Sciencemadness Discussion Board - precipitating silver chloride from nitric acid?

precipitating silver chloride from nitric acid?

skippy - 14-5-2006 at 15:17

Hi!

I have a pretty simple question. Ive been playing around with purifying junk silver and I was wondering if you could tell me whether my idea is bad or not. I was thinking that after dissolving silver in nitric acid that maybe the nitric acid could be recyled by adding hydrochloric acid, which would (in my perhaps wishful thinking) recycle the nitric acid by precipitating AgCl. Here are my queries. Will the silver chloride precipitate? I'm thinking that HCl is a stronger acid and it would be thermodynamically preferrable to have the weaker nitric acid dissocated and for the AgCl to precipitate. Is this thinking right?

enhzflep - 14-5-2006 at 16:57

Well,
to precipitate silver chloride from nitric or sulphuric acids we used to pour a solution of table salt in water into the acid until the cloudiness ceased to be produced. At this point, the precipitate was silver chloride.

1)So, I believe that adding the HCl will cause your silver to precipitate as chloride.
2)Since the (I forget the terminology here, sorry) AgNO3 -> Ag & NO3 ions in solution,
by adding Cl ions, you form the insoluble AgCl, hence precipitation
3)Don't know how you'd go recycling the nitric, as liquid HCl is ~66% water, your solution will get weaker and weaker every precipitation. If you compensate with strong nitric at the start and your nitric concentration is too high you can oxidise the silver -> silver oxide IIRC.

Try a couple a small batches of silver with a modest amount of acid and see.
I would try with maybe 50ml-100ml Nitric 70%, and 2 or 3 batches of 1gm silver.

But remember,
(1)slow addition of HCl
(2)stop immediately when the precipitate ceases to form
(3)the percentage of other crap in the silver will also be a limiting factor to how many times (if in fact it does work), that you may recycle the acid..

neutrino - 14-5-2006 at 18:10

>liquid HCl is ~66% water

Concentrated HCl solution is 37% water

>If you compensate with strong nitric at the start and your nitric concentration is too high you can oxidise the silver -> silver oxide IIRC.

Silver oxide would just redissolve in the nitric acid. For that matter, I don't see how any would form in the first place.

The other problem with this idea is that only a part of the nitrate would remain after dissolving silver. When a metal like silver dissolves in nitric acid, a fraction of the nitrogen is lost as nitric oxide. For Ag + HNO3 the reaction is

2HNO3 + Ag → AgNO3 + NO2 + H2O

The NO2 gas is lost so only half the nitrate ions remain after each dissolving.

garage chemist - 15-5-2006 at 04:50

Yes, AgCl will precipitate completely when HCl is added to a solution of Ag in HNO3 (I use HCl for AgCl precipitation instead of NaCl, since an excess of HCl doesn't decrease AgCl yield opposed to using NaCl), though it's advisable that the solution be diluted before addition of HCl, because it will filter easier that way.

Neutrino is right in stating that you already lost half of your HNO3 as red fumes during dissolution of the silver. I don't think it is worthwhile to recycle the HNO3.

A better idea for reducing HNO3 consumption would be to use only as much HNO3 as actually needed.
For a gram of silver, you'll need a few ml of 70% HNO3 at most (I use 53% acid, which already works well for dissolving silver and is significantly cheaper than the 70% acid even when taking into account the larger amount needed).

Add the HNO3 slowly to the silver, while heating.
At some point, the water from the HNO3 will accumulate in the mix and nearly stop further reaction, even under reflux. This is the point where it is advisable to distill away some water from the mix until reaction starts going again. That way you can dissolve more silver with your HNO3 than without using this technique.

enhzflep - 15-5-2006 at 05:47

63% HCl eh?
Commercial HCl is 33%. Up to %40 if you're really lucky.
Sure, it's infinitely soluble in water - with the evolution of heat.
Buut, who sells it at a 63% solution???

Seriously though, can you really buy it at that concentration
as a solution in your country?
I was under the impression that it was somewhat like ammonia.
Sure you can hire cylinders with the anhydrous gas in them,
ammonia will go what, about 770g per 1g water.
I just thought that it was never easily available a concentration
greater than 330gm / kg - i.e 33%. Similarly I'm under the impression
that HCl is avail upto 40%, or anyhdrous as gas in a cylinder???
Google doesn't want to tell me anything I'm not stating here - nor
do any of the texts I have. My mistake?

