Whats the best way to go about recovering this, silver stock pot.

[Gsracer]

Good morning GRF,

So i have had my stock pot going for about 14 months and its time for a clean out. I only to this point have been processing silver, sterling flatware specifically and items, no jewelry at all. Straight nitrate process, no chlorides.

What i do is the typical process, silver nitrate, cement out on copper, silver cell etc. Spent solutions after recovery and rinses go into the 5 gallon stock pot with an abundance of copper under air agitation until they go forward into the waste process.

So after about 14 months and about 25 kg of processing i wanted to go after the stock pot which had a pretty solid inch to inch an half of metallics in the bottom. I decanted into a 2.5 gallon bucket the material. And rinsed it a little bit

This is what i have, a slightly pinkish silver cement looking material with some larger gravel like chunks of silver that appeasers to have coalesced. I assume its going to be mostly silver with a lot of copper bits and copper oxide from the pinkish tint. I don't really expect much if any of PGMS or gold. I would like to just go after the silver. It will be pushed fwd to the silver cell anyway.

Whats the best way to tackle this? Im sure i can just nitric and cement again. But given that its already cement is there any way to attack the copper/ copper oxide?

As always thank you for your feedback.

Before rinsing, notice the redish pink tint




After a little rinse

 

[Lino1406]

Add hydrochloric acid and H2O2 to the precipitate, hopefully it will leave you with silver chloride and a solution of rest materials

 

[Gsracer]

Thank you for the info lino, I am unfamiliar with the HCL peroxide method. Can you go in to the process a little bit, what are the ratios, concentration of H2o2, heating, time table? I'm sure i could do it i just don't know the method as all mentions on the forum are for Escrap and not silver specifically.

I assume i would be left with either un digested silver cement and some silver chloride?

Either way i would like to try it on a small scale before going after the whole batch.

 

[Elemental]

If you're running a silver cell, an option would be to just melt this into an anode bar and let the cell do the work for you. It will be a bit more dirty than processing regular silver cement (aka your electrolyte will foul faster), but it would give you clean silver with minimum effort/chemicals. I would make it a point to pick out any larger pieces of copper in the stock pot before melting.

Elemental

 

[Gsracer]

Elemental, thank you, while that is an option. I really want to process this batch separately. Reason being is that i have tracked every gram that has come in to my process and every gram that has come out in a spreadsheet. I obviously have lost weight along the way. I want to see where it went. I know it will come out on the silver cell eventually and i can reconcile it there. I will be processing filters next. This is mainly to empirically see where its going and also to learn.

 

[Elemental]

If that's your intent, then your assumption of using Nitric to put everything back into solution and then once again cementing out the silver would work. A tip, make sure your copper is fully submerged to reduce the amount of copper oxide created. Also, consider using thick copper which won't go to pieces as you use it. Someone once recommended copper water pipe, split and pounded flat to create sheets of copper. When I initially started silver refining I used copper wire and ended up regretting the hair-like pieces of copper I would have to pick out of my silver cement. Never again, now I use copper bus bar plates recovered from buildings.

In chemistry, every reaction has a limiting reagent which will determine your maximum yield. For this it should always be silver. Even though you may calculate out your maximum yield, there is always a small percentage of loss. The more times you handle a chemical via a reaction, the larger that loss percentage becomes. There is a point where the "bang isn't worth the buck" of trying to recover that tiny bit of loss. Excess waste stream production/management, chemical reagents, and ultimately your time are all weighted costs to consider.

I commend your documentation efforts though. Knowing where your loss is taking place; wet chemistry, transfers, melt loss, will go a long way to decrease that loss percentage. Please let us know what you discover.

Elemental

 

[Gsracer]

Thank you elemental, that's mainly my goal. I want to really see where I'm loosing it. I know in this business as some one famously said, you only loose values if you throw them away. Everything is recoverable. This is a hobby for me, i only sell to keep going forward with it. Also lower my dollar cost average when i can.

As for hard numbers.

I have recovered 19,459.89 grams of silver between silver crystal i have and cement silver as well. I got this from 21,820.91 grams of sterling. Theoretical yield should be 20,184.34.

Im off by 724.45 grams. So my recovery rate is 89.18% instead of theoretical 92.5% (which i know is probably impossible for a hobby refiner)

Looking at what's left from the stock pot from experience id say there's about 350-400 (maybe more as its coarse) grams of cement in there. Using the low end that would put me at 90.78% more in line with what i would expect. Maybe there's another 10-15 grams in filters/wipes i would be pretty close to 91 percent. Which is something i could live with.

All in all i don't feel I've done too bad considering 14 months ago i had never done this in my life and got the idea from watching Sreetips on YT. I try to be meticulous and careful with all my processes as well as documenting everything i do.

I will follow up once i get it done and let you guys know.

Im still open to trying the AP process with it, if Lino could share a methodology. I know everyone is busy, im not really in a hurry, if not ill just throw nitric at it and go from there.

Thank you all

 

[cejohnsonsr1]

I’d think that dissolving again would be the best way to go. But you can be fairly certain the copper content will be much higher than the original Sterling. Going to take a lot of Nitric to dissolve all that excess copper. Sreetips has a series that uses Sulfuric to dissolve, but there are a couple more steps to get it back into the form you want. Might be worth looking at to compare cost and time to process.

