Chemical Sodium Hydroxide -vs- SMB to Precipitate Gold

[Yggdrasil]

Bc I was was wondering if I could just skip the whole pre-process my material thing, save time and money on acids, and just dissolve it all at once and use Soah to precipitate out the iron, which I found out that I can, and I was wondering what my ph limits were by doing this... I work with Gold (III) oxide and iron, so the gold dissolves in hcl alone without an oxidizer. So no matter what I do, if I try cleaning material with pre-acid treatment, gold will still go into solution... which really complicates things for me... And because of the high iron content, the gold has hard time falling out. I'd first have to roast the material, converting back into metallic gold, and THEN pretreat it with acid to remove base metals. But anyways this response is getting way too long. Gotta roll.

As long as the Gold is dissolved just use one of the usual precipitants.
It won't touch the Iron.
Make sure the pH is no higher than 2 and then add SodiumMetaBisulfite (SMB) or Ferrous Sulfate.
The Gold should drop straight out with the Iron still in solution.

 

[Meteoriterocks21]

As long as the Gold is dissolved just use one of the usual precipitants.
It won't touch the Iron.
Make sure the pH is no higher than 2 and then add SodiumMetaBisulfite (SMB) or Ferrous Sulfate.
The Gold should drop straight out with the Iron still in solution.

Mine won't drop bc of the super super high iron content. Also ph of 3 to 3.5 would probably make larger particles. Iron, particularly in its Fe³⁺ (ferric) form, can also be reduced by sodium metabisulfite, potentially competing with gold (Au³⁺) for reduction. This is a problem for me. But we'll try adjusting the ph, and see if it works. Appreciate the advice.

 

[Yggdrasil]

Mine won't drop bc of the super super high iron content. Also ph of 3 to 3.5 would probably make larger particles. Iron, particularly in its Fe³⁺ (ferric) form, can also be reduced by sodium metabisulfite, potentially competing with gold (Au³⁺) for reduction. This is a problem for me. But we'll try adjusting the ph, and see if it works. Appreciate the advice.

I usually precipitate at 0-1 pH, The 2-4 boundary is closer to where it will not drop anymore.
If you have trouble try to cement it on Copper.
It will drop precious metals only and Mercury if it is there.

 

[Geber]

At what ph does gold precipitate from solutions? I have looked at hokes book, scoured for days online, looked at patents and can't find anything. I found a list of metals that precipitate by PH but platinum and gold weren't on it... You said by reactivity series... So this means gold would be one of the last to fall out? Appreciate any response.

Theoretically it should be the first to come out (after platinum). Metal nobility is an expression of how little energy is needed to reduce them. Not sure if that works in practice.

If you have iron and gold in solution and want to isolate the gold, why not cement on solid copper?

 

[Thomas M Joseph]

Strange, but ferrous sulfate (copperas) is the ideal precipitant as it will not reduce iron in solution to the metallic state as SMB will because of SO2.