I haven't had much luck on the jewelry newsgroup, so I'm wondering if
anyone here has some goldsmithing experience. I am recovering gold
from electronic scrap, and the current difficulty is smelting the
gold out of the precipitate. I first cook the filters down to ash
in a crucible with a propane torch. Then, I got some cupels to smelt
that ash. I do get gold out of it, but I also get a greenish-black
glassy substance that is impossible to remove from the cupel, and pretty
hard to get out of a crucible, either. What IS this stuff? Is it some
gold-bearing salts that just need to be cooked more to burn it down to
gold? Is it something combining with the flux? (I'm using borax flux
that I got for brazing.) Am I using too much flux, or not enough?
I've already destroyed one cupel, and it is hard to separate the
refractory from the gold and the green glop.
I'm doing the smelting with Oxy-Methylene (generic MAPP).
So, any tricks to make this easier would be greatly appreciated!
You're in St. Louis, right? So am I. Call, or better yet go to Hauser
Miller. They are refiners/reclaimers for the dentistry and jewelry
trade located here in St. Louis. Highly respected for their integrity.
They should be able to help you extract your gold. At the very least
they can give you a price to extract it and pay you for it. Worth a
phone call anyway. Also, is there a metalworking group here in St.
Louis? Email me off line with that info. -Good luck,
It comes as no surprise to me that folks on a jewelry group wouldn't be much
help in refining. Rarely do you find a jeweler that knows anything about the
subject. They generally don't do their own, although I know one that does.
I can't imagine what you're accomplishing. For starters, a cupel won't
give you gold of any quality when you start with low grade material-----not
unless it is a huge cupel, capable of absorbing a lot of lead, and you have
a proper muffle furnace. Are you using a cupel, or a melting dish?
They're not the same critter.
Fluxes help in absorbing some of the crud, but melting and fluxing won't
give you gold of any quality. Unless you're prepared to work with acids,
you're not going to be very happy with your outcome.
Do you have any experience in gold refining? Would you like to share with
me exactly what you're doing, so I can provide some pointers on what to
abandon, and how to accomplish your mission?
Be advised, working with electronic scrap as a source for gold isn't the
smartest thing you can do. There's generally a very low amount of gold as
compared to base metals and other waste material. Typically, so much that
it isn't worth the effort. Note I didn't say it wasn't worth the
value----good money can be made recycling such material, but not on a small
basis. It requires large equipment and a way to dispose of a lot of waste.
As far as I know, these are cupels. A soft, friable refractory, with no
glaze on it.
Well, there shouldn't be any other metal in there but gold.
I am using Technic's Techni-Strip AU, a gold salvage compound based on
the cyanide process. it is VERY effective at leaving all base metals
alone, and only removing Au and platinum group metals. But, there
should be only gold on the scrap.
Recent scrap has very thin gold plating. But, a lot of this stuff is
from the 1960's, and the gold is VERY thick, up to .0005" or so! There
may be some measurement error here, but I weighed a loss of 200 mg from
ONE 4" long piece of card edge! I later doubted my measurement, and so
did a bunch of card edges, and got about 50 mg per piece as the average.
With gold running at roughly $13/gram, that works out to $0.65 per card
edge, at 50 mg each.
The Techni-Strip AU removes only the gold, and it works like a charm.
The problem I am having is precipitating the gold back out of the
solution. I've seen all sorts of schemes, such as adsorbing it onto
activated carbon, ion exchange precipitation with Zinc (but that
contaminates the gold), electrowinning, ion exchange resins, etc.
I haven't tried the carbon yet, but the rest work, but are a lot of
effort, and I'm only getting a small part of the gold back out of
the solution. I'm a little afraid of systems to break down the cyanide,
as I don't want to gas the neighborhood!
I have gotten several grams of gold, some of it looking VERY pure, in my
pilot experiments with this stuff before I go into full-scale
production. I'm pretty sure I can burn the Zinc out of this with acid,
if that proves to be the best process.
As for the bulk of the waste, that has been discarded years ago. I have
crushed connector shells, pushed pins out of backplanes, cut card edges
off, etc. over the years, packing the gold-bearing parts into a fairly
small pile of ~ 100 Lbs.
Thanks for any insight into what I'm doing right and wrong, here!
Clay melting dishes have a similar appearance, although they're not very
soft. If you purchased them from a reputable firm that represented them
as cupels, they probably are. Cupels are typically made of bone meal, are
typically quite thick (so they can absorb litharge), and have a light tan
Chuckle! What do you think the discoloration is coming from? You're
seeing traces of oxides of base metals in your flux, otherwise it wouldn't
be colored as it is. The idea that you can extract gold in a pure state
is interesting, but it simply doesn't work that way, in spite of the claims
you may have read.
It's highly unlikely it's *very* effective at leaving base metals behind,
although it will limit their dissolution. All it takes is too much cyanide
in solution and it will dissolve copper.
Unfortunately, you made no mention of the fact that you had dissolved the
gold with a cyanide compound, so I had no clue what you were attempting to
You really should hear the (true) story of a guy that came to me after a
summer of mining placer gold. His story was much like yours, but in his
case, his father-in-law died while they were extracting their values.
