Aluminum in AP

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lawsonland

Active member
Joined
Aug 14, 2008
Messages
34
Location
pennsylvania
Hi,
I had a nice batch of AP (was a nice green cupric chloride) working on some pins and small connectors. I put in a gold plated item I thought was a substrate with copper base & gold plate.
It turns out I think it was all aluminum with gold plate.
I have a nice piece of gold foil but did I ruin the cupric chloride?
Things don't seem to be reacting right.

Is it now aluminum chloride? Is there a way to get the Al out and get back to CuCl?
Thanks
 
Lino,

When AP is used to dissolve base metals the active ingredient is the CuCl2. The acid and peroxide are used to initially form the CuCl2, then the peroxide oxidizes the resulting CuCl back to CuCl2 regenerating the reaction.

When dissolving gold, the AP is the active ingredient, with

2Au + 3H2O2 + 6HCl --> 2AuCl3 + 6H2O

as the likely overall reaction.

Lawsonland,

In either of the above reactions, Aluminum is undesirable.

On an up note, I doubt the gold plated item was actually over Aluminum as I recall gold won't plate directly onto Aluminum. More than likely it was iron and you didn't hurt your AP unless you added a whole lot of iron items to the bath.

More than likely your bath is saturated with CuCl (a few mL of water will tell for sure, white cloud= saturated with CuCl) and you need either aeration or a touch more peroxide and Hcl in the right ratio (2 HCl:1 H2O2). If you don't get a white cloud when tap water is added then add a few mL of HCl and you will be back on track.

Steve
 
I have run across quite a bit of gold plated aluminum over the years. The sulfuric stripping cell works great on it.

Almost nothing that I know of will plate directly on aluminum. If it is pretreated, almost anything can be plated on it. The pretreatment involves cleaning first and then going into a zincate solution - a solution that puts a coating of immersion zinc on the aluminum. After that, a layer of nickel is plated on the zinc and gold is plated on the nickel.
 
GSP,

Thanks for the clarification on the Aluminum plating. I was going from memory on what I had read on Finishing.com site where someone asked about electro forming gold using aluminum, if memory serves me correctly. I knew it wouldn't plate directly, but was unsure about if Aluminum could be made to accept gold plating.

Steve
 
probaby some other base metal like nickel then gold on the aluminum?
I find cheap costume jewelery gold plated on aluminum and just about every every other metal,even plastics or ceramics, propably hardly anything they dont plate gold to?
James Bond had a gold plated woman gold finger, well maybe just painted on?
 
Hmm I know this is an old post, I was just curios about the hydrogen peroxide and hcl reaction with gold, which Steve explained it, however my question is what is the gas that gets produced during this reaction feels like tear gas, is there any chlorine by product of this AP and gold reaction?

Thanks
Kevin
 
Are you using treated water in your solution? By treated, I mean plan tap water. A lot of times plan old city tap water has Chlorine and Fluoride among other things in it.

If you are trying to remove gold plate from Al, you can also try these methods...

Score the Al in several places, just like you would to defoil a hard drive platter. Then put it in HCl. The reaction is vigorous, so make sure you do it in a container that can allow for some solution expansion. I have done this with a few large pieces. Do this in a well ventilated area or under a fume hood, the gases are not pleasant to breath in.

Another way to do it, is with Lye, mix a Lye solution, and remember while you mix lye that it heats up pretty readily, so you might want to mix the Lye in a container that is in a cold water bath. When you add the Al, it should go to work on it pretty readily. The gas given off is Hydrogen, and not pleasant to breath. This should deplate the gold.

I believe Gold-N-Scrap has a video somewhere, where he is actually stripping anodized Al in a lye solution.
 
Because of the base plating on aluminum (prep for gold plating), and the fact that aluminum isn't dissolved with nitric acid, you can recover gold plating by using nitric. The base aluminum is left undisturbed, and the only acid that is consumed is in the process of dissolving the thin layer beneath the gold. It may sound difficult, but it shouldn't be. This is a win/win proposition, whereby you don't create much waste material to dispose, and you have the aluminum to be sold as scrap afterwards.

Harold
 
I have some gold plated pins in aluminum, and I can't get all the pins out in the initial chiseling, so it seems I can run them thru nitric to free them. Is 50/50 the proper ratio for aluminum or is it different?
Thank you!

Phil
 

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SBrown said:
I believe Gold-N-Scrap has a video somewhere, where he is actually stripping anodized Al in a lye solution.
Click to expand...

What is the purpose of stripping the anodized coating off of the Al?

Steve
 
hey Phil, i believe the higher the concentration of the nitric, the more it passivates the aluminum. if you dilute it, it may attack the aluminum stronger.
 
Harold_V said:
Because of the base plating on aluminum (prep for gold plating), and the fact that aluminum isn't dissolved with nitric acid, you can recover gold plating by using nitric. The base aluminum is left undisturbed, and the only acid that is consumed is in the process of dissolving the thin layer beneath the gold. It may sound difficult, but it shouldn't be. This is a win/win proposition, whereby you don't create much waste material to dispose, and you have the aluminum to be sold as scrap afterwards.

Harold
Click to expand...

I have a lot of Au plated on Al, I'm going to try this method next time I process this type of material. Thanks for the pointers Harold.

Scott
 
lazersteve said:
SBrown said:
I believe Gold-N-Scrap has a video somewhere, where he is actually stripping anodized Al in a lye solution.
Click to expand...

What is the purpose of stripping the anodized coating off of the Al?

Steve
Click to expand...
The only reason I can think of, and it's commonly practiced, is to strip existing anodizing so it can be replaced (perhaps it's defective).

Harold
 
Sodium hydroxide, scratch the surface, through the plattings, pop it in sodium hydroxide solution, and it will dissolve away your aluminium very easily, dont forget about it when it's soaking or you might find all the aluminium gone. :roll: yes, that's exactly what i did, not that long ago. 8)

Deano
 
i cleaned about 40 pounds of anodized heat sinks a few days ago as per Sam's(?) video. the scrap yard price for anodized aluminum is for old sheet or painted. after cleaning in sodium hydroxide, they were all aluminum colored.
 

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