 

[nickvc]

Just for your information remember that any solder joints will have a lower silver content than sterling .

 

[Gsracer]

Thank you Nick, i try to keep solder out completely. I havent done jewelry or any type of Escrap. All i have processed is sterling flatware with the occasional candle stick. I know there is solder at times in knife handles. But i process those separately when i have 500 grams or so of knife handles.

 

[Gsracer]

Cej, i was thinking of sulfuric and watching that process earlier tonight, but i try to avoid hot sulfuric whenever i can.

 

[nickvc]

I think Lino’s suggestion may well be the best way forward as it will dissolve all other metals leaving silver chloride which is great feed stock for your cell once converted and you can then use stannous to check for any other values which I very much doubt you will have.

 

[Gsracer]

Agreed Nick, i wanted to give a try the AP method since i really have never done it before. Since small scale is best for a first attempt. So i took a teaspoon of the more finely divided sediment and added it to 200ml beaker. I read lazer steves thread regarding AP. So i added 24ml of HCLand 6ml of fresh 3% Hydrogen peroxide, the solution turned a pale green after a about 15 minutes. I added another 2ml of hydrogen peroxide. Its been an hour an the solution is black. I ended up with a ratio of 3:1.

I don't see any silver chloride forming, and there is quite a bit of cement silver in the bottom of the beaker. From what ive read AP is a slow process so i guess ill wait

 

[Yggdrasil]

Way to much peroxide I think.
The first mls should be plenty.
A bottle cap or two pr gallon should be good.
Then just shake it every few hours or better bubble air through it.
Just be careful, the AP process also dissolves some Pd, at least so I've been told here.

 

[cejohnsonsr1]

Cej, i was thinking of sulfuric and watching that process earlier tonight, but i try to avoid hot sulfuric whenever i can.

I don’t blame you, but Nitric is pretty nasty too. As I recall the Sulfuric method took a long time to digest, but it was much less expensive and available at Ace.

 

[Gsracer]

So this is proving to be the strangest recovery i have done. Just when i though i had a good handle on silver. I dont know what the hell is going on.

First thing, this is the AP experiment outcome. I diluted it down with some distilled water and let it settle.

Looks like most of the copper is gone and im left with some cement silver or at least i think it is. No evidence of silver chloride. The reason I'm speculating will follow after this.




So as typical i was bored, i rinsed all the cemented material out of the stock pot and dried it to get an idea of what volume i was working with. I have 620.36 grams of copper, silver and the rests would be under copper in the reactivity series.

This is the material.



So to experiment, i seperated 250 grams of the dried material into a beaker and hit it with 250ml of 70% nitric and 250ml of distilled water. I assumed most of the material would be copper anyway so there was no way i would over shoot it.




After boiling for a few hours, i was left with this green mess. Virtually the same volume of material i put in to begin with, its not dry so i dont have a weight on it just yet but here is what it looks like.



The solution filtered easy enough however and i was left a fairly clean what im assuming is silver nitrate.




In either case, i threw a fresh piece of copper in there because as we all know, when in doubt cement it out.

Im curious to know if anyone has ever seen something like that green material before.

 

[nwinther]

Regarding purity of sterling silver (925), are you absolutely sure that it is ALWAYS 925?

I once read that the rules/law on the fineness of gold, say, 22 karat, means it just has to be above 21 karat (so 21,2 karat=22 karat).

I would expect there to be a similar margin when it comes to silver, where it'd be worth it putting 920 or even 910 on the market as "Sterling".
I realize that gold is much more interesting to fiddle with the numbers in, as the margin on gold vs. copper is much higher than silver vs. copper.
Or it might not be an attempt to skim silver, but just the way the producer went about it, producing Sterling - give or take - but it would pass any meaningful test.

 

[Gsracer]

I’m sure your probably right. Nothing surprises me these days.

I kept good track of what went in versus what came out. Don’t get me wrong. I’m satisfied where I’m at. Practically 90 percent.

However the stockpot does hold some values. This is the first time I have processed it so it is a learning experience for me.

 

[nwinther]

I’m sure your probably right. Nothing surprises me these days.

I kept good track of what went in versus what came out. Don’t get me wrong. I’m satisfied where I’m at. Practically 90 percent.

However the stockpot does hold some values. This is the first time I have processed it so it is a learning experience for me.

I absolutely love your idea of accounting for the materials. Great idea for improving your process because you'll find certain areas of excessive loss, and you can iron out any problems once you know what/where they are.

I'm just thinking that you should be aware of not chasing a loss in your lab that is actually in the "pocket" of the producer.

How precise are XRF-readers? I know they are expensive, but if they are very precise they could help in the identification of actual fineness of your feed stock. Here in Denmark, silverware is most often 880 or 830 fine - but we talk about it as if it's 925.

 

[nickvc]

I believe that silver has to be plum unlike gold which has I believe a half karat tolerance so unless you processed a plated item or a forged mark piece you should have all the silver you expect somewhere in your system.