Reducing Silver Chloride

[PhillipJ]

Good info GSP. Thanks.

 

[Harold_V]

The purpose of the copper is to make the crystal denser. Without it, the crystal will be fluffy and stringy and will climb all over and soon short out the electrodes.

Nonsense!

Copper is used by major refiners to minimize the amount of silver in solution. It's a matter of economics, and is not a requirement for good deposition. If anything, electrolyte without copper grows crystals that are difficult to remove from the anode because they're so robust.

I refined silver for well over ten years with electrolyte that started with no added copper, and had nothing but good results. My experience was directly opposite of your claim. Only when the copper level was beyond limits did I grow any stringy silver, and while I don't claim to have processed a huge amount, I did refine several thousand ounces.

For your perusal, I'm posting a picture of silver crystals that were grown from pure silver, in a pure silver nitrate electrolyte. You be the judge if copper is essential, or not.

Take note that the coin in the picture is one of the new $1 US pieces. The crystals in question are anything but stringy or small. Sorry for the sulfated state of the crystals. They were grown prior to '84, and have been in storage since.

Harold

 

[lazersteve]

Harold,

Those are very beautiful! Is there a way to clean the sulfur discolorations without drastically harming the overall crystal? I think I read somewhere that baking soda and/or vinegar in water ( going from memory here, I may be dead wrong! ) would clean the surface of silver without pitting or additional corrosion. Can you confirm or this? It's been a while since I saw the internet article, but I can find if need be.

Thanks,

Steve

 

[goldsilverpro]

My experience was totally opposite than yours. Without copper, the crystals would sometimes even grow up the sides of the non-metallic tank. It seems like you were running at a lower current density than I was. This could make a difference. You mentioned that you kept the current low so you could leave the cell unattended without shorting it out. I ran max and had to push the cell at least every 4 hours to prevent shorting. Sometimes, every 2 hours.

The crystals in the photo are, no doubt, beautiful. Although I have produced similar large solid crystals, I always thought that they were undesirable, from a production standpoint. According to the literature and, my own experience, the best crystals were about the consistency and size of sand. Heavy, brilliant, small crystals are much easier to filter, rinse, and handle. I have never seen these produced without the presence of copper.

There are some thiourea based tarnish removers on the market. A common one is Tarn-X (I think that's right). I think Walmart has it. You just dip and rinse.

 

[Harold_V]

Is there a way to clean the sulfur discolorations without drastically harming the overall crystal? I think I read somewhere that baking soda and/or vinegar in water ( going from memory here, I may be dead wrong! ) would clean the surface of silver without pitting or additional corrosion. Can you confirm or this? It's been a while since I saw the internet article, but I can find if need be.

Like you, I've read an article on polishing silver without manually abrading. I recall reading about using aluminum foil, which apparently creates the small voltage needed. Never tried anything. Chris already mentioned the commercial product(s) that are available.

While it's hard to see in the photo. the small crystal looks better with the sulfide coating than it does without. For reasons I don't understand, the sulfide coating is only on the interior, and only on the flat bottom area. It's very light in color, and evenly distributed. It's as if someone had gone out of their way to create a contrasting background. It's nothing short of cool!

Can't say the same for the large crystals sitting on the pale blue foam. It's obvious the sulfation has been caused by the foam-----and it's not pretty, although certainly not ugly.

The crystals shown were purpose grown-----not from a refining cell. The point I was making is that copper does not make crystals grow dense and small----it makes then grow weaker, so they shed faster. That makes for small, more uniform crystals. I got to witness that every time I ran my cell. The first deposition was often almost a sheet, which quickly changed to crystals as the copper content increased, and finally started growing hair that shorted the cell, and was contaminated with copper. That was consistent, with the contaminated silver confirmed when it was used to make new electrolyte, or refined a second time in electrolyte made from pure silver. By running without copper, it was obvious what the effect was.

I would advise anyone making electrolyte for a small cell to make it from pure silver-------add no copper. It's not necessary for good production, and extends the useful life of the electrolyte. It may perform a desirable function on a production level, but serves no useful purpose when used in a cell that is run on a batch basis, as mine was. The only real negative is that the silver, at first, starts out plating a sheet that can be difficult (but not impossible) to remove.

