Sciencemadness Discussion Board

silver from silver-solder ?

chief - 14-7-2008 at 06:26

I have at least 200 g of solder, in an old copper-boiler, and witnessed myself, that it was still solid (not melted) at ~ 600 [Celsius].

Is it silver-solder, and how much may the content be ? Before I try to flex it all off and dissolve it in HNO3 ....

Mr. Wizard - 14-7-2008 at 07:33

It may be only a few percent silver. The copper in the boiler may be worth more than the silver you could recover from the soldered seams. Perhaps if you posted a picture, someone might give better advice. 200 grams may only contain 1 Troy Oz (about 31 grams) of liver, and that is a very optimistic estimate. If it was a boiler for potable water or food it may be tin , not silver solder, but your mention of the high temperature rules that out. Silver solder used on air conditioning copper pipe may actually look like copper after it is brazed on. The alloy contains a lot of Copper and Phosphorus with anywhere from 5% to 50% silver.

Try dissolving a very small weighed piece, in Nitric Acid, and after it is all dissolved, neutralize the remaining acid with sodium carbonate, lye or some other available base, low in Chlorides. Don't use ammonia. Then put in a clean piece of copper wire and let the silver nitrate react with it. The silver should fall off the wire as it is formed, leaving copper nitrate in it's place. After washing and drying you can either weigh the dust, or fuse it to a bead on a piece of charcoal with a blowpipe.. Once you get the silver you can figure the percentage and decide if it's worth doing the whole thing.

Silver is magnificent when molten, it is so shiny you will never forget the look.

I have a 300 gram chunk from melted electrical relay contacts. It has a lot of copper and other impurities. I plan to do an electrolytic separation but I haven't worked out the exact plan yet. Almost every electrical switch of quality has a small pad of silver in it, with the high current devices such as relays having 6-10 mm 'coins' on each side. These are usually welded or riveted to the relay armatures.

chief - 14-7-2008 at 09:26

One piece in HNO3 (15-20 %, goes slowly) : looks like yellowish-silvery (paler yellow than brass)
one piece melted : solidification at 950 +/- 10 [Celsius]

Guess ?

[Edited on 14-7-2008 by chief]

12AX7 - 14-7-2008 at 09:36

First, a lesson in subtle metallurgical terminology.

Soft solder is any filler which melts at a temperatuer below 800°F. Above that temperature, it is usually referred to as braze. Examples are tin-lead solder, which melts around 361°F, and brass brazing filler, which melts around 1600°F.

Some soft solders replace lead with silver. Disadvantages include a higher melting point and a tendancy to form tin whiskers (primarily a hazard to electronic equipment). Advantages include higher strength.

Silver alloyed with copper gives a mixture melting as low as 1435°F, commonly referred to as "silver solder" (even though it is clearly a braze). This is different from the soft solder, which is called silver-bearing solder to differentiate it.

So, if you have 200g of silver solder (braze) in your copper boiler, you're probably not going to get it out by torching it. Not for the higher melting point, which is not at all insurmountable, but because it's very sticky stuff. Your best bet is cutting out the joints and seperating the large amount of copper.

Tim

chief - 14-7-2008 at 09:51

Yes, its sticky ! Besides, my temp. was in [Celsius], not Fahrenheit, but you probably noticed it.

Also, I observe, that the solder seems to dissolve more readily than the copper. Wasn't copper halfway hard to dissolve in dilute HNO3 ? But harder than a silver-alloy ?
Maybe galvanic resons, but then silver should be more noble than the copper ...

Mr. Wizard - 14-7-2008 at 11:08

I don't know what conclusion to draw from your observations about the color and the speed of the dissolving. It sounds normal. The temperature you give for the small piece of solder is below the temperature of pure Cu and below the temperature of pure Ag, which makes sense if it's a silver 'solder'. You will have some real information to work with when you get it all in solution and then precipitate out the Ag dust, wash it, and then fuse it to a button on a piece of charcoal. Look for the 'blick' or shiny surface of the silver when you fuse the dust. You may have to burn the filter paper you use to separate the dust out, so as to get all the silver. I have used a large piece of wood and burned a shallow pit into it with a torch, instead of a chunk of charcoal, and except for the extra smoke and flames it works OK.

crazyboy - 14-7-2008 at 11:28

I'm pretty sure silver solder is 95% tin and 5% silver. Test by dissolving the solder in HCl with heat wet a cotton swab and add a drop of auric chloride followed by the HCl/solder soln. if it turns black/purple its tin.

