Sciencemadness Discussion Board

au out of sea water

c12h22o11 - 31-1-2006 at 23:15

u no how 4 every cuibic meter of salt water there is 1 ounce
of au!!

how would u get it out?

could u get the nacl out of the water and melt it and electrolysis the nacl in a down's cell would the gold fall
nere theanode?

Polverone - 31-1-2006 at 23:31

There is nowhere near an ounce of gold in each cubic meter of ocean water. There is no known economical way to extract gold from seawater, but it is an interesting theoretical question: given a cubic meter of seawater, how could you recover the minute amount of gold contained in it?

Your written communication skills are atrocious and if you continue to post like that your messages will be deleted without further consideration. You're composing messages for a forum, not IMs or text messages.

c12h22o11 - 1-2-2006 at 00:09

would my idea work thow

c12h22o11 - 1-2-2006 at 00:14

and how much au is there per cubic meter of sea water

Polverone - 1-2-2006 at 02:01

According to this ugly but informative page, modern estimates give up to 50 ppt gold in seawater. A cubic meter of seawater has a mass of ~1020 kg. You could get about 51 micrograms of gold from that cubic meter of seawater. Even if electrolysis is a viable method of metallic gold liberation, you would have a hell of a time seeing any gold. I would expect it would dissolve in other components of the melt.

Really, do take time to write: the next careless post you make, this thread is going to detritus.

darkflame89 - 3-2-2006 at 02:36

There's a significant amount of gold in the oceans, but the difficult thing is the process required to extract the gold is so much more expensive that all the gold dredged up from the ocean cant pay for it.

You are nt the only person thinking about it, Haber once thought it too, because he wanted to help his country(Germany) to pay off the heavy debts. But he did nt succeed. The problem is as said above, the process is too expensive.

JustMe - 3-2-2006 at 17:49

I wish, really wish I still had an old magazine. Waaaaaaaay back in the late 1960's/early 1970's I used to have a subscription to Chemistry magazine. I don't even know if it still exists. It had cutting edge articles on the latest in Chemistry. But I eventually threw out my old issues 20 years ago or so.

Why am I bringing this up? Because in one of those very issues was an article about this very question. Seems that a chemist had come up with an agent (chelating, of course) that would selectively extract 100% of the gold from seawater. But at a mere $30 an ounce the process was ludicrous. I remember reading something like gold would have to reach something like $300 and ounce to even consider the process feasible. So it was just a nice little theoretical exercise.

Excuse me, but where is gold priced now??? Gosh I wished I had saved that issue! As a side note, he also had come up with an agent that extracted Uranium, but, of course, that was even less feasible.

So actually, it HAS been done... but, I fear the article has been lost in time. All I remember is that it was in Chemistry magazine, sometime between 1968 and 1974. Microfiche anyone???

runlabrun - 4-2-2006 at 00:49

"Pump the sea water to a vat, then heat the water off, the stuff you are left with try heating up to 1000C(argon atomsphere) to remove O2, then use magtnics to remove iron materials, then use cynical tubes to remove heavy materials, then use fraction destalion eg.... "

Yes granted you can do that... but the point which has already been made several times in this thread is that the cost of such an excercise would outweigh the value of the amount of gold obtained.


neutrino - 4-2-2006 at 10:28

Originally posted by JustMe
But at a mere $30 an ounce the process was ludicrous. I remember reading something like gold would have to reach something like $300 and ounce to even consider the process feasible. So it was just a nice little theoretical exercise.

Excuse me, but where is gold priced now???

$113/ounce, adjusted for inflation to 1970.

That article might still be worth looking at. That regent may have dropped in price if its precursors got cheaper.

Thanks for the math!

JustMe - 4-2-2006 at 19:40

Yeah, you'd have a lot of issues of the magazine to go through (if they still exist someplace). Still, krypton and xenon are extracted from air even though they are not exactly abundant - they just get caught in the process.

So with a chelating agent that selectively binds to gold all you've gotta do is just keep running the water through it (like zeolites???) and wait, and wait and wait. What is "practical?"

Oh, I'm not saying it is really viable, still it isn't much different than a fractioning column, is it?

Anyway, maybe one brave soul will try and track down that article to see if this old time chemistry enthusiast's memory is right.

