
Down on the farm that harvests metal from plants - andrewl
https://www.nytimes.com/2020/02/26/science/metal-plants-farm.html
======
Pfhreak
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?)

~~~
hinkley
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
> _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
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
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.

------
zkms
i am not a biologist but i saw an article
([https://www.nature.com/articles/s41598-019-38740-2](https://www.nature.com/articles/s41598-019-38740-2))
about a related subject a few months ago; namely, that certain species of
algae preferentially uptake uranium-235 (the fun fissile isotope) over
uranium-238 (the more prevalent isotope), and the numbers they quoted imply an
isotopic separation factor that is,,,significant.

~~~
jimkri
I did not know this, so thanks for sharing!

Micro-algae and Macro-algae are great for absorbing metals that are in water,
its used in wastewater treatment:
[https://www.sciencedirect.com/science/article/pii/S1319562X1...](https://www.sciencedirect.com/science/article/pii/S1319562X12000332)

When you take an algae supplement it also helps to remove metals from the body
as well. Algae is great

------
Gravityloss
The Talvivaara mine in Finland uses a novel bio based method to get nickel out
of the ore but it has not been super successful so far. But it is in
operation, after quite major problems. AFAIU the concentration is so low that
traditional methods would not have been profitable.

------
dehrmann
> After a short purification, farmers could hold in their hands roughly 500
> pounds of nickel citrate

How many rounds of this can you do before you've stripped so much nickel from
the ground these trees won't grow?

~~~
andrewl
I wondered that myself. They'd need a succession plan. But high concentrations
of certain metals are toxic to many other plants. So maybe the nickel
harvesting plants are a first step to preparing the soil for another crop.
Only this step allows the farmers to at least partially recover some of their
investment in the cleaning step.

~~~
pfdietz
Another possibility would be to grind up olivine and spread that on the field.
Olivine is a nesosilicate (orthosilicate) so it dissolves readily in weak acid
conditions. And it's typically a few tenths of a percent nickel.

The dissolution of olivine would liberate magnesium ions, which could react
with water and CO2, permanently sequestering the CO2 as carbonate.

------
neonate
[https://archive.md/P2sSl](https://archive.md/P2sSl)

------
hinkley
> Where nickel is mined and refined, it destroys land and leaves waste.

Sounds like this process might have more immediate use as a preventative
measure to reduce the footprint of conventional mining processes. Catch the
residuals in the tailings and the slag.

------
Anointmous
"The father of modern mineral smelting, Georgius Agricola, saw this potential
500 years ago. He smelted plants in his free time. If you knew what to look
for in a leaf, he wrote in the 16th century, you could deduce which metals lay
in the ground below."

------
ptah
it sounds like this only works for nickel?

