Need help with refining silver and platinum alloy

[edged]

I have several kg. of silver bars that I'm haveing trouble with. I had it tested with an XRF gun and they contain 80% silver, 3.8% platinum, 11% zinc and the remainder Nickel. My first choice would be to sell them but was told by a couple of refining companys that they would only pay for the silver. I did the math and the platinum is worth twice as much as the silver so I can't just give it away.
I've done a lot of gold refining with inquartation/nitric and AR methods but I'm having trouble with this.

I tried to granulate it but It won't melt. I've been torch melting and casting gold and platinum for years and I've never had anything I couldn't melt. It smokes like hell at high temps (I'm guessing Zinc vaporizing, toxic I know) A few beads of meltal will drain out of it but I'm left with a heavy black spongy bar that would not melt even above platinum melting temps.

So next I tried rolling it thin to increase the surface before digesting but it quickly got brittle and broke after a few passes. Annealing did not help.
I cut it with a saw and tried to dissole thumb size pieces of it in boiling 93% sulfuric acid with a little distilled water) but it's very very slow to dissolve. I also tried to digest in boiling nitric acid/distilled water (which I know would also dissolve some platinum) but large chunks dissolve way too slowly.

Any tips on how to melt this stuff to granulate it? any fluxes I should try?

I have rectifiers (20 and 50amp), I 'm thinking about making a 1 gal. cell. and using the bars as is as the anodes.
I know 80% silver is low for a cell but since there is no copper to contaminate the electrolyte do you think it's worth trying? Or is the Zinc and nickel just as bad?
I don't need a perfect seperation, I would be happy to just get the silver out and be left with the remaing metals in a powder form that I could deal with later.

Thanks in advance for any tips of suggestions. I love this Forum and have learned a lot from you guys.

 

[Harold_V]

Something isn't making sense. Have you checked the bars with a magnet?

What color is the solution when you attempt dissolution with dilute nitric?

Parting with a cell probably isn't a good idea, as it rarely works well when you don't start with relatively pure metal. The zinc and nickel would quickly foul the electrolyte, and I'm not all that convinced you have 80% silver, anyway. If you did have, the small amount of platinum that is present wouldn't be an issue, as it, too, would readily dissolve in the presence of silver. Zinc and nickel both dissolve in nitric, so they shouldn't be a problem, either. My thoughts are you don't really have all that much silver (if any), which is why I wondered if the material might be magnetic. What you described sounds a lot like trying to melt stainless. Do keep in mind, the 300 series of stainless is not magnetic, so that may not be a reliable test. I was hoping the material might be magnetic, which would go a long ways towards explaining what you have.

Can you post a good picture of the material after it has been saw cut? I'd be interested in seeing how the cut looks.


Harold

 

[butcher]

Interested also in how easily the hack saw will cut it, non magnetic stainless steel would be hard to cut, silver, zinc, and nickel would cut easily.

 

[nickvc]

The brittleness of this material is the key to the problems your having, I suspect there is another element in the mix as those that you mentioned shouldn't cause the brittleness. I'd be tempted to have another test done to determine what exactly is in there, if you know the source of the material it should give us some clues as to what it could possibly be. Another thought try the material in hot hydrochloric and see if you get any dissolution it might again give some idea of what the troublesome element is.
Melting unknown metals into a bar yet again causes major problems that could well have been avoided.

 

[NobleMetalWorks]

Have you attempted to melt it with another metal that has a lower melt temp? I'm not sure adding another metal will help or compound your problem, it could resolve it.

Also, XRF only will test to a certain depth. If the bars include other metals that are harder, and heavier, and the melt was not originally homogenous, the heavier metal would sink to the bottom and your bar would be stratified.

Have you tried drilling the bar, top and bottom, both ends and center so you have 6 samples? Also, if you are able to hack saw it, have you had the center scanned via XRF? If the center is Tungsten for

I suspect the same as others that posted, that there are other metals involved that your XRF scan did not pick up. Also, many XRF scanners are only set to test specific metals, and would not test for whatever metal is causing you troubles. Depending on the XRF analyzer, it may only give you the percentages on the metals it's able to scan, and not giving you any percentages for unknown metals.

One metal that is commonly used in electronics, and could be causing the exact problems you are experiencing is Tungsten. It can be cut with a hack saw, yet brittle at the same time. It has a very high melt temp, and has a density very close to that of gold. It has also been used as filler for bullion bars.

http://en.wikipedia.org/wiki/Tungsten

Scott

 

[edged]

It's definitely not stainless, I could tell stainless from 5 feet away. but you guy are right that it does contain a few other metal which I didn't mention because the percentages were less then 2 percent each and I didn't write them down. I'll test it again tomorow on my friends Niton XRF (It's fairly accurite) and post the other metals. Maybe a small amount of tungsten or something could keep it from melting? I didn't think of that.
I also tested a cross section and inside of drill holes on a second XRF (also Niton) And the results were the similar.
Its non magnetic, filings won't stick to even a strong magnet and it cuts like butter, just like sterling.

The nitic (50/50) soloution remained clear after 3 hours of gentle boiling with a few 2mm. thick slices that did not dissolve at all, maybe I should try full strength Nitric?. I had better luck with boiling sulfuric which after maybe 6 hours dissolved about 30% of a 1"X3/4"X3/4" cube. I'm sure this would work better if I sliced them up thin but that would take forever.

Tonight I'll try to dissolve some filing in HCL like suggested by nickvc just to see if it will. At least the zinc might in the filings but again the problem is that It doesn't have much surface area in bar form.
I forgot to mention that these bars are more like rods then bars and measure about 3/4" X 1/2" by maybe 12" long each. I'm guessing they are some kind of industrial contacts because they are precision ground and have uniform weight.
It looks porous or spongy where it fractured from rolling but looks just like sterling when it's cut.
The second picture is the fractured end at 30X.

Thanks for the suggestions.

 

[edged]

Did a little research on tungsten silver alloys , and It seems to be pretty common (sintering tungsten powder and infiltrating the sintered material with silver) and would explain everything if it was in a high enough percentage. and I think this might be what I have. I checked Nitons website and although they mention tungsten a couple of times they are not very clear if the XL2 will recognize it. I don't know much about the XRF technology but I wonder what happens to the accuracy of the recognized element percentages if there is a large percentage of an unrecognized metal?

 

[NobleMetalWorks]

Did a little research on tungsten silver alloys , and It seems to be pretty common (sintering tungsten powder and infiltrating the sintered material with silver) and would explain everything if it was in a high enough percentage. and I think this might be what I have. I checked Nitons website and although they mention tungsten a couple of times they are not very clear if the XL2 will recognize it. I don't know much about the XRF technology but I wonder what happens to the accuracy of the recognized element percentages if there is a large percentage of an unrecognized metal?

You can purchase different packages for the Niton XRF analyzers. The precious metal package does not include Tungsten. Best thing to do is to ask the person who owns the XRF analyzer if the package they have on their Niton includes Tungsten, I would wager it does not. Most of the time the XRF analyzers are purchased for specific applications, leaving out many of the other types of metals.

So far as percentages are concerned, I am not sure if the Niton will report unknowns unless it's programed to do so. The percentages could be just in what it's able to scan, the XL2 is the older model, again you might want to ask the person using the scanner about this. And if you had to pay for the scan, I would mention this and ask if next time you could get a discount or free scan if you were charged. Really, if their unit is not able to scan for Tungsten, it seems like the fair thing for them to do, considering how much trouble the unknown metal has caused you.

It honestly seems like Tungsten to me, and if powder was used in the casting, it might explain the spongy look as well.

Scott