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Offline Bushka

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Questions about electrolyzing AgCl in ammonia
« on: October 18, 2010, 02:27:31 AM »
Hi - great forum here!  I have a couple of bottles of silver chloride that have been sitting in the basement for literally 30 years!   I decided to try and extract the silver through electrolysis.  I’m dissolving the silver chloride in ammonia and then electrolyzing it.  I had a couple of questions if anybody would be good enough to comment.

Question 1: When I dissolve the silver chloride in ammonia I have silver and ammonium cations and chloride and hydroxide anions in solution.  When I electrolyze this solution, I precipitate silver at the cathode and evolve chlorine gas at the anode.  I assume that I will also evolve hydrogen at the cathode and oxygen at the anode as time passes and there is less and less silver chloride in solution.  Assuming this is correct, what am I left with in solution when I’ve gotten most of the silver plated out?  I’m thinking some of the ammonia would have evaporated as NH3, but that the remaining NH4 and OH balance would be maintained in solution.  Given this, I should be able to reuse this “spent” solution to dissolve some more silver chloride.  Does it make sense that I can reuse this solution, or am I depleting the strength of the ammonia somehow during the electrolysis?  Are there other reactions of significance that I need to be aware of?

Question 2: The silver chloride salt has a very pale greenish tint.  When I put an excess of it into an ammonia solvent and let it sit for awhile, the solution turns very blue.  I’m thinking there may be some copper compounds in the salt.  Would that explain the color?  I don’t see anything that looks like copper during electrolysis, but it could be there in small amounts.

Thanks!

Offline vmelkon

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #1 on: January 21, 2011, 12:27:08 PM »
If there was copper, it would form Tetraamminecopper(II) chloride
http://en.wikipedia.org/wiki/Tetramminecopper%28II%29_sulfate

which would have a deep blue copper.

For silver, it would form diamminesilver(I) chloride, which should be colorless.

http://en.wikipedia.org/wiki/Tollens%27_reagent

also, it mentions risk of formation of silver nitride (explosive) as it ages. WARNING WARNING WARNING.

Wouldn't it be better to heat the AgCl to some high temp, perhaps 1000 C and you get molten silver?

Offline Enthalpy

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #2 on: January 22, 2011, 10:10:14 AM »
What are the electrodes made of?

Evolving chlorine is so corrosive it will bring nearly any electrode metal into solution.

Offline eprigge

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #3 on: February 10, 2011, 10:38:42 PM »
Electrolysis would be a very slow way to recover the silver.  You can reduce silver from the diammine complex with an aldehyde like formaldehyde and I suppose glucose would work too (though you might need some heat to help the reaction along, depending on pH and such).  This is just the old Tollen's reagent reaction.  There are definitely better ways to reduce the silver than electrolysis.

Offline Bushka

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #4 on: November 25, 2012, 11:37:52 AM »
Hi everybody.  I guess about a year has passed and I haven't done anything with my silver chloride.  Part of the reason is that I didn't want to blow myself up after reading comments here, and part is because I just haven't had time/priority to try and extract the silver from the silver chloride powder.  I would like to take a shot at getting this done now, though.

To recap, I have dissolved what I believe to be AgCl with ammonia bought at the local supermarket.  In the past I have heated this solution to improve the solubility of the AgCl, and yield of silver.  I electrolyze the solution with a 2/10 amp battery charger and collect what looks like silver at the cathode.

I've included some photos of what I get:

1. dark blue solution (looks lighter in photo) after mixing AgCl with ammonia.  This appears to be a copper compound based on replies I've received here.

2. I am using stainless steel for the cathode and anode, and while there is some corrosion, it seems minimal.  The second photo is from the cathode.  Black/grey film grows quickly and nearly fills the entire beaker if I let it.  The film collected in this photo took about 15 seconds.  I just wanted to show what the cathode deposit looked like.

3. When the precipitate is dry it forms a grey powder.  If I take the side of a screwdriver and compress the powder as best I can, I do get a shiny silvery surface.

