Which Process for only gold plate on brass

[cmgiscool]

I have a kind of unique supply of scrap. My father owns a machine shop that makes mil-spec pins and has saved gold plated parts that were either rejected, damaged, or had poor plating over the years.

Scrap I have dealt with before has always been less "pure" for lack of a better term and has always been from taking apart ewaste. I am wondering which process would be best suited for just gold on brass (alloy 360). Would you use Acid Peroxide, just pins in Nitric, or something else entirely?

Thank you for your help.

 

[Martijn]

Hi cmgiscool, welcome to the forum.
Dissolving pins to recover the gold plating is very inefficient, creates way to much toxic chemical waste and consumes large amounts of acid.

There are different ways to get the plating off without dissolving the base metals.

I have had good succes with the sulfuric stripping cell, stripping 4 kilo's of plated pins. It is a time consuming process that you can not leave alone for long. And you will work with 96% H2SO4, which requires a level of understanding of the process and dangers involved.

There are other stripping solutions, most are bought ready to go.
You can sell the stripped pins as brass scrap at your scrapyard when done stripping.

If this is your first attempt at recovering precious metals chemically, please take your time to study and start small.

First big don't with concentrated sulfuric acid: never add water to concentrated H2SO4! You will be scarred for life, if your'e lucky enough to live and tell the tale.
Keep your spray bottle far away from this, should you ever attempt this process.

Another way is to melt (preferably smelt and oxidize some base metals out into the slag) the pins into anodes and run them through a copper sulfate cell. The precious metals will be collected in the anode bag for further refining while the copper dissolves and plates out on the cathode.

A good process to start with learning this science, is the AP process, but on ram fingers, not on plated items.

To get you started: https://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=28521

Martijn.

 

[FrugalRefiner]

You can take several different approaches.

1.) Sell the scrap to someone else,

2.) Strip the gold off the base metal with something like the sulfuric stripping cell or a chemical leach like a cyanide, or iodine, or chloride leach,

3. Dissolve the base metal core, leaving the enriched gold foil to refine.

They each have their pros and cons.

Dave

 

[cmgiscool]

Thanks for the info! The reason I was leaning towards dissolving the cores is that the shop has some of the acids needed which they currently use in passivation of stainless steel parts. One of the acids we have never used is sulferic acid.

Thank you for the safety warning about it. I work at a company where we do a lot of chemical manufacturering but unfortunately most of the chemistry I have experience with is organic and I can't use work's fume hoods or safety showers while doing this. So I am researching it as exhaustively as possible.

 

[nickvc]

A question, what sort of quantity do you have to work with and is it a steady supply ?
The answer to that would dictate my processing method.

 

[cmgiscool]

A question, what sort of quantity do you have to work with and is it a steady supply ?
The answer to that would dictate my processing method.

Right now I would estimate it at about 5lbs. If everything goes right there should never be any rejected parts. I would say some get rejected every few years though for some reason. I would guess that the pile of parts accumulated over the last 10 years so maybe one half pound of pins a year, but that is a very rough estimate.

It is not a steady supply. Some of these are even perfectly good pins that were made for a customer who went out of business before buying them all.

Knowing your thoughts on which method(s) would be good for a supply that small would be really great. I would also be curious to know what your thoughts would be on if the supply was larger.

 

[nickvc]

With a small amount I would suggest using the AP process which would leave the gold foils for final processing, the beauty of the process is that it’s fairly easy to understand and takes little effort or cost, what you have is a small amount. The other good thing is that once started you can keep using the acid with additions of HCl to keep it working.
I don’t like the sulphuric cell as I find it far too dangerous to use but would use weak nitric to remove the base metals, cyanide is a possibility but the problem there is the cyanide likes copper and zinc as much if not more than gold so a weak solution would be needed to make it more selective which means large solutions and hence more waste.
I believe Patnor is trialing a couple of processes that may be viable for this type of product so do some reading and research on his posts.

 

[kurtak]

I believe Patnor is trialing a couple of processes that may be viable for this type of product so do some reading and research on his posts.

That would be this tread

:arrow: Iodine leach

Kurt