Aqua Regia leaves me with a lot of salts after dissolving gold.

[Danenorris]

I am having a hard time washing my gold after two types of gold dissolving methods. One is where I add 70% nitric acid to computer pins to eat away at the metal causing it to release the gold. The other is when I dissolve the gold off of a new set of pins with aqua regia. Both seem to leave a lot of salts behind.

 

In the first method with just nitric acid the salts are so bad I end up loosing a lot of gold flakes trying to rinse the salts out. Any idea how to dissolve the salts so I can wash the gold easily? Also I would really like to know what these salts are. Is it silver chloride?

 

In the second method of using aqua regia on a new set of gold plated computer parts I am always left with a lot of salts that I assume are retarding the process where the liquid gold turns back into a solid and sinks back to the bottom. What are these salts? Are they the same thing as the first method? Is it silver chloride?

How can I keep the salts away.

 

I know my gramor is lacking. Being dyslexic is very frustrating at times.

[THX-1138]

Welcome to SFN!

 

I have no answers for the aqua regia method; I prefer my gold where I can see it.

 

When you say 'salts,' do you mean precipitate, or salts in solution? I assume the former.

 

I don't know what the precipitated compounds may be, but if you're trying to separate out the gold particles with simple washing, I can see why you'd be losing a lot. Gold leaf (essentially what you're getting off the contacts) has so much surface area per unit mass that it doesn't settle out quickly.

 

Rather than straight washing, I'd suggest experimenting with different reagents to try to find one that will dissolve the precipitate. In this scenario, gold's very nobility is your friend.

 

I'm in a similar situation. I used FeCl₃ to release the gold by etching away the metal onto which it was plated. I then diluted the solution to translucence. The first batch had no precipitate, so I was able to agitate it to 'shake loose' any clinging gold, let it settle, and remove the gross fragments of PCB and dross with forceps. Then I let it settle again, and siphoned off most of the solution. I repeated this a few times, and when the solution was clear I siphoned most of it off, washed the remaining solids with H₂SO₄, rinsed them, and finally filtered them out. I still had some impurities when I melted the result, so I still have a little more work to do.

 

On the second batch, I have a large quantity of white precipitate, which I plan to remove by finding an appropriate solvent. Then lather/rinse/repeat as above.

 

Hope this helps.