Half a croissant, on a plate, with a sign in front of it saying '50c'
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Gold Separator

Interesting way to separate gold from dirt
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Simple Gold separating device first separates dirt by size using standard screens in a shaker. Each category of dirt is subjected to the following treatment. The gravel is sent down a tube that rotates while the exit end is under water. another tube sucks as much material back in as possible. This "recovery" tube is set back and lower so it cannot suck up any gravel because the gravel hasn't fallen through the water far enough yet. It does however capture the gold because it fell faster and got there first.
Brian the Painter, Dec 10 2012

Apollo 15 lunar hammer & feather drop http://nssdc.gsfc.n...5_feather_drop.html
As mentioned in an annotation. [Vernon, Dec 10 2012]


       You will need to do this in very compressed air if you want this to work as well as you describe. Remember in a vacuum ALL things fall at the same rate (link). Air resistance is a factor on Earth, but not an obvious factor for short falling distances and fairly dense objects (like stones and gold, compared to leaves and feathers). So, if you boost air pressure in the place where you do this, then the gold will be more resistant to that effect than the stones, and so the gold will fall faster.
Vernon, Dec 10 2012

       Isn't this pretty much what is already done? Using water to separate according to size and density is one of the oldest methods of concentrating gold.
spidermother, Dec 10 2012

       Oh boy.   

       As an aside [Vernon] - what made you think this was to operate in a vacuum? Or have we got mystery post-post editing going on?   

       Anyhoo, the author needs to understand that density separation and flow separation are different things, and that also, both exist in an industrial context, also both for gold extraction.   

       Think about it like this. An aluvial particle of gold is admirably dense. But it's likely small compared to the hard rock, quartz or sand that surrounds it. So a straight flow separation device like a classifier - where upwards flowing water is used to separate particles due to differential "terminal velocity" - tends to separate materials more due to size than density. Water is a viscous meduim and so higher terminal velocity is attribuited to - size, sphericity, then density. In that order. These things exist, and are widely used. But not for direct gold extraction.   

       Second, there's direct density separation, usually by centrifuge. There's a type of centrifugal separator called a nelson separator (good luck finding much out about them, they're usually pretty secretive) which is basically a big centrifuge. they separate directly on density, and are great at generating a "high grade" stream of concentrated gold from your wet stream in the crushing plant prior to floatation or chemical extraction, which you may choose to send directly to an onsite gold smelting room (which will have riffle decks and other gizmos in it), if you have one. However they neither separate all the gold, nor do they produce pure gold, they only concentrate it. These exist and are widely used. But not for direct gold extraction.   

       Lastly, you have hydrocyclones, which are a bit of both, and actually, a bit closer to what you're describing. I suggest you read up on them as the tuning of the vortex finder is exactly what you're saying to do with your tube. They separate for the ratio of centripetal force to fluid resistance. Once again, they're only good for concentrating dense and/or large patrticles, and won't selectively separate. These exist and are widely used. But not for direct gold extraction.   

       This leaves us with the problem that all gold mines have, and that's how to get the gold out. There's three main methods I know about- 1) float separation where finely crushed gold bearing slurry is put into tanks with air bubbled through and a surfactant "floculant" added. The gold, as well as other desired materials like copper ore coagulates at the bubble boundaries, rises, and can be skimmed off for later chemical extraction. 2) direct chemical extraction, like cyanide leeching, mercury amalgam etc. Nasty, but usually necessary. 3) physical separation - a rather laborious process of crushing, concentration, screening and then finally riffling. This is not usually used in larger operations due to it's inneficciency, however riffle decks are used in some goldrooms as the final stage before smelting, and also most "backyard" or small operations.   

       So anyway, it looks like you're trying to reinvent either the hydrocyclone, or some sort of classifier tank. I suggest you read up on both, and work out what you're trying to achieve, and whether it's likely to work.   

Custardguts, Dec 10 2012

       Oh, if searching, they're Knelson concentrators. If forgot the K.
Custardguts, Dec 10 2012

       I'm from the Yukon and the son of a goldsmith/miner. My question is not weather or not this would replace the 97% effective methods they have now. Instead i wondered if equal sized and shaped particles fall through water at different enough rates. I think this would look cool if the barrel was made of a clear material.
Brian the Painter, Dec 10 2012

       If the particles are equally sized and weighted, the denser ones will of course sink faster. Or in your example, fall faster through a rising column of water. It's just that normally, you don't get equal sizing and shape.
Custardguts, Dec 10 2012

       Yeah I remembered later that nuggets tend to be a bit flattened. I see now that this would look a lot better in my head than in reality. I'm still going to try it with jelly one day.
Brian the Painter, Dec 11 2012


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