At this point I am assuming the blue color indicates that I am plating out some copper with the silver, but it may be in small enough quantities as not to see visually.  Also, I'm not sure how great the risk of silver nitride is.  I looks to me like I need to have silver nitrate and silver oxide involved in the reactions in order to get to the explosive silver nitride.  I don't believe I have nitrides in any appreciable quantity.  Also, I've electrolyzed enough in the past to have a small cup full of "silver" and nothing has blown up yet.  While not 100% comforting, at least I'm probably not forming anything explosive.

Any comments are greatly appreciated.  I'd like to avoid buying more and more reagents because I don't even know if the final product will be worth anything.  I mainly wanted to see if I was on-track in getting a blue solution (which it seems I'm not), and to be sure I wasn't going to blow up by doing this.

In answer to one other comment, it isn't practical for me to melt the AgCl at 1000C.  I don't even have enough heat to melt the silver powder to see if I really have silver pure enough for sale.  I'll have to buy a small acetylene torch or figure out some cheap way to melt this stuff, but that's a subject for down the road.

I would appreciate any comments!!

Dan

Offline Tittywahah

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #5 on: November 25, 2012, 05:29:17 PM »
Hi there, I have not done anything with silver chloride or ammonia, but have made batches, as needed, of silver nitrate from sterling silver (92.5% Ag and 7.5% Cu), I use the fact that copper sits higher on the reactivity scale and displaces the silver immediately before it in order to eliminate the copper.  However one tip about melting, since I also do that.  Either, buy a cheap jewelers torch that heats beyond 1100c, available from rio grand in USA, or, buy a weed burner, they usually come around 1200c, the weed burner I have was only 20 Euros.  Take a piece of wood, burn the surface thoroughly, until there is just a charcoaled area (keeps the heat very high as opposed to trying to melt silver on wood itself), place your clump of silver mud on the piece of wood and burn away - the wood will not catch fire if you aim at the charcoaled area, I have done this so many times.  Hope something here is of use.

Offline Bushka

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #6 on: November 25, 2012, 06:24:44 PM »
Thanks Tittywahwah.  I've been googling around and there seems to be a lot more stuff on the internet about silver than there was even a year ago.  There are several videos (maybe yours) on charcoaling wood and using it for a mold.  Anyway, I saw one video where they just put a copper pipe in silver nitrate solution due to the electronegativity difference.  I tried that about an hour ago and I was surprised to see the silver precipitating out pretty nicely!  I don't know how the yield would compare to electrolysis.  My fear with electrolysis was that I might be precipitating out other things like copper in with the silver.  It would appear that wouldn't happen as long as there was enough silver still in solution.  I suppose if I electrolyzed beyond the point where silver was still in solution, I could start plating out copper on the cathode at that point.  If the simple copper pipe trick gives a near complete yield, then copper contamination is not an issue.

Also, since I don't really know what I'm starting with as far as purity (silver chloride), I could redissolve any silver I get with nitric acid and use one of the methods to improve purity.  However, do you have any idea of the yield in this kind of thing?  For example, if I dissolve 1 oz of pure silver in nitric acid, what percentage of that silver could I expect to have back after precipitating and melting it?

Thanks a lot for your post!

Offline Tittywahah

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #7 on: November 25, 2012, 07:42:26 PM »
<<<<<<<<<<If the simple copper pipe trick gives a near complete yield, then copper contamination is not an issue.  Also, since I don't really know what I'm starting with as far as purity (silver chloride), I could redissolve any silver I get with nitric acid and use one of the methods to improve purity.  However, do you have any idea of the yield in this kind of thing?  For example, if I dissolve 1 oz of pure silver in nitric acid, what percentage of that silver could I expect to have back after precipitating and melting it?>>>>>>>>>>

Firstly dissolving silver in nitric acid will yield silver nitrate.  You need to heat it.  Once dissolved allow to cool, the silver nitrate crystals will appear within seconds, but you will need to allow to evaporate for some days depending upon how much solution you made.  I advise you to follow the strict stoichemetry here.  If you want to turn the Ag(NO3) crystals into silver just heat this to a very high temperature to get the elemental silver.  As for the copper issue, the copper will displace every bit of silver out of solution.  Once you filter the solution and you have silver mud in the filter - take a few drops of the filtrate into a test tube and add a single drop of HCL; if it turns cloudy then there is still silver in your copper/silver nitrate solution, if it remains clear then all the silver is out.  There is no contamination of copper mixed with silver, as far as my limited chemical knowledge is concerned this is impossible with a displacement reaction, unless it happens on a microscale which is not important for me since I never need super high purity reagents or products.  As far as loss is concerned I would expect always some loss, my loss seems always to be just a few grams each time, but this could be also my maths, or even the amount of copper alloy in the original scrap silver that I use has been miscalculated.  I can not help you with electrolysis here I am sorry to say.  Hope something here helps you.

