Aqua Regia used in recovery

[teabone]

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.

 

[Rag and Bone]

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?

 

[teabone]

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.

 

[Rag and Bone]

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?

 

[lazersteve]

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

 

[Harold_V]

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

 

[Rag and Bone]

Harold,

How would you approach a ceramic cpu?

 

[Harold_V]

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

 

[Scott2357]

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

 

[Shecker]

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

 

[lazersteve]

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

 

[Harold_V]

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

 

[jaun]

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]

 

[goldsilverpro]

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.

 

[Lou]

Amen! Chris hath spoken the word!

 

[Harold_V]

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

 

[goldsilverpro]

You're right, Harold,

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

 

[jaun]

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

 

[enragedcow]

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

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.

 

[goldsilverpro]

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.