Dissolve tin metal

[joninrockies]

I have a large quantity of WW2 era dental filling pellets, 75% Ag, 25% Sn, in the form of pellets of compressed powdered metals (not an alloy). I see that I can buy 15% HCL at Home Depot. How do I proceed to dissolve the tin away? Do I need to crush the pellets first? I'm not a chemist, and wasn't paying too much attention in freshman chemistry. Any advise would be appreciated.

[Externet]

Heating the pellets should melt the tin by 240 degrees C, leaving the silver. Perhaps you can manage a fun way to do it in a microwave oven. Search terms as smelter and microwave oven, you should get many leads.

[pippo]

dissolving tin as pellets/teardrop/etc is not easy , even with HCl. You have to boil it, and boil it, forever. Now, if it was ground finer, even better. Also, HD HCl should be closer to 20-25%, not 15%. Concentrated is 37% (about 12 molar), hardware store /masons muriatic is about 9 Molar. Way more than 15%.

 

I dissolve tin with HCl and a tad of Nitric. hard to come by, I know..........It really does the trick.

[joninrockies]

Response to externet: won't this result in every grain of silver being coated in tin "solder"?

[Suxamethonium]

I would suggest dissolving everything in nitric acid (should be able to get away with a hot solution of concentrated HCl and sodium/potassium nitrate). Once dissolved then add HCl (not needed if used HCl/Nitrate) followed by diluting and collecting the silver chloride precipitate which can then be heated to obtain the silver (note: produces chlorine gas). Alternatively could try dissolving the silver chloride precipitate in ammonia and plating it onto a preferred surface using electro-chemistry. The tin (IV) chloride (I'm kinda guessing IV because of nitrate oxidation?) should be soluble enough to stay dissolved but can be precipitated later. Reaction with base and heating/smelting should get you the tin back.

Edited June 20, 2012 by Suxamethonium

[joninrockies]

These have been some great suggestions, but let me add some furthur information. I'm an old man, a retired nuclear physicist, who is trying to suppplement his social security in order to survive by selling stuff in his garage. The quantity of material here is fairly large, about 30 pounds. At 75% and $29 per Ag ounce, it's max value is about $10k. I figure as dental fillings, it isn't worth much, but as purified (sterling?) it might be worth half the $10k. I had hoped I'd be able to remove the tin fairly easily, and then melt the silver into an ingot, but from the comments here, maybe it isn't so easy. I'm very limited in equipment, an oxy-acetylene welding torch, crucibles, simple chemicals. To me, the unique thing is that it is in the form of co-mingled powdered metals, not an alloy. A suggestion: Dentists stopped using silver for fillings several years ago, so there must be litterally tons of similar dental filling pellets to be had by an enterprising young chemist for essentially nothing. You may wonder, why does a physicist have old dental fillings? Silver absorbs thermal neutrons like a sponge, becoming gamma radioactive, and tin doesn't.

[John Cuthber]

Response to externet: won't this result in every grain of silver being coated in tin "solder"?

Close, actually it may be a bit worse than that. there's a fair chance that a lot of the silver will dissolve in the tin and form a single homogeneous blob.

 

Joninrocies,

how cold is your garage?

I't not a rhetorical question.

If it's cold then there's some chance that the tin will have converted to the other allotrope. That will make the stuff brittle and so it would be easy to powder.

In any event, if it's really a mixture of the powdered metals, rather than an alloy then treating it with HCl will remove the tin and leave the silver behind.

But I doubt that you will get it pure enough to sell at the market price of silver (or even half that).

Powdered metals will dissolve a whole lot faster than pellets of course.

 

Another (odd sounding) approach would be to add several times the bulk of zinc and melt the lot together.

Then take the zinc/silver/tin alloy and dissolve that.

Zinc dissolves readily anyway.

The clever bit is that the silver and tin are left behind as very fine powders. The tin will dissolve and the silver will be left behind.

 

Another simpler approach would be to heat the mixture in air and burn the tin off.

 

However there's no way I can be sure if any of these would work. I'm afraid you will have to experiment.

Let us know how you get on.

 

Suxamethonium,

Once the surface of the metal is covered by silver chloride the dissolution will practically cease. The solubility in conc HCL is a bit marginal.

Heating silver chloride does not make it decompose (at least not up to stupid temperatures, it boils over 1500C) though heating with soda does.

solutions of silver salts in ammonia are annoyingly explosive.

Also the tin will form SnO2 with HNO3 and that too will stop the reaction

Edited June 20, 2012 by John Cuthber

[pippo]

I would suggest dissolving everything in nitric acid (should be able to get away with a hot solution of concentrated HCl and sodium/potassium nitrate). Once dissolved then add HCl (not needed if used HCl/Nitrate) followed by diluting and collecting the silver chloride precipitate which can then be heated to obtain the silver (note: produces chlorine gas). Alternatively could try dissolving the silver chloride precipitate in ammonia and plating it onto a preferred surface using electro-chemistry. The tin (IV) chloride (I'm kinda guessing IV because of nitrate oxidation?) should be soluble enough to stay dissolved but can be precipitated later. Reaction with base and heating/smelting should get you the tin back.

 

Tin will not dissolve in nitric.Unless I read your 1st sentence the wrong way......Just a tip. HCl is the way. With nitric trace added......