Precipitate silver in aqua regia ?

[Noxx]

Hello,
Is there a way to precipitate silver in an Aqua Regia solution ? Either before or after gold.
Thanks

 

[Anonymous]

Hello,
Is there a way to precipitate silver in an Aqua Regia solution ? Either before or after gold.
Thanks

The scientific answer is yes, there is always a method to attempt this. The difficulty comes in justifying costs versus results. What is your goal?

a man named Sue

 

[Harold_V]

Hello,
Is there a way to precipitate silver in an Aqua Regia solution ? Either before or after gold.
Thanks

The scientific answer is yes, there is always a method to attempt this. The difficulty comes in justifying costs versus results. What is your goal?

a man named Sue

Nonsense!!!

One can not have silver in solution in AR. Any silver present as a nitrate will immediately precipitate as chloride when AR is introduced. That's why gold and silver as so easily parted.


Harold

 

[Noxx]

OK ! I understand. Thanks

 

[Anonymous]

Harold V,

It would appear you just agreed with me.

Are you now saying that silver which you identified correctly exists as in AgCl compound as a precipitate, due to the presence of HCl in a muriatic nitric aqua regia, cannot be isolated?

The question before the forum is:

Is there a way to precipitate silver in an Aqua Regia solution

I said it could. You said it could.

So, why, when I say so, you label it as "nonsense" but when you say so, it is not nonsense? Your response is not a logical response but an emotional one it would appear.

My point remains: economics.

a man named Sue

 

[Harold_V]

Harold V,

It would appear you just agreed with me.

Are you now saying that silver which you identified correctly exists as in AgCl compound as a precipitate, due to the presence of HCl in a muriatic nitric aqua regia, cannot be isolated?

The question before the forum is:

Is there a way to precipitate silver in an Aqua Regia solution

I said it could. You said it could.

No, I did not. I said you can't have silver in solution in AR-----that is not possible. You can have silver and gold in solution in cyanide, but that's not the topic of discussion..

Before you can precipitate silver from a solution, it must be in the solution. It is not in solution in AR, and that was the question. That silver chloride can be separated from gold chloride is a no brainer. I did that routinely for more than 20 years, as does anyone that filters their gold chloride before precipitation. Total separation, however, is almost impossible. I'll provide my years of practical experience as the reason, below:

When you allow silver to progress to the stage of dissolving your gold in AR, it will usually be in the form of silver nitrate. When silver chloride is formed, a result of introducing AR to the gold, it is hugely voluminous as compared to elemental silver, and acts like a sponge to absorb gold chloride. The silver chloride will hold a respectable amount of gold chloride after filtration, even after washing well. It is not lost, but recovered in subsequent operations, but if you're trying to account for all the gold in a given lot, you come up short.

Harold

 

[Bluebloomer]

I hope it's ok to bump this topic, but according to your last post I have a follow up question;

If the silver chloride consumes some of the gold, what would be the best way to recover the gold ? Will the gold be pushed out during the conversion process of AgCl to metallic silver, or will that conversion produce a silver contaminated with gold alloy of sorts ?

 

[nickvc]

It's not so much that the chloride consumes gold it's that the chloride powder will hold onto some of the gold solution, not much if you rinse well on a powered filter, but some maybe 1/2% of the total depending on the volume of silver chloride. That's why using a silver cell is recommended, it recovers the gold and any PGMs that may have been present in the slimes. It's also accepted that AR can hold small quantities of silver in solution that's why adding water is recommended as when it dilutes the solution the silver will drop out as chloride and be recovered on the filter.

 

[g_axelsson]

I don't understand exactly what you mean with silver chloride "consumes gold".

The most commonly reason that we get gold chloride with our silver chloride precipitate is when dissolving gold with small amounts of silver in the alloy in AR. The silver is then turned into silver chloride and we can both have small particles of metallic gold encased in silver chloride as well as gold chloride mechanically trapped in the silver chloride.

The gold chloride can be washed out with rigorous washing but the solid gold particles will follow the silver chloride. When we turn the chloride back into metal the gold will already be there and contaminate the silver. A silver cell is a good way to increase the purity of the resulting silver metal.

The art of refining is to know which reactions and processes to use to get as pure product as possible with the least amount of work and chemicals. No process is 100% effective, side reactions and mechanical processes more or less works against the higher purity. The good refiner learns how to use that and minimize the side reactions.

Have you read Hoke yet? Done the acquaintance experiments yet? Page 36 to 38 is relevant to this question.
http://goldrefiningwiki.com/mediawiki/index.php/Hoke_acquaintance_experiments

The most common mistake by a newbie (I've done it myself several times) is to use too much or too little of chemicals or time. This will increase the side reactions and suddenly we got problems we never expected. Lack of experience easily confuses and makes a bad situation even worse.
Here reading and learning what could and should happen is a great way to prepare before doing a process for the first time and the forum is an unique place for that.

