Medium to large scale silver refining

[elfixx]

I curently experience a lot of demand from people who want to sell silver scrap, mostly silver coin and sterling, probably due to the silver price getting intesresting. I know we have quite a few experienced large scale refiner on the forum and I was hoping to find a answer on how to refine large lot of silver without having to use expensive nitric acid in large quantity. Since most canadian coin are 80% silver and some can go down to 50% it is impossible to simply melt the material and process it directly into the electolityc cell. How do the big boys get rid of most copper before casting into anode for the cell?
I started to think about it last week when I received 2 call from customer for over 60kg of silver scrap.

Thank You

 

[4metals]

The simple method is to digest in 50% nitric and cement out clean silver for the cell. I've set up a few smaller refiners to do this on up to 4000 ounces a week of sterling down to 40% silver scrap. The waste treatment from the spent acid is affordable and straight forward and the cell generates little waste due to the cleaner feed. You also have the option of formic reduction of the silver to bypass a cell totally but formic can cause waste treatment headaches.

A second option is to use a reverberatory furnace to slag off the base metals by using a very hot oxidizing flame to oxidize the copper and melt the oxide and take it up in the slag. This works for bigger operations and eliminates the nitric. I've never seen a small reverb furnace to do the same job so it's a question of scale.

Smaller refiner, the numbers work out for digestion and silver cell processing, and even 60 kg a week is small in the scheme of things.

 

[elfixx]

Well I guess nitric is prety much the only option here, thing is I need to find a cheaper source of it. Right now 70% nitric is costing me 65$ per gal.

 

[element47]

This is a question of mine as well, being in a similar position, and I appreciate the posting of this query. I have dozens of kilos of sterling forks & spoons I've bought over the years and I'd like to turn them into .999, preferably in known-name bar/ingot form. My current calculations and ponderings are whether I can re-capture the "refiner's cut" processing myself. It appears to be a close shave and it's of course largely dependent upon the cost of nitric, and whether the mandatory investment in safety gear and "competent" glassware & torch & torchware is worth it. I also do not treat the generation of NO2 lightly.

I'd like to hear a brief discussion from the veterans as to what happens when one uses nitric made from sodium nitrate and sulfuric acid in this process. Can the sodium and sulfate ions necessarily in solution be completely ignored?

And when this is all done, there is that appointment with an assay that is implied. Meanwhile, each and every sterling fork made in the last 120 years says STERLING on it exactly as it sits and is thus self-assaying, although I do not believe sterling is a preferred form of bullion.

 

[HAuCl4]

Well I guess nitric is prety much the only option here, thing is I need to find a cheaper source of it. Right now 70% nitric is costing me 65$ per gal.

You must find a cheaper source of nitric, or recycle all of it, or use sulphuric acid instead which is a lot cheaper. IMO.

Some large guys use a variation of the Parkes process, but it has several disadvantages, including the use of lead, fumes, etc. :shock:

 

[elfixx]

Anyone ever heard of the Janus Electrolysis process? I found this website http://www.joachimjanus.de/index.html, M. Janus claim different electrolytic process to refine silver scrap from as low as 1% Ag. Unfortunatly there is no precision on how those process actualy work. He's got a cell design to refine 62% ag scrap up to .9997 in one step without adding/replacing silver nitrate electrolite, which would be very interesting in refining of silver coin.

 

[Harold_V]

Anyone ever heard of the Janus Electrolysis process? I found this website http://www.joachimjanus.de/index.html, M. Janus claim different electrolytic process to refine silver scrap from as low as 1% Ag. Unfortunatly there is no precision on how those process actualy work. He's got a cell design to refine 62% ag scrap up to .9997 in one step without adding/replacing silver nitrate electrolite, which would be very interesting in refining of silver coin.

I'm calling BS on that claim.

Harold

 

[qst42know]

They refine the copper first in sulfuric concentrating silver as anode slimes? The "modified" is a mystery.

http://www.joachimjanus.de/Electrochemical_Processes_for_Separating_Ag_and_Cu.htm

Alloys to be separated with

1. 1 - 50 ‰ Ag are pre-separated in a modified Cu - electrolysis with H2SO4 electrolyte,

2. 50 - 600 ‰ Ag are pre-separated in a H2SO4 - electrolysis to 920 ‰ Ag as a skeleton,

3. 600 - 985 ‰ Ag are refined by the JANUS - electrolysis without stock directly to fine silver of usual commercial purity,

4. 985 - 999 ‰ Ag are electrolysed by the conventional Möbius or Balbach - Thum electrolysis with equivalent stock to fine silver of usual commercial purity.

 

[EDI Refining]

I curently experience a lot of demand from people who want to sell silver scrap, mostly silver coin and sterling, probably due to the silver price getting intesresting. I know we have quite a few experienced large scale refiner on the forum and I was hoping to find a answer on how to refine large lot of silver without having to use expensive nitric acid in large quantity. Since most canadian coin are 80% silver and some can go down to 50% it is impossible to simply melt the material and process it directly into the electolityc cell. How do the big boys get rid of most copper before casting into anode for the cell?
I started to think about it last week when I received 2 call from customer for over 60kg of silver scrap.

Thank You

Elfixx,

Careful its against the law to melt Canadian coins that are currentency. I believe only one refiner in Canada has permission to melt these coins, other wise it has to go to the states.

 

[elfixx]

Just found a bunch of chinesse supplier for niric at 290$ per metric ton, minimum order 25MT. Anyone want a gal or 2? loll

 

[jimdoc]

Just found a bunch of chinesse supplier for niric at 290$ per metric ton, minimum order 25MT. Anyone want a gal or 2? loll

I don't think I would trust anything from China at this point.

Jim

 

[Drewbie]

Probably has mercury, arsenic and cadmium mixed in there for good measure

 

[joem]

Just found a bunch of chinesse supplier for niric at 290$ per metric ton, minimum order 25MT. Anyone want a gal or 2? loll

I would not buy anything labeled niric from china