# Question about excess Hydrochloric acid



## Saddiq NG (Jun 9, 2022)

Hello members of this blessed forum I need you to help me with an answer to a question I do not know about based on your experience or knowledge regarding excess acids in aqua regia after dissolving gold

So far we know what excess nitric does to gold precipitation. That is it re dissolves the gold back into solution.

My Question now is what is the effect of excess Hydrochloric acid, assuming you added too much to dissolve gold? Could it be possible that it can cause less gold to precipitate while retaining most of the gold to be retained in solution? Or could it even test negative with stannous chloride when in excess.


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## Martijn (Jun 9, 2022)

Welcome to the forum. short answer: No. 
A deficiency of HCl can prevent a selective reagent from working. 
Any free nitric will not stop SMB from working, but will re-dissolve the pm's. 

An excess of HCl is no problem. 

Martijn.


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## butcher (Jun 9, 2022)

Copperas or a pure crystal of green ferrous sulfate, in a small test tube or in a spot plate with a few drops of solution to be tested the crystal of iron sulfate can be used to test for excess nitric (or to see if gold will precipitate).

With an excess nitric acid in the solution, we see the green crystal turn brown at its edges, and then the brown disappears, if the solution contains gold and is free of excess nitric acid the green crystal will dissolve leaving a brown powder.

Iron II sulfate, ferrous sulfate, copperas, FeSO4, and green vitriol, are all names for the same green iron-based sulfate salt, which can be easily made from soft iron and 10% dilute sulfuric acid.


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## Saddiq NG (Jun 9, 2022)

Martijn said:


> Welcome to the forum. short answer: No.
> A deficiency of HCl can prevent a selective reagent from working.
> Any free nitric will not stop SMB from working, but will re-dissolve the pm's.
> 
> ...


Thanks Man. I just realised that I got a good amount of gold recovered from Pin Grid array CPUs and I used less HCl than usual. So I was curious


butcher said:


> Copperas or a pure crystal of green ferrous sulfate, in a small test tube or in a spot plate with a few drops of solution to be tested the crystal of iron sulfate can be used to test for excess nitric (or to see if gold will precipitate).
> 
> With an excess nitric acid in the solution, we see the green crystal turn brown at its edges, and then the brown disappears, if the solution contains gold and is free of excess nitric acid the green crystal will dissolve leaving a brown powder.
> 
> Iron II sulfate, ferrous sulfate, copperas, FeSO4, and green vitriol, are all names for the same green iron-based sulfate salt, which can be easily made from soft iron and 10% dilute sulfuric acid.


Thanks Butcher


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## Jimbriese (Jun 9, 2022)

Correct me if I’m wrong but won’t an excess of HCL cause a finer precipitation and take longer to settle vs a more concentrated solution?


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## butcher (Jun 10, 2022)

I cannot see where the amount of HCl acid would have much effect on the size of the cluster of atoms of gold or how big the clusters can grow, or where these clusters can grow heavy enough to overcome the gravity of the solution.

Excess HCl does no harm and having free or excess HCl in solution (above what is needed to make the metal salts in the solution), some excess acid is needed for many of the different chemical precipitants like SMB to be able to do their job in the chemical reactions.

I can see where the temperature of the solution, the concentration of ions, excess base metals in solution, or base metal contamination of a pure gold solution, pH, seed crystal effect, and maybe a dozen other variables would have more effect on the size of the gold atom clusters can or will grow before they overcome gravity to settle in the solution.


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## Yggdrasil (Jun 10, 2022)

Jimbriese said:


> Correct me if I’m wrong but won’t an excess of HCL cause a finer precipitation and take longer to settle vs a more concentrated solution?


I believe I have seen that the more dilute the solution is, the smaller the particle will be.
If you want large particles settling fast, a clean concentrated solution is best.
Excess HCl are often needed.


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## Saddiq NG (Jun 10, 2022)

Jimbriese said:


> Correct me if I’m wrong but won’t an excess of HCL cause a finer precipitation and take longer to settle vs a more concentrated solution?


Yes indeed I've also observed that it takes longer for the gold to settle in more concentrated solution and shorter in a dilute solution.


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## Yggdrasil (Jun 10, 2022)

Strange. That is quite the opposite of what i have observed.


