Aqua regia and sodium bilsulfite

[Robertleegrant]

Hey guys,

Newbie here. Mixed up a batch of AR and dissolved some gold chain. Added the sodium bilsulfite assuming I would eventually get precipitate and mud.
Instead I got fizz. Super fizz. Aqua seltzer fizz. No precipitate at all? Any thoughts on what I did wrong?

Thanks in advance,

R

 

[Martijn]

Welcome to the forum.

The mistake most often made is too much nitric.

If may guess, you premixed a batch of HCl and HNO3 and dissolved an amount of gold.
To make sure all gold would dissolve, you made enough to do the job?

Now exactly how much of these three ingredients did you use and how did you perform the process? (Steps, tools, safety, ...)

Martijn.

 

[4metals]

Instead I got fizz. Super fizz. Aqua seltzer fizz. No precipitate at all?

While it was busy fizzing were red fumes coming off?

 

[Robertleegrant]

I made up about 20ml of nitric from potassium nitrate and sulfuric acid. I added 80ml of muratic (20% concentration?). Trying to get to 3:1 molar.
So I got to a beautiful yellow AR that dissolved some gold like a champ. I never quite got to red fuming.

I appreciate the assist.

Thanks,
R

 

[608927101la]

Don't you have to neutralize with urea before precipitation?

 

[Martijn]

How much of the last ingredient, gold, did you add? And what was the purity? 14K? 18K?
Did everything dissolve?
The red fumes question is about upon adding SMB. Not during the dissolution.

 

[Martijn]

Just looked at your picture: the chain did not fully dissolve.
To dissolve carat gold you need to inquart to 25% gold or 6K, and then dissolve the silver and base metals with nitric from the alloy, leaving a porous golden skeleton to process in AR.
The silver will otherwise 'protect' the gold inside the alloy in AR, by forming a crust of AgCl.
It needs some calculation to get the amount of silver right, so you don't have to use too much nitric.
Most refiners inquart with scrap sterling silver to kill two birds with one stone.

I'm not sure if you have any other material to process or this chain is the one thing you want to refine.

But you have passed that point. The silver chloride layer may result in losses when melting. Others will have to jump in here.

Now your solution: it will surely contain some of the gold, but may also still hold free nitric, hence the red fumes question. That will redissolve any gold pushed out by the SMB.

Try to answer each question we ask.

I think the most gold will still be in the chain.

Martijn.