RE: Ag + 2HNO3 -> AgNO3 + NO2 + H2O
Oh, okay then. I'd not realised that the reaction necessarally
entails the realease of NO2, as does copper. So thanks for that
neutrino.

unionised - 15-5-2006 at 10:58

"Sure, it's infinitely soluble in water"
Er, no, at one atmosphere pressure and room temperature it disolves to the extent of about 37%. That's excatly why conc HCl is about 37%
Of course, this doesn't matter too much. You can boil off quite a lot of the water once you have recovered the Ag as AgCl. Beware of using too much HCl- you will get Cl2 etc.
Of course, you will lose half the HNO3 as NO2 each time, but it's still worth thinking about.

quicksilver - 26-6-2007 at 06:53

-=silver oxide=-

I wanted to piggy-back this on another post through my search as it's a simple question: but what I am curious about is weather there is a method to increase yield? Silver oxide (along with quite a few other metal salts) are so damn expensive that I am going to set aside a few days sometime and put together some oxides, nitrates, etc of the metals that will continue to rise in value as reagents.
I was simply going to use the HNO3 - Ag route with adjusted PH to the same ends as HgO2 or whatever.... Has anyone worked with a practical method for a good yield? I found one for HgO2 that I followed and the author was correct; the yield did seem quite good. What is a convenient OTC method for a higher yield Silver Oxide?

not_important - 26-6-2007 at 08:54

Silver oxide is more soluble in alkali than in pure water, so you want to avoid any excess base. As I remember the Ka of Ag2O as being about the same as HPO4(-2), which is on the alkaline side, and is not the same as HgO.

Ag2O has a low solubility, only a mg or two per liter, so if you use boiled distilled or deionized water the trick is in getting the oxide in an easy to filter form. All the preparations I've seen just used weights for the AgNO3 and base, can't remember if there were any tricks done to control the precipitate form. Filter on glass is best, I suspect.

quicksilver - 27-6-2007 at 05:14

Crap, I had a gut feeling that AgO was going to be a problem...... The local supplier puts a higher price on the oxide than the nitrate! That's never a good sign.... Even the giant suppliers have silver oxide as being well past a dollar a gram!

I really do appreciate any hints you all could give me. - When doing a search through the board, I've noticed how often expensive reagents come up for discussion. I don't think that I will be giving my chems away anymore; this is now getting to be an investment

[Edited on 27-6-2007 by quicksilver]

Fleaker - 28-6-2007 at 20:21

@ quicksilver, couldn't you just melt silver and stir in NaNO3 til it all converted. I've never done it with silver, but with gold containing silver, NaNO3 brings the silver to the top of the gold as Ag2O.

Alternatively, assuming you dissolve the silver in nitric, you could then precipitate it with NaOH and heat the resulting AgOH til it gives up the H.
I would say pyrolyze silver nitrate, but that doesn't work, it withstands red heat. Industrially, AgNO3 is melted and cast.

not_important - 28-6-2007 at 20:50

Quote:

Originally posted by Fleaker
@ quicksilver, couldn't you just melt silver and stir in NaNO3 til it all converted. I've never done it with silver, but with gold containing silver, NaNO3 brings the silver to the top of the gold as Ag2O.

Alternatively, assuming you dissolve the silver in nitric, you could then precipitate it with NaOH and heat the resulting AgOH til it gives up the H.
I would say pyrolyze silver nitrate, but that doesn't work, it withstands red heat. Industrially, AgNO3 is melted and cast.

Ag2O starts to lose oxygen at about 160 C, quite quickly at 250 C. If you get a silver compound at the temperature of molten gold, it's in part because the the Na2O formed from the nitrate, it may be a complex salt.

Adding hydroxide to a soluble silver salt makes Ag2O, the hydroxide doesn't exist under normal conditions. The problem with making Ag2O is that it is soluble in dilute HNO3 and somewhat soluble in NaOH, so the reactants must be carefully measured. It also will absorb CO2 from the air. And it can't be completely dried by heat, as it loses oxygen. Best bet seems to be used recently boiled water to make up the solutions, to wash the precipitate with 50% alcohol, then 95%, then acetone; keeping CO2 away from it all the while. And use fritted glass to filter it, not filter paper.

However moist Ag2O seems to be the common use of it. In this case just wash with 50% ethanol and use it right away. It's a bit light sensitive, by the way.

Melting silver nitrate is a traditional small scale way of removing copper from it. Heat until it melts - say 220 C, hold at the temperature for a few minutes. Let it cool, dissolve in distilled water, filter off any copper oxide, add a few drops of nitric acid and evaporate to dryness while keeping dust away. Repeat if there was a lot of copper in the original solution.

