after the 3rd evaporation of aqua regia

[solarsmith]

after the 3rd evaporation of aqua regia should you add distiled water or hcl. and is it to three times the original volume?

I ask because I am reading some instructions are not clear on this. headed for hoke now. thanks Bryan

 

[solarsmith]

per Hoke -----

"Let the evaporation continue until the liquid becomes syrupy;
then slowly add a little full-strength hydrochloric acid. Brown
fumes will bubble off; this is the unused nitric acid being expelled.
Usually this evaporation must be repeated at least once, maybe twice
evaporating to a syrup and adding a little hydrochloric acid in
order to get rid of all the unused nitric acid.
Do not carry the evaporation far enough to form a hard crust.
One reason for the sulphuric acid is that it hastens the expulsion of
the nitric acid, and when it is present there is less tendency for a
hard crust to be formed. The sulphuric acid also serves another purpose
to get rid of lead which is described fully in a later chapter.
When you are sure that the excess nitric acid has been driven off,
let the dish cool, wash down its sides with a little water (use the
wash bottle) and get the solution into a jar or pitcher, preferably
a tall one.
Now dilute the solution with three or four times its bulk of water,
preferably hot, and let it stand (for some days if possible) for the
silver chloride to settle. The solution must be perfectly clear and
separated from the sediment before you go to the next process.
Usually it settles well in a couple of days, and you can pour off the
bulk of the solution, filtering only the last part.
The sediment of silver chloride should be collected and washed,
and put in the Silver Jar (or in the sweeps if very dirty). If there
was any lead in your original material, the silver chloride will be
contaminated with lead salts."

so the corect answer is both? just a bit of hcl and a lot of water? are there any modern improvements to this or changes any one want to talk about? Bryan in Denver Colorado.
"

 

[FrugalRefiner]

I think you've got it. Note that "three" is not a magic number. When you evaporate and add HCl, if you see brown fumes it's NO_x being driven off. Repeat the process till you no longer see brown fumes. It may take two, or three, or more repetitions, depending on the amount of excess nitric, base metals in solution, how far you evaporate, etc. Then dilute with water.

Dave

 

[Shark]

My understanding is that the evaporating and addition of the HCl is to aid in the removal of the nitric acid. If you look at that section explaing this as one step....

Let the evaporation continue until the liquid becomes syrupy;
then slowly add a little full-strength hydrochloric acid. Brown
fumes will bubble off; this is the unused nitric acid being expelled.
Usually this evaporation must be repeated at least once, maybe twice
evaporating to a syrup and adding a little hydrochloric acid in
order to get rid of all the unused nitric acid.
Do not carry the evaporation far enough to form a hard crust.
One reason for the sulphuric acid is that it hastens the expulsion of
the nitric acid, and when it is present there is less tendency for a
hard crust to be formed. The sulphuric acid also serves another purpose
to get rid of lead which is described fully in a later chapter.
When you are sure that the excess nitric acid has been driven off,
let the dish cool, wash down its sides with a little water (use the
wash bottle) and get the solution into a jar or pitcher, preferably
a tall one.

This would be where step two starts.....

Now dilute the solution with three or four times its bulk of water,
preferably hot, and let it stand (for some days if possible) for the
silver chloride to settle. The solution must be perfectly clear and
separated from the sediment before you go to the next process.
Usually it settles well in a couple of days, and you can pour off the
bulk of the solution, filtering only the last part.
The sediment of silver chloride should be collected and washed,
and put in the Silver Jar (or in the sweeps if very dirty). If there
was any lead in your original material, the silver chloride will be
contaminated with lead salts.

Here is where you dilute it by three times the water.
This would make your take on the read the same as my understanding of it. Hoke explains things very simply, sometimes all most to simple.

(I see Dave posted before for me, but here is my take on it)

 

[flyfisherman]

I think you've got it. Note that "three" is not a magic number. When you evaporate and add HCl, if you see brown fumes it's NO_x being driven off. Repeat the process till you no longer see brown fumes. It may take two, or three, or more repetitions, depending on the amount of excess nitric, base metals in solution, how far you evaporate, etc. Then dilute with water.

Dave

I been watching some videos of European refiners who instead of doing multiple evaporation would add some high proof alcohol to get rid of excess nitric. I dont know of how this process whould work, but it seems it is pretty effective.

 

[Geo]

I am no chemist but adding alcohol and nitric acid together sounds risky. Have you ever dripped nitric acid on cellophane?

 

[butcher]

Nitric acid is an excellent oxidizer, it can make explosive mixtures gases or compounds with metals and organics like alcohol.

Mixtures of ethanol and nitric acid are potentially explosive. This commonly occurs by gas evolution, although ethyl nitrate can also be formed.

A solution of ethanol and nitric acid will become explosive if the concentration of nitric acid reaches over 10% (by weight). Solutions above 5% should not be stored in closed containers. Nitric acid will continue to act as an oxidant in dilute and cold conditions.

http://www.ab.ust.hk/hseo/tips/ls/ls005.htm
Nitric can be a dangerous oxidizer for organic materials or metals which can make dangerous or explosive mixtures.