# Silver chloride once again



## golddie (Dec 19, 2009)

When you add table salt (sodium chloride) to silver nitrate you get = silver chloride

What happens to the nitric acid 
Do you boil it and it evaporates

If there is still some nitric left 
what is it called and can it be reused for dissolving silver all over again


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## goldsilverpro (Dec 19, 2009)

golddie,

You have silver nitrate and, unless you dissolved enough silver to deplete all the nitric, you still have some nitric acid left in the solution. When you add the NaCl or HCl, to precipitate the AgCl, you probably added an excess of chloride ion. So, essentially, you now have aqua regia, which won't dissolve silver. Even if you add some more nitric, the presence of the chlorides would inhibit the dissolving of silver.

One time, we had about 50,000# of stainless steel brazed with silver solder. The total silver content ran about 1% - 2%. We set up a series of stainless tanks containing a total of several hundred gallons of 50/50 nitric acid. Some of the tanks were rinse tanks. We filled stainless mesh baskets with the parts and lowered them into the nitric, with a hoist, until the silver solder was dissolved. 

When the dissolving rate slowed down, I analyzed the silver in the solution and added just enough HCl to precipitate 90% of the silver, as silver chloride. Therefore, 100% of the chloride ion added was utilized for AgCl precipitation - there was no free Cl- left in the solution. The hydrogen ion from the HCl increased the nitric acid concentration and this increased the dissolving rate. After separating the AgCl from the solution, we re-used the solution to dissolve more silver. 

However, since we were also dissolving copper (which remained in the solution) from the silver solder, the nitric percentage and the dissolving rate were less for each succeeding cycle. After several cycles, the rate was so slow that we stopped and precipitated 100% of the final silver. At this point, however, the 50,000# had been completed, since I had pre-calculated everything before we started. 

I know that I answered your question in a round about way. I hope this helped you to understand what's going on in the solution.

To produce nitric acid, you need both hydrogen ion (H+) and nitrate ion (NO3-).

Chris


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## golddie (Dec 19, 2009)

Hi Chris
How are you 
Thanks for taking the time to write a detailed reply.
Take care


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## SilverNitrate (Dec 20, 2009)

you will be left with dissolved sodium nitrate sol'n and will likely have more chloride thus the acid aspect goes from nitric to hydro-chloric. However you could add in sulfuric acid to this liquid (seperate the silve percip) and you'll have a solution that can dissolve a small amount of gold; otherwise distill the vapors and collect nitric acid from the mixture to dissolve more silver for turning into the chloride.


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## goldnugget77 (Dec 22, 2009)

Hi SilverNitrate
Thanks for that tip
So what you are saying is when I add table salt to nitric & water solution.
I get silver chloride
I can take the silver chloride 
As for the liquid I can boil the liquid to get nitric to reuse for desolving silver


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## goldnugget77 (Dec 22, 2009)

The silver chloride poweder we save for refining 
How about the liquid we pour off from the silver chloride solution


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## butcher (Dec 23, 2009)

AgNO3 (aq) + HCl (aq) --> AgCl (s)+ HNO3 (aq) with(water involved)
silver nitrate plus hydrocloric acid (muratic acid), yields silver chloride plus (diluted) nitric acid.

now as GSP stated this would be with (exactly the right amount of chemicals for complete conversion, and no excess of one, or the other) stoichiometric,

AgNO3 (aq) + NaCl --> AgCl (s)+ NaNO3 (aq)
silver nitrate plus sodium chloride (table salt) yields silver chloride plus sodium nitrate

so your byproducts :
with salt you get sodium nitrate in liquid.
with muratic acid you get dilute nitric acid

but if you added excess HCl (most likely as GSP stated) you would have a form of aqua regia (nitric and HCl mix).

and if excess table salt in that equation would just be some table salt with your sodium nitrate solution.

these byproducts could be used for recovery but you will also have to account for their purity and what impurity is involve and how it will affect your use of these, and also there strength as nitric will be dilute, these can be concentrated or purified if necessary.
or treated for waste disposal.


