Aqua Regia used in recovery

[Harold_V]

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

 

[jaun]

Thanks Harold. That helped

What's the buffering reagent you used?

 

[goldsilverpro]

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!!!

 

[Shecker]

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

 

[Harold_V]

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

 

[goldsilverpro]

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.

 

[Harold_V]

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

 

[renatomerino]

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

That means SMB

 

[Anonymous]

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?!!?

 

[Harold_V]

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

 

[Anonymous]

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.

 

[Harold_V]

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

 

[EVO-AU]

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

 

[lazersteve]

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

 

[Palladium]