Silver Refining, Which process would you recommend and why?

Dear All,

I am new to the forum, but not refining. I've been doing bits of silver and small scale gold for about a year now. I did search the forum, but nothing came up. I would appreciate any input.

I have always wondered which technique/process is better for refining silver, too get maximum purity?

1)Scrap silver dissolved in Nitric-> Then Copper cements out Silver

or

2)Scrap silver dissolved in Nitric-> then precipitated out as silver chloride-> silver oxide -> Silver

Thank you.

To get maximum purity, you'll want to make a silver cell.

Dave

Nitric acid digestion followed by dropping out of solution with copper.
That turned into shot and run through your silver cell once for normal needs twice for extra purity if needed.
Just wash your silver to excess at each stage using distilled water and replace the silver cell solution early.you can run it until your silver crystals cease to form properly but you will be producing tainted silver before that point.
Silver chloride is not a very practical way to go but when you have to empty your wast pot the aluminum or zinc reaction is much nicer than trying to use a caustic flux.

To get the highest purity the chloride method. Not very practical on a large scale though.

Martin

The problem is, copper will cement other PMs along with the silver and silver chloride will drag down some other PMs, too. For the cell you need minimum 90% silver (search: "silver cell 90"). So in most cases it is no either/or-question, but it depends on what you are starting with.

I normally refine .925 scrap jewellery, or broken silver items, both .800 and .925

Because copper cements out the Silver and other PMs, could I add DMG (Dimethylglyoxime) to it, to remove the PMs( Orange precipitate?). Then cement the silver out with copper?

I haven't set up a silver cell yet. It is something that I need to read up on and research. If anyone has any good websites or tutorials that could send me in the right direction I would appreciate it.

I'm just getting back into silver 'refining', now that silver is so 'cheap'. I can buy hallmarked silver for 15p/gram all day long, as I have lots of good contacts

I make ingots for my own personal pleasure and sell the odd one to friends and family as paperweights!

Thank you for your input so far. This forum is proving to be very helpful and friendly

DMG will only remove palladium, I think. Very old silver might be "contaminated" with even gold, which will not be removed. In my opinion, this is a typical case for the standard procedure: Dissolve in diluted nitric, cement on copper, wash well, melt, run through the silver cell.

Good basic info in C.W.Ammen's book.

I can't understand why more members of the forum don't recommend Solvent eXtraction (SX) for (precious) metal refining, particularly where purity is an issue. I can't admit to personal experience of SX for silver, but I can for gold and I'm very satisfied with the results. A quick Google for selective organic extractants for silver produces at least a dozen, most with long unfamiliar names, but TBP (Tri-Butyl Phosphate) is on the list.

Here's a link to an instructive article: http://www.halwachs.de/solvent-extraction.htm

solar_plasma said:

DMG will only remove palladium, I think. Very old silver might be "contaminated" with even gold, which will not be removed. In my opinion, this is a typical case for the standard procedure: Dissolve in diluted nitric, cement on copper, wash well, melt, run through the silver cell.

Good basic info in C.W.Ammen's book.

Click to expand...

Thank you. I will look at C.W. Ammen's book.

The issue with S/X is the waste treatment--organics build up in the extracted raffinate and make disposal expensive and entrain values.

Hmmm, I don't think I agree.

1) Organics don't build up in the raffinate. They are chosen specifically for their low aqueous solubility; butyl diglyme (aka dibutyl carbitol - tm Dow Chemical), for example, I believe is around 0.3gm/L. The entrained values can be easily calculated from this solubility and the loading in the organic - but it ain't much. Certainly no more than that lost through the various unit processes in a chemical route.

The organic can be separated, if appropriate, via distillation. Extracted raffinates are, more often than not, recycled to the leach, with a bleed off to limit build up of contaminants that haven't previously been extracted at the pregnant lixiviant stage.

The OP asked:

Ollie1016 said:

I have always wondered which technique/process is better for refining silver, too get maximum purity?

Click to expand...

For gold, even I can get 4 x 9's purity and I have even heard of 7 x 9's being possible. Try that via another route, although I think I remember GSP publishing a long and arduous method (somewhere on the forum) involving multiple dissolutions and precipitations.

OK, so my examples are for gold, but I don't think silver is significantly different.

Gratilla
That is very interesting.
Perhaps you could start an other string and run through your process.
I for one would like to see it in more detail photo's of kit and a video of you running it would be very good.
I am still wading through the basics but very interesting.
Just

1.) Organics DO build up in large aqueous volumes and necessitate removal. TBP has its own set of problems as it ages anyway. Alkyl sulfides will gradually oxides to alkyl sulfoxides, which are much more soluble in aqueous feeds but yet coordinate precious metals. Even dibutyl carbitol...the solubility you quoted is in water, not in strong acid milieu and it's actually 3 g/L. I'm well familiar with leach recycling--we use this technology and I'm telling you, it's no magic bullet. If you wish to make a thread on solvent extraction, please do so (in fact, make it by metal, i.e. S/X of Pt, S/X of Pd, S/X Au, and so on) and I will gladly participate. I might be the only participant in that thread, but I've done SX on Pt/Pd/Ir/Rh/Au both lab, pilot, and process in the case of Au.


As to the original post:

Silver refining of feeds over 80-85% wt silver are best done in an electrolytic silver parting cell. The two methods you quoted do not work well because 1.) cemented silver often contains copper impurities, 2.) silver chloride generated Ag2O contains other impurities that are stuck onto the precipitate and difficult to remove. Both of those methods should be looked at as a preliminary upgrading step. There is a method using sodium formate for silver refining that can yield 4N silver, but not if palladium or nickel is present, which contaminates the silver. To remove those, either a cell with good electrolyte pH control, or dissolve in nitric acid and heat until the oxides of these metals form, then cast the silver nitrate onto hot stainless pans like peanut brittle, break up and dissolve in UHP water, let settle, decant, then formate. That silver will be in excess of 6N.

Lower grade feeds can be melted and upgraded in a reverberatory furnace with excess air and some flux to produce a slag rich in copper and impurities, that can be sold to the copper refiner when you have a semi truck worth.

Feeds less than 40% Ag by weight should be melted with copper and sent to the copper smelter or, if in small quantity, used to cement out silver from contaminated cell baths.