ShadowWarrior4444 - 14-7-2008 at 17:39

[Edited on 7-14-2008 by ShadowWarrior4444]

chief - 14-7-2008 at 23:52

It dissolved overnight; now its a blue solution, but with some >> yellow dust << at the ground !
May that be gold ?
I used pure HNO3, and can't imagine anything else ...
The volume of the liquid is about 200 ccm, and only little material was dissolved, maybe 1-1.5 ccm.

Or can it be any oxide (PbOx) ?
Maybe someone has hidden some gold-reserve that way ?

12AX7 - 15-7-2008 at 00:00

I wouldn't expect to see gold there.

Tim

chief - 15-7-2008 at 00:16

It was a jewish boiler, from maybe the 1920s or 1930s, in Germany, the boiler was owned by the house-owner !
What else can it be, yellow dust ?
The boiler is from within an old industrial baking-furnace, at the top of the construction, surrounded by several tons of sand, dug well within it. So a repair would have been a lot of work, and maybe the gold increases the reliability, in the always-hot environment ?

But first I'm gonna find out, if it's really gold ...

[Edited on 15-7-2008 by chief]

[Edited on 15-7-2008 by chief]

ShadowWarrior4444 - 15-7-2008 at 01:07

Quote:
Originally posted by chief
It was a jewish boiler, from maybe the 1920s or 1930s, in Germany, the boiler was owned by the house-owner !
What else can it be ?

[Edited on 15-7-2008 by chief]


The tears of Brahma. (Not related to the convenient closet installation for dealing with overly 'emo' children.)

Adding a bit of HCl should discern quite quickly whether it is gold or not. Utilizing Tin Chloride would help, too.

P.S. Best to decant and filter before aqua regia/tin chloride testing on the powder.

chief - 15-7-2008 at 01:49

Yes, but with the HCl the silver is gonna ppt. as chloride, so it couldn't be seen, if the gold-dust dissolved.

chief - 15-7-2008 at 02:07

Besides: That jew survived the war, nothing bad happened to him; he then sold the house to an ancient of mine, so it would be good gold.

chief - 19-7-2008 at 10:35

What can it be ? The yellow dust, now separated, in some rest oft solution,
==> sinks quickly to the ground, except the finer colloid fraction
==> but with the mixture of {1 part HNO3 (53 %); 2.5-3 parts HCl (34 %)} it does not clearly dissolve,
although at the beginning (when inserting the droplet to be checked) it _seems_ to give a little reaction, but with _no_ real color change.
==> heating the reaction to boiling still does not give any red color (which I, from memory, would expect)

So: It was in the solder, it was among the remains after dissolving the solder (with the copper it was attached to) in HNO3; there was no uncleanniness, except from the surface-CuOx, before the dissolving.

Since it was within the metol, it got to be either metallic, or an metal-oxide, which formed during the HNO3-dissolution . Can it be some PbOx ? (Pb alone gives nitrate usually, but who knows the local galvanic reactions when the solder/copper dissolves in strong HNO3 ...)

Or is it just gold, and my HCl/HNO3 was too weak ? (both are clean chemicals, from the industrial provider, with the concentrations from above,and proven to work)

And I forgot: When applying the HNO3/HCl and boiling/heating the solution turns a little brownish, not anymore clean yellow, but this may be due to the NO2, as I speculate, for it's about the same color ...

