Digesting Gold Plated Stainless Items in Nitric

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Fever

Fever

Well-known member
Joined
Mar 25, 2007
Messages
158
Location
Eau Claire, WI
Are there any problems associated with digesting small amounts of gold plated SS materials in Nitric Acid?

(more specifically, the low-yield pins found in the ends of hard drive connector cables)

I'm saving my good gold plated pins for my Cell, but I wanted to try and get the small amounts of gold from the low-yield pins too. I realize that my pay-off will not justify my costs, and I'm more or less just doing this as an experiment to see how much gold I can actually squeeze out of a measured volume of these pins.

Do Nickel or any of the other SS alloyed metals interfere with the reaction?

Thanks all.....

Fever
 
Fever,

Those cable header pins are usually copper or brass base material not SS. The silvery color is most likely nickel. It's easily taken into solution by nitric.

Steve
 
If you're curious about the presence of nickel on electronic scrap, and don't know why it's there, Rose discusses the phenomenon of element migration in his book The Metallurgy of Gold. He discusses placing an ingot of silver in intimate contact with an ingot of gold, as I recall, and found that there was migration of one to the other over a period of time, even at room temperatures. It has nothing to do with heating, although that would likely accelerate the migration.

Nickel is plated on the brass prior to gold plating to eliminate migration of gold to the base metal. Given a short period of time, gold plating will disappear completely if plated directly on copper or copper alloys.

Harold
 
Thanks Harold and GSP!

That definitely answers my question. Will Nitric dissolve the Nickel coating and then the Copper base metal, or will the Nickel shield the copper underneath from being digested?

Thanks guys....

Fever
 
Nickel readily dissolves in nitric. You won't know it's there----but if you apply a drop of ammonium hydroxide to a drop of the solution, than add a drop of dimethylglyoxime, you'd get a beautiful pink reaction, which would be the nickel you've put in solution.

Harold
 
Hello,
I am new to this but learing fast!
I am interested in this because I have a bunch of gold plated brass parts, I am not sure if they have a nickel barrier or not but my question is :
What is the best way to get the gold off. if the nickel goes into solution will it drop out with the gold? How do you get JUST tje gold out.
thanks,
John

I don't have a cool tag line yet. But I will :D
 
If you process the material properly, you won't have much, if any, nickel in solution with gold. Just don't process with AR. Start by either stripping the gold with a cell, or by dissolving the base metals with nitric, or a nitric substitute. The nickel should go into solution along with the brass, leaving behind the gold as foil, or even finely divided particles. It all depends on the thickness of the plating, and how hard and long you boil the material, assuming you do. It can be done cold, it just takes longer, and you may not wring out the entire useful life of the acid.

If you're smart, you won't melt material so recovered. It won't be pure, regardless of how many hoops you jump through. It is best dissolved in AR, the selectively precipitated with a precipitant of your choosing. I favored using SO2, which is really how most folks precipitate their gold, although they arrive at the SO2 in different ways. Mine came from a bottle.

It stands to reason that if you dissolve a lot of garbage with your gold, it will drag down a portion of the contaminants that go in to solution. For that reason, you should adopt very good work habits right from the get-go---eliminating as much of the garbage as is possible before dissolving the gold.

Harold
 
If you do end up with SS, the AP formula works well for me. I just processed some SS cellphone antenna contacts that nitric couldn't touch.
 
Why doesn't nitric dissolve SS? Fe - reacts with nitric, Ni reacts with nitric, Cr ? is that the reason? EM chart list Cr above Fe and Ni
No particular reason, just curious.


thanks,

Jim
 
The answer is in the mixed layer of oxides that forms over the stainless. It is passivated.

Recall how alumina (Al2O3) is unaffected by nitric acid? Very similar.
 
Yep----as Lou suggested. Passivation of stainless is one of the critical steps if rusting isn't acceptable, so it is common practice in the aero-space and defense industries.

Most stainless rusts slightly when exposed to the elements unless it has undergone passivation.

For the record, if you purchase volumes of nitric, it is typically dispensed in stainless drums, usually 304 or 316 stainless.

Harold
 
I boil my gold plated stainless items in nitric. The nitric attack the stainless very slowly when you boil it, but it loosens the gold foil. :roll:
 
I boil my gold plated stainless items in nitric. The nitric attack the stainless very slowly when you boil it, but it loosens the gold foil. :roll:
 
I've been reading and learning alot but a couple things aren't quite clear.

1. If I use AP to strip foils or pins then at least some gold will be disolved right, if not all if left too long? Then I can just precipitate that with SMB after I filter out the gold?

2. I keep reading about using nitric to disolve base metal. Does nitric disolve gold? Some of the posts make it sound like it disolves the base metals only. If some gold is disolved then can I preciptate like the AP above?

Thanks, this is a great site!

Steve
 
Nitric alone will not dissolve gold, and is used regularly to eliminate base metals. It is the acid of choice, but is difficult to buy, and often expensive beyond reason.

One must use care when working with gold that has been introduced to chlorides. The addition of nitric to such material will result in the dissolution of gold---until the nitric is consumed, or the chlorides are. It is for that reason that incineration between acid washes is recommended. Rinsing well, alone, is often not enough to prevent dissolution of values.

Harold
 

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