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Aqua regia IS acid. It's a combination of HCL & HNO3.

If you don't have a copy, look for the book Refining Precious Metal Wastes, by C.M. Hoke. It's a wonderful book, published in the early '40's, as I recall, that will teach you to process gold wastes properly. Hoke was a chemist that wrote for folks (like us), that may not have a chemical background. I learned refining from that very book, back in the early 70's.

For your information, Rio Grande (Jewelry) Supply, I think in New Mexico, used to sell a reprint of the book for a reasonable price. Don't know it they still do.

Aqua regia isn't proper for dissolving yellow alloyed gold. The presence of silver makes dissolution difficult, if not impossible. You can literally boil heavy cross sections of 14K gold indefinitely in aqua regia and not dissolve the gold due to the impervious layer of silver chloride that encapsulates the gold, protecting it from further action. It's the presence of chlorine (HCL) that creates the problem. I've had minimal success with 10K, but it's a struggle. Much easier to inquart the stuff with silver and run it with nitric first.

Processing karat gold is accomplished either by raising the gold content such that it represents no less than 90% of the alloy, and is then dissolved in aqua regia. The alternative is raising the base metal content until gold comprises only 25% of the alloy, at which time the base metal is dissolved with nitric acid. Once the base metal is removed, the gold will then dissolve easily in aqua regia for purification.

If the items you have in your possession are thin enough, you can run them in nitric to eliminate the base metal, then go after the remains with aqua regia. It's likely that the little remaining silver won't be adequate to stop the gold from dissolving. If it is, you'll find a thin layer of gold that has a green appearance (that's the silver chloride) that refuses to dissolve. I feel that scenario is highly unlikely, however. It should work fine if you start with nitric and water, and pour off the solution before starting with aqua regia. Be sure to recover the silver from the solution. In this case, it's wise to do that with copper plates, for there may be lead present. Use the nitric sparingly---use only enough to do the job. Boiling helps get the mileage out of the acid. I used a gas fired hotplate for that purpose. You can do that outdoors if you don't have a fume hood.

For your information, it's always a good idea to heat things to redness before starting the refining process. The presence of oil creates problems later-----and there's no better way to eliminate it than by incineration. It makes the stuff look ugly----but does no harm if all you intend to do is extract the values.

Good luck!

Harold
 
THANKS FOR THE INFO ILL TRY YOUR METHOD I KNEW AQUA WAS ACID BUT FIGURED IT WOULD WORK LOTS TO LEARN
VAN
 
The amount isn't really important. When water is added, the hydronium ion assists the dissolution, so you actually get better mileage from the acid, or so I'm told. I'm not a chemist.

My usual practice was to add about as much water as nitric. Too much just makes the action slower, but if you heat the work it won't make much difference. The one thing to learn is to control the amount of nitric you use. It's clearly a PITA when you use more than is required. A little experimenting will get you familiar so you'll have a sense of direction.

Be careful with some of these metals. They are quite eager to react with nitric and can do so almost violently. Use a large beaker with a little solution, so there's enough room for the foaming without boiling over. If that does happen, depending on circumstances, wipe everything up with paper towels, then incinerate well. As long as you don't toss anything, you won't lose the gold, even if it boils over. It's a good idea to do your work in a confined area, with a surface that lends itself to being cleaned up under such occasions. I worked in a fume hood with a colorlith base----made it easy ------and safe.

Harold
 
Van, when I do gold filled I bought a coffee maker. The automatic kind. Then I cut the top off and trimmed it up a bit. The hot plate is built in and the temp seems to be constant. It has a nice pouring handle and a plastic lid! It also has a timer if you want to get real fancy.
MIDAS
 
Great idea Midas!

Welcome aboard.

Please post a picture of your setup if you can.

Steve
 
AFTER I BOIL THE JEWELRY WITH NITRIC ,THEN POUR OFF EXCESS ACID, THEN THE SLUDGE AT BOTTOM IS THE GOLD? SHOULD YOU WAIT AND LET THE SOLUTION SETTLE A LITTLE? THE SPOURED OFF SOLUTION IS THEN MOSTLY COPPER AND SOME SILVER. HOW DO YOU GET THE COPPER? ADD SALT FOR THE SILVER.
VAN
 
VAN said:
AFTER I BOIL THE JEWELRY WITH NITRIC ,THEN POUR OFF EXCESS ACID, THEN THE SLUDGE AT BOTTOM IS THE GOLD? SHOULD YOU WAIT AND LET THE SOLUTION SETTLE A LITTLE? THE SPOURED OFF SOLUTION IS THEN MOSTLY COPPER AND SOME SILVER. HOW DO YOU GET THE COPPER? ADD SALT FOR THE SILVER.
VAN

I expect that you may get varied responses on this subject. Best I can offer is how I dealt with gold filled objects when I ran my refining business.