DeAdFX - 4-2-2006 at 21:26

You could extract other things from sea water to make it worth your time. However table salt NaCl isn't exactly the most sought after compound by women. Then and again you will probably have to sell your gold that you collect from the water to stay in bussiness.

I think the only viable way towards easier gold is to get your pan out and do some sifting...

unionised - 5-2-2006 at 02:46

Gold is something like $550 per ounce.
That's about $17 per gram.
Each cubic metre of seawater contains something like 50 micrograms.
That's worth $0.00088
Where I live electrical power costs the equivalent of about $0.10 per KWHr
That's $0.000000027 per Joule.
Let's say I build my "gold mine" 10 metres above sea level (otherwise it may be washed away by the tide).
Pumping each tonne of water up to my factory will take (E= Mgh) 98000J and cost me 0.0027$

I spend $0.003 to recover $0.0009 worth of gold.
I'm losing money before I look at efficiency, capital costs, labour, R+D or anything else.

Can we please stop wasting bandwidth talking about this?

Microtek - 5-2-2006 at 05:31

But when you are done with the water and pump it back into the sea, you can use a large percentage of the work to suck up more water. In total you will only be paying for the frictional work in your pipelines ( and whatever process you would be using ).
I imagine a process conceptually like a blue whale sifting through the oceans to get the plankton.

Mr. Wizard - 5-2-2006 at 06:54

Wasn't that mention of the quantity of Gold in sea water for a cubic mile?

densest - 5-2-2006 at 14:54

Mr. Sucrose is a troll or can't handle decimal points.

According to the CRC Handbook of Chem & Phys., there are some interesting and expensive elements which are orders of magnitude more abundant than Au. All values in ug/L:

Indium and Vanadium look like interesting candidates.

Instead of filtering ordinary seawater, what about investigating salt mines? There the seawater has already been fractionally crystallized...

Marvin - 6-2-2006 at 11:44

Personally, I think we've allready been given a model that works by nature. Iodine only gets extrated from seawater (60ug/l random webpage) cost effectivly by burning seaweed (and selling it at a higher price to meth heads). I think most of these elements will only come into their own from seawater when we genetically engineer the chelating agent into a marine plant.

unionised - 6-2-2006 at 12:49

"But when you are done with the water and pump it back into the sea, you can use a large percentage of the work to suck up more water."

An admirable point, except that you can't do it the easy way because of outgassing. (At the plant, the system would be under a fairly good vacuum, which is why I ignored this- I'm not saying it's impossible- it's just rather more difficult). The more slowly you run the plant, the more nearly you can recover the potential energy, on the other hand, your income gets smaller so you can't pay the interest on the capital that you used to build the plant.
You also run into potential problems of local depletion, but these might get solved as they have been for Br2 from seawater.

has this been done

Ephoton - 6-2-2006 at 13:53

I remeber reading about that dude who tried it as stated
what if one was rather than extract only au but
to do a full extraction of elements obtainable from the sea.
then the au would just be kind of iceing.
I must agree I cant see this being finatualy feasable.
there is a lot of info on sea extraction of au but I have
yet to see anyone ever make a buck from it.

Microtek - 6-2-2006 at 14:45

Why would the system be under reduced pressure ? Are you thinking of a specific extraction process that requires a vacuum ?
The pump would have to be placed below sea level ( and so would be generating an overpressure to pump the water up ) precisely in order to avoid boiling the water ( which would likely wreck the pump ).

unionised - 7-2-2006 at 12:47

Imagine you get 2 pipes, one in and one out. Both dipping in the sea and reaching 10 M up to your plant.
Between them you put you gadget the extracts Au- say some magic absorbtion column.
Then you fill the system with sea water (say, you put bung in the bottom of each pipe and pour it in through a hole in the top, then close the hole and remove the bungs).
When you remove the bungs the water at the base of the pipes will be near atmospheric pressure. The stuff at the top will be at a pressure of 1 atmopsphere minus the water head. For 10 M head that's pretty near a vacuum.
If the water were not volatile, and didn't have any air in it then even the weakest pump would push water through the system.

