Scrap Gold

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as best i can tell from reading on the subject: cleanup should be done in a fume hood WHILE wearing s.c.b.a. minute traces of hydrogen cyanide can be deadly at 225 ppm. you were advised to use sodium hypochlorite with H2O2 and/or nitric acid. i have never used cyanide and hopefully never will, of coarse it would be beneficial to know how to deal with it if the opportunity arises though.

You'd be well served to ask the opinion of one of the chemists on the forum before introducing H202. With free cyanide present, the addition of oxygen may simply re-dissolve some of the gold. I don't know that it would, or would not. Get that clarified.

Harold

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Be sure all of the glassware and filtering setup (buchner, hoses, pump, and beakers) have been treated inside and out with a soda ash solution before it is used for the cyanide filtration process to remove any traces of acid on/in the equipment. Before using the equipment for acid reactions again be sure to wash all of it with 30% peroxide to convert the cyanide to cyanate. Wash the soda ash scrub off with water into your acid wastes. Wash the peroxide scrub off with water into your cyanide wastes. Do not mix these wastes!!!

Vaccum filter off the zinc/gold into a large buchner setup that has been prepared as listed above. Wash the mud throughly with water until the wash liquid runs clear through the buchner. An extra water wash never hurts.

In a fume hood add your HCl to the mud to dissolve the zinc. If you suspect silver to be present use 35% HNO3 to dissolve the zinc instead of HCl. The silver will report in the nitric acid wash.

The Zn/Au mud is allowed to react with stirring for several hours. Continue additions of acid if the reaction is still vigourous after stirring and waiting. Allow each acid addition to react throughly before adding more. Once the zinc has all reacted, vaccum filter again (in the peroxide scrubbed equipment) and proceed to refining the dark brown mud again in AR.

Steve

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Gold dissolved in cyanide solution is clear. The gray color must be from fine particles in suspension. After vaccum filtration my solutions are always 100% transparent to the point where you can read the newspaper through the liquid.

The red color is common and is likely from iron and cyanide together in solution.

Steve

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Noble Metals Recovery said:

OK, now's a good time to tell the whole story. Here's how it was told to me. About 12 years ago a manufacturer was planning on plating some metal with gold, (my guess is that they would have to have been making their on plating solutions). They would get in the some gold metal, and then the employees would steal it. So, when they received 20 ounces of gold, they put it in a Nalgene plastic jug, filled it with water and dropped in about a pound of cyanide.

That's how it has set for the last 12 years or so. I recently had it delivered to me to retrieve the gold. The pH tested at about 5. I've done sporadic gold refining for the past 15 years, but have never handled cyanide before. My plan from the beginning was to NEVER handle cyanide. I have to admit, the prospect of retrieving 20 ounces of gold was enough to tempt me. I'm working on a commission basis, part of the gold is mine. I did not have to put up any money up front. The owner is completely trusting me regarding the yield of the gold. My goal is to safely extract as much gold as possible for my benefit, and mostly for my client's benefit.

When I got the jug it had a fine brown powder on the bottom, a pinkish red liquid, and about 3/4 of a pound of cyanide crystals. I separated the mud and melted it, that's the nugget you see above in my first post.

Last night I took about 3/4 of a gallon of the liquid, added in some cyanide crystals, and with potassium hydroxide I raised the pH to over 12, (actually I went to far, closer to 14). Then I sifted in about 3 ounces of 325 mesh zinc powder, and put in a piece of zinc metal. There was a strong reaction. This morning things have quieted down. There's a layer of zinc looking mud on the bottom of the 5 gallon plastic bucket.

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Hey, Steve,

I doubt if the company's intent was to make a homemade plating solution. Probably 99% of the gold baths in the world are made from proprietary salts.

The proprietary, water soluble, gold plating salts sold for either the initial make-up or gold replenishment of a plating bath are potassium gold cyanide (PGC). If this is a common hard gold bath, which has a pH between 4-6, these salts can also contain a pink cobalt salt (thus, the color of the solution). At room temp, the solubility of gold, as PGC in water, is about 3 tr.oz. per liter. Some proprietary hard gold baths also contain EDTA, which complexes the cobalt and produces a more intense pinkish/reddish color. There also can be a little citric acid/potassium citrate in there to buffer (maintain) the 5 pH.There are also blue or blue/violet cobalt compounds (the slag on the button?). If these solutions sit around for a long time, they can decompose and produce a crystalline precipitate which usually contains part of the gold.

It sounds like this is what you have - everything seems to fit. The pink solution can be treated as in the process I gave here (last post on this page). The cobalt, citrates, and EDTA should not interfere with this process.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=45&t=12735&hilit=cyanide+zinc&start=60
Note in step 1 the addition of some extra free cyanide. Since there is no free cyanide in that solution (the pH is supposedly about 5), it can very well help the zincing to add some cyanide after adjusting the pH to 12.

On the 3/4 gallon you have already zinced: It sounds like you added too much sodium hydroxide (a pH of 12 is adequate) and that's why the zinc was so reactive. If you have filtered and rinsed the zinc precipitate very well with hot water, I would put it in a plastic bucket, outside, cover with distilled water, and add small increments of nitric until an addition produces no reaction. Then, filter, rinse well, and dissolve the residue in AR.

What you are calling cyanide crystals (3/4# - those in the original solution) very possibly could contain gold. You need to try and dissolve these before doing anything else to them. This may be as simple as adding some water and heating the solution. If they do dissolve in the hot water, adjust the pH to 12 and go through the zincing procedure. Here again, an addition of cyanide will help. If they don't dissolve in hot water, let me know. If all the crystals dissolve but some brown powder remains, it is likely gold. I wouldn't filter this out. I would just let it remain and collect it along with the zinc.

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I made mention of the possibility of dissolving gold if H2O2 was added.

It might pay you to explore the process known to jewelers as *bombing*. Free cyanide and H2O2 are used to instantly clean the surface of gold by dissolving a small portion.

Harold

Harold the bombing solutions still have cyanide in them so the only way to reclaim them I know of is zinc dust and then dissolution of the filtered and washed powder with acids. Not sure if this is a step forward or sideways as it's another process that get you no further forward.

nickvc said:

Harold the bombing solutions still have cyanide in them so the only way to reclaim them I know of is zinc dust and then dissolution of the filtered and washed powder with acids. Not sure if this is a step forward or sideways as it's another process that get you no further forward.

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I agree on the recovery, but my concern is that there may be enough free cyanide present in the case in point where the addition of the H2O2 will simply re-dissolve some of the gold.

I guess the real question is, will there be enough zinc present in the proper state of oxidation to cause any gold that might be dissolved to re-precipitate?

These are the kinds of issues that make me wish I had gone for an education in chemistry. Sure would be nice to just *know* things like this.

Harold

I agree on the recovery, but my concern is that there may be enough free cyanide present in the case in point where the addition of the H2O2 will simply re-dissolve some of the gold.

I guess the real question is, will there be enough zinc present in the proper state of oxidation to cause any gold that might be dissolved to re-precipitate?

These are the kinds of issues that make me wish I had gone for an education in chemistry. Sure would be nice to just *know* things like this.

Harold

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Harold I'm fully behind you on that, I know things work but haven't a clue why.
I was just chatting on the PMs to another member and said honestly that much chemistry might as
well be written in ancient Hebrew for all the sense it makes to me.

Edited due to posters idiocy