High Grade gold coat screw where nitric not attack

HI,
I do have some high grade gold coated screw where the nitric acid cannot attack the base metal.

My first sample was done by direct dissolve in AR, where the AR mix only little HCL for the gold coated to dissolve and expose the base metal, next, I keep adding nitric to dissolve base, when the nitric is saturated, the base metal dissolve will push the gold where dissolve early to come out, so , I filter off the gold foil and the gold particle and refining it again.

The AR which more in nitric believe is saturated, and I add SMB to try precipitate any gold left in it.

Is this produce prefect? Is there any better work flow to deal with this high grade screw / pin where nitric acid cannot attack the base metal behind the gold coating.

Appreciate any comment and ideal.

Thanks

Look up "sulfuric" or "sulphuric" cell.

You mean electrolysis with sulfuric? Thanks

Sulphuric Cell - it uses concentrated Sulphuric acid and electricity to de-plate the gold without attacking the base metal (if you are doing it right) It has it's own dangers, but using Nitric acid to dissolve away masses of base metal is creating a lot of toxic waste, so worth you looking at.

If they are truly base metal with an extremely heavy gold plate, you could cut into them or cut them in half to expose the base metal. I'm suggesting this as a test on a few pieces. Once the base metal is exposed, a nitric leach should dissolve the base metal and leave the gold plating, which you can then dissolve and refine.

If it works, and you have large quantities, you can probably develop some kind of automated basher/smasher/whacker/chopper to expose enough base metal for the nitric to do its job.

Dave

Can you post a picture or two these, please?

My first thought is that you have stainless steel screws plated with gold. That would explain why nitric does not dissolve the base metal. If this is the case, then another option besides (and possibly better than) the sulphuric cell is "reverse AR".

You may have almost been doing this already when you added some HCl. Search the forum for "reverse AR" and see what you think.

MGH said:

My first thought is that you have stainless steel screws plated with gold. That would explain why nitric does not dissolve the base metal. If this is the case, then another option besides (and possibly better than) the sulphuric cell is "reverse AR".

You may have almost been doing this already when you added some HCl. Search the forum for "reverse AR" and see what you think.

Click to expand...

That's a very good point MGH. If as you say the base is SS and if the gold is all dissolved from the coating then why worry about dissolving the base material?

Jon

"Reverse AR" is what I did for sample.

Attached is screw pic. few layer for this screw. Outer layer is the threading, then a ring layer between the plastic and threading, then inside have 1 pin.

Sulfuric cell cannot completely recover the gold, cut half of this screw is the way to expose the base metal, but time consuming. I will consider it if Reverse AR cannot completely recover the gold.

The first sample was done with reverse AR, and the base is copper/nickel. A question the reverse AR is to use to expose the base metal for nitric to dissolve the base metal, until nitric had finnish react, but still have base metal left behind, this will cement out the gold which previously dissolve, right? I remember the dust I collect is gold when i test it. the sampling was done few months ago.

And to play safe, I do add some SMB in order to get some more gold if any left inside the reverse AR.

Then the left over screw, i just add nitric to dissolve the base metal and collect the foil.

The point is, with Reverse AR on copper base item, will copper cement out the gold? If yes, then this should recover all the gold. Beside, safe time to cut the screw 1 by 1.

Dave, if have large quantity, is sure i will look for machine to crash the lot. But i have only few kg of this, and is no long term supply for this screw.

Thanks

With the inserts there is no way for a complete recovery without dissolving the base metal so perhaps put a small cut into the body of the screw and that should allow the nitric to penetrate and dissolve the base metals, while it may take a little time it will get you a full recovery and you only have a few kilos, you should get a good return from these items.
The reverse AR will dissolve the gold which will then cement back out once the base metals are exposed, perhaps using the sulphuric cell first and then dissolving the base metals in nitric would be less messy and with less chances for losses.

I would call that a connector and not a screw.

Instead of cutting, just flatten it with a hammer, the stress will crack the metal and break open the gold plating so the nitric can dissolve the base metals. If you turn the connector 90 degrees and hit it again it will split in four pieces and you can remove the plastic inset. It might also loosen the central pin so it can be pulled out of the plastics.

I crack similar connectors with a small anvil, a hammer and flat pliers. When I have a lot of connectors I put up some cardboard pieces to contain the metal parts, then I can sort the pieces afterwards when all connectors are crushed.

Göran

Look like the best way is sitting there and hammer it like what your said.

This connector is really good gold coating and have high yield, I bought it actually after sample test with reverse ar.

I haven't try sulfuric cell for recovery, because is hard to filter for sulfuric, and also the lead piece for cathode.

Hi Nick, what you use to filter the sulfuric?

Thanks guy who join here.

A "charmin plug" made out of fiberglass insulation. Thats probably one of the few filter media that can handle concentrated sulfuric.

Great. Will try it out soon. Thanks

Define "High Grade."