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.
> 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.
Unquestionably safer to dessicate. I mean to say the lead could be leached if one were of a mind to; I did indicate it's probably not a good idea.
No supercritical anything was sketched out however; just a reducing pyrolysis (making charcoal) and leaching it once or twice with nitric acid. Some lead would undoubtedly escape during pyrolysis unless the fumes were washed, which is tractable (just bubble it through the nitric acid and reuse it for the leachate) but this just adds to the already considerable expense.
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.