Silver chloride and ammonia

[Blacktoadd]

Ammonium Hydroxide may be used alone to Disolve silver chloride if used in sufficient quantities to turn the solution basic.

Ammonium Chloride needs the Prior addition of Sodium Hydroxide to turn the solution basic and oxidize the silver.
The ammonium Chloride will disolve the silver oxide.

Am I correct that the ammonium chloride is not adaquate at raising the PH.

 

[Lou]

Second statement is correct. Ammonium chloride is weakly acidic, it being the salt of a strong acid (HCl) and a weak base (NH3). By adding base to ammonium chloride one will generate ammonia which will dissolve in the extra water giving an ammonia solution. Ammonia water is cheap though as it is used all the time in cleaning. If one wishes to concentrate it, it will be in one's best interest to add a strong base solution to ammonium chloride and then bubble the ammonia gas through your weaker ammonia water solution. It can become a very concentrated solution then.

I should emphasize that ammonia is a very dangerous base--it easily gases a person; this gas gets into the eyes and does:
NH3(g) + H2O(l) --> NH4+ OH- which will damage the eyes.

While a basic (NaOH) ammonium chloride solution can work, it will not work as well because there will be a greater concentration of chloride anion.

 

[arthur kierski]

i have a solution of nitric acid on which i added nacl,so in the botton of the becker i have silver chloride +lead chloride--.can i filtrate the solution and add to the chlorides nh4oh,filtrate again to eliminate the lead and them add karo to precipitate the silver?
if so is the silver pure to melt and sell?
i am asking because i use silver chloride +steel wool and is a very tyring method and i always end with silver mixed with silver chloride

 

[peter i]

Lead chloride is sparingly soluble in hot water, so washing with that should remove limited quantities.

EDIT: As Lou originally posted; if there is a lot of lead in the precipitate, precipitating everything as chloride, washing the chloride with water, then selectively dissolving the silver chloride with ammonia, discard the undissolved lead chloride (in an environmentally responsible way), re-acidify the ammoniacal solution with more hydrochloric acid is the way to go.
.... the silver chloride should become quite clean from that procedure, by the way!

How much lead do you have in your alloy?


Iron is rather bad for the reduction, anything more noble than iron will also be reduced to the metallic state, and iron is a bad contaminant in silver alloys for jewellery.


A better approach would be to precipitate as chloride, wash thoroughly with several batches of boiling water (until no PbCl2 precipitates from the wash-water on cooling, or a test with potassium iodide is negative), then reduce with zinc or aluminium.

Or even better:
"Cement" with copper, thus leaving anything less noble than copper in the solution (including the copper), wash, dry and melt the silver powder.

The second approach will give a far better product than reducing with iron, and should you then run the silver in a silver cell, the result will be very fine silver. (99.99 or 99.999)

 

[arthur kierski]

thanks peter, i will do what you advised and then give you a return

 

[peter i]

in about 2kilos of silver chloride i suppose 100 to 200grams of lead chloride

OK, The solubility of lead chloride in boiling water is 33 grams per litre, if we take it conservatively, and assume that not more than 20 grams is dissolved under practical circumstances, that will mean at least washing with ten litres of boiling water.

Its is doable, but draining it as dry as possible, then dissolving in concentrated ammonia and precipitating again with hydrochloric acid after discarding the insoluble PbCl2, would be my preferred method in this case.

One kilo of AgCl is approximately = to 7 mole, as it forms silverdiamine, we need two moles of ammonia per mole silver, 14 mole total.

Regular concentrated ammonia is 25% = 13 mole/litre or better, meaning that you theoretically should be able to dissolve 1 kg of AgCl in a litre of concentrated ammonia. You will need it in excess, but start by adding a litre, let is dissolve as much as possible, then pour off the solution and treat the remains with some more ammonia in small batches.
When pouring of the small batches, make them acidic and stop leaching silver when no appreciable amount of silver chloride forms.

hope this helped

regards
Peter

 

[arthur kierski]

thanks peter , you helped me a lot because my specialization is pgm--specially rhodium---but sometimes i come across some silver and gold and is good to know something about it.

 

[skulls_box]

Hi Peter, thanks for all the information.
I have just a question:
i which way can i make the solution acidic?
because the reaction is very strong with the HNO3

 

[FrugalRefiner]

Peter hasn't visited the forum in a couple of years, but as he and others mentioned, use HCl to acidify the solution and precipitate the silver as AgCl.

Dave

 

[skulls_box]

Thanks Dave you are so kind.
But i'm not sure that 1 litre of ammonium hydroxide at 25% is able to dissolve 1kg of AgCl.

Francesco

 

[Barren Realms 007]

If you use concentrated ammonia you dissolve your silver chloride you can use copper to cement it back out of solution then acidify the ammonia therfore saving the step of converting to the silver chloride to elemental silver.

 

[sar]

If you use concentrated ammonia you dissolve your silver chloride you can use copper to cement it back out of solution then acidify the ammonia therfore saving the step of converting to the silver chloride to elemental silver.

Barren:
Is it possible to cement silver from ammonia solution with zinc powder?
If yes, can we use dilute sulphuric acid to dissolve excess zinc after cementing silver ? Isn't it dangerous to dissolve sulphuric acid in ammonia solution?
I don't have any experience in dissolving silver chloride with ammonium hydroxide
Any advice would be appreciated.

 

[Shark]

This is a great study in using ammonia and silver chloride. It deserves to be revived.

 

[4metals]

This is true, but it cannot be stated enough that leaving an ammoniacal solution of Silver too long is dangerous. Even more so if it tends to dry out, it can become explosive. I’ve seen it. Not just a little burp but a violent boom. So if you want to deal with the dense white stinky fumes, make sure you drop the Silver out as Silver Chloride with Hydrochloric Acid to acidify the solution and recover the Silver as Silver Chloride.

 

[Shark]

Sounds like another good reason for having a fume hood, even if you have to build it yourself.