# Aqua Regia used in recovery



## teabone (Jul 25, 2008)

I'm one of those idiots or morons that uses aqua regia as a primary recovery step. Its the fastest way I've found to recover gold from board fingers and ceramic cpus, which is mostly the material I deal with.
My method is to dilute the acid with a two to one ratio of hot water after the gold bearing material has dissolved. Neutralize with urea,and then filter into a precipitating container. I then add smb and once everything has settled out, I run the precipitated powder thru the process again to purify.
The first run is a emerald green solution and the second run is golden yellow. 
I know some of the old timers will disapprove of this method, but it works for me and I've processed many ounces of gold this way.


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## Rag and Bone (Jul 25, 2008)

I'm getting ready to try AR for recovery on cpus. I will stick with AP for fingers, I just can't imagine a better method.

Teabone,

Do you have any recommendations on the amount of AR to use on different ceramic cpus? Do you use real AR or poormans?


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## teabone (Jul 25, 2008)

Sorry, I should have specified. 
I use poorman exclusively, since nitric acid is hard to get.
I was just thinking that maybe this weaken version of a.r is the reason I don't have some of the associated problems that happens with real aqua regia ?
I usually use a five gallon bucket and cover the material with enough hcl and then add six to eight ounces of nitrate of soda dissolved in about twelve ounces of hot water. This will do about a hundred 486s. You will have to adjust the ratio according to batch size. After you've done a few batches, you will start to get the hang of it. I've been doing this method for over five years now.


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## Rag and Bone (Jul 25, 2008)

Interesting. How do you prepare the 486's or other ceramics? (I've done some ceramic cpu batches with AP. I found it slow and didn't strip complete.)

How does the gold look on the first precipitation?


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## lazersteve (Jul 26, 2008)

Rags,

I'm putting the finishing touches on a yields post from 44 ceramic 486 cpus. The AP took 6 days to fully strip the housings. The bottom plates were removed with a MAPP gas torch prior to the soak. I used left over AP with fresh peroxide added twice during the course of the soak. 

The cores were left whole (uncrushed ) for future processing in a ball mill. My goal is to identify the yields for each section of the 486 cpu:

1) surface gold in the exposed cores, wiring, and pins (2.5 grams for 44 cpus),
2) gold on the plated lids,(1.65g)
3) gold in the ceramic cores in the form of hair fine wires.
4) gold in the gold alloy solder holding on the lids (1.4 g)

The cpus stripped 100% in the AP. 

The lids and housings have not been processed yet. 

I'll try to get all my photos together for the intial post by Sunday night.

Steve


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## Harold_V (Jul 26, 2008)

teabone said:


> I'm one of those idiots or morons that uses aqua regia as a primary recovery step.


The problems consist of unclean gold from the first precipitation (which you have addressed nicely be a second refining). 

The other is the fact that precious metals that are dissolved in the presence of base metals have a tendency to precipitate prematurely, possibly leading to losses. 

Considering the base metals must be dissolved in either case, it makes far more sense to eliminate them prior to dissolving the values. 

Mind you, I've not said it doesn't work----there's simply better methods that offer fewer problems. If you're comfortable with your procedure and you are assured you are not losing values, no need to change. I might not see it that way were you using commercial acids. 

Harold


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## Rag and Bone (Jul 26, 2008)

Harold,

How would you approach a ceramic cpu?


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## Harold_V (Jul 26, 2008)

Rag and Bone said:


> Harold,
> 
> How would you approach a ceramic cpu?


AR! No doubt about it. Or, I'd run them through a ball mill and process with cyanide, screening out any metallic solids. 

AR is a wonderful processing medium, but it is not best when working with base metals. I've already outlined the reasons, but there are times when even that can be used to advantage. Assuming you have a mixture of values and unwanted metals (often the case with dental appliances) and they are difficult to sort, you can dissolve everything with AR, using less than is necessary, then allow the values that have gone into solution to precipitate on the undissolved base metals components. When the solution tests barren, it can be discarded and the process renewed with fresh AR. By this method, you can eliminate the vast majority of base metals before dissolving all of the values. Then benefit is, or course, a much cleaner yield, often with the benefit of a smaller volume of solution. That can mean a great deal when you have a number of beakers waiting for the next available spot on the burner. 