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## Platdigger (Dec 23, 2009)

Actually with excess sodium chloride you would also have a form of dilute AR.


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## butcher (Dec 23, 2009)

wouldn't we need hydrogen to make it acidic enough?

2HNO3 (aq) + Ag2 (s) --> 2AgNO3 (aq) + H (g)
when you dissolve silver in nitric acid, you produce silver nitrate and hydrogen gas. 

so in my calculation unless you had exess nitric the hydrogen and acid is used up.

(not like us to use exact stoichiometric amounts true), in that case I agree it could be possible,to have some hydrogen left.
(and then you would possibly have also made some HCl in the equation below?)
i would think then the excess table salt would come into play also with using excess nitric for acidic HCl, thus dilute aquaregia would be possible.

AgNO3 + NaCl --> AgCl + NaNO3 

or do I need some more study on this?


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## goldsilverpro (Dec 23, 2009)

A few more comments about the process I outlined above.

The beauty of working with silver, nitric, and silver chloride, is that everything is stoichiometric. Everything can be calculated and everything is predictable with great accuracy.

A secondary reason for precipitating only 90% of the silver was that, had I added a excess of Cl- ion and precipitated all the silver, the resulting aqua regia solution would have attacked the stainless steel tanks. It wouldn't have taken much Cl- to do this.

This was one of the few times in my life that I intentionally produced silver chloride. It was necessary in order to be able to re-use the nitric solution. I converted the AgCl to Ag using sodium hydroxide and light Karo syrup. Here again, since I knew exactly how much AgCl I had, I could easily calculate exactly how much of those 2 chemicals I needed for conversion (20 grams of NaOH, 13.3 ml of syrup, and 133 ml of water per tr.oz. of silver contained - just to make sure, I probably added a 5-10% excess of these chemicals). 

The conversion was done in open-top 55 gal plastic drums using a fair-sized Lightin' mixer. Once the AgCl was rinsed well in a vacuum filter, until no trace of copper came through in the rinse water, it was not allowed to dry and was immediately converted to silver. The Ag settled immediately and there were no difficult-to-settle fines. When melting and casting the final silver into bars, there was no intermediate layer of AgCl between the slag and the silver, so I know I got 100% conversion. The silver bars were well covered with crystal so I assume they were near pure - at least 999 Fine.

The only times that I have ever produced fines in this conversion method were those cases when I didn't know how much AgCl I was starting with and, therefore, by necessity, added a great excess of NaOH + syrup.


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## Frankk12 (Dec 23, 2009)

Hi Folks



> strength as nitric will be dilute, these can be concentrated or purified



I was thinking about how to do this ,for example Harold and 4metals have said they use ice in Aqua Regia before precipitation with sulfur dioxide
So this will be HCL+HNO3+water+sulfur dioxide
What would I have to do to this mixture to be able to reuse it as AR.
Also can I store this solution a few days without any danger of hazards.
If I cant use it as AR what can I use it as.
Thanks


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## PreciousMexpert (Dec 23, 2009)

How about if you boil off the water that will remove and then you can maybe use it as AR.
As for the sulfur dioxide residue I dont have an answer to that.


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## goldnugget77 (Dec 23, 2009)

> strength as nitric will be dilute, these can be concentrated or purified
> 
> I was thinking about how to do this ,for example Harold and 4metals have said they use ice in Aqua Regia before precipitation with sulfur dioxide
> So this will be HCL+HNO3+water+sulfur dioxide
> ...


when you boil down the aqua to syrup then add sulfuric acid and hcl then there is nothing to reuse.
I guess you can use 4metals dealing with waste thread after that.


