff that's fun to imagine in a science fiction context and probably doesn't make much practical sense in the real world. Though, maybe getting metals out of the soil is useful in other ways (e.g. cleaning up mine tailings?)

odyssey7 7y ago
> Obviously, there's a finite amount of metal one could draw from any given location, and depending how deep root systems grow there's maybe not a lot of long term value in mining the surface this way. My concern was, if this goes into wide use, then we'll be using these specialized species to extract the non-renewable resources that they depend on from their habitats, leading to the species' demise. Edit: Considering "hundreds of mines shovel topsoil into smelters," maybe this is already at risk to begin with.
- bottled_poe 7y ago
  Sounds a lot like modern agriculture. What’s the difference?
  - odyssey7 7y ago
    Interesting. I guess both can make a location uninhabitable for native species. This one is ironic because the plant being both cultivated and harmed by the agriculture could be the native species itself. Another difference is that with most farming there's an incentive to add things back to the soil and rotate crops, since you want the soil to keep working for you. In this case, there's no incentive to add nickel back to the soil, since extracting that element is the goal. And nature's ability to replenish the nickel is limited.
hinkley 7y ago
Bioremediation? Might depend on the plant. Turns out for instance that if you plant sunflowers in lead contaminated soil, most of the lead ends up in the stalk. So you can cycle through the rest of the green matter as compost and dispose of the stalks and slowly reduce the lead content of the area. However, the only part of a sunflower that might even remotely work as bio char is the stalk so in that case they would be mutually exclusive. Meanwhile, heavy metals tend to accumulate in leaves of broadleaf plants (which also exacerbates the many problems with tobacco smoke). These people are working on a different angle. Refining minerals commercially requires that the input have a certain concentration to begin with. So any source below that threshold is unusable. Unless you have a low input way to concentrate them first. Which is why about every 10 years someone tries to figure out how to get gold out of seawater by using the effluent of some other process as input. From what I understand though the output of desalination equipment is still far too dilute for that. Or maybe the salts screw up the process, I was never clear on that.
- samatman 7y ago
  > However, the only part of a sunflower that might even remotely work as bio char is the stalk so in that case they would be mutually exclusive. Not necessarily. The char could be ground and leached with nitric acid, producing soluble lead(II) nitrite from metallic lead (which you'd most likely have after a reducing pyrolysis of the stalks). Nitric acid is cheap as chips, but this would be somewhat labor-intensive and you're not going to get much lead out of it. Just charring the stalks before burial would reduce the volume of lead which needs to be sequestered, in comparison to the stalks themselves, and it would be carbon negative for much longer.
  - hinkley 7y ago
    We know that lead is airborne. Is that what you meant by reducing the volume? Dessication is probably a safer way to reduce volume. I don't think lead is pernicious enough to warrant the cost of supercritical oxidation.
    - samatman 7y ago
Zenst 7y ago
It has many uses, pulling out toxins and other metals from soil to turn contaminated soil into something healthier. 2003: https://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-21655111 https://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-2...

odyssey7 7y ago

> Obviously, there's a finite amount of metal one could draw from any given location, and depending how deep root systems grow there's maybe not a lot of long term value in mining the surface this way. My concern was, if this goes into wide use, then we'll be using these specialized species to extract the non-renewable resources that they depend on from their habitats, leading to the species' demise. Edit: Considering "hundreds of mines shovel topsoil into smelters," maybe this is already at risk to begin with.

bottled_poe 7y ago
Sounds a lot like modern agriculture. What’s the difference?
- odyssey7 7y ago
  Interesting. I guess both can make a location uninhabitable for native species. This one is ironic because the plant being both cultivated and harmed by the agriculture could be the native species itself. Another difference is that with most farming there's an incentive to add things back to the soil and rotate crops, since you want the soil to keep working for you. In this case, there's no incentive to add nickel back to the soil, since extracting that element is the goal. And nature's ability to replenish the nickel is limited.

hinkley 7y ago

Bioremediation? Might depend on the plant. Turns out for instance that if you plant sunflowers in lead contaminated soil, most of the lead ends up in the stalk. So you can cycle through the rest of the green matter as compost and dispose of the stalks and slowly reduce the lead content of the area. However, the only part of a sunflower that might even remotely work as bio char is the stalk so in that case they would be mutually exclusive. Meanwhile, heavy metals tend to accumulate in leaves of broadleaf plants (which also exacerbates the many problems with tobacco smoke). These people are working on a different angle. Refining minerals commercially requires that the input have a certain concentration to begin with. So any source below that threshold is unusable. Unless you have a low input way to concentrate them first. Which is why about every 10 years someone tries to figure out how to get gold out of seawater by using the effluent of some other process as input. From what I understand though the output of desalination equipment is still far too dilute for that. Or maybe the salts screw up the process, I was never clear on that.

samatman 7y ago
> However, the only part of a sunflower that might even remotely work as bio char is the stalk so in that case they would be mutually exclusive. Not necessarily. The char could be ground and leached with nitric acid, producing soluble lead(II) nitrite from metallic lead (which you'd most likely have after a reducing pyrolysis of the stalks). Nitric acid is cheap as chips, but this would be somewhat labor-intensive and you're not going to get much lead out of it. Just charring the stalks before burial would reduce the volume of lead which needs to be sequestered, in comparison to the stalks themselves, and it would be carbon negative for much longer.
- hinkley 7y ago
  We know that lead is airborne. Is that what you meant by reducing the volume? Dessication is probably a safer way to reduce volume. I don't think lead is pernicious enough to warrant the cost of supercritical oxidation.
  - samatman 7y ago

Zenst 7y ago

It has many uses, pulling out toxins and other metals from soil to turn contaminated soil into something healthier. 2003: https://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-21655111 https://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-2...