Gold drop challenges (gold filled)

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Noggin

Well-known member
Supporting Member
Joined
Nov 10, 2021
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50
Location
Illinois
Hi all,
Not sure if this has been discussed before but I haven't been able to come up with a search that helps find the solution.

I'm trying to attempt to precipitate a very stubborn solution of metals that lurked in a 350g batch of mostly 1/10 10k gold filled.
The color is greenish brown, which I assume is mostly copper, iron, and/or nickel.
No reasonable amount of SMB (stumpout) was dropping all the gold. I got some to drop but it was way under what's expected. Stannous test is positive.
Today, I put some copper pipe and solid copper wire in the solution on a hot plate at 80c but a pretty tenacious black precipitate is coating it. After two hours, little copper has dissolved, likely because of passivation.
If this has been covered/explained, I'd be grateful for the link. Otherwise:

1. Please share what you think I'm dealing with and where I went wrong
2. What might I do to force the gold to drop so I can re-refine.

How I got here (if it matters)
350g gold filled jewelry heated to redness in a melt dish under torch into large beaker with small nitric boils. Did that until the nitric was clear. Magnet test noted some magnetic items were still in there. If you ever refined GF, it's not ever pretty the first round. I removed all small magnetic items like screws, springs, etc. that I found though.
I didn't weigh the items before adding HCL, which I think is a good step (as if I had, say, 60g I could rethink my process since I'm expecting to leave the nitric boil phase with <35).

Got it to dissolve with HCL and nitric, added sulfuric, filtered. Added SMB. Strong reaction. Kept going... I suspected too much nitric, added maybe 2 heaping tsp of sulfamic crystals and added heat. Stir /w stir bar till dissolved, then cooled to room temperature. Started again with SMB. Went through half a bottle of stumpout. Slept on it.

The next day, I started evaporating. When it dried it was like concrete. My stir bar was now a fossil. Started reconstituting using HCL and distilled water. When done, saw a precipitate on the bottom of the beaker. Stannous test is positive. The color is so horrible I only could guess it was gold so I decanted after a day of settling and actually located maybe 5-10g. It looked pretty decent.

I saw a post from January where someone was having issues getting their gold to drop, and the hail Mary was to add copper start over.

So as I said above, the copper is in and I'm currently slowly doing another evaporation round. As of my writing this, stannous test is still positive. Note, I've not re-filtered the solution after reconstituting, and it's still clear.

Thanks in advance for any help!
 
Noggin said:
Hi all,
Not sure if this has been discussed before but I haven't been able to come up with a search that helps find the solution.

I'm trying to attempt to precipitate a very stubborn solution of metals that lurked in a 350g batch of mostly 1/10 10k gold filled.
The color is greenish brown, which I assume is mostly copper, iron, and/or nickel.
No reasonable amount of SMB (stumpout) was dropping all the gold. I got some to drop but it was way under what's expected. Stannous test is positive.
Today, I put some copper pipe and solid copper wire in the solution on a hot plate at 80c but a pretty tenacious black precipitate is coating it. After two hours, little copper has dissolved, likely because of passivation.
If this has been covered/explained, I'd be grateful for the link. Otherwise:

1. Please share what you think I'm dealing with and where I went wrong
2. What might I do to force the gold to drop so I can re-refine.

How I got here (if it matters)
350g gold filled jewelry heated to redness in a melt dish under torch into large beaker with small nitric boils. Did that until the nitric was clear. Magnet test noted some magnetic items were still in there. If you ever refined GF, it's not ever pretty the first round. I removed all small magnetic items like screws, springs, etc. that I found though.
I didn't weigh the items before adding HCL, which I think is a good step (as if I had, say, 60g I could rethink my process since I'm expecting to leave the nitric boil phase with <35).

Got it to dissolve with HCL and nitric, added sulfuric, filtered. Added SMB. Strong reaction. Kept going... I suspected too much nitric, added maybe 2 heaping tsp of sulfamic crystals and added heat. Stir /w stir bar till dissolved, then cooled to room temperature. Started again with SMB. Went through half a bottle of stumpout. Slept on it.

