Gold/silver plated blocks

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Wingedcloud

Well-known member
Joined
Nov 6, 2014
Messages
96
Hello everyone.

I have been handed some samples of the following plated blocks of metal.

67394455_368287853858448_1852898395287453696_n.jpg68421340_438626993400189_8986740942530674688_n.jpg67778189_861534594247130_1172245597558669312_n.jpg

I am told the gold plated one is nickel base and the silver ones are aluminum base.
I was wondering if someone could point out some effective ways of stripping these blocks of the PM. Don't need it to be fast, altough I have several kg of each type.

I read that if the gold plated block was aluminum, I could use conc. nitric, as the acid would form a passivation layer on the aluminum, dissolving only a layer of nickel that might be between it and the gold plating, leaving the plating to float around and be filtered.. Don't know if the same principle applies if the metal is nickel instead of aluminum.
As for the silver plating, I was thinking about the same process, but wanted some input on it, if anyone is able.

Thanks in advance!!

Winged.
 
The gold ones are usually on Aluminium. Weak Nitric is the best to get that off. Leave it for a few days in here (fully stripped of components) and it'll be clean.

The silver is on Aluminium too. Again weak Nitric, dissolve the silver off and deposit with copper. The Aluminium will pacify in both cases is you use Nitric. The circular things need taking out because they are silver on brass and you don't want that mixing up with your Nitric reaction because the silver will be pretty pure in that so trip out all the components.

That's Telecoms Microwave equipment there in case anyone was wondering.

Hope that helps.

Jon
 
anachronism said:
The gold ones are usually on Aluminium. Weak Nitric is the best to get that off. Leave it for a few days in here (fully stripped of components) and it'll be clean.

The silver is on Aluminium too. Again weak Nitric, dissolve the silver off and deposit with copper. The Aluminium will pacify in both cases is you use Nitric. The circular things need taking out because they are silver on brass and you don't want that mixing up with your Nitric reaction because the silver will be pretty pure in that so trip out all the components.

That's Telecoms Microwave equipment there in case anyone was wondering.

Hope that helps.

Jon

Hey Jon. Thanks for the input !!
When you say weak nitric, is 50/50 nitric/water starting from a 30% nitric ok?

I said the gold plated base was nickel because that's the info I got from the person that left it with me. Will try your method though.

Since you know these blocks, you have any info on yields?

Winged.
 
Depending on the size of the gold blocks some are a white metal which is iron based. Do try weak nitric first and see what happens- by weak I mean 10% or less to start with and check after leaving overnight.

Judge the base metal by the weight - if it's heavy its the iron based one if light them Al. They use both. It doesn't hurt to only put a small amount of it into the weak acid solution just to be careful. As always, test and check, test and check.
 
I was wondering, after taking a look at the reactivity series: won't the dissolved silver cement back out on the aluminum, since it's way up on the list?

Also, been looking at the drak grey block and I think there is also silver below that dark grey "paint". Is there a way to remove the ink and get the silver below? Maybe wash with ink thinner?

Winged.
 
Wingedcloud said:
I was wondering, after taking a look at the reactivity series: won't the dissolved silver cement back out on the aluminum, since it's way up on the list?

Also, been looking at the drak grey block and I think there is also silver below that dark grey "paint". Is there a way to remove the ink and get the silver below? Maybe wash with ink thinner?

Winged.

No it won't redeposit out onto the Al if you leach and pour off, and don't overload the nitric. You can see when it does because it redeposits black. Instead of guessing about the silver, spend a few euros and buy some silver test solution. Then you'll be sure.
 
Wingedcloud said:
I was wondering, after taking a look at the reactivity series: won't the dissolved silver cement back out on the aluminum, since it's way up on the list?
For cementation to happen, the base metal has to be soluble in the acid. Since aluminum is passivated in nitric, it can't dissolve, so it can't give up it's electrons to the dissolved silver.

Dave
 
FrugalRefiner said:
Wingedcloud said:
I was wondering, after taking a look at the reactivity series: won't the dissolved silver cement back out on the aluminum, since it's way up on the list?
For cementation to happen, the base metal has to be soluble in the acid. Since aluminum is passivated in nitric, it can't dissolve, so it can't give up it's electrons to the dissolved silver.

Dave

Plain and simple. Thanks Dave !!!

Just a quick update on the gold plated blocks. Started with a small test on some small pieces that were screwed to one of the gold plated blocks and got some nice and honestly quick results, considering I started this morning.
67919267_408269146477405_3388317992080113664_n.jpg
68797087_490243704872285_3474666312406401024_n.jpg

There is still a small amount inside the screw housing, but gives good indications for the big pieces ^^

Winged.
 
Looks good. You'll not get 100% of it without taking a lot more time and it will probably outweigh the benefit. Recovering 98% is pretty good.
 
Hello everyone.

A quick update on the plating recovery.
The gold ones were pretty straight forward. Like anachornism said it's only a matter of how much one wants to recover versus the amount of time it will take. By the following picture I'd say I am pretty much done.
68694896_363960074531947_9143355610719322112_n.jpg

Now for the silver ones, the same method was applied.
After a day or so, got the following.

68893884_329783764566984_91898216936636416_n.jpg68326293_421603688442272_5015604435368280064_n.jpg

The silver plating seems to be peeling off, as the intermediate layer (which I believe to be nickel, given the green color of the nitric solution) is dissolved.
Now this would be one case where the dissolved silver would cement back out on the undissolved nickel, as it is being exposed to the solution, considering what Frugal said about cementation.
Why is the silver not dissolving right away though, being peeled off and slowly dissolve, to cement back out and dissolve back again? I am to understand that, being as I said, this process will take much more time that the gold plated ones.

Winged
 
Hello Jon,

Performed the test and it showed negative for silver in solution, meaning not a single sign of silver chloride was formed.

Winged.
 
Hello everyone.

Updating on the silver plated block.
After several days of weak nitric bath (with some nitric additions meanwhile), I took the block out of the bath and reached the following conclusions:

69215657_749593322144142_6473980371934380032_n.jpg69290511_401912347122164_990973045382316032_n.jpg68691982_2587731627950169_3552197850853015552_n.jpg

- After performing tests with HCl, I realized no silver was being dissolved (or rather no silver was in solution), despite the nitric medium. At first I thought that it could be a process of cementation on the base metal on the the "intermediate" metal in between the silver and the aluminum, which I believed to be nickel, given the grren color of the solution, as I said in a previous post. However, my solution started to go dark blue, which gave me the hint that copper was present somewhere, which would also lead to some dissolved silver cement out. I noticed that some of the "rods" (I called it rods in lack of a better word) started to get loose as the acid dissolved them, so after I removed the block from the acid, I got them all out and grinded one of them to understand which metal they were made of. Turns out they are brass (as shown in picture). Still got some silver and brass in the block.

- I ended up peeling off all the silver foils I could from the block with some tweezers, and I noticed they were like dirty with what seems to be copper. Is it possible that the zinc that composes the brass makes the copper cement out? As it is an alloy I am not sure. I am willing to bet the answer is yes, given that that seems to be "copper mud" from cementation.

If I used a stronger nitric solution from the start, would I be able to push through all the brass and silver, to get a nitric solution of zinc, copper and silver, to recover the silver later, in the form of chloride or cement silver? Did not went how I expected, but the truth is I wasn't expecting for there to be brass :lol:

Going to try and dissolve the "rods" and all the silver foils in a new nitric solution.

More updates in the future :)

Winged.

PS: I am realizing that this topic is turning more into a processing descrition rather than showing a type of PM scrap, so if the moderators want to move this topic to some other section, feel free :roll:
 
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