It is generally noted that there are many ways to skin a cat. I agree, but there is often one way that is far better than all others. The trick is to know which one it is. 

Harold


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## Scott2357 (Jul 26, 2008)

Steve,

Your 486 surface gold numbers (.05 g per CPU) are little surprising to me. I've been estimating .15 grams per whole CPU. I know you don't have exact numbers for the other two sections yet but do you think there is really .10 g in those combined? The bulk must be on the lids?

Obviously I haven't fully processed anything yet. I'm still gathering PM material and absorbing knowledge. I want to get it right the first time and minimize risk or PM losses.

Thanks


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## Shecker (Jul 26, 2008)

There is a formula for AR that is pretty much gold specific (will of course leach base metals is present). To a 200 milliliter mixture add one milliliters of water, 81 milliliters of HCL and 19 milliliters of NHO3. The leach is do at room temperature and is slow enough that it is possible to load with gold only. This can be particularly useful on thin platings of gold.

Randy in Gunnison


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## lazersteve (Jul 26, 2008)

Scott,

I have a previous yield post for the lids (mixed cpu and ic lids, not straight 486).

Here's a link to that thread.

Assorted Gold Lid Yield Data

I did not process a specific type of lid just an assortment, but I'm sure the yield percentage should be very close.

The lids from the 486s weighs 68.1 grams so I expect about :

68.1 x 2.445% = 1.665 g Au for all 44 CPUs

or 

1.665 / 44 = 0.038 grams Au per cpu lid average.

Photos Added
Here's the photo of the batch, I stacked 5 others on top that are not in the photo.







Steve


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## Harold_V (Jul 26, 2008)

Shecker said:


> There is a formula for AR that is pretty much gold specific (will of course leach base metals is present). To a 200 milliliter mixture add one milliliters of water, 81 milliliters of HCL and 19 milliliters of NHO3. The leach is do at room temperature and is slow enough that it is possible to load with gold only. This can be particularly useful on thin platings of gold.
> 
> Randy in Gunnison


Nonsense. 

You can't address the gold as if there was no base metal present. Almost everyone here knows and understands that base metals precipitate values---regardless of any clever thinking. It is for that reason that processing plated items with AR isn't a great idea. If all the base metal must be put in solution (where it no longer is able to precipitate the values), there is NO advantage to processing everything in a single step. Eliminating the base metals before dissolving the values is almost always in one's best interest, regardless of the degree of success one enjoys by not doing so. Not only is dragdown minimized, but volumes of solution that must be filtered are often drastically reduced. 

Harold


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## jaun (Jul 27, 2008)

Harold wrote:


> AR! No doubt about it. Or, I'd run them through a ball mill and process with cyanide, screening out any metallic solids.



Will SMB precipitate gold from cyanide solution, or is zinc the best to use?

I spoke to a refiner last week, who is refining for more than 30 years, and forgot to ask him. He was a chemist for the platinum and gold mines in SA for 20 years, and refines for himself the last 10 years.
He uses cyanide for electronic scrap, and says it is the fastest way to process electronic scrap. He crushes the gold plated parts and treats with cyanide, or put the edge connectors (after cutting them of the boards) just as is with plastics and all in cyanide. Takes a half our and you’ve got your gold. He uses zinc to precipitate the gold.
The only problem I have with cyanide is, its poisoness stuff. He told me that if you don’t want to use cyanide, AR is the second best way to recover the gold from electronic scrap, but not for jewellery or dental scrap. You just have to refine the powder a second time to get the gold purer.[/quote]


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## goldsilverpro (Jul 27, 2008)

Everything is poisonous. Even water, if you drink 30 pounds of it. It all depends on quantity. I love cyanide. It is the ultimate gold refining chemical. NOTHING works better, when it comes to gold plated objects. Nothing! A pox on the EPA for eliminating the use of cyanide. A huge advantage of cyanide, over acids, is that you can destroy it. You can break it down to CO2 and N2.


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## Lou (Jul 27, 2008)

Amen! Chris hath spoken the word!


