Chemical Purple Au question

[RevMatt]

So, here’s the deal: A jeweler friend of mine was experimenting with purple gold, aiming for a very specific shade. These pictures show two out of five pieces that didn’t make the cut—literally and figuratively. Since he wasn’t happy with the color, he asked me to retrieve the gold.

In total, we’re looking at about 1 troy ounce of gold, with varying amounts of aluminum mixed in (somewhere between 15% and 25%).

Now, before I dive in, is there anything I should particularly know? For example, would I be better off using inquartation, or should I just go full aqua Regia and let chemistry do its thing? Any tips before I accidentally create a science experiment gone wrong?

 

[Yggdrasil]

View attachment 67284View attachment 67285
So, here’s the deal: A jeweler friend of mine was experimenting with purple gold, aiming for a very specific shade. These pictures show two out of five pieces that didn’t make the cut—literally and figuratively. Since he wasn’t happy with the color, he asked me to retrieve the gold.

In total, we’re looking at about 1 troy ounce of gold, with varying amounts of aluminum mixed in (somewhere between 15% and 25%).

Now, before I dive in, is there anything I should particularly know? For example, would I be better off using inquartation, or should I just go full aqua Regia and let chemistry do its thing? Any tips before I accidentally create a science experiment gone wrong?

Just from the top of my head.
Nitric will passivate Aluminum and HCl will dissolve it.
Aluminum is somewhat soluble in weak Nitric.

So maybe a weak AR can do the trick?
But I'll try a small piece first, it may go well in standard AR.

 

[RevMatt]

Just from the top of my head.
Nitric will passivate Aluminum and HCl will dissolve it.
Aluminum is somewhat soluble in weak Nitric.

So maybe a weak AR can do the trick?
But I'll try a small piece first, it may go well in standard AR.

Thanks! It seems fragile enough that I could probably crush it without too much effort, so running a few small experimental batches shouldn’t be an issue.

Anything I should watch out for, or am I about to discover a brand-new way to make a mess?

 

[RevMatt]

Quick chemistry check: Since this stuff is fragile enough to crush, could I just hit it with straight hot muriatic acid to take care of the aluminum? Or would that be the kind of bad idea that lands me in the "Well, that escalated quickly" section of a science textbook?

 

[orvi]

If it is fragile, put it into some durable bag or anything that holds and smack it with hammer to at least halve it - then it would dissolve much more easily.

I would go with straight AR for this. If there is no silver of course (shouldn´t be any inside since purple gold should be just AuAl alloy). When you dissolve it, drop the gold on copper. That should suffice. If you want 999 purity, you will need to re-refine it. But cementation will also deal with excessive nitric etc.

 

[Yggdrasil]

Quick chemistry check: Since this stuff is fragile enough to crush, could I just hit it with straight hot muriatic acid to take care of the aluminum? Or would that be the kind of bad idea that lands me in the "Well, that escalated quickly" section of a science textbook?

Maybe, but Aluminum in HCl have sometimes a tendency of becoming a gel like substance.
I believe it has to do with the amount though.

But as Orvi says it should be ok in AR, but test first.

 

[goldandsilver123]

I would just AR for 1 troy ounce 100 mL of HCl 37% and 10 mL of HNO3, if reaction stops and there's still metal 5 mL steps of HNO3

Keep at 80 °C

I would precipitate with sodium metabissulfite that would make your gold 99.99+% if the alloy is just gold and aluminium

 

[RevMatt]

Maybe, but Aluminum in HCl have sometimes a tendency of becoming a gel like substance.
I believe it has to do with the amount though.

But as Orvi says it should be ok in AR, but test first.

Many thanks to both of you! I ran it through a wire roller inside a heavy bag—because, you know, controlled destruction is the best kind. After some testing, I’ve decided to go with aqua regia for the next step. I’ll keep you posted—assuming I don’t accidentally create a sci-fi supervillain origin story in the process!

 

[snoman701]

I'd probably try to scorify it first. I'm not sure it would work, but fluxing a melt with cryolite or just fluorspar should dissolve the aluminum that will be readily oxidized to alumina. Again, could be dead wrong, but it's what I'd look in to first.