Aqua Regia vs HCl and Bleach

[Wizzlebiz]

Hello Wizzle back with another question.

When looking at the differences between AR and HCl/Bleach, when is the appropriate time for HCl and Bleach?

I feel it would be safer with HCL/Bleach. If I can live a life without Nitric that would be dandy.

It seems to me it is easier to work with the HCl and Bleach method due to not having to denox.

However I have been scolded before here for trying before asking so here I am laying myself at the mercy of the forum.

Whats the benefit to either? Whats the draw back for either?

Thanks,
The Wizzy one

 

[butcher]

Wizzlebiz,

Bleach is a basic solution of chlorine gas in water, NaOH sodium hydroxide (a base) is used to keep the chlorine in the solution.
When mixing bleach sodium hypochlorite NaClO with hydrochloric acid HCl we have a couple of reactions, A portion of the acidic HCl and the basic NaOH neutralize each other in the solution to form a neutral solution of NaCl salt water, and the solution forms chlorine gas in solution which is the oxidizer for the gold.

Hydrochloric acid and sodium hypochlorite work well on gold which is finely divided as in powders, foils small flakes, flattened gold nuggets... It does not work as well where gold is very thick or larger pieces of metal.

It is much easier to remove the oxidizer from the solution the chlorine will only form chloride salts (it will not form nitrate salts which can be acidified back into nitric acid again with the addition of acid) the chlorine gas is removed easily with a little heating, overuse is easily removed with heat.

sodium hypochlorite drawbacks:
Lowers solutions acid content of the solution, can form copious amounts of NaCl, slow to react cold, but will not stay in a heated solution very well to be able to use heat to assist the reaction, the gold needs to be finely divided like powders or flakes.

 

[Wizzlebiz]

Wizzlebiz,

Bleach is a basic solution of chlorine gas in water, NaOH sodium hydroxide (a base) is used to keep the chlorine in the solution.
When mixing bleach sodium hypochlorite NaClO with hydrochloric acid HCl we have a couple of reactions, A portion of the acidic HCl and the basic NaOH neutralize each other in the solution to form a neutral solution of NaCl salt water, and the solution forms chlorine gas in solution which is the oxidizer for the gold.

Hydrochloric acid and sodium hypochlorite work well on gold which is finely divided as in powders, foils small flakes, flattened gold nuggets... It does not work as well where gold is very thick or larger pieces of metal.

It is much easier to remove the oxidizer from the solution the chlorine will only form chloride salts (it will not form nitrate salts which can be acidified back into nitric acid again with the addition of acid) the chlorine gas is removed easily with a little heating, overuse is easily removed with heat.

sodium hypochlorite drawbacks:
Lowers solutions acid content of the solution, can form copious amounts of NaCl, slow to react cold, but will not stay in a heated solution very well to be able to use heat to assist the reaction, the gold needs to be finely divided like powders or flakes.

Makes a world of sense.

Just to confirm I am understanding. As long as I am working with thin scrap: foils, powder, basically tiny fragments HCL/Bleach is good.

If I were trying to re dissolve a button I should be using AR.

Correct?

 

[butcher]

After recovery of the gold, you can refine it with HCl acid and sodium hypochlorite, after precipitating it and washing the powders you can refine them again, there should not be a reason to dissolve your melted pure gold buttons.

30% H2O2 is also a good oxidizer, which also forms chlorine in solution with the HCl acid, its benefit is it does not reduce the acidity of the solution, and thus does not form the sodium chloride salt content, thus it can be reduced in volume without the problems you will encounter with the caustic bleach solution...

 

[g_axelsson]

Yes, bleach and HCl works for powders and foils but not so well for massive gold.

And just as Butcher told you, 30% hydrogen peroxide is a good substitute for bleach. Actually I think it's better than bleach, just not as easy to get for everyone.

Göran

 

[anachronism]

30% H2O2 is also a good oxidizer, which also forms chlorine in solution with the HCl acid, its benefit is it does not reduce the acidity of the solution, and thus does not form the sodium chloride salt content, thus it can be reduced in volume without the problems you will encounter with the caustic bleach solution...

Thanks I never knew that. 8) 8)

Jon

 

[butcher]

Pool and spa chemical supply houses have several oxidizers or reagents that are useful in recovery or refining.

 

[Lino1406]

To dissolve gold in bulk HIGH chloride + HIGH chlorine environment is needed. E.g.: concentrated H2O2 + HCl.
The reaction: 2Au + 3Cl2 + 2Cl- = 2AuCl4-

 

[Shark]

30% H2O2 is also a good oxidizer, which also forms chlorine in solution with the HCl acid, its benefit is it does not reduce the acidity of the solution, and thus does not form the sodium chloride salt content, thus it can be reduced in volume without the problems you will encounter with the caustic bleach solution...

Thanks I never knew that. 8) 8)

Jon

I never looked into it's use as well. Now that I know where to source it locally I may have to give it a shot.

 

[butcher]

Be careful with 30% or higher H2O2 it likes to burn skin.

 

[Shark]

Be careful with 30% or higher H2O2 it likes to burn skin.

Very well aware of that. It isn't very gentle on clothing as well. Also it will be no telling how long before I get to try it, just to many things going on right now.

 

[anachronism]

Be careful with 30% or higher H2O2 it likes to burn skin.

Yeah I know Richard- I buy it at 35% and dilute it for other uses - it's really unpleasant stuff isnt it. 8) 8)

Jon

 

[bengie84]

How does one tell if the solution is clear of chlorine gas and ready to have a smb drop

 

[rickbb]

When it stops dissolving gold. You can gently heat it to drive off and residual chlorine or set it out in the sun for an hour or 2.

 

[bengie84]

Well I ban marined it for a hour or so on a gentle simmer now leaving it to cool down and settle over night.
I did do a stannous test before leaving turned immediately almost black so looking forward to smb drop tomorrow

Ps once I did the stannous test it stunk like rotten eggs is that normal

 

[bengie84]

So morning has arrived I have a nice tan coloured percipitate but I did another stannous test but I’m confused weather or not it’s false reading or not see pics now ones is slightly orange

 

[anachronism]

If you have purple/black then it's gold.

The false positive colour isn't black. Frankly calling it a false positive is something we need to change as it's confusing.

Your "false positive" is more often than not the browny colour and comes from base metals.

 

[rickbb]

Ps once I did the stannous test it stunk like rotten eggs is that normal

How are you doing the test?

Put a drop of the gold bearing solution on a white paper towel, then put a drop of stannous next to it. The area where the two drops bleed together will turn purple/blackish if gold is present.

Should not be enough of solution to make much of a smell, if any.