Half gold chloride didn't drop gold

butcher

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The little bit of added sulfuric acid is normally used to help remove lead from solution as the insoluble lead sulfate.

Actually if you had nitrates in solution adding an acid like HCl or H2SO4 would convert the nitrate salts in solution to nitric acid, Hydrogen from the acid, and the nitrate salt would make nitric acid.
H + NO3 ---> HNO3
nitric acid which can decompose as NOx gas (normally with added heat, or a reducing agent like a metal copper for example), or even excess SMB...

The sulfuric acid would not decompose excess nitric acid, both would be in solution.

You may have just added enough reducing agent to overcome a small excess of nitric acid, which may have happened if you had just added a bit more SMB or potassium metabisulfite.

The sulfite salt and ferrous sulfate both can reduce gold from solution, but the chemistry and how they do so is completely different, sulfites produce SO2 gas with the acid, it is actually the SO2 gas that is the reducing agent that gives gold ions the missing electrons to become atoms of gold which join together to form a heavy enough powder to precipitate from solution.

A few chemical formula’s using reagents to precipitate gold

Sodium bisulfite and gold chloride solution
2 HAuCl4 + 2 NaHSO3 --> 2 Au + 8 HCl + Na2SO4 + SO2
or
2AuCl3 + 3NaHSO3 + 3H2O --> 2Au + 3NaHSO4 + 6HCl

sodium metabisulfite and HCl
Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2

gold chloride and sulfur dioxide gas
2AuCl3 + 3SO2(g) + 3H2O --> 2Au + 3SO3 + 6HCl


Sodium metabisulfite in gold solution:
Na2S2O5 + H2O --> 2 NaHSO3

Notice we actually make sodium bisulfite
Then
2 AuCl3 + 3 NaHSO3 + 3 H2O --> 2 AU + 6HCL + 3 NaHSO4

Ferrous sulfate (iron sulfate) (copperas) (FeSO4) and gold in chloride solution:
2 AuCl3 +6 FeSO4 --> 2 AU +2 Fe2(SO4)3 + Fe2Cl4
(Note we do not make sulfuric acid above).

potassium metabisulfite and HCl acid
K2S2O5 +2HCl --> 2KCl + H2O + SO2(g)

Adding SMB (or K2S2O5), and ferrous sulfate in the same reaction to precipitate gold, there is no benefit, and would complicate matters for the most Part, and would be recommended.
just because it happened to work for your particular circumstance or one certain reaction (which may be because you finally decomposed the excess nitric acid redissolving your gold with excess reagents, does not mean it will not complicate the next batch in another circumstance, there is no benefit, and it is not recommended...

There are ways to deal with excess nitric acid in your gold chloride solutions.

Do not use more than needed.

Sulfamic acid can be used to destroy the excess HNO3 in solution.

Dissolving a metal like (an added button of gold) to consume the nitric in solution (with heat), (Harold's method).

Or the 3 evaporation process ( discussed in Hoke's book) where a little HCl acid is added towards the end of each of the three evaporation's in which you concentrate the gold chloride solution to the point of driving off the excess nitric acid as NOx gas, (where HNO3 decomposes to gas before most of the HCL or gold chloride decompose.
A few drops of sulfuric also have the benefit here. if you happen to get carried away by mistake or inexperience, with the evaporation process, and go to far with the evaporation, where you can form salts of the gold chloride or cook those salts, (driving off too much of the HCl or chloride salts as gas by mistake) the sulfuric aids in helping to keep the gold salts in solution, sulfuric acid is less volatile and will not decompose even after the HCl has or the chloride salts decompose to gas...
 

FiP

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Jun 15, 2015
Messages
37
butcher said:
The little bit of added sulfuric acid is normally used to help remove lead from solution as the insoluble lead sulfate.

Actually if you had nitrates in solution adding an acid like HCl or H2SO4 would convert the nitrate salts in solution to nitric acid, Hydrogen from the acid, and the nitrate salt would make nitric acid.
H + NO3 ---> HNO3
nitric acid which can decompose as NOx gas (normally with added heat, or a reducing agent like a metal copper for example), or even excess SMB...

The sulfuric acid would not decompose excess nitric acid, both would be in solution.

You may have just added enough reducing agent to overcome a small excess of nitric acid, which may have happened if you had just added a bit more SMB or potassium metabisulfite.

The sulfite salt and ferrous sulfate both can reduce gold from solution, but the chemistry and how they do so is completely different, sulfites produce SO2 gas with the acid, it is actually the SO2 gas that is the reducing agent that gives gold ions the missing electrons to become atoms of gold which join together to form a heavy enough powder to precipitate from solution.