Also------do not try to part any silver of questionable quality. It if has not been precipitated on copper, or recovered from silver chloride, it likely has too much copper within for the cell to yield pure silver for very long. (Read that "don't try to part sterling or coin silver unless you don't care about the quality"). The objective of the silver cell is to produce high quality silver, with the added benefit of recovering traces of greater values. It makes no sense to do anything to defeat the purpose.

Harold

 

[Noxx]

Hey, maybe ultrasonic jewelry cleaner could do the trick ?
Just my taught.

 

[aflacglobal]

It put my post in the wrong section. :?: :?: :?:

:evil:

 

[Palladium]

Awesome thread. :wink:

 

[Shecker]

Before he died, Walter Lashley of New Mexico's American Society for Applied Technology, discovered that silver chloride will spontaneously reduce to silver metal in the presence of chemically pure iron. The iron will change into ferrous chloride and the silver will be reduced. I use to use this process when I was processing photographic wastes for the silver content.

Randy in Gunnison

 

[Sylar]

I have a bit more then 1 kg AgCl which I want to refine to pretty pure silver metal.

For this amount I set out to find the best way to do this, and from Harold I got the Aluminium proces. This proces was completed yesterday, and the reduced silver was filtered today, pressed to allmost dryness and fired up in my home made furnace.

So I placed the still slightly damp grey silver powder sample in a quartz cup, placed the cup in my furnace and let 'er rip. 30 minutes later the entire furnace (diameter 80 mm, height 100 mm) was as hot as it would get with the modified butane burner I placed in it. Temperature measured to 1020°C with my type K thermocouple but the inside of the quartz cup was still powder, with a speck of molten metal here and there.

1 hour later (about now) I sit here behind my 'puter ... a little confused. I have a light brown powder, definately not metallic, but shiny silver beads the size of a pinhead in it are smiling my way, still slightly warm to the touch.

What have I made, and why didn't it all melt around 950°C to a wonderful glob of relatively pure silver?

 

[goldsilverpro]

No offense, Shecker, but Lasley was an idiot. I read everything he wrote in the California Mining Journal. He was a spiritualist and not a realist, when it came to PMs. Most of his systems were BS.

 

[Harold_V]

What have I made, and why didn't it all melt around 950°C to a wonderful glob of relatively pure silver?

It's silver-----you should have used some borax as a flux. Sorry I didn't make mention. You don't need a lot----a sprinkling on the surface will immediately cause the powder and bits of silver you see to become one. It the flux gets quite dirty, add a little more. An excess does no harm. Heat until it is a common mass, then pour to a well blackened mold. You must have the blackened surface, or the silver will solder to the mold. Make sure the mold is iron or steel. Don't use a lower temperature alloy or copper.

You would be best served using a small graphite/clay or silicon carbide crucible. Also, small clay melting dishes are readily available from jewelry supply houses. They are not expensive and will serve very well for the purpose. Fluxing your quartz crucible/dish will likely not be the wisest thing you do.

If your choice becomes either the graphite/clay crucible, or a clay melting dish, be advised that each of them are subject to cracking when they are put to work. If you heat either of them slowly, to expel residual moisture, then put them to work, you will avoid the potential cracking.

Harold

 

[Harold_V]

Before he died, Walter Lashley of New Mexico's American Society for Applied Technology, discovered that silver chloride will spontaneously reduce to silver metal in the presence of chemically pure iron. The iron will change into ferrous chloride and the silver will be reduced.

You left out the little part where you must include some sulfuric acid, or HCl. That's hardly a secret. He likely learned it from Hoke. Also, it need not be chemically pure, although should that be the case, you wouldn't be adding any contaminants to the silver. Silver and iron will not readily alloy.

Harold

 

[Sylar]

Aha, that's on my todo list for tonight then, I have several kgs of borax sitting here doing jack anyway.


I have a SiC crucible, but it doesn't fit my oven, and I have a graphite dish, which I don't like in my oven because is will tend to oxidise, right? So I'm likely using thinwalled clay/porcelain then.

 

[Harold_V]

I have a graphite dish, which I don't like in my oven because is will tend to oxidise, right?

I used to own one of those small electric furnaces that use a crucible that is machined from graphite stock. Very handy, but life of the crucible was short. While the cover minimized oxygen exposure, that in and of itself was not enough. The crucible had a short lifespan due to the head burning away. The inner portion of the crucible sustained almost no wear or oxidization---but the crucible was rendered useless because the head was destroyed quickly. As a result, I don't recommend that type of furnace, nor do I recommend a graphite dish of any description. They are an excellent choice in that they help prevent molten silver from absorbing oxygen, but expensive to use. Graphite mixed with clay tends to have a much better lifespan, although anything that you use that is combined with flux will suffer a greatly shortened lifespan. That includes your furnace lining. Truth be told, the clay dishes are the best choice.

