# Recovering Ag from Tungsten/ Carbide



## philddreamer (Oct 8, 2010)

I was given a few weeks ago 500g of some plated tungsten carbide & the silver strips used to plate the tools. Today I processed 32g of the strips & here are some pic's. Please notice the colors of the sediment & cemented silver. Is that Cu? Also notice the color of solution after dropping silver w'salt. I didn't process any of the carbide. It got late, so I couldn't dry the silver in order to weigh it, but it looks like a good amount, 50 to 60% is silver. The other stuff... :roll:


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## goldsilverpro (Oct 8, 2010)

In my experience, the silver solder used to attach tungsten carbide to steel is primarily a silver/copper alloy, with small amounts of other metals, such as cadmium.


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## philddreamer (Oct 8, 2010)

Thanks GSP!

I have 500lbs available, if I can figure a way to recover values. The solder is not much of a problem, but recovering the ag from the carbide... :roll:


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## goldsilverpro (Oct 8, 2010)

philddreamer said:


> Thanks GSP!
> 
> I have 500lbs available, if I can figure a way to recover values. The solder is not much of a problem, but recovering the ag from the carbide... :roll:



Here's a patent. In example 1, the guy simply made a solution of 54% nitric (technical 70%) + 46% distilled water, both by volume, and dissolved the Ag/Cu at room temperature. Please note that he was dissolving this from both WC and steel. He says the solution was used at that strength to prevent attack on the steel. In your case, all you want to do is dissolve it from the WC. Evidently, nitric doesn't attack the WC. I would just put some in a bucket and try 50/50 nitric at room temp. Sounds like it might take several hours. You should end up with clean WC, which you can sell.

http://www.google.com/patents?id=7sEzAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_overview_r&cad=0#v=onepage&q&f=false

I once experimented with the dissolving of silver from steel aircraft bearings using full strength nitric acid. Each bearing had several oz of silver on it. For this particular type of steel, all went well as long as there wasn't more than 3-4% water in the nitric and the temperature was kept low. When the reaction raised the temp to much over 100F, the steel would start dissolving. Quite vigorously, I might add. We ended up buying a big cheap Chinese lathe and cut the silver off.

Another time, we had several tons of silver plated Kovar lead-frame material. The silver ran 7% - about $21/pound today. We used a large barrel plater to tumble the material in concentrated nitric (or very close to it - I can't remember the exact concentration). Talk about fumes! It didn't attack the Kovar, no matter how hot it got.

About 20 years ago, a guy that lived close to here was reclaiming the Ag and WC from used coal mining bits. He was getting at least 10-15 drums at a time from a coal mine in Arkansas. Unfortunately, he was using cyanide to do this in an enclosed area and it killed him. His son was then on a anti-cyanide crusade and I talked to him a few times. It was hard to tactfully convince him that his Father's ignorance was what killed him.


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## philddreamer (Oct 8, 2010)

Would it be worth the effort to try & recover the cadmium, or just recover the ag & the WC? How can I get rid of cadmium properly?


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## goldsilverpro (Oct 8, 2010)

Cadmium is very cheap nowadays because most manufacturers don't want to use it due to the hazards. It will stay in the solution when you cement out the silver. There may not be any Cd in that solder, but there probably is. You could probably selectively precipitate the Cd from the solution but I don't know exactly how without doing a search. You could do this yourself. Maybe one of our chemists could help you out. If I get some time, I'll look for a method. 

When dissolving the solder, I would remove the finished material and keep adding fresh material until the acid is saturated. Then, start over with fresh solution. That way, you won't waste a bunch of copper during the cementation. With 50/50 nitric, you shouldn't get any crystallization when saturated with Cu.


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## philddreamer (Oct 8, 2010)

Thank you brother!


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## philddreamer (Oct 9, 2010)

wiki says cadmium is soluble in HCI, sulphuric & nitric. So is copper; but silver wont be in HCI!  So I'll try incenarating 1 oz of the solder material, then digesting in HCI; filter sediment & rinse; digest in nitric. Hopefully I wont have the turqouise sediment this time, just silver, (for the most part) :roll:.