One bit of advice. Don't let gold take over your good sense. If you do
so, you're going to be unhappy with everything you do in the process of
extracting it, having unreasonable expectations being the chief cause.
The problem with your calculations is you're basing your findings on the
idea that you're taking off nothing but gold. I seriously doubt you are.
Been there, done that, got the T shirt. Before I closed the doors on my
machine shop, I was refining on the side, for pleasure. One of the
products I produced in the shop was a wire wrap connector for Univac. I
purchased a standard connector from Cinch, then modified it, making three
from one. Granted, this was in the late '70's, but the amount of gold on
the pins was known, and it was about .000080". While I don't doubt you
may be finding higher levels of deposition, unless you go back to wave-guide
assemblies, very early (when gold was still $35/oz) , it's pretty hard to
find gold that is plated very thick.
Or, you're getting a good recovery, but you aren't getting as much gold off
as you think you are. It's also entirely possible you are unwittingly
tossing the gold out with the sludge, having self precipitated. That's not
uncommon, either. As long as you haven't discarded any of your waste
materials, you haven't lost anything, however. Are you titrating your
solution so you know the concentration level of free cyanide?
I've seen all sorts of schemes, such as adsorbing it onto
Forget all the *schemes* and use zinc flower, particularly at the level
you're working. Your gold is already contaminated, like it or not. Zinc
is virtually 100% effective, and very inexpensive to use. Getting rid of
excess zinc is no trouble, and can be as simple as distilling it off,
although it's very easy to remove with acid. Do you have a fume hood in
which you can work safely?
Looks can be VERY deceiving where gold is concerned. Gold, in the pure
state, melts with NO oxides on the surface, and stays bright yellow with a
glistening surface when cooled. It has a green luminescence in the molten
state, and is free of surface scum. It also pulls a deep pipe as it cools.
If your gold doesn't pull the pipe, or it's dull, or frosty looking, it's
hardly pure, although it could be quite good. If you'd like to see pic
of a dish of (pure---9995+ purity) gold pellets, ask and I'll send it to you
for comparison as to color and appearance.
Cool! It helps a lot to have information. I've recovered gold from
almost anything you can imagine, including carpets, but providing good
guidance is difficult without knowing the circumstances at hand.
I won't bullshit you, Jon. I had countless people laugh in my face when I
started playing with precious metals, but my "hobby" turned into a full time
job and a business that I sold when I retired. You can do it, just as I
did, but you'll have to learn to walk before you run. Take it slow and
easy, until you clearly understand what the reactions are, and how to
control your losses.
What might be best for you to do is contact me on the side, and give me more
details on what you're doing. Frankly, I think you're going about it
wrong, but I'm not sure. One thing I am sure of is you won't be able to
achieve a high degree of purity without actually dissolving the gold and
precipitating it after you've recovered it-------or running it through a
gold cell. It should be of high quality to do that, though, and you must
have several ounces of pure gold just for the electrolyte. Chemical
refining is much easier. If you don't adhere to this, you'll end up
selling your gold as scrap, when it can be sold to jewelers at spot prices
or slightly above if you provide good quality.
I did a boat load of gold and silver refining back in the late 70's.
In fact for several years, The Jewelery section of the art department
was a larger consumer of Nitric acid than the chemistry department,
thanks to my efforts.
The main thing I learned is that it is cheaper in the long run, to pay
someone else to do it.
The problem is that you are burning out the paper filters with the
borax flux. This turns the borax into a glassy substance that seems to
be completely insoluable.
You have to minimize the amount of paper charcoal that mixes with the
First rinse the filter down well with distilled water until clean and
white and your precipitate is all collected in the bottom of the cone.
Allow the filter to dry completely and snip off the section with the
precipitate. Don't sweat small amounts stuck on the paper, even at
todays gold prices it doesn't amount to much.
Then, when you collect enough filters, get a clean castiron frying pan
with a lid, put the filters into it and roast it until the filters
turn to ash. A little salt peter helps consume the paper.
Then put this residue in your crucible and melt it.
Paul K. Dickman
But not a cast iron pan. Takes too much energy to get it hot enough to be
useful, and you risk cracking it with a torch when you apply it to the
bottom. I recommend old stainless pans for such use, or just plain steel,
which doesn't last as long, and contributes oxidized iron to the results.
No big deal if you're going to refine properly, anyway. Used them for
more than 20 years with good results. By burning filters until they're
carbon, you can raise the temperature high enough to ignite the carbon by
playing a torch on the bottom of the pan. It takes very little time to do
it. I used to use a large Hoke torch, sort of a rose bud, for lack of
We roasted ours over one of the coal forges at school, so cast iron
worked out well. Harolds right though, if you're using a torch,
stainless seems a better choice. It would also be easier to clean all
the dust out of it.
Paul K. Dickman
On Fri, 12 Aug 2005 10:50:27 -0700, "Harold and Susan Vordos"
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