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BromicAcid
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Precious Metal Recovery from Scrap
eBay offers a number of lots simply by searching 'gold scrap' or other similar phrases for cell phone boards, outdated processors, etc that are gold
plated or contain silver/palladium or other metals. Apparently there is some kind of market for it because they do in fact sell and there are CD's
available on eBay for $$$ that offer to tell you the secrets of recovering these metals at home.
With that background out of the way there are two questions that I pose here:
1) Is this cost effective on a home level?
Gold is at an incredibly high price at the moment that corresponds to something like $20 a gram and if you can get 450 grams of waste for $11
including shipping, you got to wonder if it is worth it. Although I am assuming you can with some practice pick out the lots that are going to give a
higher percentage of gold though I would think things are just gold plated with that gold leaf and therefore you'd get almost no gold.
2) Providing you would get some noticeable gold/silver/etc from the circuit boards/transistors/etc what would be the best way to obtain it?
I'm guessing the best way would be some sort of cyanide bath. Barring that I was thinking soak in HCl to get rid of the less noble metals, then
HNO<sub>3</sub> to pull out the silver and copper and such and finally some aqua regia to get gold but I'm sure there is a better way.
This is just something I was thinking about after noticing the auctions for these boards and how much some of them go for coupled with the high prices
of these metals as of late.
(I did some google sleuthing and found a few commerical sites that preform this service, I also found a small amount of information on doing it at
home, but nothing really about how economical it can be.)
Edit: I overlooked a similar though more focused thread:
https://sciencemadness.org/talk/viewthread.php?tid=5317
Edit again: Made the subject more expansive.
[Edited on 4/28/2006 by BromicAcid]
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The_Davster
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Have you seen http://webpages.charter.net/kwilliams00/bcftp/front.htm
?
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12AX7
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Commercially they melt it all, treat the stack gasses (chlorinated plastics, eh?), add flux (if needed- fiberglass boards, being glass, melt well
enough already) and let the metal fall to the bottom. Electrorefine the blob.
These days, it's just barely econominal, with economy of scale and less-than-free scrap.
I know a fellow who was a refiner for many years, for instance he would clean up used crucibles and dishes and stuff from jewelers, etc. He says
electronics that aren't chock full brimming over with gold are *not* worth it.
FWIW, he used a lot of fluorospar, which you can imagine ate through his high-alumina furnace lining, requiring a replacement every so often.
Tim
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BromicAcid
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Yes, I saw that site some time ago though not relating to this. I knew something of the halide leaching but it slipped my mind. I might give it a
try, I have 1 old processor, too bad my scale doesn't go to the first decimal place. Still, how much gold would say 500 grams of scrap contain,
that's where the real quesion lies.
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The_Davster
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Well depending on the age of the electronics, you want them as old as possible from before they switched from pure gold to electroplating. Test the
flexibility of the pins I guess?
The other day I was thinking about this myself, so I ripped ~5 prongs off a p2 processor and dissolved it in 3:1 aqua regia. I got the charastic gold
colour within seconds. I had not done my research so I had forgotten how to recover gold from this so I just basified and got a blue ppt, must be all
the copper in the prongs. How would the HAuCl4 react with base anyway?
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denatured
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A while ago i watched a documentary about what you are talking about ... it was about a successful business in Japan (making platinum & gold out
of garbage) ... cause as you know in japan there are a lot of cell phones thrown in garbage every hour... they said it is profitable...
About the yield ...
The amount of metals in a metric ton (1,000 kilograms, or 2,205 pounds) of cellphones (about 16,670 handsets):
GOLD -- 0.4 pounds
SILVER -- 2.6 pounds
COPPER -- 255.7 pounds
PALLADIUM -- 0.2 pounds
STEEL -- 205 pounds
ALUMINUM -- 83.8 pounds
Edit:sorry .. link to article requires registeration ... i've attached it.
[Edited on 27-4-2006 by alnokta]
Attachment: article.zip (28kB)
This file has been downloaded 1074 times
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BromicAcid
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12AX7, I was under the impression they used cyanide as the main tool to get the gold due to:
http://www.cyanidedestruct.com/precious_metal.htm
It was one of the first pages that came up with respect to searching for precious metals and recovery from circuit boards. I decided to put my one
processor from 1995 into a beaker with some sodium hypochlorite and sodium bromide and let it sit for a day, if I get anything I will post about it
here for fun.
