Seawater Greenhouses

Discussion in 'Earth Science' started by geordief, Jul 17, 2020.

  1. geordief Valued Senior Member

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  3. exchemist Valued Senior Member

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    I found this very interesting. The only bit that looks fishy to me was the throwaway remark that "any brine left over" is turned into salt. Any? There will be masses of concentrated brine produced by this process and it will have to be disposed of. If, as they say, they are not putting the concentrated brine back into the sea, then they will make a lot of salt. What will they do with that? It's dangerous stuff, from the point of view of living plants.
     
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  5. geordief Valued Senior Member

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    They could do fish farming.When I was in Norway ,near Kirkenes from memory we used to salt the fish ( mainly Cod ) by laying them out on pallets so that the "village elder" * could throw the salt over each layer with a wide shovel

    They used to ship this stuff off to Nigeria and South Africa .

    * just mean it was a fairly skilled job and he had it.
     
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  7. exchemist Valued Senior Member

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    Hmm, but seriously, there's a big issue here. In the Persian Gulf the salinity is 4%. For every cubic metre of water fresh consumed by this form of agriculture, 40g of salt is generated. That will soon mount up. In desalination plants, they return the concentrated brine to the sea, which is OK so long as there is a enough coastal mixing to ensure it doesn't raise the ambient salinity in the local waters. But with a lot of this agriculture, there could be problems - or an awful lot of salt to dispose of in some other way.
     
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  8. geordief Valued Senior Member

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    Couldn't be a game changer ,could it?

    Might the prize be many times more valuable than the expense of dealing with that waste product?

    And is the hope that these seawater production centres will create micro climates so that conventional agriculture would also have a place to take off?
     
  9. exchemist Valued Senior Member

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    Well possibly it could. I don't dismiss it at all. I'd just like to know how they will deal with all this salt.

    There could be some valuable elements and minerals in it, I expect, which would be economic to extract from a ready-made pile of salt, but wouldn't be if you had to concentrate it yourself. I wonder. Apart from Na and Cl there is a lot of Mg for instance, and some Ca, K and Br.
     
  10. geordief Valued Senior Member

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    I saw Lithium and Cobalt mentioned in that article.

    They sound valuable to me ,but I don't know much chemistry or economics.
     
  11. Michael 345 New year. PRESENT is 71 years old Valued Senior Member

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  12. billvon Valued Senior Member

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    I just checked - and apparently there's also URANIUM in sea water! And lead! And fallout from nuclear testing in the 1950's! And mercury! And cadmium! And thorium!

    People are thinking about piping TOXIC NUCLEAR WASTE into YOUR CHILDREN'S FOOD!!!!!!!
    [/im off]
     
  13. exchemist Valued Senior Member

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    I've read that section again. I now think this this guy is a bit scammy and the BBC has been suckered by his sale pitch.

    Li and Co are vital for modern battery technology - so obviously very topical and trendy things to mention. The sources are few and far between and, in the case of Co, the mining takes place in often very unsavoury conditions, in poorly regulated countries. So it would be fantastic if we could get it from seawater if his process were to enable that.

    However, the amount of Li in seawater is about 0.1ppm. So it would be 2.5ppm of the solid salt extracted. That's very low, but possibly not too low for some kind of separation to be possible. In the case of Co, it is 0.0001ppm in seawater, so 0.0025ppm of solid salt. So this looks like a bullshit speculation to me.

    More importantly, he talks what appears to be crap about brine cooling being an alternative to returning the brine to the sea. But it obviously isn't. Brine used for cooling doesn't just magically disappear, whereas the fresh water extracted from the seawater does get lost continually, to the atmosphere and in the bulk of the growing plants. So there will inescapably be a buildup of either brine or solid salt. Using brine for cooling does not solve this problem. Nor is it obvious why brine is any better than seawater for cooling. Nobody suggests either temperatures close to boiling or to freezing would be required in the process, so the boiling point elevation and freezing point depression of brine, both of which he mentions as advantages, seem to be irrelevant to the operation.

    So I'm afraid I'm now suspicious that this is being oversold in a misleading way. Unless I've missed something, which is always possible.
     
  14. geordief Valued Senior Member

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  15. billvon Valued Senior Member

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    Put it in a deep hole.

    There are salt caves all over the world; plants grow above them just fine.
     
  16. exchemist Valued Senior Member

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    I'd still like to see the maths. The amount produced will be huge.
     
  17. geordief Valued Senior Member

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    https://edition.cnn.com/style/article/uae-pavilion-biennale-sabkha-cement-spc/index.html

    Does this move the story along?

    "Dubai architects Wael Al Awar and Kenichi Teramoto have developed a cement inspired by the UAE's salt flats (pictured) and made from salt minerals found in desalination brine. Dubai has become a hotbed of architectural innovation."

    Just saw this article on CNN.Seems related.

    Might it solve the problem of potential salt waste if the Greenhouses took off?
     
  18. exchemist Valued Senior Member

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    Possibly, though I'd like to see how good this cement is in the rain! (It does rain in the Emirates, sometimes, in the winter.)

    At least this article acknowledges that generating masses of brine leads to a waste disposal problem, whereas your previous greenhouse man seemed to shrug the issue off entirely.
     

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