Method for producing pure silver metal

Hello,
I'm currently developping a simple process to make pure silver nitrate (or metal if you prefer) from Sterling silver. This should yield a product a least 99,9% pure. I'm not the inventor of the process in any ways, it's just ideas I gathered from ScienceMadness.org. Special thanks to Fleaker who helped me indirectly lol. If you think there are any flaws in my process, please let me know ! Any comments is also welcomed.

Cementation of silver with copper is a well know technique to produce silver metal of an acceptable purity, but you will always get some impurities from the Copper.

Method for producing 500 grams of photo grade AgNO3

-Start with incinerating you scrap silver to remove any dirt and oil residues. Do not melt the silver. More informations are available on this forum on how to do it properly.

-Let it cool then add your sterling (343,25 grams in this case) in a large beaker. 2000mL should suffice.

Following steps must be performed in a low light environnement.

-Add at least 1100mL of 30% nitric acid. When the reaction has stopped, add small amounts of HNO3 to dissolve the remaining pieces. Try not to add too much acid.

-Vacuum filter your solution to remove any insoluble particles. Use a fast to medium speed filter paper.

-Add NaCl (lab grade, food grade or equivalent) until no more precipitate forms. You now made Silver Chloride (AgCl) and Lead Chloride if there was any present.

-Decant your solution, you only want to keep the precipitate. Rinse the powder once in tap water.

-Then add enough HCl to cover it. Digest the powder in boiling HCl for one hour. This will dissolve any remaining metals. Use a magnetic stirrer if you have one. Keep your beaker covered with a watch glass. Decant the solution and rinse the powder two times with tap water. Not sure if this step is useful or not.

-Rinse you powder two times with boiling distilled water.

-Now dissolve your powder in Ammonium Hydroxide (lab grade, try not to use too much). Ammonia water will form a complex with silver but will not dissolve any lead chloride that may have still been present.

-Vacuum filter your solution using a medium to slow filter paper. Discart any precipitate.

-Add HCl to neutralize the ammonia and destroy the complex. This will form new AgCl. The amount of HCl used is not critical. Better too much than not enough. Add HCl until pH becomes acidic (under 7).

-Decant the solution and rinse your powder two times with tap water and two times with distilled water. This will remove the NH4Cl that formed during the neutralization.

-You can convert your Silver Chloride to Silver Oxide by the addition of an alkali solution like NaOH or KOH. Both are soluble in water in all proportions.

-Rinse your powder again with water a few times and heat to 300°C (590°F) to decompose your Oxide back to silver metal.

-At this time, your silver powder should be very pure, with only traces of other metals. You can either melt it to cast ingots or dissolve it back in Nitric acid (lab grade or higher) to make silver nitrate.


That's it !

Any comments ?

Looks like you made AgCl instead of AgNO3. I assume you're not finished. I would use hot water rinses and rinse until a small sample of the rinse water shows no blue color, against a white paper background, after being made alkaline with ammonia. Test tubes are nice for this. You can also test a small amount of the AgCl, after the HCl leach, by dissolving it in ammonia in a test tube and looking for blue (copper). Also, the hot water will get rid of lead chloride. The HCl wouldn't hurt and might help, but you'll have to rinse it all out. I would probably use HCl, instead of salt, to drop the AgCl.

The 1100 mLs of 30% nitric sounds right on. The best way to avoid using too much nitric is to only use enough to dissolve about 95%+, of the silver. Get the acid just below boiling to make sure it's used up. After dissolving, there should be a little bit of undissolved silver left.

AgCl is hard to work with. It traps stuff. Don't ever let it dry. Try to prevent clumps. Light is a problem. Maybe you could use a red photo lab light.

99.5 isn't very pure and, with care, you shouldn't have much trouble making it.

Lou is the master formulator. He probably has some better ideas.

GSP, I still haven't finished the process yet !
You was not supposed to see what I am writing since I checked the box: Make this post a draft, but since you're a moderator, you can see it lol. That's why all my writings are in red. What you see is about half of the process.

I will continue the writing later, I now have to got back in class.

Noxx,

We can all see it, and now that I know it was to be hidden, it makes more sense.

Oh, I taught it was hidden lol.

Sorry Chris, my bad

About the purity concern, I must admit that the number I gave was a wild number. I have no idea exactly what purity the silver will have. What I know is that I can remove all Lead Chloride and copper metal that may be present in standard copper cementation.

We'll discuss that later, when I'll finish the process.

Ok I'm done. So now you can have a good idea of the process.

Anyone knows the silver purity it should yield ?

Thanks

"-You can convert your Silver Chloride to Silver Oxide by the addition of an alkali like NaOH or KOH."

How are you adding the hydroxide? With water?
So the purity of water is not critical?
Randy

Sorry, forgot to mention that your dissolve the NaOH in water.
Purity of water is not critical but you should use distilled water if you think some strange things may be in yours.

As a rule, I use distilled water. Harold has mentioned obtaining 99,95+ percent pure gold using tap water. Being somewhat on the anal side, I just use distilled water. It is easy to setup a water distiller (Barne's type) that will give 5-6 megaohm water.


My comments on the silver:

1.) use no more HCl than you must, otherwise it will bind up some silver in solution as a complex. While boiling in HCl will remove many impurities, it will also form that AgCl2- which you can wash away. Guess what though, this only happens to an appreciable extent when there is very concentrated amounts of chloride in solution. So decanting off the HCl, rinsing (3 times, 400mL dH2O per 200g) the AgCl and then pouring the rinse water into the HCl that was used for the boil. You should see some silver chloride drop out of it.

