# Purifying Silver Solder



## symbolensemble (Nov 17, 2020)

I have some silver solder that I'd like to purify. I don't need it nessesarily 99.99 percent pure, but something like 90-95% pure would be just as ideal. I've thought about using a Nitric acid solution, but from what I understand, this is costly, dangerous and produces large amounts of waste bi-product.

I've thought about different ways of doing this and so far the best I've come up with is to use a conical mold, which brings me to my question.

If I were to melt the silver solder (containing around 40% silver, 30% copper, 3% tin, and 27% zinc) in a kiln and poured the entirety of the liquefied combination of metals into a conical mold, would the metals naturally separate making it possible to purify the silver in the solder without having to use any corrosive chemicals?

I'm looking for a way to purify with just a melting kiln, if possible. Any help would be appreciated.


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## geedigity (Nov 18, 2020)

No. Melting will allow some stratification of the metals, but the separation of them just wouldn't get you the results you want. You could oxidize the melt by blowing O2 through the molten mixture, and some of the base metals will report to the slag. I have done this on relatively pure silver in the past and it worked okay for me. I know some members have used that method with a fair amount of success. 

Using nitric acid to dissolve the solder will present other problems, since there is tin in the mix. 

Take a look through the forum and search around. You will learn things you never thought were there to learn.


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## symbolensemble (Nov 18, 2020)

I'll look into that, thanks! When you say blow oxygen through the mixture, I'm not entirely sure how that would work. Do you by chance know of any links/videos/threads which go into this (or a similar) technique in detail?

This is what I was talking about... You don't think the silver, being the heaviest, would end up at the bottom? https://www.youtube.com/watch?v=VSPn2O9yu_A

I wonder if I kept the melting point only low enough to melt the silver but not the copper, etc... no idea what the end result would be, but it's an interesting thought!

Lastly, the silver solder also has a flux core, which I forgot to mention. Not sure if this would interfere with the melting process at all. I don't really see why it would.


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## kurtak (Nov 18, 2020)

symbolensemble said:


> If I were to melt the silver solder (containing around 40% silver, 30% copper, 3% tin, and 27% zinc) in a kiln and poured the entirety of the liquefied combination of metals into a conical mold, would the metals naturally separate making it possible to purify the silver in the solder without having to use any corrosive chemicals?



Per the underlined --- NO !!!

the solder (braze) is an alloy (of silver copper tin & zinc

An alloy is a combination of metals "well mixed" together in a melting process to make an "alloy" of the mixed metals

When making an alloy - depending on the different metals used to make the alloy - it will cause the melting point (temp) to be ether higher then the melt point of the individual metals - or lower then the melt point of the individual metals 

In other words - once the metals are "alloyed" - the alloy takes on a melt point "of its own" wherein ALL the metals in the alloy melt (all together) at the melting point of the "alloy"

Example; - copper has a HIGH melt point - zinc has a LOW melt point --- when you melt them together you make an alloy of brass --- the brass will now have a melt point that is lower then the copper - but also higher then the melt point of the zinc --- meaning the brass will now have its own melt point wherein both the copper & zinc melt at the same time --- rather then the zinc melting (first) at its lower temp thereby allowing the copper to separate because of its higher melt point 

In other words - what you have is an alloy - you can NOT simply separate the different metals based on the different melting points of the different metals --- & that is because the alloy has "its own" melt point of the alloy --- all the metals will melt at the melt point of the alloy --- which will be lower then the melt point of the copper & silver but higher then the melt point of the zinc & tin

Kurt


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## kurtak (Nov 18, 2020)

symbolensemble said:


> This is what I was talking about... You don't think the silver, being the heaviest, would end up at the bottom? https://www.youtube.com/watch?v=VSPn2O9yu_A



In that video they are NOT separating the different metals in the "dental alloys" --- ALL the metals are being melted "together"

The "flux" they used in the melt was used to separate the metal (ALL the metal) from the organics

the organics would be things like oils, epoxy fillers & even pieces of broken teeth

