Sciencemadness Discussion Board - Red solution from gold processing, WTF is it ?

Red solution from gold processing, WTF is it ?

Sulaiman - 10-7-2018 at 04:32

I dissolved gold jewelry and e-scrap in aqua regia, expecting about 2+ g pure Au total.
I used too much nitric acid so when trying to drop the gold I had to use a lot of sodium metabisulphite,
one of the additions was too much and foaming caused the contents to overflow slightly.

What I do not understand is why I have sediment in a RED solution

Before adding SMB the solution was green with a tinge of gold/yellow.
I have done gold scrap + aqua regia + SMB four or five times before and never seen this colour.

Anyone guess what causes the red solution ?

HeYBrO - 10-7-2018 at 04:43

My guess is colloidal gold

j_sum1 - 10-7-2018 at 04:50

That's my guess also. It is pretty cool.
You can actually get different shades if you can change the particle size.
I would ampoule some for the element collection.

There is not much gold there but if you dilute it sufficiently, bottle it up, label it as Ormus Gold and sell it to New Age types, it is worth a fortune.

XeonTheMGPony - 10-7-2018 at 05:11

Quote: Originally posted by j_sum1

That's my guess also. It is pretty cool.
You can actually get different shades if you can change the particle size.
I would ampoule some for the element collection.

There is not much gold there but if you dilute it sufficiently, bottle it up, label it as Ormus Gold and sell it to New Age types, it is worth a fortune.

About the only good the new age types are good for is selling overpriced air too lol, look up "Energized" water lmao

woelen - 10-7-2018 at 05:18

It may also be palladium. Palladium ions have this very typical brown/red color.
I hardly can believe it is colloidal gold:
1) Colloidal gold has amuch brighter color, more like pink/red instead of brown/red.
2) In the strongly salted solution you have here, colloidal gold quickly would precipitate, giving a dirty brown paste of very finely divided impure gold.

What is the source of your gold? This also may give a clue of whether it may contain palladium or not.

If it is colloidal gold ...

Sulaiman - 10-7-2018 at 05:28

I just tested the red liquid with SnCl₂ and got no reaction,
so I assume that most of the gold is in the precipitate and some in colloidal suspension.

1) how to separate the colloidal gold from the (presumed still) dissolved copper etc. ?

2) can an excess of SMB/SO₂ drop copper out of solution, even temporarily/transiently/ephemerally ?
I ask because as I was adding SMB to the gold-bearing solution,
what looked like fine copper powder appeared in the froth, then dissolved away.
I have seen gold powder/sand look similar, and there was still probably some nitric acid in solution at that stage.

... (why red ? I'd expect a lot of green copper ions to remain in solution)

In my previous attempts at anti-bacterial colloidal silver synthesis I found that above about 25 ppm the colloidal particles eventually settle out as a precipitate, so if this is colloidal gold, then as suggested I doubt that there is a significant quantity of gold in suspension.
IF I can get just the colloidal gold without the contaminants then I may try selling some via eBay, just for fun

EDIT:
@woelen the starting material was;
. a little gold plated electronics scrap, common stuff I've refined before
. 7.37g jewellery, various bits of cheap scrap jewellery from my family and a friend: chains, rings, earrings etc. mostly .375 or plated.

In my waste bottle (from the initial nitric acid wash/soak) I see two green coloured liquid layers, one like copper, one like nickel, and precipitate/crud at the bottom.

This is becoming much more interesting than just getting a sample of gold

#################################################
On dilution the red liquid became yellow (slightly green) and did not react to SnCl₂ (even after a little aqua regia added) or excess SMB so I discarded it.
Whatever the red liquid was, I can not determine now.
Nett = 2.06g Au and a bottle of corrosive toxic waste & a mystery.

[Edited on 10-7-2018 by Sulaiman]

diddi - 10-7-2018 at 17:22

did you digest any other components in your ewaste. eg tiny surface mounted capacitors. they have Pd. i have had that sort of colour from monolithic surface mount capacitors

Sulaiman - 11-7-2018 at 07:19

No palladium bearing components electronic components that I noticed,
but possibly Pd used to plate earrings ?

In any case, dilution changed the red/brown solution to yellow,
no amount of SMB/SO₂ added produced any precipitate or visible change.

MrHomeScientist - 11-7-2018 at 08:13

Out of curiosity, how did you "discard" your "corrosive toxic waste"?

Sulaiman - 11-7-2018 at 13:34

I have not decided yet,
it consists of about 200ml and it is in a bottle waiting for me to decide its fate.

The 'corrosive' part is easy to neutralise,
the toxic part is because I expected some lead and nickel.

Sulphuric acid produced no precipitate indicating no lead,
but there could have been enough nitric acid to keep any lead oxidised so I'm not certain.
I doubt that I will try to recover anything from the waste so the metals will end up in landfill as sulphates.

kadriver - 3-9-2018 at 13:49

Quote: Originally posted by Sulaiman

I dissolved gold jewelry and e-scrap in aqua regia, expecting about 2+ g pure Au total.
I used too much nitric acid so when trying to drop the gold I had to use a lot of sodium metabisulphite,
one of the additions was too much and foaming caused the contents to overflow slightly.

What I do not understand is why I have sediment in a RED solution

Before adding SMB the solution was green with a tinge of gold/yellow.
I have done gold scrap + aqua regia + SMB four or five times before and never seen this colour.

Anyone guess what causes the red solution ?

The red is probably junk metals in solution. What was the source material Karat gold? Gold filled? Gold plated? Each requires a different procedure. For example, if you hit gold filled scrap with AR you'll end up with a very dirty solution. It's even worse with gold plated stuff. Even karat gold can have problems if you just add it to some hot aqua regia.

Then there is escrap. Most of it has very little gold to get from it. Escrap requires a different process than the other three.

As far as the red in solution, it doesn't look like colloidal gold to me. The colloidal gold that I've seen usually tends to separate into distinct layers with the color pink and or purple being observed.

If you tested the red solution with stannous with negative results then it would be safe to conclude that the solution is void of any precious metals. But it looks like the sediment on the bottom of the beaker might be gold.

If it were me, I would siphon the red solution off of the dark solids (the gold) and into a separate beaker for waste treatment. Once the bulk of the red solution is siphoned off I would filter the solids (the gold powder) from the bottom of the beaker and rinse these solids with water while it's still in the filter. Then I would add the wet filter with the gold inside into a clean beaker with 1/2ml concentrated sulfuric acid (to precipitate out any lead) and dissolve the gold powder a second time using hydrochloric acid and incremental nitric acid additions 1ml at a time with heat and stirring until the gold dissolves completely. Premixing the the aqua regia three or four to one wastes chemicals and GUARANTEES that you'll have problems with excess nitric when the gold gets precipitated.

Once the gold is dissolved completely I'd filter the solution to remove any solids such as lead sulfate from the sulfuric acid, then precipitate the gold a second time - should get it nice and clean, three nines fine.

kadriver

Sulaiman - 3-9-2018 at 15:05

Thanks.
I've basically followed the steps that you mentioned,
I also added my entire stock of previously recovered gold (0.84g) to the initial 2.06g Au from this session
and did two rounds of dissolving and precipitating (incl. H₂SO₄ to precipitate Pb)
final result ... 2.75g total, a nice gold sand, now in a cute vial,
I'm not sure where I lost 0.15g Au, I thought that I was quite careful.