Göran

 

[Justincase]

As even silver chloride(AgCl) is soluble in H2O I find I get a little AgCl carried over in my AR.
Even on second run Au after reduction I get a small amount of white precipitate once I re-hydrate the reduction.
For some reason a concentrated Gold Chloride solution keep's this small amount of impurity's in solution until I add a bit more water.
Which seems counter intuitive as the rest of the low solubility impurity's drop out with out the re-hydration.
So Technically you can precipitate silver out of AR but as AgCl and only in very small amount's .
Or is that to fine a line to be considered a precipitation,it is more of a release of trace impurity's rather than a true compound precipitation.

 

[Palladium]

As even silver chloride(AgCl) is soluble in H2O I find I get a little AgCl carried over in my AR.
Even on second run Au after reduction I get a small amount of white precipitate once I re-hydrate the reduction.
For some reason a concentrated Gold Chloride solution keep's this small amount of impurity's in solution until I add a bit more water.
Which seems counter intuitive as the rest of the low solubility impurity's drop out with out the re-hydration.
So Technically you can precipitate silver out of AR but as AgCl and only in very small amount's .
Or is that to fine a line to be considered a precipitation,it is more of a release of trace impurity's rather than a true compound precipitation.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=22433&hilit=silver+chloride#p235367

 

[solar_plasma]

I like your explanation in your link, Palladium!

Here I posted some aditional infos about AgCl and solubility, even though this is not important for the practice, it might be interesting to know for some.

http://goldrefiningforum.com/phpBB3...=21519&p=222326&hilit=solubility+agcl#p222326

 

[Geo]

Björn, I have found that acid concentration also is a factor in how much silver can remain in solution and as you said, temperature is a huge factor. If there is a large amount of silver in the starting material,there will sure to be some silver follow the gold all the way to the final wash and melt.

 

[Anonymous]

Geo I too used to have this problem until I followed some advice that Lou gave me. I use one set of AR as a recovery process, don't dilute it, follow his wash process and then I'm left with powder that will have some small amount of silver there. Then I use AR again to refine the gold.

This true refine process is much lower volumes of liquid so diluting it three times to get the AgCl to precipitate out doesn't involve large amounts of waste. I've learned over the last three years to not treat the first dissolution in AR as a refine- merely a recovery process.

Excellent filtering using good papers and a Buchner funnel is the way forwards for getting rid of this pesky powder.

 

[g_axelsson]

In concentrated AR or just hydrochloric acid some silver chloride is soluble. This is because of the high concentration of chloride ions in solution.

So the solubility drops when you add water as the chloride ion concentration drops, just as copper II chloride does.

On http://www.saltlakemetals.com/Solubility_Of_Silver_Chloride.htm you can see various liquids and how much silver chloride can be dissolved in them.

Göran

 

[Justincase]

In concentrated AR or just hydrochloric acid some silver chloride is soluble. This is because of the high concentration of chloride ions in solution.

So the solubility drops when you add water as the chloride ion concentration drops, just as copper II chloride does.

On http://www.saltlakemetals.com/Solubility_Of_Silver_Chloride.htm you can see various liquids and how much silver chloride can be dissolved in them.

Göran

Thank you very much for the explanation.
Very interesting,I have been curious about the mechanism.
Much obliged.

 

[Anonymous]

If you filter gold powder in a Buchner funnel using gravity with concentrated HCl it will take AgCl through with it. (Not my process, I am quoting Lou, and it works)

 

[goldenchild]

If you filter gold powder in a Buchner funnel using gravity with concentrated HCl it will take AgCl through with it. (Not my process, I am quoting Lou, and it works)

The key here is that it must be very concentrated. The type of concentration that can hold the small amounts of silver in solution in aqueous form (as discussed above). Even then I think you would be hard pressed to get all the aqueous silver to filter down unless dealing with very small amounts of gold sponge. Getting the silver to filter through when adding HCL to inquarted gold sponge would be impossible as adding HCL would instantly ppt silver chloride on contact.

 

[nickvc]

You can chase your tail over this but you can remove any silver in the precipitated powder fairly easily, personally I can't be bothered as I get the same payout for 99% as 97% Au, adding water in the recommended volumes will remove 95-99% of the silver, want better use the wash techniques described here on the forum, still not happy refine it again Nile still in powder form using a different method.

 

[goldenchild]

You can chase your tail over this but you can remove any silver in the precipitated powder fairly easily, personally I can't be bothered as I get the same payout for 99% as 97% Au, adding water in the recommended volumes will remove 95-99% of the silver, want better use the wash techniques described here on the forum, still not happy refine it again Nile still in powder form using a different method.

Most anywhere you won't get the same payout for 99% vs 97% purity. In your case it sounds like you should actually be aiming for 97% and nothing more.