Edit: Thank you alnokta, that's one of the things that I wanted to know 
[Edited on 4/27/2006 by BromicAcid]
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12AX7
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Yeah, but the thing is, you've got all those wires and stuff coated with epoxy (black or PCB) and ceramic (inside the sealed 486 chip and etc!), for
maximum yield (profit) you really have to break it all down and fire is a pretty cheap way of doing that.
Tim
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BromicAcid
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Following the procedure on the link Rogue Chemist provided, I preformed the halide leaching method that A.K Williams describes. Lets see, a Pentium
100 mhz chip was put in a beaker with a large pinch of NaBr, enough bleach to cover it, then just to be sure about two ml of elemental bromine. The
beaker was covered with a plastic bag and allowed to sit for 17 hours or so.
The result was the first image in the upper left-hand corner after it was agitated. Previous to that strange stalactites (the ones that grow down) of
what looked like rust grew off the pins of the processor. So, I removed the processor, washed it off into the beaker and set the processor in some
HCl, all of the rust looking material sure enough dissolved and it kept reacting, there are some silver colored pins under everything that refuse to
dissolve that might well be silver or something.
But onto the gold extraction. The second picture to the right shows me filtering the material using suction filtration and I was left with a deep red
solution that was without free particulates. I made a solution of KOH by dissolving maybe 5 grams of KOH in 50 ml of water and it is shown in the
bottom left-hand corner picture next to the filtered red crap.
Upending the pretty red solution into the KOH solution resulted in a immediate discoloration of the redness and a heavy black precipitate (Bottom
right-hand corner). You can still see bromine vapors in the other flask. So, I tried to filter out the black crap but it is too fine for the filter
paper for the most part, though some remains trapped.
So I have all of this black precipitate which may be gold or something else. The site says that it is gold which make sense in that the driving force
in Aqua Regia and indeed in this method is the formation of the AuCl<sub>4</sub><sup>-</sup> anion and once you add KOH you
destroy the ability for this to exist but what else is carried along with it I have to wonder? Copper likes to form a similar chloro anion as do a
number of other transition metals. I guess I will smelt what I have after I process a few more computer pieces and see if I get something that looks
like gold.
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Twospoons
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Did you expose the chip? There's probably as much gold in the bond wires as there is plated onto the pins.
Helicopter: "helico" -> spiral, "pter" -> with wings
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BromicAcid
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Yeah, I broke open the ceramic looking part of it to reveal the chip itself. I never thought it would look like it did, very shiny covered in glass
or something. The chip itself looks like it might be made of gold but I didn't break it open, the wires leading to it were thinner then hairs and
looked to be made of silver. If I honestly give this a go I will smash up the chip better first.
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12AX7
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If you actually broke the chip, you'd see shiny silicon. If you desolder the bottom panel, you'll reveal the "modern cathedral" as it has been
called.
Here's some I opened up. 
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zoomer
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The "glassy" top to the chip is the passivation layer applied to prevent contamination during further processing.
The "silver" looking bond wires are actually aluminum. Nether silver or copper are used in the manufacture of ICs. Newer ICs (like 2005+) use copper
bond wires.
There are a few micrograms of gold used in the bond areas, but you will find far more gold plated on the pins. Total that with any exotics used in IC
manufacture is still probably less than 10 milligrams precious metal / chip. It's probably not worth the money you paid for the calories you had to
ingest to hold the hammer to smash them in the first place.
Z
[Edit] Nonetheless, a very interesting experiment, Bromic, thanks for the pics!
[Edited on 28-4-2006 by zoomer]
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Fleaker
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Nice to see you have an interest in this Bromic. Unfortunately, it really is not worth your time, even with the astounding prices of all precious
metals lately (market uncertainty or what eh?...actually, heard a very good lecture by a VP @ B&W about oil's influence on energy market a week
ago, but that's OT). Unless you can acquire material from specific year that assays for a known value in precious metals, it's a losing proposition,
trust me, I've looked into it. You also need a lot of it. If, however, you manage to get enough, don't bother with basified cyanide stripping baths,
or aqua regia for that matter. I wouldn't even use the late doctor's method (I have it on good info that the man who authored that website died
recently) of halide extraction, which in my honest opinion, is best applied to the extraction of PGMs from catalytic converters (that's a winning
proposition--if you have the right connections--you can make a LOT of money by doing that). I'll try and dig up a patent # for one such process.