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## Jimbriese (Jun 10, 2022)

When I say excess HCL say the amount of gold would need say 500ml but you used 3L HCL might be exaggerated but for the point of discussion. Before finding this site when I did my first couple attempts I used way too much HCL I noticed that the perception was very fine and took days to settle. But then again with what butcher said those were very dirty drops as they were first attempts from watching u tube before find this site and I was for the most part doing it blind as most of those videos don’t tell you even half of what you need to know before the first attempts


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## Shark (Jun 10, 2022)

When using AR many new people tend to over do their acid volumes. Often the same people will attempt to use AP or CuCl2 and then use way to little trying to conserve the acids.


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## Saddiq NG (Jun 15, 2022)

Martijn said:


> Welcome to the forum. short answer: No.
> A deficiency of HCl can prevent a selective reagent from working.
> Any free nitric will not stop SMB from working, but will re-dissolve the pm's.
> 
> ...


Is Ferrous Sulphate among the reagents that deficiency in HCl can affect


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## Jimbriese (Jun 18, 2022)

Hello so I had something happen that fits in here I had a small amount of gold foil I was dissolving in AR I used just enough HCL to cover the foils and the filter they were in about 50-75 ml and about 6 ml of 58% nitric.
Everything dissolved great little faster than I expected so figured I had excess nitric. Denoxed with one plastic spoon of sulfamic acid. Added handful of ice to cool. Filtered crystal clear.
At this point with the ice and rinse water I have about a total of 400ml so I added a couple ice cubes and then SMB.
My solution went from deep yellow to completely clear and not much reaction and SMB crystals in bottom of beaker not dissolved. Tested with sncl2 showed positive for gold. Added small amount more of SMB and still no reaction. So I added 100-125ml HCL then more SMB solution instantly went dark with typical SMB reaction. Gold settled out in about an hour about 1 gram gold powder in bottom of beaker to be added to the rest of my powdered gold
So this is a perfect example of over diluting with rinse water will cause the gold not to drop.


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## Saddiq NG (Jun 18, 2022)

Jimbriese said:


> Hello so I had something happen that fits in here I had a small amount of gold foil I was dissolving in AR I used just enough HCL to cover the foils and the filter they were in about 5-0-75 ml and about 6 ml of 58% nitric.
> Everything dissolved great little faster than I expected so figured I had excess nitric. Denoxed with one plastic spoon of sulfamic acid. Added handful of ice to cool. Filtered crystal clear.
> At this point with the ice and rinse water I have about a total of 400ml so I added a couple ice cubes and then SMB.
> My solution went from deep yellow to completely clear and not much reaction and SMB crystals in bottom of beaker not dissolved. Tested with sncl2 showed positive for gold. Added small amount more of SMB and still no reaction. So I added 100-125ml HCL then more SMB solution instantly went dark with typical SMB reaction. Gold settled out in about an hour about 1 gram gold powder in bottom of beaker to be added to the rest of my powdered gold
> So this is a perfect example of over diluting with rinse water will cause the gold not to drop.


Thank you for sharing this experience I believe this is the reason why gold won't drop well.


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## dpgold (Jun 18, 2022)

Jimbriese said:


> Hello so I had something happen that fits in here I had a small amount of gold foil I was dissolving in AR I used just enough HCL to cover the foils and the filter they were in about 5-0-75 ml and about 6 ml of 58% nitric.
> Everything dissolved great little faster than I expected so figured I had excess nitric. Denoxed with one plastic spoon of sulfamic acid. Added handful of ice to cool. Filtered crystal clear.
> At this point with the ice and rinse water I have about a total of 400ml so I added a couple ice cubes and then SMB.
> My solution went from deep yellow to completely clear and not much reaction and SMB crystals in bottom of beaker not dissolved. Tested with sncl2 showed positive for gold. Added small amount more of SMB and still no reaction. So I added 100-125ml HCL then more SMB solution instantly went dark with typical SMB reaction. Gold settled out in about an hour about 1 gram gold powder in bottom of beaker to be added to the rest of my powdered gold
> So this is a perfect example of over diluting with rinse water will cause the gold not to drop.


How did you fix that ?


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## Jimbriese (Jun 18, 2022)

I added HCL and then more SMB got the normal fizzing reaction with the SMB and solution went dark with the percipient


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## Yggdrasil (Jun 18, 2022)

Jimbriese said:


> I added HCL and then more SMB got the normal fizzing reaction with the SMB and solution went dark with the percipient


Sulfamic reaction need to be done over 70C to have good effect.


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## Jimbriese (Jun 19, 2022)

It was had small reaction with first spoon then added small amount more and no reaction then added ice to cool and filter


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