What do I have now? Gold-filled in HCL only

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Marvinm4u

Member
Joined
Oct 10, 2020
Messages
13
In an effort to “save money” on nitric, I’ve been using HCL for weeks on cleaned GF pocket watch cases. Even after evaporating the waste, I’m showing no gold in solution. Good, I assume. When I have nothing left but gold skins, what are they? Carat gold? Do I then need to use nitric, in a greatly reduced volume from original weight, to get to 24k, before I go to the AR? I felt lIke genius when I started, now I’m clueless.

Thanks,
MarvinM
 
When you have nothing left but gold "skins" you have the gold plating at whatever karat it was plated on the item you started with.

If you started with 14K GF, you have 14K gold "skins".

What you are doing now is recovering gold, to take you recovered material to 24K you would be refining gold. Two different processes.
 
Thanks. That’s what I thought, but got more confused as I looked into more and more recovery/refining methods.
 
Lino1406 said:
Nickel, iron, copper, silver do not easily dissolve or not dissolve at all in HCl
I may be reading the post incorrectly, but from my experience, copper easily dissolves in HCL, hot or cold. Silver won't, or very little if any gets dissolved. I have some silver I dropped with copper, but some copper pieces broke off and I had too many small pieces to redissolve everything again. I added HCL in the dried copper powder and all of the copper dissolved, but the silver powder remained. I didn't use any heat, so it took about 3 days to dissolve all the copper.

In a nutshell, HCL does dissolve copper.

scrapparts
 
The reaction
Cu+2HCl=CuCl2+H2 has a positive change of free energy, 15.5 kcal/mole. Hence to get dissolution, you should have an oxidizer present in solution
 
I'm with Lino on this. HCl by itself doesn't dissolve copper but it can do it in a roundabout way.

1. Oxygen slowly oxidize the surface of copper and HCl can dissolve copper oxide creating copper chloride (CuCl or CuCl2). Going on to step 2 or 3.

2. Copper II chloride (CuCl2) easily dissolves copper creating copper I chloride (CuCl).

3. Hydrochloric acid with the help of oxygen transforms CuCl back into CuCl2. Go back to step 2.

Each cycle 2 -> 3 doubles the amount of copper II chloride that actually does the dissolving of copper. This is the process that we are trying to call copper chloride etch but most people wrongly calls it AP from acid peroxide.

A deeper understanding of what goes on in our beakers only makes it easier to control it and correct problems when you is facing one.

WARNING!!!
Do NOT, I repeat do NOT add hydrogen peroxide to a beaker with metallic silver. It can be in best case wasteful or in worst case cause a steam explosion or a serious boil over.

Silver decomposes hydrogen peroxide into water (steam) and oxygen and is used to fuel rockets!
The large surface area of cemented silver would instantly decompose even weak peroxide into oxygen bubbles and hot water.


If you take a piece of clean shiny copper and boil it in a flask with a reflux condenser (or in a beaker with a watch glass lid) virtually nothing happens, but if you take out that piece, let it sit in air a couple of days to get a decent oxide coating and then toss it in a shallow beaker with some cold HCl and put it outside for a few days and the copper will dissolve. This is from the oxygen n the air diffusing down into the HCl and working it's magic. You could actually see how far the oxygen gets in a beaker without a bubbler, there is a clear difference in color between the oxygen starved layer with dark brown CuCl and the oxygenated layer of emerald green CuCl2

But just as Lino said in so much fewer words, HCl needs the help of an oxidizer to dissolve copper.

Brown copper chloride, both in solution and precipitated as white crystals from a saturated solution.
CuCl-1.jpg

Green copper II chloride, both in solution and as needle-like crystals.
CuCl2-1.jpg

Göran
 
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