Offline Tittywahah

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #8 on: November 26, 2012, 08:38:15 AM »
Bushka, actually forgot something obvious, too focused on one thing.  Since you have AgCl, you might try this:  Add  NaCl and take into natural light, or UV source if you have it.  Watch the silver being separated from the Cl and the solution turn black slowly.  This black is actually silver's natural colour when it is so small, particle size.  But this black is actually silver metal.  Just giving you more info, sorry if you already know this.

Offline Bushka

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #9 on: November 27, 2012, 10:27:29 PM »
Hi TWW: Can you take it back a step when you mention to add NaCl to AgCl?  What solution are you referring to?  I'm not sure how I'm precipitating silver by adding NaCl to a solution of AgCl.

Also, I'm finding that the solubility of AgCl isn't great in ammonia, even when boiled for awhile.  I'm going to need gallons of ammonia to dissolve everything, and how much Ag I will lose in solution is unknown to me.  Of course, if the copper pipe really will convert 100% of the Ag in solution back to solid silver, then having lots of ammonia isn't such a problem I guess.

I thought I read someone who said you can just melt AgCl crystals at high temp, and the Cl will burn off, leaving pure silver.  Do you know anything about this?  I assume I will need something like a MAPP torch from Home Depot.  Any other options (ie, the cheapest way) to melt silver, or melt AgCl into silver?

Offline Tittywahah

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #10 on: November 28, 2012, 06:45:20 AM »
Ok, firstly I am not a student of chemistry, all my knowledge is self taught.  Here is the best I can offer, I have never done this experiment, but parts only, as for ammonia i have never tried that either.  I simply use silver nitrate for different things and make it as needed from scrap silver alloy.  So here is my best:  Adding NaCl to water with AgCl mixed in increases the Cl- ion in solution.  NaCl is highly soluble as you know but AgCl is not, however the Cl- ions will dissociate in the water so that you have Ag+, Na+ and Cl- ions all having a party and not dancing together.  The solubility of the AgCl will naturally go right down because of all this, add the UV light to the equation and you will see the silver particles turn dark brown to black, these will be your precipitates, not the Cl ions and not the Na ions, these will remain dissolved.  Now all this is theoretical and not based on any observation I have made.  I do know that when you add silver nitrate to tap water it turns milky white.  This is because there are chloride ions in the tap water and the silver nitrate is losing its silver ions and becoming silver chloride precipitate, which as you know is insoluble.  All that I have said is my best knowledge on this, it would need a student chemist or teacher to take it any further.  But Light will force the silver to separate from it's chloride bond in solution - though on this I have never experimented, I have seen a couple photographs of this some time ago.

HAve you seen:  http://www.youtube.com/watch?v=zJd0EnLwt44

http://en.wikipedia.org/wiki/Silver_chloride

Offline Bushka

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #11 on: November 30, 2012, 08:51:19 PM »
TWW: Thanks for the reply.  I'm kind of the opposite of you.  Although I've been out of it for about 15 years, my background is in chemical engineering.  So I understand some/many of the interactions if I brush off my brain, but I have no practical experience in refining silver.  I don't want to reinvent the wheel, nor create something that can be dangerous.

I understand how adding Cl- ions can shift the equilibrium of AgCl solution back to solid Ag.  However, the problem is that AgCl has low solubility in water, and from what I can tell, limited solubility in ammonia.  The other issue I'm running into is that everybody says something different and contradictory to each other.  I've seen the links you provided (thanks).  I've seen other links that say not to heat AgCl, not to put copper pipe into your silver solution, and so on.  I decided to take a step back and see how much silver I'm likely to recover, and if any of this is worth the effort.  (Part of my effort is for the fun of it, part is the financial gain).  So I weighed all the silver and silver chloride I have with an electronic scale and I have around 770 grams.  AgCl is 75% Ag by weight, so 770 works out to 578 grams.  I can't expect 100% yield, but some of that 770 grams is already pure and/or dirty silver.  So if I go with the 578 gram yield, this equates to about 20 ounces of silver.  Not bad and more than I thought.  The spot price for silver is about $34/oz..  How close to spot can I expect to get for homemade silver ingots?