You could put a pump down near the sea to ensure the whole system was under pressure (near 2 bar abs at the bottom and near atmospheric at the top). In fact, if you did that the system would be easy- you could just drain away the water from the plant- but you would lose all that energy. In order to recover the energy, you would need to close the system and install a turbine at the bottom of the outlet pipe. All perfectly possible but awkward.
What you can't do is just "syphon" the water through- helped along by a little pump.

neutrino - 7-2-2006 at 14:42

How about this: build the plant at or below sea level. Many such places exist (New Orleans, much of the Netherlands, etc.) so you could pump water through easily with almost no loss, as long as it didn't have to go above around 10m. How high are the dykes and dams in the Netherlands and New Orleans? I imagine they aren't that high.

Microtek - 8-2-2006 at 07:47

OK I see your point, but I'm not quite convinced. Let's say you had an empty 10 m high narrow siphon ( and we'll just ignore for the moment why you would want to build it so high above sea level ) with a pump at sea level. You then start pumping water into one end of the pipe and as the water level rises, the pump has to deliver more and more force. Surely when the water reaches the top and starts to descend the other side, the pump will experience less strain....

unionised - 8-2-2006 at 12:04

"Surely when the water reaches the top and starts to descend the other side, the pump will experience less strain.... "
Yes, precisely.
At the point where the water reaches the top of the syphon, the pump is working at its hardest. Once the descending leg starts to fill it sucks the water so the pump's job gets easier. That suction will pull air out of solution from the water.

Let's face it, extraction of bromine from sea water is marginally ecconomical. Bromine is rather less valuable than gold (about 3 orders of magnitude in a rather old catalogue I just looked in)but it's about 7 orders of magnitude more dilute. This is, pending some remarkable new discovery, not going to work.

Microtek - 8-2-2006 at 13:35

Oh, I have no doubt it won't be economically feasible. At least not as a huge plant for brute force extraction. I still think it should be ( conceptually ) possible to make a submarine field of some sort of sea weed or a synthetic analog which could fixate the minute concentration of gold. Then you would "harvest" the field to work up the gold.

The point of our discussion ( from my point of view ) was just to indulge in a thought experiment.
When you say "That suction will pull air out of solution from the water." do you think of atmospheric air dissolved in the water ? I was under the impression that you were talking about cavitation at the pump ( if it was placed at the top ) or at the top of the siphon.
If the former was the case then I don't think that there will be that much gas dissolved in sea water.

12AX7 - 8-2-2006 at 16:29

You'd be suprised. I always see gas bubbles on fresh containers of water sitting out, and that's ground water, not sea water. You'd have to continuously pump out the air -- which, once you get a current going, might create a convection current.

Addmittedly, the ground is all dolomite around here, so a lot of that gas might be CO2. It sure keeps the Ca and Mg ions floating, until you boil it.


Microtek - 9-2-2006 at 00:38

If the bubbles were dispersed in the water it would not be neccessary to actively remove them, as long as the flow rate in the system was significantly greater than the speed with which the bubbles rise. You would then just pump them out along with the rest.

It would be interesting to do the experiment with a 20 m long strong garden hose. If it was filled with water and the middle part was raised 10 m so one end was 1 m higher than the other ( without allowing any of the water to leak out ). What would happen when both ends of this siphon were released ? I'm inclined to think it would work like any other siphon, but maybe the under pressure at the top will disrupt the flow. Still, if this is the case, forcing water into one end should provide enough forced flow I think.

[Edited on 9-2-2006 by Microtek]

unionised - 12-2-2006 at 11:03

1 atm = 103 KPa
10 m head of sea water is equivalent to
9.81 *10 * about 1020 = 100.0 KPa
At the top of the "syphon" the pressure is only about 1/33 of an atmosphere.
On a warm day the water will boil- never mind the dissolved gases.
Let's calculate them anyway. Air disolves in water at 30C to the extent of about 16 ml/l (measured at NTP).
Drop the pressure and the volume increases while the solubility drops. In moles/Litre the solubility is proportional to the presure so 32/33 of that air bubbles out and- because the pressure has dropped- it occupies 33 times as much space. It takes up over half a litre. We are not talking about a few little bubbles here- we are talking about nearly as much air as water and the problem gets worse if you use water that is cold enough not to boil.

[Edited on 12-2-2006 by unionised]

Microtek - 13-2-2006 at 01:49

That is all true in a static situation, but I think the result will be very different when when water is allowed to flow into the low pressure zone ( or indeed when it is forced in there by a pump ).
Anyway, I don't think this discussion is really going anywhere at this point, but if I decide to conduct the experiment I'll let you know how it turns out.