Down on the farm that harvests metal from plants | Hacker News Reader

Down on the farm that harvests metal from plants

nytimes.com

131 pointsandrewl27 comments

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?)

> 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.

Sounds a lot like modern agriculture. What’s the difference?

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.

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.

> 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.

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.

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.

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-2...

i am not a biologist but i saw an article (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.

That's very unexpected. I wonder how do the microbes do it? According to the article, the higher concentration of U235 happens within the cell.

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...

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

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.

> 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?

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.

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.

The succession plan is reverting to stocks that can handle the elevated levels of nickel still remaining after the commercial viability of bioremediation has been exhausted.

In the areas where they evolved, they've presumably been present for a very long time. Human action could possibly increase their nickel-concentrating abilities by some small multiplier, but that won't turn human timescales into geologic timescales.

Those trees would overwhelmingly be falling and decomposing in the same soil they grew in though, so the movement of minerals out of the soil would be minimized.

Nickel is not really needed in any large amount for the growth of plants, I assume even these plants don't need it in more than a trace amount to grow.

The hydroponic fertilizer I use doesn't even list it on the label and I assume that the only way my plants get it is from impurities in the other minerals.

https://www.jacksnutrients.com/online-store/5-12-26-Part-A-p...

> 500 pounds of nickel citrate

That would be 115 pounds of nickel (plus some water and C02)

Isn't the idea that you remove the nickel and then go back to farming "normal" crops? So this is a one off way to mine without destroying the environment. And maybe a way to remove excess metals from soil too. Not a continuous supply.

Edit, I guess you could use this technique in waste cleanup too, so maybe once a mine stops producing you plant these trees on the site for one last load. Or you bring waste from the mine (high nickle etc) to farms like this and "replenish" the sites

https://archive.md/P2sSl

> 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.

"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."

it sounds like this only works for nickel?

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