gold smelting

Hello, all,
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!
Reply to
Jon Elson
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Yep. Talk to Harold - and all will be revealed.
Reply to
jim rozen
Jon: 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, -Mike
Reply to
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.
Reply to
Harold and Susan Vordos
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!
Reply to
Jon Elson
They may not like this type of scrap - PC boards and plastics mixed in, may create noxious fumes when burned.
The St Louis Yahoo group is
Reply to
Jon Elson
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 coloration.
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 do.
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.
Reply to
Harold and Susan Vordos
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 flux.
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
Reply to
Not exactly. I roast the filters first at modest temperature, until they are reduced to ash.
Ah, the ashing I do may not be hot enough to burn out the carbon before I go to the high temp firing with the torch! Thanks, that may be my problem.
Well, I use a Buechner funnel and vacuum filtration setup, so the precipitate is evenly covering the filter.
Great! Harold Vordos recommended the same thing.
Thanks much,
Reply to
Jon Elson
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 better description.
Reply to
Harold and Susan Vordos
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
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