A few chemical formula’s using reagents to precipitate gold

Sodium bisulfite and gold chloride solution
2 HAuCl4 + 2 NaHSO3 --> 2 Au + 8 HCl + Na2SO4 + SO2
or
2AuCl3 + 3NaHSO3 + 3H2O --> 2Au + 3NaHSO4 + 6HCl

sodium metabisulfite and HCl
Na2S2O5 + 2 HCl → 2 NaCl + H2O + 2 SO2

gold chloride and sulfur dioxide gas
2AuCl3 + 3SO2(g) + 3H2O --> 2Au + 3SO3 + 6HCl


Sodium metabisulfite in gold solution:
Na2S2O5 + H2O --> 2 NaHSO3

Notice we actually make sodium bisulfite
Then
2 AuCl3 + 3 NaHSO3 + 3 H2O --> 2 AU + 6HCL + 3 NaHSO4

Ferrous sulfate (iron sulfate) (copperas) (FeSO4) and gold in chloride solution:
2 AuCl3 +6 FeSO4 --> 2 AU +2 Fe2(SO4)3 + Fe2Cl4
(Note we do not make sulfuric acid above).

potassium metabisulfite and HCl acid
K2S2O5 +2HCl --> 2KCl + H2O + SO2(g)

Adding SMB (or K2S2O5), and ferrous sulfate in the same reaction to precipitate gold, there is no benefit, and would complicate matters for the most Part, and would be recommended.
just because it happened to work for your particular circumstance or one certain reaction (which may be because you finally decomposed the excess nitric acid redissolving your gold with excess reagents, does not mean it will not complicate the next batch in another circumstance, there is no benefit, and it is not recommended...

There are ways to deal with excess nitric acid in your gold chloride solutions.

Do not use more than needed.

Sulfamic acid can be used to destroy the excess HNO3 in solution.

Dissolving a metal like (an added button of gold) to consume the nitric in solution (with heat), (Harold's method).

Or the 3 evaporation process ( discussed in Hoke's book) where a little HCl acid is added towards the end of each of the three evaporation's in which you concentrate the gold chloride solution to the point of driving off the excess nitric acid as NOx gas, (where HNO3 decomposes to gas before most of the HCL or gold chloride decompose.
A few drops of sulfuric also have the benefit here. if you happen to get carried away by mistake or inexperience, with the evaporation process, and go to far with the evaporation, where you can form salts of the gold chloride or cook those salts, (driving off too much of the HCl or chloride salts as gas by mistake) the sulfuric aids in helping to keep the gold salts in solution, sulfuric acid is less volatile and will not decompose even after the HCl has or the chloride salts decompose to gas...

Thank you Butcher! Very clear and hélpful. Thank you for the time you put into this!
 

au-artifax

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Jun 5, 2013
Messages
80
I didn't denox as I was pretty sure it had completely stopped reacting and I tested a small bit to see if it would drop and it did you I did it to the entire batch. It was definitely sodium metabisulphite. They were in the same jug, I separated them out and then added the smb, one dropped and the other started to then drew back in the gold.
I'm actually waiting for the stannous chloride to be delivered but if one went clear I don't see why the other one didn't. I've been going over it in my head and the only difference is that I added two scoops of smb to the pot that didn't react. I think I need to reverse what I've done there but I'm not entirely sure how! It really has me scratching my head. I'm assuming it must have become alkaline from the smb and unable to react.
That's why I thought if I add Hcl it would acidity it and then be able to drop with smb?

It's the weirdest thing!
I may be wrong, but I don't think SMB would make your solution more "base". As far as I know it creates another acid when it mixes with H2O and reacts with an acid.
 
Last edited:

au-artifax

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Jun 5, 2013
Messages
80
I'm not guessing or experimenting. I've read on here from other members that heating the solution can help push out the gold. As I said I tried, it didn't work so I'm asking. I get it to a gentil boil, barely enough to have bubbles break the surface.
All of the things I've mentioned I've seen on other posts on here apart from adding the extra H2o, that ones on me.

I guess I'll have to go down the copper came ting route then. Thanks
Heating doesn't help "push out the gold". What heating does is help fine particles in a cloudy suspension coalesce and drop to the bottom. But of the gold isn't "reduced", it won't coalesce.
 

au-artifax

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Jun 5, 2013
Messages
80
Just a quick thought, but have you tried adding a bit of HCl? Sounds like you've added enough SMB, but without some excess HCl, your gold won't drop.

Dave
This true... you need an acid to release the sulfur from the SMB (via the formation sulfamic acid). It is not the SMB that precipitates the gold..... it is the byproduct of its reaction with an acid, which releases sulfur (to which gold has an affinity for).
 

VK3NHL

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May 29, 2015
Messages
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Always de-nox even if you think you don’t need to. Use Sulfamic acid Not Urea. (Urea is for the garden)
Always STANNOUS test you solutions before & after your drop.
We are all learning all the time.
Good luck..
 

cejohnsonsr1

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Sep 20, 2020
Messages
32
Precipitation with SMB produces an exothermic reaction. What you need to do is cool it down with ice made from distilled water. You should do this the 1st time right after you remove it from the heat after the AR has dissolved all of the gold. Cooling this way at this point will precipitate any residual silver chloride and other solids which are removed by filtration. Then use more ice to keep the solution cool during precipitation with SMB. The SMB will denox a good bit of excess Nitric because whatever is precipitated will simply redisolve until the excess Nitric is consumed (up to a point). Much better to use small, incremental doses of Nitric when dissolving so there isn't any excess to worry about/deal with. You'll know when you've used enough SMB because it will foam up on top. Double check with stanis. I've mentioned this in a couple of other threads, but Sreetips has some excellent videos showing this process in great detail. He just released a new one today. I highly recommend checking him out on YouTube.
 
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