h a l f b a k e r yCompound disinterest.
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The only two things mankind has profitably extracted from seawater is salt and magnesium, but I don't think we've really tried hard enough to give up on extracting the more interesting things, we just need to combine the processes a bit better.
The first step to profitabity in a ocean mineral extraction
scheme will be to sell the water. Assuming distilled water is marketable, the rest of the scheme gets easy, due to a certain material: PVC. Uniodized common NaCl salt is so easy to produce that the market for it will saturated, but that of course will be sold too, likely at a "loss", for whatever price the market will bear.
PVC is a very simple plastic, to make it, one needs ethylene, or c2h4, and hydrochloric acid. It is considered safe for water pipes. It's is dangerous if it burns, but hey, most things are dangerous when they're on fire.
Ethylene can be produced via hydrocarbons, or via plants. Since it's chemically only carbon and hydrogen, there should be no problem developing a cheap process for ethylene production on the sea.
Hydrochloric acid should be equally easy to produce, especially as a waste product of magnesium production.
the PVC thus made could be molded into small seaworthy craft and storage containers. Some can be filled with refined common salt and stored whereever, but I imagine that most of the salt will be excess salt and have to be re-mixed back into the ocean, hopefully in a eco-friendly way, and far away from the mineral extractors.
The remaining barrels can be used to store various mineral almagams, as more and more minerals are removed from the mix.
At first, the calcium and potassium, et all will be too abundant, but once you get past those, then you get at the rarer metals. You'll have sold astronomical amounts of water by the time you get much gold out of it, but the magnesium is of course useful, and large amounts of PVC created will be a carbon sink, as well as a fuel source which can be cannabalized in times of fuel crisis.
The energy source used for such operations is matter of other discussion, but there will be an obvious solar element to the endeavor, which will likely be supplemented with whatever else is appropriate.
There might be a wide variety of ships that would need to be floated, the "standard" ship which produces salt, distilled water, and a brine, then a ship which extracts the magnesium and calcium from the brine, then another ship to manipulate the next "waste" stream to extracted the next profitable mineral.
These ships could topographically be arranged throughout the ocean to minimize transport, avoiding hurricanes or other hazards when necessary, the pvc ships and containers stacked up and tied down when necessary.
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//Since it's chemically only carbon and hydrogen, there should be no problem developing a cheap process for ethylene production on the sea.// |
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Cost effective chemical synthesis is much more than having the required elements. Ammonia is just hydrogen and nitrogen (quite plentiful in air and water) but was difficult to product for a long time. Bun anyway for the idea of the ship producing its own shipping containers. |
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"The only two things mankind has profitably extracted from seawater is salt and magnesium..."
What about seafood? |
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// Since it's chemically only carbon and hydrogen, there should be no problem developing a cheap process for ethylene production on the sea. // |
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Trouble is, there isn't a huge amount of free C and H. Those hydrocarbons which do exist are in such a wide variety of forms, that synthesising ethylene from them would be very expensive. Prohibitively expensive in all likelihood. |
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The sediments do show reasonable levels of hydrocarbons, but not the water itself. |
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I spent the weekend spearfishing off La Jolla....had a wonderful time, got circled by a 150 lb. black sea bass, bit by a cabezon (my fault, not his), shot two barracuda and three calico bass, but it's all about the adventure. There's no profit in spearfishing - my gas expense outweighs my fish costs. |
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But I see your point, [phoenix]. |
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Seafood isn't dissolved in the seawater. But yes, if you include the ocean life, then we've extracted all sorts of things. |
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As far ethylene goes, it is given off by many (green) plants. Perhaps it can be harvested from algae in some manner. |
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otherwise, we may have to somehow gain carbon from sea life or some chemical air filtration scheme. |
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//As far ethylene goes, it is given off by many (green) plants. Perhaps it can be harvested from algae in some manner.// |
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I haven't come across algae giving off ethylene - in plants it's generally a ripening mechanism. It's given off by bananas for example. |
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//The sediments do show reasonable levels of hydrocarbons, but not the water itself.// |
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Even in areas of high productivity you'll be lucky to get much more than a few percent total organic carbon. Of that, some will be hydrocarbons, but it's not really viable as a source of chemicals for other things. |
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More importantly [Madai] as others have said, a chemical synthesis isn't just about bringing together atoms - it's a lot more complex than that. |
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Obviously there are a few technical hurdles for mobile PVC production. Hence, why this is the HALFbakery But, the fact is we have multiple pathways from which to develop a solution-- we could go with a strict chemical route, or pursue a solution by utilizing known existing ethylene producing plants, or genetically modify some plant to increase ethylene production. |
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Or perhaps you can go with some fast-growing algae to use as both a carbon source and the energy source for the process. |
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It might be possible to produce organic compounds
by using bacteria to process plankton harvested via
artificial baleen. |
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The thing is this. The only supposed advantage of
doing this stuff at sea is the presence of useful
stuff in seawater. |
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However, most of that useful stuff is much more
abundant in terrestrial mud, or even desert sand,
than it is in seawater. Yet, even then, we don't
bother trying to refine stuff from mud because,
for any mineral you're interested in, it's possible
to find deposits which are much, much richer in
that mineral. |
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So, I don't see the advantages of recovering
minerals from a very, very, very, very dilute
aqueous solution, as long as there are much,
much, much more concentrated deposits on land. |
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A while back some plants got the same idea, MB. If we are now contemplating a return to the sea and the peaceful sustenance of sun and dilute minerals, then things on land have really gone to pot. |
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Extracting minerals from seawater is as simple as
boiling off the water, which produces mostly salt.
