# Methods of recovering silver from silver nitrate



## autumnwillow (Feb 22, 2018)

I'll just create a list of what I know including their advantages and disadvantages. Hopefully somebody can chime in to help me with what I'm looking for.

1- Cementation by copper
+fastest process, easy to wash as most nitrates are water soluble, easy to melt
-copper will be the contaminant along with anything below the copper series, copper price will be significant when processing large lots

2- Silver chloride - HCl/Salt NaOH glucose
+little to no contaminant if done properly
-lots of steps, will require breaking of the chlorides/oxides to very fine powder for it to be successfully converted to metal, washing is also a problem

3-Silver chloride - HCl/Salt iron sulfuric
+faster compared to the 2nd option
-contaminant is mainly iron, washing is tricky because if you increase the pH to about 5 or more you will precipitate iron hydroxide, iron will also drop other base metals if silver chloride was not washed well.

Is there an easier way? I process about 2kg of silver in a week using paint buckets, I use option three and I do the tumbling manually :lol:


----------



## Palladium (Feb 22, 2018)

Hcl/zinc or Sodium formate reduction.
What is the source material?


----------



## snoman701 (Feb 22, 2018)

Wash you AgCl in dilute HCl. Wait for it to settle and decant, removing 90%+ of the leach. I do this on a table, then siphon the leach out so as to not disturb the AgCl. Then add wash, mix up really good, settle and decant. Then switch to your suphuric/iron tumble, then final rinse with borax/nitrate. Even with this I still include some soda ash in the melt just in case. 

I only precipitate 95% of my silver with hcl so that I can reuse the nitric. 




Sent from my iPhone using Tapatalk


----------



## FrugalRefiner (Feb 22, 2018)

snoman701 said:


> I only precipitate 95% of my silver with hcl so that I can reuse the nitric.


Very frugal. 8) 

Dave


----------



## Palladium (Feb 22, 2018)

I use pool salt. 
40 lbs of pool salt is $6!


----------



## autumnwillow (Feb 23, 2018)

Palladium said:


> Hcl/zinc or Sodium formate reduction.
> What is the source material?


Inquarted gold. 



snoman701 said:


> Wash you AgCl in dilute HCl. Wait for it to settle and decant, removing 90%+ of the leach. I do this on a table, then siphon the leach out so as to not disturb the AgCl. Then add wash, mix up really good, settle and decant. Then switch to your suphuric/iron tumble, then final rinse with borax/nitrate. Even with this I still include some soda ash in the melt just in case.
> 
> I only precipitate 95% of my silver with hcl so that I can reuse the nitric.


For sulfuric and iron do you wash in the filter or do you do it in a bucket? When I wash in a bucket I end up with iron hydroxide precipitate due to pH being high.


----------



## g_axelsson (Feb 23, 2018)

Just add a bit of acid to the rinse water to make it acidic, that will take care of any iron hydroxide precipitate.

Göran


----------



## goldsilverpro (Feb 23, 2018)

snoman701 said:


> I only precipitate 95% of my silver with hcl so that I can reuse the nitric.


Aha. You found my old method. I only used it once, but it involved about 50,000 pounds of silver braze on stainless. The Ag yield was 1% of the total weight, about 7000 oz. The braze also contained copper, and that made the nitric weaker each time I dropped silver. I can't remember how many cycles of dropping Ag with HCl I could do but it was probably 4 or 5. When the nitric was so weak that it slowed the process too much, I dropped out all the silver and made up fresh 50/50 nitric. It was a fun project and it went 100% as projected, with no hiccups. This was a case where I HAD to drop AgCl, since cementing the silver with copper was too costly. I kept the AgCl wet after filtering and rinsing it fast in an 18" Buchner and didn't give it a chance to age. I used 10% extra NaOH and Karo syrup in a cut off plastic drum using a Lightin' mixer with a prop for several hours to convert it

How are you analyzing the dissolved silver before adding the HCl, or are you basing the dissolved silver on knowing the Ag content of what you are processing? In my case, I had to analyze it because the Ag content of what I was running was too variable. Of course, the reason of only adding enough HCl to drop out 95% (I did 90%) of the Ag is so you won't add too much HCl and produce aqua regia. Also, to re-constitute some of the nitric, you must use HCl and not NaCL 

AgNO3 + HCl = AgCl (solid) + HNO3

However, dissolved copper forms Cu(NO3)2 and this continually builds up and uses up HNO3. Therefore, the nitric gets weaker. If you were dissolving pure silver, you could drop 95% of the silver with HCl and re-constitute the nitric 100% each time, theoretically allowing you to do this an infinite number of times.


----------



## g_axelsson (Feb 23, 2018)

goldsilverpro said:


> If you were dissolving pure silver, you could drop 95% of the silver with HCl and re-constitute the nitric 100% each time, theoretically allowing you to do this an infinite number of times.


I'm not so sure about it. Some nitric acid (half of it?) is going up as the well known red fume. Each time you add HCl you also add water so the acid gets more diluted each time. It's not only copper nitrate buildup that might limit the practical number of times you can recreate the nitric acid.
... would it be possible to use sulfuric acid and precipitate silver sulfide to avoid buildup of water?  

Anyhow, it's a very nice process to master, I just wish I could end up with some scrap where it would be usable so I would have a reason to try it out myself.

Göran


----------



## snoman701 (Feb 23, 2018)

goldsilverpro said:


> snoman701 said:
> 
> 
> > I only precipitate 95% of my silver with hcl so that I can reuse the nitric.
> ...




What I posted is a conglomeration of about three different people's method, but you were one of them! The other was Lou, as well as my local melt shop owner. My local melt shop owner told me to do cadmium contacts with HCl, but he just used AR waste to drop the precipitate the silver and then smelted it. This was the first time I had ever heard anyone tell me to make silver chloride on purpose...I was skeptical. Then I think I stumbled upon your post, on the regeneration of nitric by swapping NO3 for Cl. 

But I do really like it. I don't use it that many times, because the lower acid percentage just takes too long, and I am time limited in most everything I do (which I'm finding REALLY works against you in refining, the good stuff just takes time)

I am determining 95% by using an aliquot of leach, with an excess of silver chloride, then drying and weighing it, and assuming no impurities...it's been close enough.


----------



## snoman701 (Feb 23, 2018)

autumnwillow said:


> For sulfuric and iron do you wash in the filter or do you do it in a bucket? When I wash in a bucket I end up with iron hydroxide precipitate due to pH being high.



I do it in a bucket tumbler that I made. It's like a mini-cement mixer. I tried doing it in beakers with a magnetic stir bar & steel bar...that worked for small amounts only.

Shark posted a picture of a frame of a bucket tumbler for mixing mortar, it would be perfect, but I couldn't find a cheap one. You really need good mixing.


----------



## g_axelsson (Feb 23, 2018)

Have anyone tried heating silver nitrate until it decomposes into silver oxide and then into silver metal?

Theoretically it should work but practically it might be explosive or just violent enough to lead to large losses.
Silver nitrate starts to break down to silver oxide at 250 C and is totally decomposed at 440 C. Silver oxide decomposes into silver and oxygen between 200 C and 300 C, so the nitrate should turn into silver quite easily.

A byproduct will be the well known red cloud of NOx usually produced by nitric acid.

Göran


----------



## geedigity (Feb 23, 2018)

I clean my silver nitrate by melting (fusing) it until all of the base metals oxidize. Then I redissolve the fused mass and filter until the silver nitrate is fairly clear. Only when the silver nitrate gets to a high temperature does it seem to break down with off gassing NOx. It is possible that some of the residue is silver that has been reduced.


----------