[Edited on 29-6-2007 by not_important]

quicksilver - 29-6-2007 at 05:20

I think I'll give it a shot this weekend. I had thought about Fleaker's concept first actually as that was what I used with HgO and it came out great. However I thought there was a complication with Ag (& the old brain ain't remembering that well) So I thought I would ask first......These are very workable ideas.
@not_important : do you think silver nitrate will give better results than silver-nitric acid?

Pyridinium - 29-6-2007 at 05:33

Quote:

Originally posted by quicksilver
Crap, I had a gut feeling that AgO was going to be a problem...... The local supplier puts a higher price on the oxide than the nitrate! That's never a good sign.... Even the giant suppliers have silver oxide as being well past a dollar a gram!
[Edited on 27-6-2007 by quicksilver]

I think that's because the oxide has a higher weight-percentage of the precious metal than does the nitrate, although there could be other variables such as energy cost to produce a given compound. The suppliers usually base their prices on what they have to pay for a given compound from the source (manufacturer).

I think I remember this price difference being the case also with cobalt (II) carbonate vs. cobalt (II) oxide.

[Edited on 29-6-2007 by Pyridinium]

not_important - 29-6-2007 at 06:53

Quote:

Originally posted by quicksilver...
@not_important : do you think silver nitrate will give better results than silver-nitric acid?

I'm not sure what you mean. Do you mean to just dissolve silver in HNO3, then directly precipitate that? You can, but you're going to have excess HNO3 and thus can't just use weight ratios, you'll have titrate after figuring out the the target pH. If your silver is very pure this is OK, otherwise you want to at least crystallise the AgNO3.

But then this could just be me. I've almost alway started from scrap silver, including alloyed stuff, so I've needed to go through a purification process. And silver nitrate is the common starting point, so I'd convert everything to a batch of that before making other salts, and toss the evaporated mother liquors from crystallisation into the silver recycle bottle. And I always made Ag2O just before I needed it, because I've always needed the moist oxide.

Fleaker - 29-6-2007 at 13:21

Quote:

Originally posted by not_important

Ag2O starts to lose oxygen at about 160 C, quite quickly at 250 C. If you get a silver compound at the temperature of molten gold, it's in part because the the Na2O formed from the nitrate, it may be a complex salt.

Adding hydroxide to a soluble silver salt makes Ag2O, the hydroxide doesn't exist under normal conditions. The problem with making Ag2O is that it is soluble in dilute HNO3 and somewhat soluble in NaOH, so the reactants must be carefully measured. It also will absorb CO2 from the air. And it can't be completely dried by heat, as it loses oxygen. Best bet seems to be used recently boiled water to make up the solutions, to wash the precipitate with 50% alcohol, then 95%, then acetone; keeping CO2 away from it all the while. And use fritted glass to filter it, not filter paper.

However moist Ag2O seems to be the common use of it. In this case just wash with 50% ethanol and use it right away. It's a bit light sensitive, by the way.

Melting silver nitrate is a traditional small scale way of removing copper from it. Heat until it melts - say 220 C, hold at the temperature for a few minutes. Let it cool, dissolve in distilled water, filter off any copper oxide, add a few drops of nitric acid and evaporate to dryness while keeping dust away. Repeat if there was a lot of copper in the original solution.

[Edited on 29-6-2007 by not_important]

@not_important
I learn something everyday! I've refined silver on several occasions but never studied the chemistry before so I was just speculating on making Ag2O. Thanks for the evident "I've done this before" knowledge. Next time that I get in the lab, I want to do an experiment with it.
**OT Question for not_important or anyone in the know: do you know anything of rhodium chemistry regarding plating solution? I've dissolved powder before for AA and other testing, but I'm curious about a plating solution for Rh? I have a few possible ''recipes'' in mind, but I'm keen to hear if you have any experience with this metal? I was thinking either Rh (IV) sulfate in sulfuric, or sulfamate perhaps.**