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## Harold_V (Jul 28, 2008)

jaun said:


> Will SMB precipitate gold from cyanide solution, or is zinc the best to use?



To my knowledge, SMB will not precipitate values from a cyanide solution. I used zinc flour exclusively, even without removing excess oxygen from my solutions and enjoyed perfect results, precipitating both silver and gold. That's the one negative---zinc isn't selective, so you must refine the precipitated values once recovered. 

Harold


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## goldsilverpro (Jul 28, 2008)

You're right, Harold,

SMB won't precipitate gold from a cyanide solution. Zinc dust is the standard.


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## jaun (Jul 28, 2008)

Thanks guys for answering.

So, if I understand correctly cyanide will dissolve silver as well. What else will the cyanide dissolve?

And what must you do to the cyanide before precipitating the gold, to ensure the precipitated gold doesn’t dissolve back in solution?

How do you “destroy”/neutralize the cyanide after use?

Thanks


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## enragedcow (Jul 28, 2008)

jaun said:


> Thanks guys for answering.
> 
> So, if I understand correctly cyanide will dissolve silver as well. What else will the cyanide dissolve?
> 
> ...



I'm actually quite interested in this as well. I'm interested to find a method to remove PMs selectively from other metals, without dissolving the base metals. 

As the experts here have oft mentioned, any process that dissolves everything will be tough to make profitable, if total recovery is the goal (rather than straight refining).

I know cyanide will help pull gold from base metals, but I haven't yet found out if it will do PGMs as well, quite curious.


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## goldsilverpro (Jul 28, 2008)

Gold, silver, copper, zinc, cadmium, nickel. All require the addition of an oxidizing agent, such as hydrogen peroxide or one of several nitroorganic compounds, such as m-NBSS. 

The oxygen can also be provided at the anode of a cyanide containing electrolytic cell. However, I don't think that nickel can be dissolved in this manner.

For leaching ore, a very weak sodium cyanide solution is used. Air dissolved in the solution provides the oxygen.


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## Harold_V (Jul 28, 2008)

As Chris alluded, cyanide, used very dilute, becomes very selective. It's one of the reason's it has been used with success. Consumption tends to be only on the values involved, so a ton of ore can often be treated with an ounce of cyanide. All depends on the volume of values contained within the ore. It won't react with the gangue under normal circumstances, so there are few losses. 

When ores are processed, if the level is kept down around .02% or less, no copper will be dissolved. It's a little different with plated objects, where base metal tends to interfere with recovery, but there are buffering reagents that limit the problems. I used a commercially prepared buffered compound with great success after I closed the doors on my refining business. I had bought and stored about 180 pounds of very lightly plated wire wrap pins and related materials years earlier, and had placed them in storage because my time was better spent working on customer materials. I recovered nearly six ounces of gold from the components. All action ceased when the nickel barrier was exposed, where, by sharp contrast, some heavily plated copper alloy items I had tried stripping years earlier, using just cyanide, were very troublesome once the gold perforated. Base metal dissolved instead of the plated gold, so the process was abandoned. 

It is recommended that free oxygen be removed from cyanide solutions before introducing zinc, to minimize zinc loss, but I didn't worry about that. At the time, a pail of zinc cost so little that it wasn't worth the time to mess with the solution. I simply introduced a greater amount of zinc than I expected to recover in values, then decanted the solution immediately upon settling. As I recall, an ounce of zinc will precipitate an ounce of gold. I then precipitated a second time to insure that no values were left behind. A small amount of free cyanide should be in solution, which accelerates the conversion. When conditions are proper, it happens almost instantly. My practice was to stir the solution well, getting it in motion, then I'd sprinkle the required amount of zinc in the solution and continue to stir. I used a 20 gallon Nalgene container and stirred with an aluminum rod. The zinc almost immediately turned dark brown, a sure sign it was precipitating the gold. There was a minimal reaction with the aluminum rod, but it was exposed to the pregnant solution only briefly. 

Regards destroying cyanide for disposal, I'm at a loss to recall the compound used, but it liberates a huge amount of chlorine, which kills the cyanide. It can then be safely discharged to a sewer. Perhaps Chris, or one of the others can provide the common name of the compound. I believe Lou has made mention in one of his posts some time ago. 