So with the above in mind, I'm thinking which way to go.  I have to spend $50 for a MAPP torch from Home Depot (you know any cheaper way to get hot enough?), need borax and then possibly some chemicals other than ammonia if melting the AgCl is found to be the best bet.  If I can get anywhere near the spot price for silver, it makes sense to spend a some money on getting the right chemicals to get the silver.  The AgCl I have appears to have some copper contamination because it turns light blue when I add ammonia.  I'm thinking that even if I just melted the AgCl with a torch, I would need to dissolve away the copper first.  So maybe I should first wash my dirty AgCl with ammonia to dissolve the copper, and flush it until there is no more blue color (I suppose I'm not really dissolving the Cu, but more dissolving some of the AgCl, which then sets up the solid Cu to be oxidized by the silver in solution).  Then I can recover the silver from the spent solvent by dropping in a copper pipe and precipitating the silver.  That would give me silver from the dirty copper solution, plus clean AgCl precipitate that maybe could be melted directly.

Does anybody know of any solvent that will dissolve AgCl better than ammonia does?

Offline eprigge

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #12 on: November 30, 2012, 11:55:59 PM »
Have you looked into reducing AgCl to Ag using NaOH and dextrose?  This is one common way to get the reduction done and it is fast and exothermic.  I've done it and the yield was good despite the clumpy AgCl I started with.  I think the yield would be improved the more fine AgCl particles are. 

After you have that silver 'cement' it's just a matter of melting it in a crucible.  Some sodium carbonate with borax/boric acid flux will help to reduce any left over silver chloride in the cement during the melt.

Offline Bushka

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #13 on: December 01, 2012, 12:41:09 AM »
Have you looked into reducing AgCl to Ag using NaOH and dextrose?  This is one common way to get the reduction done and it is fast and exothermic.  I've done it and the yield was good despite the clumpy AgCl I started with.  I think the yield would be improved the more fine AgCl particles are. 

After you have that silver 'cement' it's just a matter of melting it in a crucible.  Some sodium carbonate with borax/boric acid flux will help to reduce any left over silver chloride in the cement during the melt.

Hi.  Thanks for the reply.  If you check TWW's last post, he provides a link to this method.  It looks like the way to go if I can clean up the copper first.  The problem is that instructions are pretty vague.  How much NaOH to use - stoichiometric or an excess?  how much dextrose? sodium carbonate, borax and so on.  If you or somebody could help me with those questions then I think I'd be all set!

Regards.

Offline Tittywahah

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Re: Questions about electrolyzing AgCl in ammonia
« Reply #14 on: December 01, 2012, 04:57:27 AM »
Hi Bushka:
 Ammonia is not then the good way to go at all....Found this

Dissolve the silver chloride in a solution of ammonia. This is a complexation reaction.

AgCl(s) + 2NH3(aq) --> [Ag(NH3)2]+ + Cl-

Add copper metal or almost any metal above silver in the activity series. This is a redox reaction. The silver is reduced and the copper is oxidized.

2[Ag(NH3)2]+ + Cu(s) --> 2Ag(s) + [Cu(NH3)4]+

============= Follow up ==============

Placing copper metal into solid silver chloride will not result in any appreciable reaction. In order for the replacement reaction to occur, silver ions must come into contact with copper metal, but the silver ions are tied up in an insoluble compound.

The above was something that I found on the net.  HOWEVER, very important, copper works very very well at displacing silver from nitrate solutions where you have just dissolved silver alloy - I do it all the time.  Now then,  have you read this by any chance?

http://www.chemicalforums.com/index.php?topic=32471.0

also this:  http://www.finishing.com/195/29.shtml

Sorry if I can not answer all of your questions, I wish I could. 

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