Non-Chemical Just Precipitated Gold, Now What?

[g_axelsson]

Exactly, sodium hypochlorite needs to be basic to be stable, pH 11-13 usually. If a solution can remain chlorinated for a week then the pH is too high, probably around neutral. At pH around 2-3 the hypochlorite breaks down to Cl₂ and NaCl.

So instead of boiling at close to neutral, add some HCl and simmer.

I'm using bleach now and then whenever I have dropped gold from a very dirty solution and gotten this black ink-like precipitate that never settles. Decant, add some HCl and a dab of bleach, swirl for a couple of minutes and then add some more SMB, the new precipitate is a lot easier to handle and it's faster than fighting with that black fine powder.
The low solubility of Cl₂ guarantee that there isn't a large excess, not like nitric acid. So even if there are chlorine dissolved with the gold chloride, there isn't a lot and the little SMB that is needed to fight it is inconsequential so I usually never bother driving it off.
If you are dealing with liters of solution it can be another story, but for a concentrated second precipitation I don't bother.

If it doesn't bubble when you add bleach then the pH is too high, add more HCl.

Another alternative is strong hydrogen peroxide, have only done some minor tests with that though.

Göran

 

[g_axelsson]

It took a week until I pointed this out, then the discussion exploded. :lol:

I've been sitting on this post for a week now. I'm in a middle of a big move and I haven't had the time to do the research I needed to do for a week... don't have the time now either but I took a break.

Göran

 

[UncleBenBen]

Exactly, sodium hypochlorite needs to be basic to be stable, pH 11-13 usually. If a solution can remain chlorinated for a week then the pH is too high, probably around neutral.

Well that makes sense now! Raised the pH with all the bleach. I wish I would have realized that a couple years ago. Thanks Göran!

don't have the time now either but I took a break

That's ok, I'm a big fan of breaks!

 

[ARMCO]

I have just been sitting back and reading this thread over time. It has answered alot of questions that I had, but didn't ask. Thank you for having the discussion!