Fleaker

[Edited on 29-6-2007 by Fleaker]

silver precipitate

Captain Zen - 24-1-2011 at 13:19

Hi, I can buy from my Pharmacy 68% Nitric acid but it cost $86, and comes in a brown glass bottle, in hard foam in a wooden box. Much too strong and expensive for m e. I make my own weak nitric acid from 5 gallon box of car shop battery acid $40 and 2 lbs of Sodium Nitrate for $8 from the Garden supply shop in measures I need and warm it on a hot plate in a glass coffee jar. I mill silver fine and flat to have greatest surface and it boils for a while softly. Condense drips back from the lid.
Question 1. "What boils first, the sulphuric acid or the water in it?
. Next, the silver is dissolved, and I pour table salt saturated water until the yogurt clouds form no more.
Then I pour it in triple coffee filters and wash it, until ammoniac water does not turn blue no more.
Then the filters with the white stuff in go in a crucible in a oven to heat to 800 C so the filters are gone quietly away
Then I take the crucible and torch it with a butan/oxigene flame. In the crucible forms black liquid that slowly under moving the crucible around turns into liquid silver. That cooled looks like pure silver to me.
Question 2. "How come I end up with 15 grams where I started of with 30 grams. My starting silver was stamped .925.
I appriciate your comments.
I must have lost somewhere about 10 grams...
I am new to this.
I also purify gold, later about that if you want
.

cyanureeves - 24-1-2011 at 16:11

dry the white yogurt next time and weigh it. my guess is some of the white yogurt goes up in the smoke. the white yogurt turns black instantly like a rapid spreading fungus when you put it in hydrochloric acid/water and then drop a penny without the copper skin(zinc).then melt the black grey silver mud and most of the zinc will go up in smoke and not the silver. you'll get pretty much all your 92.5% silver. it will be clean enough to silverplate with.

Captain Zen - 24-1-2011 at 16:56

I will have to filter, wash and dry the gray silver mud no doubt before I put the torch on it no?
and what boils first, the water or the acid in the car battery sulfuric acid?

cyanureeves - 24-1-2011 at 17:55

no filtering just decanting, wash if you want but chlorine will just burn also. people here have been boiling or evaporating battery acid to rid it of water to concentrate the sulfuric acid. if you evaporate your acid you will have 1/3 of 5 gallons of very concentrated sulfuric acid. so i would say the water boils first.wiki says sulfuric acid boils at 639 deg.f. hard to believe! and water boils at 212, but both together i dont know.i've recovered over 3 oz. of silver using zinc and hydrochloric acid. i've also done it using copper metal by dropping it into the diluted nitrated sterling solution(before converting it to the yogurt). but i dont like this method because the silver sponge although purer is alot lighter and i tend to blow some of it away with my torch flame when i melt it.

Captain Zen - 25-1-2011 at 05:26

Soon I will try this new part , I will sandpaper a penny to get the copper coating off. I have understood that
Once I have the white yogurt I put it in muriatic acid and add a little zinc.
You do not have an oven to burn away filters and get the muddy stuff to solidify a little before you put the torch? Then put it in tissue paper and drench in alcohol before torching to prevent particles to fly out of the crucible.
Cheers, nice to be here.

cyanureeves - 25-1-2011 at 11:58

captain zen you still have to dry the silver mud or it will pop when heated probably unless the torch dries it on contact, i dont know. what i like about the hcl method is that i can dilute the hcl acid and not use very much. scraping the copper of pannies is exactly what i use. i like the tissue paper in alcohol thing. glad you like it here. i love seeing these guys go back and forth with all kinds of methods.check out what theyre doing to obtain potassium metal.

Captain Zen - 25-1-2011 at 12:30

I appreciate your comments very much. I am an amateur goldsmith and make molds from wax in heat resistant plaster. The wax burns away in an oven and the hot liquid metal goes in the mold, sucked in by vacuum or thrown in by a centrifuge. Because of the filings and dust going all over the place when finishing and polishing I learned to clean it. That's why I am here. Thanks for replies, I 'll be back when I am doing a new batch. Always small amounts, gold is so crazy expensive these days! See you later.

not_important - 25-1-2011 at 12:45

If you go the chloride route consider the wet reduction using a solution of NaOH and glucose to get elemental silver. This avoids issues with piking up copper from those pennies, even after sanding.

Also, one again, making crude silver nitrate, evaporating, drying, and melting it, then cooling and dissolving in distilled water is a decent route for removing other base metals. The resulting AgNO3 solution can be treated with NaOH and glucose or even sucrose - table sugar (have to boil for a longer time, but it works). I will not that some do not like this method, but it is cheap and avoid s adding metals back into the silver; any organics burn off when melting the metallic silver.

http://www.sciencemadness.org/talk/viewthread.php?fid=2&...

http://www.sciencemadness.org/talk/viewthread.php?fid=2&...

Captain Zen - 25-1-2011 at 17:38

Wow, I have to look up all the abbreviations and am learning, but most of what I read is above my knowledge. In a next life I have time to go into it maybe.