So I'm likely using thinwalled clay/porcelain then.

Coors? They've extremely sensitive to thermal shock, so handle with great care. I personally avoided them for the most part.

Do investigate the small clay dishes I recommended, when you get a chance. They're made from a white clay and are available in a few sizes. They even offered white clay crucibles at one time. Don't know if they still do.

You can melt ten ounces of silver in the largest dish. They used to be marketed under the Vigor name. Don't know if they still are----it's been more than 15 years since I bought any. I used to use them for all my melting, including inquartation and the melting of pure gold. For the money, they are the best possible melting dish available, and have a reasonable lifespan. An added benefit is they're very easy to clean when they're coated with dirty flux. If you get involved with one and need that operation, ask on the forum. It has been well discussed previously, but I'm always happy to post on the subject again. Makes it easier for the new guys to learn some of the useful tricks.

Let us know how the silver goes. You should end up with some nice buttons.

Harold

 

[Oz]

I used to own one of those small electric furnaces that use a crucible that is machined from graphite stock. Very handy, but life of the crucible was short. While the cover minimized oxygen exposure, that in and of itself was not enough. The crucible had a short lifespan due to the head burning away. The inner portion of the crucible sustained almost no wear or oxidization---but the crucible was rendered useless because the head was destroyed quickly. As a result, I don't recommend that type of furnace, nor do I recommend a graphite dish of any description. They are an excellent choice in that they help prevent molten silver from absorbing oxygen, but expensive to use.

Many years ago when I was looking into investment casting of silver I heard several individuals talk about floating carbon (charcoal) on top of their silver in a crucible while in their furnace to create a barrier between the molten silver and any possible oxygen in the furnace. They would use a bar across the lip of the crucible to skim off the carbon when pouring to give themselves a clean pour without the oxidation problems. I should add that I never did this myself but thought it might be useful commentary considering Harold was talking about the problem of molten silver wanting to oxidize.

 

[Harold_V]

Harold was talking about the problem of molten silver wanting to oxidize.

Actually, it doesn't oxidize, but absorbs nine times its volume in oxygen, expelling it as it solidifies. In a sense, the silver is not effected. It can, however, be the cause of a very rough and irregular surface on cast silver.

The floating carbon prevents the oxygen from entering the molten silver. The addition of even a small amount of copper also controls the oxygen problem-------but that's not a solution for the guy that wants to cast pure silver.

I think Hoke talks about this very subject. Not sure. My copy is not at hand, and I have not looked at the download as of yet. Readers-----what does Hoke say about silver and oxygen?

Harold

 

[Oz]

This sounds very much like the problem Louis was talking about with pouring Pd bars. I’m with you on having a physical copy of Hoke. Perhaps I’m just too old, but nothing replaces being able to turn actual paper pages for me. I do like being able to do key word searches in large PDF files though.

 

[Lou]

You can really cut down on how much oxygen the silver absorbs by melting it in a rich furnace atmosphere. Be exceptionally careful doing this--by richening the flame, you produce carbon monoxide. I can vouch that it works quite nicely.


Harold, if you're talking about those white, fused silica crucibles that are bone white, then yes indeed, those are premium! They work well for gold, silver, and palladium. Platinum is a bit much for them though.

 

[Harold_V]

Harold, if you're talking about those white, fused silica crucibles that are bone white, then yes indeed, those are premium! They work well for gold, silver, and palladium. Platinum is a bit much for them though.

No, the dishes I speak of are just clay. They do not have the characteristic straight sides and thick bottom of the ones you reference. Fact is, they look very much like small Coors evaporating dishes, only thicker.

I used the type you're talking about for melting my platinum, what little I melted, anyway. It was important to remove the button immediately upon solidifying, otherwise the melted silica would trap the button in the dish. The problem with this type of melting dish is they don't have a large capacity, unlike the larger sizes of the one I mentioned.

I pickled the recovered button in hydrofluoric acid once removed. I had a small platinum dish that served the purpose. Aside from killing a wart, I can't think of another use for the acid, which I still have.

Harold