2.) Similar to what I said about the chloride complex...this can also happen with the use of too much base giving you Ag(OH)2- which is colorless and is easily tossed out! Use only as much base as is required to stop the precipitation of silver oxide.
Sodium carbonate can be substituted in lieu of sodium hydroxide or potassium hydroxide. Both will give the same results.



A test for purity: take a sample of pure silver powder and dissolve it in quality nitric acid. Note if there is ANY color whatsoever to the solution--it should be colorless. Evaporate this (still watch color) to dryness and heat in a porcelain dish to 440*C. Cool this and dissolve in hot distilled water and look for any sediment on the bottom. Sediment on the bottom indicates metal oxides that formed during the fusion of the silver nitrate at 440C...just about every impurity will form an oxide at that temperature. No oxides and no color mean that your silver is over 99,995% pure.

This procedure can be repeated and high quality reagents used to yield silver that is factors of ten more pure. Eventually, however, there comes a point where Ksp and solution equilibria put a cap on what ultimate level of purity you can get. Just think, 107g of silver, roughly a mole, contains 6.02214 X 10^23 atoms. Even if your silver were 99,9999999% pure you would still have a large number of other atoms!! There is interesting chemistry behind the purification of metals, both from the analytic and from the physical standpoint!

Thanks Louis for the answers.

But do you think I should use the HCl boiling process or the ammonia water dissolution ? (or both ?). I don't know if the difference in purity would be negligible. HCl is cheaper for me than ammonium hydroxide.

If I had to pick one, certainly ammonia water. If you suspect lead, ammonia will get rid of it. You can also rinse out the lead with copious quantities of hot water, but depending on how much lead chloride is present that may not be an option. What you want to do and what you can do is something you must decide upon.

Yesterday I was washing my AgCl with 30% HCl (I forgot about what Lou said) and my solution turned yellow (almost canari). I did not understand what was happening at first but I remembered what Lou said... I diluted the solution and it turned white again...

So obviously, AgCl IS soluble in HCl.

hi every one,a question about silver chloride.. I think that I read in one of the posts that if you had a piece of material that had formed silver chloride on it's surface, that a dip in Ammonium Hydroxide would disolve the AgCl,?? then rince and return to further disolve in main solution, If this would work at may take a little more time and an extra container, But may be able too process some jewelry this way, poor man's AR may have been used in the thread ,I remember this from..

Thanks MARK


P.S still trying too not have too inquart jewelry- melting the small gem stones i cant remove..

Mark, unless you roll out that jewelery to very thin pieces, forget about it! It would be too much trouble to keep putting them in and out of solution.

Inquarting isn't a big deal--do it right and it's a huge time saver and you'll get a superior product in the end.

Even if you make thin pieces, you'll still get a scruff of silver chloride forming on the karat gold. You'll need agitation and heat to get rid of it. Also, some of the AgCl dissolves in the aqua regia and gets carried along when you go to purify your gold.

Inquarting is the easy way out.


Lou

Lou said:

Inquarting is the easy way out.

Click to expand...

It never ceases to amaze me how some folks will go 1,000 miles out of their way to avoid a ten mile trip.

Inquartation is key to easy success, and is a very useful tool in gathering traces of platinum and palladium for later recovery. I'm mystified why the process isn't broadly accepted.

Harold

Trying too make a short cut will usually get u're self lost in the forest !!! allright ,.. I do have HOKE'S book and she say's simply to inquart , and I should listen too the wise !!! Thank You All
MARK

Harold_V said:

Inquartation is key to easy success, and is a very useful tool in gathering traces of platinum and palladium for later recovery. I'm mystified why the process isn't broadly accepted.

Click to expand...

Perhaps one reason for the crazy work arounds is the problem in purchasing nitric for many.

A person new to chemistry is also unlikely to have the skill and knowledge to make their own nitric. They are also the most likely to have crazy ideas about how to refine from the online world trying to sell a process.

Excellent points. I think you may be right.

I've commented a few times how there's way too much BS being promoted where refining is concerned. If readers had the ability to sort out what is factual and what is promotional, they'd be well served.

Frankly, that's one of the reasons why I promote Hoke's book. It may not be all inclusive, but it provides reasonable guidelines to the processing of precious metals. Once digested, it makes the task of sorting good and useful information from the garbage that is often promoted, usually at a price, much easier. I can't think of a better bargain than a copy of her book-----for a person interested in learning the art of refining. It builds a very solid foundation from which a person can launch in any direction desired.

Harold

edit: completed the intended message

Well as you and perhaps a few others on here may know, I am a reader. I have not yet seen a text that makes a better foundation for an individual wishing to learn refining. It gives all the fundamentals and one can specialize from there if they so desire. On this forum it is for free, as well as experienced individuals that can answer questions one has in reading it. What modern book comes with that?

One can go from silver nitrate to silver metal and preserve the purity of the silver (no introduction of copper or other transition metals) using sodium carbonate. Sodium carbonate will react with the silver nitrate to give silver carbonate, a very weakly soluble salt. This is then filtered and heated to 350C/660F yielding silver metal.

The following happens:

AgNO3 + Na2CO3 --> Ag2CO3 + NaNO3
[NaNO3 is removed in filtration step.]
2Ag2CO3 --> 2Ag2O + 2CO2 --->4Ag + O2.
[220C for first decomposition, 310C for second decomposition.]

This is useful because carbonate is cheap and less hazardous than using lye.