oxalic acid question

[yvonbug]

Is oxalic acid better than sodium sulfite to use for dropping gold out of AR?

 

[4metals]

Oxalic acid will drop a higher purity of gold particularly if some Platinum is mixed in with the gold. The down side is it works on aqua regia only after you perform the tedious triple boil down to drive off the nitric, and both the oxalic acid solution and the acid containing the gold need to be almost boiling when they are used. Plus the gold doesn't always drop immediately.

I'd stick with sodium sulfite and reserve the oxalic for assaying gold/platinum alloys gravimetrically and making very high purity proof gold for assay usage.

 

[EVO-AU]

4metals: Reading your reply to Yvonne, I would like to know: Can I get a good result using oxalic acid as a ppt with SSN, or Iodine and other related leaches. I don't care for A/R and use mostly the above combos. Thanks, Phill

 

[4metals]

I'm not really sure, most of my work has been with Aqua Regia, and Hydrochloric and Chlorine gas, I've never leached with SSN, I've recovered gold from Iodine etches using straight Potassium hydroxide which replaces the gold in the gold iodide complex. Almost all of the gold I've recovered was from high grade sources so complete digestion was the rule, not selective leaching.

 

[Platdigger]

4metals, when recovering "gold from Iodine etches using straight Potassium hydroxide"

What form is the gold in? Or, more importantly, what was your next step?
Thanks

 

[4metals]

We often receive solution of gold etch, which is an iodine based etch. By simply making the solution alkaline using potassium hydroxide the gold drops out and the solution goes from deep brown to a light yellow.

 

[Platdigger]

OK, but, the gold drops out as what?
What do you do next?
Thanks

 

[Lou]

Not as gold metal per se, but rather something odd . Let's just say it dissolves, filters and melts like regular ol' gold!!

As far as oxalic acid goes: it is notorious for its use in removing palladium. 4metals, see my post stickied in Techniques on ultra high purity gold--you will likely appreciate that procedure.

Another pain in the butt about oxalic acid is that the solution has to be simmering. Ammonium oxalate actually works better than straight oxalic acid, should anyone ever want to try it!

 

[4metals]

Lou,

Your method for producing 6 nines fine gold is excellent. Unfortunately between reagent and pure water costs, I doubt if I'd ever try it. I wonder if it's possible to maintain that purity after melting?

 

[Noxx]

Oxalic acid works well, but I wouldn't use it to precipitate gold from a «dirty» AR solution since it tends to co-precipitate copper along with gold.

 

[DNIndustry]

Not as gold metal per se, but rather something odd . Let's just say it dissolves, filters and melts like regular ol' gold!!

As far as oxalic acid goes: it is notorious for its use in removing palladium. 4metals, see my post stickied in Techniques on ultra high purity gold--you will likely appreciate that procedure.

Another pain in the butt about oxalic acid is that the solution has to be simmering. Ammonium oxalate actually works better than straight oxalic acid, should anyone ever want to try it!

You can precipitate it as Au203 or Au(OH)2
Some times it will drag down some Auric Iodide and you will get purple haze.

 

[4metals]

What is deceptive is the volume of the precipitate from the iodine vs. the actual gold recovered. It seems like there is a size-able quantity of gold after dropping with KOH but in reality it's not what it looks like.

Reminds me of the old assayers rule, never guess what an assay result will be by what judging how much metal is in the parting cup. The balance never lies!

 

[goldsilverpro]

In 40 years, I can't ever remember guessing low.

 

[Platdigger]

:shock: ....... 8)