I tried earlier melting, the copper became very obviuos & so did the silver. A smoke that left a yellow film on the fire brick...

The result from the previous 1 oz test yielded 8g of silver from the solder material. 8g/1oz x 12ozT x several hundred lbs... :shock: 

Today Bill told me his brother gave him another 300lbs of silver plated carbide. That makes 800lbs, not all is solder material though. I hope to get some of the material on tue.


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## T3sl4 (Oct 9, 2010)

Incineration is a bad idea if cadmium is suspected. Cadmium is more volatile than zinc, and just as combustible. If you thought zinc fume fever was bad, just wait 'til your kidneys get a whiff of cadmium...

I've discovered WC grindings burn very hot in potassium chlorate. If you want total recovery (including tungsten and cobalt), this type of incineration might be a good start. I would guess, leach the ashes with NaOH, extracting sodium tungstate and leaving cobalt oxide (possibly Co3O4). These could be sold, or processed into salts, or reduced to yield metal, etc. Alternately, if you are interested in just the cobalt content, it can probably be dissolved electrolytically, leaving a pile of WC powder (which should be leached with acid, because there will probably be more cobalt stuck to it). Electrolysis is tempting, because cobalt is refined electrolytically; I don't know what leveler agents are necessary to get a good deposit though.

Tim


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## philddreamer (Oct 9, 2010)

Hi Tim!

Thank you for reminding me of the zinc & cadmium fumes. I've been a welder for over 36 years & having expirienced zinc fever early in my career, I've since used an approved respirator every time I work with these metals. Having taken this precaution already, question is then, is it still a bad idea to incinerate?

I want to get rid of the cadmium before I digest the rest of the silver solder strips in HCI, that way I should mainly deal with copper in solution & silver as sediment. (@ least in theory.) :roll: 
The WC material I'll run thru nitric to recover the silver, without digesting it. At this time, its too complicated for me to try & process the WC. I'll return it to the owner, & he'll then sell it. He just gave me all the silver I can recover from the material.  

Thanks for sharing your expirience!

Phil


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## goldsilverpro (Oct 9, 2010)

philddreamer said:


> Thank you for reminding me of the zinc & cadmium fumes. I've been a welder for over 36 years & having expirienced zinc fever early in my career, I've since used an approved respirator every time I work with these metals. Having taken this precaution already, question is then, is it still a bad idea to incinerate?
> 
> I want to get rid of the cadmium before I digest the rest of the silver solder strips in HCI, that way I should mainly deal with copper in solution & silver as sediment. (@ least in theory.) :roll:
> The WC material I'll run thru nitric to recover the silver, without digesting it. At this time, its too complicated for me to try & process the WC. I'll return it to the owner, & he'll then sell it. He just gave me all the silver I can recover from the material.
> ...



I'm confused and I may have misunderstood what you guys are saying. It sounds like something very simple has suddenly been made very complex.

Since the Ag content of these brazes runs about 50%, what makes you think you can leach out the copper with HCl? I see no way you can get rid of the Cd before digesting the alloy.

Dissolving the WC seems ridiculous to me.

Why not just simply dissolve the solder (whether the strips or the Ag on the WC) in nitric and cement out the Ag with Cu? That way, the WC is intact and you can sell it. The only problem I see would be if the solder contained tin, which some Ag solders do. If you dissolve a small piece in nitric and a slimy precipitate is produced, you have tin. The tin can be handled, but it complicates things a bit.


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## philddreamer (Oct 9, 2010)

Somewhere "down the line" I came under the assumption that HCl dissolves copper. My mistake, I'm sorry for the confusion.


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## goldsilverpro (Oct 9, 2010)

philddreamer said:


> Somewhere "down the line" I came under the assumption that HCl dissolves copper. My mistake, I'm sorry for the confusion.



It does dissolve copper, especially with some H2O2 added. However, in the case of this particular alloy, the high silver (50%) in the alloy would prevent penetration of the acid. Even with much less silver, silver chloride may (or, may not) form a heavy enough crust to prevent penetration.


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