Silver Stock Pot Processing - Metallic silver cement + Silver Chloride

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CAustin

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Hi everyone - first post here but long time lurker and huge Sreetips fan.

I recently started refining silver using both the nitric-->copper cementing method and the nitric-->silver chloride/lye/sugar method. I have done a couple of runs of each, and have learned a lot along the way with varying degrees of success.

I now come to the point where I have to treat the stockpot. Inside are rinse/waste solutions from both types of silver refining. The scrap material was almost entirely scrap sterling flatware and candleholders, so I'm not expecting much in terms of gold or PGMs.

My first few runs were via copper cementing method - so the remaining solution was stored in a 5 gallon bucket with copper strips in it. All is fine and dandy there.

Until...

I added in the waste solutions from the silver chloride method. There was obviously excess NaCl from the silver chloride conversion, as well as chlorides present from tap water rinses. Thus, when I poured this into the stockpot over my next couple of runs, I noticed silver chloride being precipitated in the stock pot.

So now I have a stock pot with cemented metallic silver particles AND silver chloride precipitate. The solution is pretty much just dilute copper nitrate - maybe some iron in it from a messier batch of scrap I processed (slightly green but pretty much royal blue solution).

Obviously there is silver in there between the metallic cement and silver chloride. But with both being solid, I'm not sure what the best way to process this is.

If it was just the metallic sludge, I could filter it, melt it into shot, and put it through an electrolytic cell or re-refine with the silver chloride method if dissolved in nitric again. However, when I filter, I will have silver chloride present. I am not clear on the chemistry of melting down silver chloride, but my understanding is that it will NOT produce metallic silver. Please correct if I'm wrong.

I believe I have also read that if I filter the solids from the stockpot, and then rinse with boiling water, the silver chloride will dissolve back into solution. I can then process the filtered silver cement, and then I can process the new rinse solution by dropping it back out of solution with NaCl, rinse it, convert with lye and sugar.

I know some of my chemistry knowledge is missing here. I appreciate the help and knowledge from you experienced guys on here.

Thank you!! Let me know what I left out so I can fill in the details.
 

FrugalRefiner

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You can melt silver chloride directly, but you will lose some silver in the fumes.

Boiling water will NOT dissolve silver chloride.

You could filter out the combined cemented silver and silver chloride and add some distilled water and nitric acid to the combined solids. It will dissolve the metallic silver and leave the silver chloride as a solid. Filter, then cement the dissolved silver back out of the solution and process the silver chloride by your choice of method.

Others may have better alternatives.

Dave
 

Shark

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FrugalRefiner said:
You can melt silver chloride directly, but you will lose some silver in the fumes.

Boiling water will NOT dissolve silver chloride.

You could filter out the combined cemented silver and silver chloride and add some distilled water and nitric acid to the combined solids. It will dissolve the metallic silver and leave the silver chloride as a solid. Filter, then cement the dissolved silver back out of the solution and process the silver chloride by your choice of method.

Others may have better alternatives.

Dave

Question. Since he already has silver chloride to deal with would it be easier to convert all the silver to a chloride then have only the one silver chloride conversion to deal with thereby eliminating the cementing process.
 

FrugalRefiner

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Shark said:
Question. Since he already has silver chloride to deal with would it be easier to convert all the silver to a chloride then have only the one silver chloride conversion to deal with thereby eliminating the cementing process.

That's certainly another option. I guess for me it's a personal preference. I just avoid creating or dealing with silver chloride unless I have to, but everyone has their own favorite methods.

That's why I suggested he wait to hear other options.

Dave
 

justinhcase

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Well Unless you have the luxury to have separate processing arias for silver nitrate and chloride based chemistry and wash all material passing from one to the other scrupulously you are going to produce silver chloride in some quantity.
That is a minor inconvenience, have you ever mixed your nitrate acid wash with a sulphuric acid wash by mistake.
Both are silver compounds, one would think you would be safe putting them in the same cementing. But no, thick white silver sulphide.
No real problem.
Waste drums are actually a refinement opportunity on their own.
Copper plated with anything of interest, no problem, don't wast effort, put them in your waste drum and let the copper be sacrificed.
Little bits of digested waste that may have one or two pound or gold left, waste a day chasing it or put it in the piggy bank and recover it all later.
I looked at a lot of options and tested small runs.
What I found most effective after washing was a drum agitator with iron and sulphuric acid.
You will lose no silver or gold and if you run to excess you should get a good conversion.
Then simply smelt everything with a good loiter and more iron to make sure you convert all the sulphides if any still exist. Then wet process.
Though I did use my last recover as the bases of an inquartation, so I have no recovery weights.
But it took a lot of heat and flux to the point of having to build a new larger furnace to accommodate larger melts.
 

snail

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My preference would be to rinse it clean and use the dilute sulfuric and iron method. It will convert the chloride and the metallic silver will not be affected.
Cover with about 1/2 inch of 10% sulfuric acid, badd iron.
I’ve used roofing nails, bolts, rebar, small scraps o 1/4 inch plate.
Many say it needs tumbled but if your patient, shake around once a day, it will completely convert.
I’ve opened the lid of a 5 gal bucket and observed a 1 inch ring of converted silver chloride around the iron pieces in 24 hours.
I follow with a dilute sulfuric rinse after removing the iron pieces to remove most of the iron bearing liquid. Then rinse clean.
Melt with borax.
Lou commented that the iron will not want to alloy with the iron residue because of the dissolved oxygen in the
silver melt and the borax will pick it up.
 

g_axelsson

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Another option is to treat the silver cement and silver chloride with sodium hydroxide, converting the silver chloride to oxide, then after proper washing you can dissolve it in nitric acid again or convert it with sugar to elemental silver. If you go to direct conversion to silver you probably end up with a dirty result as the cemented silver from the stock pot probably have a lot of copper and other trash in it (oxides), making it harder to melt.

I like silver chemistry, it's an easy metal to work with and there are several ways you can go between silver, silver nitrate, silver chloride and back again. The price also lets you work with decent test batches without worrying too much about losing a few grams.

Biggest losses is probably if you try to melt it directly, silver chloride trapped in the slag and going off as smoke.

Göran
 

justinhcase

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So what are your opinions on filter papers.
A large mix of Chlorides and elemental metal even if you have washed them of most solids very well.
Then lots of organic matter which needs incineration.
Do you attack the chemistry first to stabilise the volatile compounds then incinerate?
If so how?
Or do you incinerate, trap any volatiles that have been released and go from there.
I must admit with the drop in price of Electrostatic Air Filters I am considering starting to use the latter.
 
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