# Large quantity of silver solder on carbide



## snoman701 (Oct 9, 2016)

I have a large quantity of silver solder that is attached to tungsten carbide inserts. 

Composition of the silver solder should be at least 50% silver, with base metals. This is all modern, and cadmium has went out of favor due to inherent dangers in the manufacturing process of this tooling. 

From what I've read, it appears that cementing of silver nitrate via copper electrode is the most economical process, even with AP and reverse plating options that exist. The AP or reverse plating could then be used to further refine the silver if cadmium was present in the cemented silver.

I just want to make sure that my searches and research is correct.


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## FrugalRefiner (Oct 9, 2016)

Welcome to the forum. 

You've got more research to do. AP is not used with silver. It is a chloride based leach, and is not useful with silver. Reverse plating, or stripping, is typically used to remove gold plating from objects, though it could be used on silver plating, but that's not what you have.

Let us know what a "large quantity" is (ounces, pounds, tons) and exactly what state it is in right now and we may be able to help. Pictures of your material would probably be helpful.

Dave


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## snoman701 (Oct 9, 2016)

Sorry, too much reading for one night, everything blurred together. A couple of people had built cells for further purifying silver in a silver nitrate electrolyte. Given that the tungsten carbide would be largely non-reactive, I wasn't sure if it might actually be a reasonable process...but the unknowns in solder could very well pose a problem and bugger up the electrolyte solution. 

Michigan

I'll say I'm in the pounds category for now. But I have been disposing of the silver solder with the carbide scrap. It wasn't until recently that I realized that the silver is of appreciable quantity.

I've also got a bucket full of silver contacts from motor starters...not little ones, these are the ones that are at least dime sized, and usually 3/4" square, 1/16-1/8" thick and soldered on copper bus. I fully expect these to have cadmium.


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## FrugalRefiner (Oct 9, 2016)

That "blurred together" period is typical of the learning curve. We've all gone through it. Keep studying and it all starts to come into focus.

Silver cells are used for the final purification of silver. There are usually two steps in dealing with precious metals; recovery and refining. Recovery processes allow you to separate the precious metals from _most_ of the base metals. Refining processes take the recovered metals to a high state of purity.

Silver contacts come in many varieties. Some can be separated from the copper bus by simply heating with a torch till the solder melts, but if there is cadmium involved they should NOT be heated this way. There is much to read here. Start with the Safety section. Read everything in the Silver section. Be sure you know how to properly deal with your waste before you start any of the processes here.

Dave


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## goldsilverpro (Oct 9, 2016)

As I understand it, WC parts are made using powder metallurgy techniques. Either molten cobalt or nickel is used as a binder to glue the WC particles together. Ideally, it would be great to use nitric acid to dissolve the silver and then cement it with copper. However, although the WC is not attacked by nitric alone (it requires hot HF/HNO3 to dissolve the WC), the Co or Ni binder is attacked. I assume the nitric would leach out at least some of the Co or Ni, resulting in some of the WC being in a heavy powder form. Very small scale experimentation would be required to test this. I would probably start experimenting with a weak HNO3 (say, 25% by volume) at room temp and go from there. I would think the less Co or Ni dissolved, the better this would work. The only problems that I can see with the WC powder is that it might interfere with the filtering or it might pack tight around the parts and stifle the acid exchange. In production, a bucket with holes in it inside of a larger bucket might work well. That would provide a good solution exchange when you occasionally move it up and down. The WC has a density of 15.6 and should settle rapidly. 

Cyanide would dissolve the silver braze without affecting the solid WC. About 20 years ago, near my hometown in rural Missouri, a guy was using cyanide to recover silver from carbide coal mining bits. He had many drums of these and got them somewhere in Arkansas. I don't know the exact process he used but he ended up dying of cyanide poisoning. I can think of several ways, both leaching and electrolytic, to use the cyanide safely.

Other than nitric OR cyanide, I can't think of other good methods.


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## snoman701 (Oct 9, 2016)

I wouldn't be comfortable using cyanide without a full fledged lab & isolated shop just for refining. 

But thank you!


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## nickvc (Oct 10, 2016)

A thought, would it be possible to melt the silver from the carbide, Im guessing the melting point of the carbide would be fairly high, would using zinc be possible once the silver started to melt as the collector metal as it would be possible to dissolve the zinc using HCl, or perhaps using I believe the Parkes process where the zinc is skimmed from the top of the values?


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## goldsilverpro (Oct 10, 2016)

I would first try the nitric on a small sample. If it worked, that might be the simplest way. Hopefully, the dissolved silver wouldn't cement onto the Co or Ni. If it did, though, it could probably be removed by tumbling.

Melting off the Ag solder might work but I would doubt if you could get it all. Every time I've tried something similar, silver BB's were left attached to the parts. Worth a try, though.


