Gold Chloride volatility

[autumnwillow]

Referring to this article: https://www.911metallurgist.com/blog/gold-chloride

Will gold be lost if you overheat an AuCl solution? If yes, how? If it vaporized what did it turn into and how do you capture it? What are the signs from the surrounding that the AuCl vaporized?

I know metallic gold evaporates when an acetylene/oxygen torch is used. But what does it turn into?

 

[butcher]

Gold will not be lost if you heat a gold chloride AuCl3 solution (liquid) to evaporate the solution, as long as you keep the solution from boiling, which can carry a mist of solution along with the mist of bursting gases violently escaping the surface of the liquid.

Note: older text may describe the evaporation process of gold wrongly and call it boiling when they are not actually boiling the solution, Hoke used a steam bath to heat the solution to evaporate it (which would not permit the solution to actually boil) although she may have described it as boiling...

That said, fine gold powder when mixed with any chloride salt (table salt)(copper chloride or any other metal chloride salt), when heated 180 degrees or above will volatilize some of the gold, just as the gold powder will volatilize in a stream of chlorine gas heated above these temperatures.

The gold sublimes, the gold changes directly into a vapor when heated, the gases of gold monochloride and trichloride are carried off into the escaping gases when cooling forming a solid deposit of reddish-gold crystals.

If memory serves me, Harold spoke of using furnace filters to capture these crystals in his fume hood...

I do not know of any gold evaporating when using an acetylene/oxygen torch, the gold metal cannot be oxidized by the torch, and is not volatile, although fine gold powder can be blown away by the force of the jet of burning gases if you are not careful. The only thing gold will turn into when using an acetylene/oxygen torch to melt it when done properly is molten gold.

 

[autumnwillow]

Thanks butcher that clears things up for me, I accidentally left an AR solution at heat overnight, it was not boiling violently and no traces of red stain anywhere.

 

[butcher]

If you are just evaporating the solution down (without boiling or bursting bubbles) you could evaporate the solution down to almost a gold salt without loss before the gold becomes volatile (with the loss of moisture and higher heating of the salts)depending on heat source used...

Hoke used a few drops of sulfuric acid (not only to help remove lead from solution) but also to help de-NOx the solution, the sulfuric helps to drive off other volatile acids (water, nitric then HCl) and is not itself so volatile that it helps to keep the gold from forming dry salts if you get forgetful and leave the solution and evaporate it too far. The few drops of sulfuric (or sulfamic acts similar) will help to keep the gold from forming dry salts which would bake dry if left unattended...