Precipitating Gold Powder out of Aqua Regia

[johnny2398]

Hello, I'm new so please be kind if I'm not in the correct board (or not following a certain posting rule). I am attempting to create a fine gold dust. I have dissolved 1oz of 24K gold in a solution of aqua regia. I am looking to precipitate the gold out with Sodium Metabisulfite. I will then rinse the solution through filter paper with distilled water. I forget the balancing of equations from college... will there be any parts of the sodium metabisulfite left? Or will I then be left with 24K gold powder and no contaminants?

NOTE: I will not be melting the gold into an ingot after the filtering step. I wish to keep it a pure powder for other experiments.

[chenbeier]

Should work work, probably need pH adjustment to 6- 6.5 first. Aqua Regina  is high acidic, it will eat first the metasulfite by releasing  a lot of SO2, very poison. Need good hood with exhaust. But if you close to neutral the Gold could be precipitate. I think there should be receipes in the net. I would use Vitamin C Ascorbinic acid instead to avoid the the release of sulfur dioxide.

After you got the Gold, a good rinsing with slight acidic water will remove all other chemicals.

Edited August 19, 2022 by chenbeier

[johnny2398]

Awesome! Thanks for the help @chenbeier. Glad to learn it'll result in a pure 24K gold powder.

I'm expecting to boil away a large portion of the aqua regia, then add the remaining liquid/acid into distilled water... and not the other way around! That should lower the pH. I'll test with a pH strip to get it as neutral as possible. Got a wide open space away from people so the fumes will be at least 50m away from any passerby.

NOTE: Looking into the Vitamin C/Ascorbic Acid suggestion.

[chenbeier]

The dilution alone will not help, to increase pH. Add some sodium carbonate carefully and get pH up.