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## butcher (Dec 23, 2009)

true its not good to use for aqua regia after sulfite etc. added, 
but these acidic solutions can be used in my opinion, for removing base metals in recovery processes, you will be dissolving base metals to drop any values or copper as part of waste treatment, why not use them on base metals you want to dissolve anyway? even weal acids dont need much acid or oxidizer to get them active again, I reuse all my solutions for one thing or another, and eventually I end up with sulfate powders after waste is evaporated, even this powder can be used, if you wanted for making sulfuric acid from SO2 gas. or chloride salts, sulfate salts most all of which can have a use.
the less liquid I have to treat for waste disposal the less dry waste I produce as it always seems to grow, and if I am not careful it can get to be alot. and the pennies also count when buying chemicals for some of these recovery processes,
Also if a person captures those vapors from evaporation processes they can get back clean acids, differences in boiling points helps to distill certain substances, water boils off before NOx,
NOx boils off before chlorine,
SO2 is harder to boil off,but can be driven out at high heat.

if you wanted to get back most of the aqua regia you can distill it off during evaporation, distilling bubbling into water, yes your distilled aqua regia will be weaker, but wont take much added acid to spice it up, and with heat on your next batch it will concentrate as it attacks metals, with the price of acid,and letting these acids evaporate in enviro, and amount of waste to be dealt with, for me reuse as much as possible only makes sense.


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## PreciousMexpert (Dec 23, 2009)

Hi butcher
You got some creative ideas
Thanks


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## PreciousMexpert (Dec 23, 2009)

Hi GSP
This is very good info that we didnt have before.
Thanks



> When the dissolving rate slowed down, I analyzed the silver in the solution and added just enough HCl to precipitate 90% of the silver, as silver chloride. Therefore, 100% of the chloride ion added was utilized for AgCl precipitation - there was no free Cl- left in the solution. The hydrogen ion from the HCl increased the nitric acid concentration and this increased the dissolving rate. After separating the AgCl from the solution, we re-used the solution to dissolve more silver.


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## Anonymous (Dec 23, 2009)

2HNO3 (aq) + Ag2 (s) --> 2AgNO3 (aq) + H (g)


I do not think that is how it works, the nitric oxides the silver and the oxide reacts with the nitric producing water and silver nitrate and nitrogen oxide which reacts with oxygen from the air to produce nitrogen dioxide.

Jim


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## butcher (Dec 24, 2009)

James, 
Thanks I believe you are right, 
But I believe the equation I wrote in post above is correct.
Are you confused? I am.
Here is why I think this away.
The equation is found written both ways, the one I stated came from C.W. Ammen recovery and refining page 35 and 36 he gives the equation.
2HNO3 + 2Ag à AgNO3 + H2
And he state hydrogen gas is freed.

(Note water involved here may not be written in formula) as we use dilute nitric.
In the equation you quoted,

2HNO3 + Ag à AgNO3 + NO2 + H2O
Silver is lower in the reactivity series than hydrogen, so the nitrate NO3 is reduced to NO2.
Note the NO2 and H2O in the equation above.
2NO2 + H2O à 2HNO3
Since we have water in solution the nitrogen dioxide mixes with water forming HNO3 again in solution, this can then pick up another silver forming more AgNO3.

The resulting solution is I believe a neutral salt of AgNO3 diluted in water, this suggests the hydrogen is not in solution thus the percent hydrogen (PH) neutral.

If this is in fact what is happening then we are both correct, and both formulas are valid.

If not I am still confused, I am just learning so it is possibly the case,

Maybe a chemist can straighten out this?


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## goldsilverpro (Dec 24, 2009)

I'm no chemist but here's the way I understand it.