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## rickbb (Oct 10, 2016)

The melting point of tungsten carbide is over 6,000F and the melting point of silver being just over 1,700F the melt method may work. 

*Providing you are 100% certain is has no cadmium in it.*

But you would still have to separate out the silver from the base metals of copper, zinc and maybe tin as well.


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## Barren Realms 007 (Oct 10, 2016)

Seems to me I remember a member running them in nitric without any issues about 3-4 years ago.


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## anachronism (Oct 10, 2016)

Given that dropping molten gold on Stainless steel can cause some alloying even given the difference in melting temperature, couldn't something similar happen here when trying to melt the silver or is it two completely different things? 

I'm not "up" on this side of it you see.


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## Palladium (Oct 10, 2016)

Chris is right. Cold (80 F) nitric 67% with lotsss of circulation and time. I've done this before for a client who recycles drilling bits for coal mining operations. The client wasn't after the silver as much as cleaning up the WC. The silver was a added plus. The client was selling the WC and they were docking him per lbs because the silver was a contaminate. The losses from the sale was costing him more than the silver was worth plus he was losing the silver.


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## snoman701 (Oct 10, 2016)

The price on carbide has come down considerably....but yes, that was my intention is to mostly clean it up.

However, on the parts that motivated this, they seem to have applied the solder with a mop. Pretty uncommon. But, if I can get a process set up that doesn't cost much to run, I will have plenty of material.

It will ultimately depend on how cheap I can find Nitric Acid. Bottle quantity prices won't work...but if I can find 5 or 10 gallon kegs at reasonable gallon prices, I should be ok.


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## Palladium (Oct 10, 2016)

The chemical side was the easy part. Handling something that dense on a large volume is the trick and required me setting up a crane on an overhead rail system for loading and unloading the processing vessel. The processing vessel was a 30 gallon 304 stainless drum that sit inside a 55 gallon stainless drum with a removable lid and seal that had taps for the scrubber to attach to. The 30 gallon drum had a hole in the very center. The 55 gallon drum had a plate welded in the bottom where the old bottom was cut out and replaced with a piece of 1/4 in stainless plate for support. In the center of the plate was a spike made out of stainless 1/2 pipe with holes drilled up and down the length of the shaft. The top of the spike or pipe was welded shut and sharpened to look like a pencil. The 30 gallon drum was placed over the 55 gallon drum and lowered in place causing the 30 gallon drum to be impaled and set into place at which time the lid was placed on the 55 gallon drum and sealed for processing. This causes the solution to enter in the middle of the materials and work its way from the inside of the materials to the outside giving good circulation and surface contact to remove the silver considering that the nitric needs to stay cold as not to attack the WC and gives maximum surface contact. Trying to just put it in a vessel and getting it to work will not work without maximum circulation because your not able to use heat. In this system you don't measure the amount of nitric required you just run it until the solution is saturated by testing and drain and repeat.


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## Palladium (Oct 10, 2016)

Cost per pound of materials processed is very low compared to other materials that we process in refining. Setup cost is your main investment here. After that it's a great way to generate unrealized profit potential considering what you are giving away. My client was an industry leader in this field and just couldn't believe the money he was giving away once i showed him how relativity easy it was after the initial investment and setup. To my knowledge he and his family have never sold an oz of the silver recovered and his bottom line increased thanks to the extra profit generated from the sale of the clean WC.


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## goldsilverpro (Oct 10, 2016)

anachronism said:


> Given that dropping molten gold on Stainless steel can cause some alloying even given the difference in melting temperature, couldn't something similar happen here when trying to melt the silver or is it two completely different things?
> 
> I'm not "up" on this side of it you see.


Silver doesn't alloy with steel like gold does.


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## goldsilverpro (Oct 10, 2016)

Ralph,

Did you use full strength nitric at room temp or did you dilute it?


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## Palladium (Oct 10, 2016)

Full strength. The system required at maximum a 24 hour turn around on the materials being processed and with dilute cold nitric it wasn't happening quick enough even with the increased circulation. Plus the solder was BAG-7 (56% ag - and i foget the tin % now), but it was causing problem with it precipitating out of the solution because of dilution and temperature. One of the added pluses was that when the client had a shipment of rejects that he could sell back to his client the non aggressive stripping made it possible to reuse the parts. It also made it possible for the client who sent the rejects to change the brazing alloy to a different type because it made the WC clean and more wettable or amendable to the solder flow which was a big reason for the rejects in the first place. Win Win for everybody! Sort of like you perfected when you stripped the cpu packages for reuse.


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## snoman701 (Oct 10, 2016)

I find that there's a lot of waste out there, but it takes someone who thinks outside of the box to figure out how to realize the profit. 

I've got more projects than time, and just do what's fun.


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