[Edited on 19-7-2008 by chief]

chief - 19-7-2008 at 10:40

Maybe the AgNO3, which probably is created from the supposed-to-be-in-solution-silver (did wash only 2x with dest. H2O) masks the dissolution of the Au by AgNO3 + HCl ==> AgCl + HNO3 ?
How then to find if gold is present without a 1000 washings ?

chief - 19-7-2008 at 10:48

After posting the above I found, that its now (20 min after reaction) a clear, yellow solution.
The conc. is quite low: 4 ccm of the acid, 1 or 2 droplets of the colloid-containing rest-solution.

Which tests could I do ?

Fantasma4500 - 19-8-2023 at 01:49

just wanted to share my success with seperating Ag15 (Cu85) brazing wire

the rods are put in a pouch and lowered into a solution of NaCl and a bit of HCl, the HCl prevents Cu(OH)2 formation

then a current is passed through, on the bottom of this container you have an electrical wire hooked to a copper plate or similar, steel sponge would probably even work
the copper plates through the HCl/NaCl solution and precipitates as copper sponge, only the copper is dissolved
meanwhile Ag / AgCl will be found in the pouch, modification im gonna try is to put the rods into a plastic bottle with holes in the side, the silver will stay in the bottle, while the copper leaves through the solution, through holes, and becomes copper sponge, as the Ag/AgCl may fall out of the pouch and into the copper sponge, and the dissolving rods also become sharp and penetrate through the pouch

AgCl should react with NaOH to form Ag2O or silver hydroxide, upon heating this would become silver metal, 300- 600*C?

unionised - 19-8-2023 at 01:57

You can certainly convert AgCl to Ag by heating it with Na2CO3 until it all melts.
The electrolytic cell idea looks plausible.

Cathoderay - 19-8-2023 at 16:27

Quote: Originally posted by Fantasma4500  
just wanted to share my success with seperating Ag15 (Cu85) brazing wire

the rods are put in a pouch and lowered into a solution of NaCl and a bit of HCl, the HCl prevents Cu(OH)2 formation

then a current is passed through, on the bottom of this container you have an electrical wire hooked to a copper plate or similar, steel sponge would probably even work
the copper plates through the HCl/NaCl solution and precipitates as copper sponge, only the copper is dissolved
meanwhile Ag / AgCl will be found in the pouch, modification im gonna try is to put the rods into a plastic bottle with holes in the side, the silver will stay in the bottle, while the copper leaves through the solution, through holes, and becomes copper sponge, as the Ag/AgCl may fall out of the pouch and into the copper sponge, and the dissolving rods also become sharp and penetrate through the pouch

AgCl should react with NaOH to form Ag2O or silver hydroxide, upon heating this would become silver metal, 300- 600*C?

What you describe is essentially a "copper refining cell". You can look that up. You really don't need to make it so complicated. Use a sheet of copper hanging in the solution for the other electrode (cathode), the silver will collect on the bottom of the single container if the copper sheet does not touch the bottom. The solution could be CuSO4 with some sulfuric acid. Some processes use a stainless steel sheet instead of copper, the accumulated (plated) copper can be scraped off later. You will have to adjust the voltage and current for best operation. It is basically a copper plating cell. If you are real lucky you might get a little gold and platinum along with the silver.
I think you may have to reduce silver oxide to the metallic silver at some point.

Fantasma4500 - 4-9-2023 at 06:13

yes it works, im assuming AgCl with a oxytorch will simply turn into Ag- assuming theres actually any AgCl there, cranked out about 120 grammes so far of silver, might be able to pull out 500 grammes in total, very cool.
made the lid by just running duct tape over a newspaper and drilling a hole in it, then inserting a copper electrode through this which touches the top of the silver alloy rods, the water doesnt go all the way up to the initiating electrode, copper foil is a poor choice i found out since the hydrogen will lift it up and it will rapidly bridge over to the Ag collection bottle

no need to add a copper salt as the electrolyte will simply drag out more and more copper as the process goes on, basically directly plating it, i tried using lead "foil" but that corroded into PbCl2 for some reason turning the solution milky white

i guess if AgCl wont play well with the torch ill have to add in some Na2CO3

as a very cool bonus the copper sponge works very well for reducing nitrate into nitrite at about 400*C