The next day, I started evaporating. When it dried it was like concrete. My stir bar was now a fossil. Started reconstituting using HCL and distilled water. When done, saw a precipitate on the bottom of the beaker. Stannous test is positive. The color is so horrible I only could guess it was gold so I decanted after a day of settling and actually located maybe 5-10g. It looked pretty decent.

I saw a post from January where someone was having issues getting their gold to drop, and the hail Mary was to add copper start over.

So as I said above, the copper is in and I'm currently slowly doing another evaporation round. As of my writing this, stannous test is still positive. Note, I've not re-filtered the solution after reconstituting, and it's still clear.

Thanks in advance for any help!
Click to expand...
If you can't find anything about Gold filled you need to improve your searches.
There are a lot of discussions on this topic.

But the general rule with Gold filled as anything mixed metal is:
Dissolve all the base metals first, then dissolve the Gold.

You have not yet detailed your process, but my guess is too much Nitric.

Cement it on Copper (with agitation) and redissolve the dropped powder for a cleaner drop.
 
Yggdrasil said:
You have not yet detailed your process, but my guess is too much Nitric.

Cement it on Copper (with agitation) and redissolve the dropped powder for a cleaner drop.
Click to expand...

Hi,
Thanks for taking the time to respond!
As I detailed in my process, excess Nitric was my guess too so I evaporated.
I'm cementing to copper with agitation (per my original post) but the noted black coating is blocking. I can't specifically find any reference to what the passivating substance might be.
 
Noggin said:
Hi,
Thanks for taking the time to respond!
As I detailed in my process, excess Nitric was my guess too so I evaporated.
I'm cementing to copper with agitation (per my original post) but the noted black coating is blocking. I can't specifically find any reference to what the passivating substance might be.
Click to expand...
Was it white Gold filled?
Evaporating the liquid may not be enough until you evaporate to syrup and add HCl.
 
You did not specifically say you filtered out the solids after the nitric pre treatment. You cannot use too much nitric to dissolve the base metals, slowly add until the reaction stops. Using too much nitric is costly but as you are filtering the liquid before moving on it isn't harmful to the process..

But if you didn't filter off the solids after nitric, as you suspected and Ygg confirmed, you have too much nitric. So the question is, did you filter the insolubles from the nitric dissolve and start fresh with new aqua regia?
 
Noggin said:
It wasn't white Gold filled. That was a good check though. I went past syrup to solid, but added HCL to reconstitute. Everything but a little gold went back into solution.
Click to expand...
There are just a few things that need to be in place for cementing to work.
Clean Copper, sufficient free acid (HCl) and agitation.
 
4metals said:
You did not specifically say you filtered out the solids after the nitric pre treatment. You cannot use too much nitric to dissolve the base metals, slowly add until the reaction stops. Using too much nitric is costly but as you are filtering the liquid before moving on it isn't harmful to the process..

But if you didn't filter off the solids after nitric, as you suspected and Ygg confirmed, you have too much nitric. So the question is, did you filter the insolubles from the nitric dissolve and start fresh with new aqua regia?
Click to expand...
Hi, thanks for the help.
The last nitric boil (pre-treatment) for my gold filled remained un-colored. I poured the solution into a large beaker where I have sterling to consume the nitric acid before putting into my waste stream.
I think my excess nitric was because I didn't pour off all that solution because I wanted to retain the colloidal gold I observed in the bottom. It didn't seem like that much but when I added HCL I didn't need any additional nitric to dissolve the gold. At this point, I surmised that I was at risk for having excess nitric but I've dealt with it before.
I filtered after the AR step till the solution was clarified but the color was very green-brown, as I said. Stannous test was, of course, positive.
New update - I shared my issue with chatgpt and it shared a few possibilities. One that stood out was this:

Iron Compounds: Since some of your jewelry is magnetic, it indicates the presence of iron. Iron can form various oxides and hydroxides that can appear black. When exposed to nitric acid and aqua regia, iron may form black iron oxide (Fe3O4) or hydrated iron oxide (FeO(OH)), which can precipitate and coat the copper.

I prompted chatgpt to give me a treatment for this and got a lengthy (but basically simple) treatment centered around ammonia. I checked Hoke's book and verified that it should work. I'll divide a small amount of the solution for experimentation and report the results.
 

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