The organics go off in the flux/slag --- & ALL the metals go to the bottom of the cone mold (as an alloy) thereby separating the organics from the metals

Kurt


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## kurtak (Nov 18, 2020)

Now then - that all said - there are some "smelting" processes that can (at least to a point) separate the silver from the base metals

I just don't have time to explain them at this time

simply using borax &/or soda ash (as flux) will NOT do "anything" to help separate the metals

Kurt


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## snoman701 (Nov 18, 2020)

symbolensemble said:


> I'll look into that, thanks! When you say blow oxygen through the mixture, I'm not entirely sure how that would work. Do you by chance know of any links/videos/threads which go into this (or a similar) technique in detail?
> 
> This is what I was talking about... You don't think the silver, being the heaviest, would end up at the bottom? https://www.youtube.com/watch?v=VSPn2O9yu_A
> 
> ...



You will not get satisfactory separation through stratification.

You can get your silver to 95%+ through oxidation, then dissolving the oxides of copper/zinc in borax/carbonate. You will not find much discussion of this on the forum....at least not as a primary method of refining. 

Simply put, you have to melt it, then find a way for oxygen to make intimate contact with the molten metal, usually the surface of the metal, while stirring, and with flux present.


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## scrapman1077 (Nov 18, 2020)

Look at my trade thread 
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=58&t=14782


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## g_axelsson (Nov 18, 2020)

Search for "oxygen sparging", it will probably give a couple of hits. Not easy to do and you would need large amounts of solder to make it economically viable.

I recommend you either sell (or trade with scrapman1077 if you want silver in the end) or use acid to refine the silver.

It all depends on the end result you are looking for and the amount of material you have.

Göran


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## symbolensemble (Nov 18, 2020)

Thank you all for the replies! If I were to melt some of the solder down into bars and such for experimentation is there a risk of losing some of the silver content in that process, through evaporation, or something?


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## nickvc (Nov 19, 2020)

There is no pint in melting the solder if you are going to refine it as you will make it much harder to dissolve, my advice if you do not wish to chemically refine the silver is to trade it with scrap an, he has very good feedback from many members.


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## galenrog (Nov 19, 2020)

This type of material is NOT appropriate for a novice to learn with. Far too many things to learn, and go wrong. Were it me, I would consider a trade with scrapman1077. Once you have some experience with silver recovery, if you still have this, then the issue can be revisited. Until then, sell, trade, or put it away.

Time for more coffee.


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## etack (Nov 19, 2020)

If you have a lot 10+ pounds cast it and sell it.

I think trading is too high for any silver. 50% is too much In my onion.

You could sell it on to a refiner for 80+ of spot all day long if you have enough.

Eric


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## symbolensemble (Nov 19, 2020)

etack said:


> If you have a lot 10+ pounds cast it and sell it.
> 
> I think trading is too high for any silver. 50% is too much In my onion.
> 
> ...




When you say cast it do you mean melt it down into bars? Somebody said earlier in the above post that this would make it "much more difficult to dissolve" ... not sure if they meant by that... as in if some future buyer I might sell to wants to melt with Nitric acid, or what?... but yeah, I have more than 10 pounds.


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## g_axelsson (Nov 20, 2020)

First of all, you don't melt things with acid, you dissolve it.

If there is a flux core you want to remelt the solder to remove it before adding it to nitric acid. If you are preparing it for dissolving it in acid you want to make "shots or cornflakes" by pouring it in cold water. The rate of a reaction is proportional to the surface area, so a solid bar dissolves slower than small grains.

If you sell it or trade it it's probably easier to handle if it is in bar form. An alternative would be to sell to someone that does the melting and sampling while you are watching it.
One way to test a bar is to drill a number of holes on top and bottom and then analyze the drilling. A buyer receiving a bar with drill holes knows that there are a sample of it somewhere and it keeps them honest. It removes some of the temptation of reporting a lower grade when buying a bar. You can read a lot of it on the forum.

Göran


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