From there you simply separate the salt from the
other substances, such as magnesium salts, etc. |
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Probably more economic to simply separate live
organisms, like fish, from the seawater, and sell them
for profit. |
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//Extracting minerals from seawater is as simple
as boiling off the water, which produces mostly
salt. From there you simply separate the salt from
the other substances, such as magnesium salts,
etc.// |
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Yes, indeed. If you boil a tonne of seawater you
get about 30kg of sludge, of which almost all is
valueless common salt. Most of the rest is near-
valueless salts of magnesium, potassium, calcium
and a few others. Get rid of those, and you're left
with a teaspoon of gunk that contains small
amounts of useful minerals. |
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Do all that about 800 times and you've got the
equivalent of a good shovel-full of modest-grade
ore. Of course, you then have to refine it. |
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Bottom line: there are no minerals in regular
seawater which can be profitably extracted, until
we get some much, much cheaper energy and
until all terrestrial reserves have been exhausted. |
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This idea was discussed //Seawater Mineral
Extracter// in HB back in 2001. |
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At the end is an anno about desalinization of
seawater in Australia to produce fresh water for
agriculture. If the mineral extraction is a byproduct
of creating fresh water from seawater and the price
of the fresh water is acceptable, then the extraction
of minerals from the sludge becomes economic. |
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Why does it become economic, because you say so? |
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The solids from seawater aren't particularly rich in
any one valuable mineral. Why is better to start a
refining process from a tank of brine with traces of
other elements, than from ore which may contain a
large proportion of a desirable element? |
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As a byproduct of desalinization, which is done in
areas with inadequate fresh water (arid places, for
example), cost of the mineral extraction is covered
by the primary business of producing fresh water, so
the "sludge" is a waste product. Separating the salt
(NaCl) from other minerals and selling it recovers
some of the cost of processing the remaining
minerals- or, don't separate the salt, leave the other
minerals in, just sell it as "sea salt," which sells for
more than traditional table salt. |
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//"sea salt," which sells for more than traditional
table salt.// Yes, it does, but the global market
for sea-salt is finite. |
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The point I disagree with is the assumption that,
because traces of valuable elements (particularly
metals) are present in seawater, it makes
economic sense to extract them. For just about
anything other than salt itself (or bromine), it's
just vastly more expensive to recover them even
from the brine that desalination gives, than it is
to refine them from ores. |
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Incidentally, old newspapers contain something like
0.5-3ppm of silver and about 20-30ppm each of
chromium, copper, and tin. |
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Seawater contains about 0.1 ppb (note - ppb not
ppm), and a few ppb each of chromium, copper and
tin. |
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The story is similar for most other useful metals. |
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If the main purpose is to extract the valuable
minerals, you're right, it isn't economic. If the
minerals are the byproduct of another process,
like producing freshwater, the feedstock (salt)
cost is "free." |
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At that point you determine whether it's going to
be more profitable to simply sell sea salt (which
you've acquired for "free," and which can be sold
at a competitive price and still be profitable), or
would it be more advantageous to separate the
NaCl from the other minerals. Note that the
competition for your sea salt is table salt, not road
salt or water softener salt. |
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It depends how much water you process, and how
much leftover salt you have; I suspect in an
industrial setting, you'd be producing millions of
gallons of fresh water and tons of salt. With tons
of "free" salt, you may be able to process a
respectable amount of "trace" minerals. |
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// If the minerals are the byproduct of another
process, like producing freshwater, the feedstock
(salt) cost is "free."// |
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You're missing the point. Even if you give me, for
free, unlimited quantities of solids from seawater,
it's not going to be worth trying to extract things
like silver, chrome, copper etc from them.
Seawater solids (solids, please note) are lower
than the lowest grade ores for any valuable
metals. The fact that water purification gives me
the solids as a byproduct (actually it doesn't - it
produces brine) is beside the point. |
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Salt is useful, and (along with bromine) is just
about the only thing worth recovering. |
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But, to return to the original idea, it would be
fantastically futile and uneconomic to create a
desalination plant on a ship, in order to create
fresh water and salt which then have to be moved
back to land. |
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One of the nice things about the sea is that it is
almost invariably to be found on coastlines. It's a
remarkably convenient property, and one that can
usefully be exploited by building desalination
plants there. |
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People seem to have a really poor understanding of how complex, and expensive, mineral extraction really can be. |
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Some orebodies in the earth are deemed "uneconomical" to extract and process, even when the desirable material is in the tens of percent concentration. That is because of the reactivity, or similarity, of other "contaminant" elements, and in some cases, simply the difficult-to-break-down oxide or whatever form the element actually comes in. |
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Think of it this way. There are many, many solar evaporation ponds along coastlines around the world for salt extraction. No one is trying to extract anything useful out of the salt - because that is uneconomical to do. |
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