Ok, coming to my point: I suggest you take all of the scrap, and either add it directly (or first burn to ashes), to molten copper. The copper will
readily absorb all precious metals and is then cast into an anode shaped ingot which is finally electrolyzed. Current density, operation temp, and
other conditions depend on cell size and target material. The more noble metals will fall to the bottom as a sludge, while pure copper will plate out
on the other electrode. Junk metals like iron and zinc will go into solution. Eventually empty the cell of the dense brownish powders, wash with
distilled water, then with 6M HCl and filter. After that you'll have a mixed bag of precious metals and you can put most of them into solution with
hot aqua regia (after simmering with HNO3 to remove silver and palladium) and then precipitate the gold and platinum at your leisure.
Copper is the easiest way to concentrate your values, and if you build a large reverbatory furnace (consult tim here) you can add the boards and
dental waste directly to the liquid metal. It's faster, just as effective, more fun, and less reagent intensive.
BTW, a good method for dropping out gold powder in an acidified, nitric acid free solution, is with SO2 which I can say from personal experience, is
fast and relatively cheap if you can find a supplier for the cylinder. Sodium sulfite works almost as well. Since AuCl3*3HOH (and chloroauric acid) is
a strong Lewis acid, it complexes readily. Also stains your hands a nice brown color for weeks on end. If you're into something more exotic, try
dibutyl carbitol (a glyme) as a selective reagent for the isolation of Au (III).
Any questions, message me privately or post further! I've done a fair bit of work with the precious metals, namely Pt, Pd, Ag, and Au.
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jimwig
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Correction that was supposed to be
The Recovery and Refining of Precious Metals.
by C.W.Ammen
(well i guess i didn't post that after all)
[Edited on 28-4-2006 by jimwig]
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BromicAcid
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Speaking of catalytic converters although a bit off topic (no longer off topic as I bordened the topic area), there is a seller on eBay that's selling books or CD's or something with instructions on how to extract precious metals from catalytic converters for $100 or
so plus exhorbrant shipping rates. And apparently they are actually selling them continuilly and additionally they have two seperate books on the
subject and encourage you to buy both at $100 each or so..... pitiful....
I considered recovery from such sources at one time when I needed some rhodium for a catalyst but abandoned it when I began to wonder exactly how I
would get a catalytic converter in my neighborhood.
[Edited on 4/28/2006 by BromicAcid]
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jimwig
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Don't have it in front of me right now But there is a government report (Google?) detailing catalytic converters. Not that impressive since the
technology for making CC's changed. They now use a different type of technology and consequently smaller amounts of PGM's. The older models were much
more viable for recovery.
From memory so don't quote me on this.
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Fleaker
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Considering the hundreds of thousands of used, older model cars, I'm not too worried about finding the proper type of converter. Irregardless, jimwig
has a good point. I do find that funny Bromic. Given our convenient command of chemistry (bit alliterative there  ), us amateur and professional chemists here could easily do what they claim, and do
it better! $100 for common sense? The claims put forth are bogus. The most net earnings I've *reliably* is about $50,000 from 710 mixed converters
(equivalent to a ton) via gas transport extraction. Still, considering that covers materials and purchase price, money can be made. The only problem:
acquisition of a steady supply.
Yes, I'm familiar with Ammen's book jimwig, it's quite nice; I prefer it over his "Metalcasting" which has a good bit of errors.
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lordmagnus
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Metal Leaching
Godz,
They do that sorta stuff in 3rd world nations, they recycle hard drives, and such, and soak the circuit boards in hot solvents, the filter out the
undisolvables, and runs them through an acid treatment, etc.. they dump the acid and solvent refuse in rivers and canals. It's really not worth it,
unless your collecting the stuff to export to them.
I\'ll kill a man in a fair fight, or if I think he is gonna start a fair fight, or if he\'s bothrn me allot, or if I am getin payed good, or probably
over a good woman.
-Jayne Cobb (Serenity) |
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BromicAcid
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They should be recycling metals a lot more, I read somewhere that each American consumes 25 lbs of copper a year and by consumes I mean they throw it
away. It's one of the contributing factors to copper being on the rise to such an extent. I have to wonder how long it will be before mining
landfills will become profitable enough.
As it is, gold is still on the rise, going from $640/ounce when I wrote the first post to $680 an ounce now. And that's in less then two weeks. A
senator was on television stating that gold is not up, the American economy is down. He told people that they should not be investing in gold but in
the economy even though gold will continue to rise.
For fun I 'harvested' two computers from the trash and took out all the gold colored parts. I've had them soaking in HCl for two days and they are
still bubbling. Then I will soak in nitric. Then Aqua Regia. I don't think I will get much but it's pretty fun. Maybe I should cut the foreplay
and just open a gold mine though.
Edit: By the way, my local scrap yard buys circuit boards for a fairly substantial sum. On par with aluminum (a shocker for me) ... and here I
thought they were trash.