(1) Dissolving silver with very dilute nitric acid:
3Ag + 4HNO3 = 3AgNO3 + NO + 2H2O (Molar ratio of HNO3/Ag = 1.33/1)

(2) Dissolving silver with very strong nitric acid:
Ag + 2HNO3 = AgNO3 + NO2 + H2O (Molar ratio of HNO3/Ag = 2/1)

(3) According to these equations, a greater ratio of HNO3/Ag is needed when using strong nitric. In most cases, the nitric usage is somewhere in between. I found a reference that suggested the actual equation for this intermediate nitric strength is:
4Ag + 6HNO3 = 4AgNO3 + NO + NO2 + 3H2O (Molar ratio of HNO3/Ag = 1.5/1)

Equation (3) is more accurate but I doubt if the exact equation is that predictable, since I also have read that the temperature has something to do with it. Another thing that will affect the ratio is the possibility of some of the NO2 created, both directly and from the reaction of NO with the oxygen in the air, reacting with water and being converted back to HNO3. If the temperature is high and the container is wide open, however, I would think the NO and NO2 gases would mainly be driven off and would thus be eliminated from the system. In essence, the actual molar ratio of HNO3/Ag needed is somewhere between 1/1 and 2/1.

Copper in nitric works the same way.


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## goldnugget77 (Dec 24, 2009)

lets say I have 22 liter Aqua regia and I would like to boil it and do what butcher said 
Evaporate it into water
How much water is need for this amount of AR


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## goldsilverpro (Dec 24, 2009)

> lets say I have 22 liter Aqua regia and I would like to boil it and do what butcher said
> Evaporate it into water
> How much water is need for this amount of AR



I don't understand the question. Why would you add water if you are evaporating the solution?


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## goldnugget77 (Dec 24, 2009)

Hi Chris
Butcher said that when you boil the AR to evaporate to turn to syrup
You can direct the fumes with a pipe into a container of water to save to save the AR 
That is what I understood


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## butcher (Dec 25, 2009)

Lets look at this distilling of aqua regia, and capture the gas in water, aqua regia 1 part nitric acid plus 4 parts hydrochloric acid, both of these acids have water involved, and if we put these into a reaction (boiling) vessel with our gold, the gold will be attacked and dissolve into solution, if we then use a tubing or glass pipe etc. (which can survive the acids), and pipe these gases to a condenser, to cool this hot gas and bubble them into a small amount of very cold water, heating our boiling vessel, our gold will dissolve into solution. It can look something like this,
Au + 5H + 4CL + NO3 + (H2O) --> HAuCl4 + NO2 + 2H20 + (H20),
The water in the parenthesis above was water in the original acids, as 70% nitric had water, and 32% muratic had water originally.
The water in the equation above not in parenthesis was water created from the reaction of acids attacking metal and hydrogen and oxygen from the acids and metal reacting,
Point being we will have more water than our original acids did, in our receiver of condensed liquids, So starting with a very small amount of water to bubble these gases formed from our boiling vessel be all we need, and a little weak peroxide 3% may be better to start with than pure water, as it is mostly water and the peroxide can help to convert our NOx gas back to HNO3 in receiver.
As we progress we will be distilling water, and NO2 these will make nitric acid back in our receiver, and also the free chlorine that has not combined with our gold will also evaporate off into our receiver,
And as we evaporate to thick syrup, these distill off at different temperatures and azeotropes.
Our reaction vessel when done will contain a more diluted form of aqua regia, but we did not just boil these gasses off into the moist air making acid rains, instead we saved as much of them as possible for reuse, saving us money buying more chemicals.

Now we have to use our newly formed dilute aqua regia,

(I do not suggest we store it as it can create gas, which can build up pressure in a closed bottle, which can possibly be an explosion hazard.)

We can use this weak acid with heat in our next batch it will concentrate as water is boiled off, we also may need to add small portions of new acids as needed.


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## golddie (Dec 25, 2009)

Hi Butcher
It would be nice if we found a soution to the storage problem because sometimes you need to use this mixture the next day


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## butcher (Dec 25, 2009)

well if dilute and kept from light, and in bottle with teflon stopper that if it did gas could be relieved it can be stored but keep it away from children, animals,your good tools, ect. uncork to check every so often,for pressure, 

but do not store in a bottle that can build pressure and explode.

you can always store it with the gold still in it distill when needed,

during the world war Aqua regia loaded with gold was stored on a shelf hiding gold from the nazis right under there nose.


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