Harold


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## jaun (Jul 28, 2008)

Thanks Harold. That helped

What's the buffering reagent you used?


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## goldsilverpro (Jul 28, 2008)

As far as I know, all the "buffering agents" are proprietary and are kept pretty much secret. Most are covered in patents. Also, some of them keep the gold so tightly bound that it is almost impossible to precipitate. Technistrip AU, made by Technic, is one of these difficult ones. You would probably have to ship it to them and have them recover the gold!!!


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## Shecker (Jul 28, 2008)

The formula for AR that I gave was developed by the American Society for Applied Technology for leaching microfine gold values, black sands, jewelry sweeps, and other situations in which the metal is in very fine state or as a plating. It was not indented for karat gold for other high value, large mass metal situations. It would work great on e-scrap with minimal solubility of base metals. This formula is actually called chloronitric acid. 

Randy in Gunnison


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## Harold_V (Jul 28, 2008)

jaun said:


> What's the buffering reagent you used?



I was given a container of the compound by my chemical supply house, who had ordered it for a different customer, but it was never delivered. They were happy to unload the thing so they didn't have to pay for disposal. I have no idea what it contained, but the material looked much like dirty sodium hydroxide (lye), but was various shades of brown in color. I have no memory of the contents, or the name of the product. Not even the maker's name. 

Unlike GSP's comments, I achieved recovery with zinc flour, so it was user friendly in that regard, and appeared to strip the gold readily. 

Harold


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## goldsilverpro (Jul 28, 2008)

Harold,

I think what you're describing is m-NBSS. I think the name is meta- nitrobenzoic acid sodium sulfonate. I think it's also called meta-nitrobenzoate and meta-nitrobenzoic acid, sodium salt. A common name is Ludigol (there are several ludigols) . A brand name I believe is Hampol.

It was one of the first chemicals used with cyanide to help prevent attack on the copper when stripping gold. It worked fairly well but not 100%. Zinc readily drops gold from it. We had a 200 gal gold stripping tank that used the above chemical, sodium cyanide, and some 120 volume (35%) hydrogen peroxide.

Later on, other chemicals were used that worked better. But, as I said before, some of them worked so well that you couldn't easily drop out the gold. I think one of the chemicals used was a lead compound. If I recall, once the copper was exposed, the lead formed a very thin coating on it and prevented it from dissolving. Doesn't seem intuitive, but that's what it did. I believe there's a patent on it.

These proprietary cyanide gold strippers weren't designed as a gold recovery chemical. They were designed for platers to be able to strip off screwed up gold plating, without damaging the base metal, so that the parts could be replated.


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## Harold_V (Jul 29, 2008)

Thanks for the comments, Chris. It would be really interesting to be able to step back in time and rerun some of these things that were baffling to me. I knew so little, and had no one to turn to. You. and others of this forum, have been a breath of fresh air for me in many ways, even when we don't necessarily agree on a given topic. There's so much I never learned!

Harold


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## renatomerino (Aug 19, 2008)

Harold_V said:


> jaun said:
> 
> 
> > Will SMB precipitate gold from cyanide solution, or is zinc the best to use?
> ...


That means SMB


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## Anonymous (Sep 29, 2008)

I'm new here and have been researching everything in and out, It seems there rly are many ways to skin a cat. Let me see i i got this. If i have some e-scrap and wish to recover gold and silver. First i bath scrap in nitric acid to dissolve silver, then recover the gold from scrap afterwards with AR? This way we do what harold keeps trying to explain in removing base metals first. 
However, can you extract everything in AR then bath precipitate in nitric to filter base metals? What difference does it make?
Whats up with the cyanide? Ive gone crossed eyed?!!?


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## Harold_V (Sep 29, 2008)

atthadrivethru said:


> I'm new here and have been researching everything in and out, It seems there rly are many ways to skin a cat.


I'm not fond of that concept. While there are many ways to achieve an end, there's usually one that stands out---offering better results with fewer risks. Also, consider that while there may appear to be parallel processes, you'll come to discover that each one lends itself to a given type of operation. Sort of supports my concept of a better way to achieve a given end. 