[Edited on 5/6/2006 by BromicAcid]
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The_Davster
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How much for circuit boards? I happen to have just seen a dumpster today pretty much full of them....
It is amazing the waste of precious metals, in my lab job I was the only one there for a little while today, I went into the 'empty' bottle disposal
bucket. There was still about half a gram of gold powder in one and about 3g of Pr in another, but Pr is not a precious metal. I also was at the
chemical recycling centre at my uni today talking to the guy running it. Apparently they get even gold and platinum there when noone needs them, they
are then free to faculty.
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skippy
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Where I could see a book on cat converters being worth it is if it gave good advice on the wheeling-dealing aspect. Its one thing to have technical
knowledge of processing the things, but unless you know what to pay and how to get the most raw material for your time, then you might just spin your
wheels.
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Till_Eulenspiegel
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REAGENT USED IN COMMERCIAL GOLD RECOVERY
(With precious metals values at or near all time highs, now seems like a good time to present the following information.)
This reagent quantitatively reduces gold from solutions of Au(CN)2 - sodium dithionite, CAS # 7775-14-6, also known as sodium hydrosulfite. It's
used routinely in large commercial gold recovery operations. Sources of gold for these systems include electronic scrap and other plated materials:
circuit boards, plated connectors, "fingers" (plated zones on circuit boards, non-gold portion mechanically removed), crushed integrated circuits,
plated wiring harnesses, pins, etc. Naturally the denser the plating, the greater the yield of gold. Mil spec items usually have the densest Au
plating.
The actual recovery process is as follows:
Solutions from the strip tanks are decanted and pumped into a stainless steel tank equipped with an efficient mechanical stirrer and submersible
heater. (You might get by using an external propane burner for smaller scale work.) The setup is located in or near a hood, since toxic gasses are
evolved, as is a rather considerable stench. The solution in the precipitation tank is heated to 180 degrees F, and with efficient stirring, the pH is
increased to 13 with predissolved concentrated sodium hydroxide. Sodium dithionite is then added in small portions. The solution transitions through
about 7 colour changes, depending on presence or absence of Cu, Ni, Ag, etc.
Course of the reduction reaction is followed by atomic absorption spectrometry. Even a single beam instrument like an old Perkin Elmer 101 will work
well. You have to matrix match standard and sample however. This is real important since the CN- anion suppresses the signal. Use the Au line at
242.8 nanometres. Just calculate the cyanide anion concentration initially present in the strip tank and prepare the AA standard with the same [CN}-
concentration.
Additions of sodium dithionite are made until the reaction is complete. Sodium dithionite will reduce the gold concentration in the precipitation
tank to 10 ppm or less. Minor amounts of Ni and Cu will also be present in the precipitate. When the reaction is deemed complete via atomic
absorption, stirring is stopped, and the tank allowed to cool to room temperature, usually overnight. Then the spent strip solution is very carefully
pumped out, and the precious metals sludge is recovered from the bottom of the tank. (Actually a turkey baster type suction apparatus works well
here). Using quantitative transfer technique, the gold sludge is transferred to a Buechner funnel & vacuum filter flask and rinsed with
deionised water prior to purification.
Use of sodium dithionite in gold recovery is essentially an industry trade secret, as far as I can tell. For example, you won't find any mention of
it in C.W. Ammen's "Recovery and Refining of Precious Metals" or George Gajda's "Gold Refining" (ISBN # 0-686-17797-8). Both texts are to be
recommended very highly, however. Zinc precipitation is the ancient traditional method usually taught to precipitate Au from CN- solutions- overall a
tremendous hassle compared to the use of sodium dithionite.
More details on purification, as well as how to set up the strip tanks, in my next post.
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evil_lurker
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The only scrap I can see worth recycling is catalytic converters.
Each is supposed to contain 1-3 grams of platinum per cat which nowadays at around $40 a gram makes them very attractive targets for recycling.
Any ideas as how to get it out?
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Fleaker
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I mentioned earlier that it can most cheaply/efficiently done with a gas phase transport, wherein the operator fills a stainless steel tube with the
crushed, pre treated converter and then passes a hot halogen gas (400+C) through. The halogen oxidizes the Rh, Pt, Pd, and other metals into their
volatile halide salts, which then can be removed from the system through a cold finger at one end of the apparatus (where they deposit as a brown red
crust).
I have done some preliminary, small scale (1-3 converters) runs and can say it is better in yield than the hot aqua regia technique which inevitably
leaves some Pt and a Rh.
Feel free to U2U!
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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