Silver scrap containing cadmium

A customer sent me 61+ oz of home made bars ( ugly bars) that contain cadmium ( 3 %). Anyone want to refine them?

I would precipitate the cadmium as an insoulable cadmium salt, then you don't have to worry about it being a problem. Dispose of it responsibly according to whatever laws prevail in your area.

I am tapping this out on my phone, when I am home, if someone has not already posted how to do this, I can.

Scott

NobleMetalWorks said:

I would precipitate the cadmium as an insoulable cadmium salt,

Scott

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I am all ears

Kurt

1. Roast the contacts until they show a faint dull red to burn off any organics. Be careful not to heat too much and make sure you do this in a well ventilated area, wear all precautionary safety equipment and a respirator just in case you do vaporize cadmium. Where a long sleeve shirt, preferably a lab coat, keep the temp well under 900 F. If you are only heating to burn off organics, you should not heat anywhere near 900 F.

2. Dissolve contacts in 50/50 solution of water/nitric acid, if you use tap water you may precipitate a small amount of silver chloride but it will be a very small amount, which you could filter off, but it would be such a small amount you will probably want to ignore it. Only add small amounts of nitric acid to your solution until all the metal is dissolved into solution. Small additions will prevent excess nitric acid.

3. Cement silver on copper, to prevent small pieces of copper from breaking off and corrupting the silver, larger pieces of copper should be used, such as copper bus bars. Large pieces of copper will prevent small pieces of copper from breaking off. Cadmium will stay in solution, refer to the reactivity scale of metals.

4. Filter off the silver, wash the silver really well to prevent any carry over from the solution with cadmium.

5. Precipitate cadmium with Sodium Hydroxide, a white insoluble ppt cadmium hydroxide or Cd(OH)2 will form. Dispose of responsibly and according to your local regulations.

If anyone has anything to add, or correct, please do.

Scott

Hmmm - OK - I was hoping you had a more selective way of precipitating the Cd so that the Cd could be removed from the copper nitrate which is the primary by product after cementing silver from dissolving contact points with nitric - & thereby rid the Cd so that it would not cement out along with the copper when cementing the copper with iron

But that wont work in this case being as Cu precipitates at a lower PH range then Cd - therefore you will have precipitated all your Cu before the Cd is all brought down

The PH "range" that Cu precipitates at is between 6 & 8.2 ---- meaning it starts to precip at 6 & should be complete at 8.2

The PH "range" that Cd precipitates at is between 8 - 10.8 --- meaning it starts to precip at 8 & should be complete at 10.8

In other words - to drop all the Cd you need to take the PH all the way up to about 11 - at which point you will have a Cd contaminated "copper" hydroxide (blue) --- not just a (white) Cd hydroxide

So ether way - whether you cement (with iron) or use hydroxide to treat the copper nitrate waste from cementing silver "from contact points" the Cd is going to go along with the copper

copper - unlike some metals (Cr, Zn, Pb, Al) does not re-dissolve as the PH is raised beyond its high end range of complete precipitation

Steps 1 - 4 I already know - I do a LOT of contact points

Kurt

Alternatively, you could run the contacts as a silver proposition in a silver cell. After you plate out the silver, you can precipitate the rest of the silver in solution as silver chloride, and then precipitate the cadmium as it's insoluble salt.

Scott

Would stopping PH at 7.9, filter copper hydroxide off, bring PH to 10.8 and filter off Cd hydroxide, work?
Needs to turn copper hydroxide back to metal if you are after it.

Marco

MarcoP said:

Would stopping PH at 7.9, filter copper hydroxide off, bring PH to 10.8 and filter off Cd hydroxide, work?
Needs to turn copper hydroxide back to metal if you are after it.

Marco

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It seems like those ranges are rough, with a bell curve perhaps? So some cadmium would start dropping out before pH = 8?

What if you cemented the silver out first with copper, then cemented out the copper with nickel or tin? They're not as cheaply available as iron, but they would theoretically cement the copper (and lead if any) without dropping the cadmium. Then you could filter your copper and cement the cadmium (and cobalt, if any) with iron.

You could then redissolve the wee amount of cemented cadmium in nitric (wouldn't need too much I would imagine), then precip as insoluble Cd(OH)₂.

A pain, but it would at least isolate out the cadmium if you wanted it out of the standard waste stream.

Edit: The above process would put your nickel in the same boat, yes? Iron would cement both the nickle and the cadmium.

Just curious. Is this nearly fine silver with just the 3% cadmium or are there other metals?

Silver contacts that contain cadmium oxide are almost always a percentage silver/cadmium with minor impurities. There are other contacts that contain silver which are either only silver, or alloyed with other base metals for specific purposes. Fine silver is so soft, that in certain applications will eat through the contact if it arcs. Cadmium oxide in one such metal that's helps to prevent this from happening.

The amount of copper hydroxide that is associated with the cadmium hydroxide is minimal if the process I posted is used. Considering the toxicity of cadmium for the average refiner this seems the best way. There are many other ways of separating the two, but I am hesitant to post them as some are dangerous and shouldn't be done unless in a proper lab, with proper equipment under the right conditions, etc. This method should suffice.

Another method that works well is finely divided iron hydroxide, when I am able I will go ahead and post this method as well. I am taking a small break and posting this from my phone, no computer in the lab yet, when I am home I will post this method as well.

I dont usually have issue when I have used this method of separation, with copper contamination. But I also make small additions and observe the reaction throughout, decanting when required, etc. But it should be noted as well, that there do exist methods for a qualitative separation of copper and cadmium hydroxides.

Scott

The silver in question is 5 ugly bars that someone made, he said it contains contacts and "other" silver scrap. XRF has the surface at 93% silver and 3% cadmium, I did not get the entire 100% readings.
I was looking for someone to refine this just as a service to my customer, if no one is interested the bars will be returned to my customer as soon as I get them back.

scrapman1077 said:

The silver in question is 5 ugly bars that someone made, he said it contains contacts and "other" silver scrap. XRF has the surface at 93% silver and 3% cadmium, I did not get the entire 100% readings.
I was looking for someone to refine this just as a service to my customer, if no one is interested the bars will be returned to my customer as soon as I get them back.

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What do the 5 bars weigh in total? Was XRF taken from the top at both ends and middle, and bottom both ends and middle? Also, when using an XRF on this type of material it is best to drill into the bars bottom, top, ends and middle so that the metal shavings can be tested.

Considering the waste is toxic, and silver is only around $14 per ounce, it might not be worth processing unless it is a larger quantity. Even professionally, and only above a certain amount, you will not get returns you would if it wasn't contaminated with cadmium. Many refiners will charge a fee for the cadmium above and beyond the cost of refining the silver. Many refineries will not even accept cadmium contaminated silver.

Scott

I did not do the XRF so I can't answer your questions. 61+ oz total.

I'd be a buyer, if like you said, its already melted into a ingot.

What payout rate are you looking for ?