> Let me see i i got this. If i have some e-scrap and wish to recover gold and silver. First i bath scrap in nitric acid to dissolve silver, then recover the gold from scrap afterwards with AR?


You're painting with a brush that is far too broad to be useful, in that one does not necessarily process fingers from a board in the same manner one would process clean pins. Often there is no silver to be recovered. You need to discern the differences in materials, and understand the objective in the given process. Often it is aimed at eliminating base metals, nothing more. 



> This way we do what harold keeps trying to explain in removing base metals first. However, can you extract everything in AR then bath precipitate in nitric to filter base metals?


Wise people don't use AR to eliminate base metals. There are various reasons not to do so, one of which is that if you don't completely eliminate all base metals in dissolution, you risk losing some of your values as they precipitate on the residual base metals. The question I always like to ask is what advantage is there? You will consume no less in the way of acids or other reagents, and will end up with more problems and lower quality. Where is the benefit? 


> what difference does it make?


Best answer I can provide is "it all depends". How dirty is your solution? What are the contaminants? How much of them got dragged down when you precipitated the values? Are you prepared to risk the re-dissolution of your values when you wash with nitric after precipitation? It's one of the hazards of washing with nitric acid. Yes, it can be controlled, but often is not. It's very hard to eliminate chlorides entirely, although not impossible. It's safer, by far, to simply wash with HCl instead. Cheaper, too. 

I always advise against re-inventing the wheel. It is sufficiently round and free running as it is------learn to use it, and restrict your creativity for the time when you have answers instead of questions. Don't mean to sound rude, but you are being handed the benefit of years of experience on this board----experience not only from education, but from the school of hard knocks. Learn the basics before you start making decisions. 



> Whats up with the cyanide? Ive gone crossed eyed?!!?


There are instances where cyanide is the answer to recovery. Recovering finely divided gold from specific ores is one of them. It is not to be considered a refining process, for it is not selective in that it will recover silver equally as well as it does gold. 

Do not concern yourself with cyanide at this point in your learning curve, spend your time, instead, on reading Hoke, and studying the various processes for recovering values from e scrap, all of which are well documented here on the forum. 

Harold


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## Anonymous (Sep 29, 2008)

Thanks for help Harold, not rude at all and your guidance/experience is greatly appreciated! Your right, i should stick with what works and not get ahead of myself at this point.


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## Harold_V (Sep 29, 2008)

When I was refining for gain, I commented many times that I could teach a monkey to refine----it's nothing more than following a procedure faithfully. Very unlike someone learning to play a musical instrument, or running machine tools, where considerable skill is involved. 

As you become familiar with the processes that are involved, you'll come to realize that refining isn't difficult, but if you don't follow procedures as intended, what should be a simple operation can turn into a terrible ordeal. The number of people on this forum that have requested assistance when they were impatient, or second-guessed a given procedure, is large. There's usually a bail-out available, and it might even be a good learning experience to do some stupid things along the way, but it can prove very aggravating and discouraging. 

I have always promoted Hoke's book. It's not because there's something in it for me----there isn't. I am not remotely connected with the book, or its publication----I'm simply a very satisfied reader. 

There is little in the book that isn't top notch information. Her promoting the use of gasoline for incineration tends to be over the top---and she treated silver with considerable contempt, but otherwise, her instructions are good----very good, in fact, and will transform the least able person into an accomplished gold refiner----assuming you follow her instructions. While there may be better procedures available, hers will allow you to provide gold that meets industry standard------or better. I'd say that for a guy working out of his garage, that's pretty damned good! 

Harold


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## EVO-AU (Nov 5, 2008)

Schecker: On your post of July 26, '08 is the 200 ml mixture the ore or what ? Evo


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## lazersteve (Nov 30, 2008)

I finished processing the solder from the (44) 486 CPUs:







The yield was 1.4 g of dried gold powder. This is not really accurate as some of the solder was processed with the gold foils and flakes that got caught up in the AP strip. Consider the additional 1.4 g to be added to the original report of 2.5 g for the exposed gold. This makes the total 3.9 grams of exposed gold (minus the lids and cores) for 44 CPUs.

I've updated the original post above.

Steve


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## Palladium (Nov 7, 2009)




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