After dissolving everything that will go into solution with nitric, the solution is taken up with water to dilute it well, then allowed to settle. Once the solution has settled, it is decanted, and a little salt introduced to the decanted solution to precipitate the silver as chloride. The solids that remain in the beaker should all be put in a filter and allowed to dry. Do not discard anything solid, especially if you find the material is purple in color. That's a sign of either silver chloride that has been exposed to light, or colloidal gold. Once dry, the filter and contents are incinerated until all the paper and resulting carbon is burned away completely. That can be accomplished in a discarded stainless frying pan, heated on a hotplate, then additional heat added with a torch when the pan is hot and the paper has quit burning. Heat until there is nothing left that burns.

The remains are then placed in a beaker and washed in boiling HCL and water. That removes substances that make filtration of the gold chloride solution possible. If you skip this operation, there are times when it can take days for the chloride solution to get through the filter.

The HCL/water solution from this operation is discarded after testing. It would normally contain very little aside from traces of copper and iron. Aqua regia is then introduced to the beaker, dissolving the values. After evaporation, the solution is filtered, then the gold precipitated. You can expect one ounce of nitric and four ounces of HCL to dissolve a troy ounce of gold. Don't use any more than you need-----free nitric must be evaporated in order to recover the gold.

When you refine chemically, never discard any filters. They should be incinerated and the resulting ash stored, for eventual processing for values. You'll recover considerable silver from chloride, plus traces of gold that are impossible to wash completely from the filters. Look at spent filters as a savings account. That's what they are.

You can recover the copper from these solutions by introducing scrap steel, which replaces the copper in solution, and precipitates the copper as a fine mud. That is best carried out in a 5 gallon plastic bucket.

Hope this helps. I know of no slick ways to process gold filled material. It's usually quite dirty stuff.

Harold
 
IS ANYONE ELSE RUNNING GOLD FILLED? IS IT WORTH TRYING ? I CAN GET SO MUCH OF IT IT ALMOST SEEMS LIKE IT WOULD BE WORTH IT.
 
Typical gold filled material is far better than anything plated, and that includes extremely high quality wave guide materials. You can expect as great as 5% recovery from GF materials, and they're easy to process, although objects so made don't lend themselves to a stripping cell. You have to think like a refiner, not a gold recovery person, if you intend to process gold filled materials.

If you want high quality gold, it should be dissolved and precipitated after all base metals are eliminated with a nitric and water boil. Also, because of the high risk of lead contamination, a trace of sulfuric acid should be introduced to the gold chloride before filtration, which will eliminate lead as lead sulfate. It is best added during the evaporation process.

You likely are beginning to understand that it's a good idea to have a small fume hood and hot plate to run gold properly, although you can work under a window with an exhaust fan. I got by that way for a short while before building my first fume hood.

Harold
 
Hello Harold,

Could you write a short post on how to design a fume hood for the forum? I've been wanting to build one but have not done the research to build one. It would be a great safety contribution to the forum.


Steve
 
To my understanding there just exhuast hoods, like over your stove.

Unless there is a special fan you can get that will last longer being subject to acidic fumes the "hood" is a "hood" I use one in my basement were i use my cell. I just blocked up the outer window and installed a exhaust hood from lowes, it has served me very well for over 6 months and still running strong. No fumes and no oder when its runnin, of course you dont want a cheapo, i got a hefty more industrial style one but there all the same concept.

Hood, ventalation pipe to an outside source i.e. window or something.
 
I'll post a picture of the last hood I built, and provide some details---but it may take a couple days. None of the pics of my refining days and lab are digital, so they'll have to be scanned and sized. I'm up to my ears in a house building project and don't have a lot of free time right now. Not to worry----I'll get it done. Just be patient.

A conventional kitchen range hood is the wrong approach. It not only won't resist the acids you'll work with, it also allows fumes to escape into the environment where you work. A fume hood doesn't. You don't work under it, you work inside it. Everything goes up the stack, it has no choice. The range hood will work fine for limited use, but when you start refining, your hood must stand up to some pretty serious acid fumes---like when you're evaporating solutions, or even when you're dissolving your gold. Further, it should be filtered, so you can recover traces that end up in the exhaust stream. I had a routine of cleaning my hood every other year and always recovered at least 8 ounces of gold when I did. I'll talk more about that, and filters, when I post.

The biggest problem you're going to face is finding a suitable material. Asbestos was still available to some degree when I built my equipment, so I didn't have any trouble finding acid and heat resistant board. Fact is, I was given a large stack of board that measured 1¼" thick, 18" wide, and 6 feet long. I used it in sections to form the sides of the hood.

The chance of finding asbestos isn't good today---so someone should do some research to see what's out there that could be used for the intended purpose. It need not be thick-----3/4" material would suffice.

Harold
 
Harold,

Thank you for sharing this invaluable knowledge with us!

Take your time preparing the post. I'll do the necessary reasearch on the material you mention.


Steve
 
I built a hood out of plexi glass and a small plastic fan. When the run off is over Ill post alot of pics on different items.
Midas
 
I'm not near as smart as Harold ,but I built a hood from plexi glass. I built a box{outa plexi} using brass or steel corner hinges the long ones drilled holes used a rivet gun then completely coated the exposed metal with silicon tube groute. then cut round hole used dryer exhaust couplers at hardware and dryer exhaust hose siliconed everything to be air tight as possible and made a front door there you go when I have more time Ill upload a pic My speeling is terrible.
Midas
 
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