Per the bold print (above quote) somewhat true but not entirely true
As I said yesterday (per bold print in below quote)
Over the 10 years that I did refining for a living I processed MANY kilos of W/Ag contact points - like the ones pictured in the OP of this thread (second picture = pic to the right)
https://goldrefiningforum.com/threa...hese-are-silver-cadmium-oxide-contacts.32311/
Those points come out of LARGE industrial "hand thrown" circuit brakers (like circuit brakers in your house electrical service panel - just much larger in industrial applications)
ALL "hand thrown" circuit brakers will have the W/Ag type contact points in them - whether household or industrial the only difference being the size of the points
Having processed MANY kilos of these contact points I can tell you it is no "easy" process to recover the silver from them
It is not as simple as simply putting them in a beaker with 50/50 nitric/D-water & applying "a little" bit of heat as you would with say sterling silver
Because of the VERY HIGH melt point of W (tungsten) Ag & W cannot simply be melted into an alloy - so they make them by sintering the W/Ag - which is a process of mixing actual W metal powder & actual Ag metal powder together & then compressing that mixed powder under VERY HIGH pressure & heat which results in a "matrix" of very fine particles of W metal powder - VERY densely compacted with the very fine particles of Ag metal powder
So - because the W & Ag metal particles are so densely compacted together - simply putting the sintered W/Ag in a beaker with 50/50 nitric/D-water along with a "bit" of heat will not separate "all" the Ag from the W --- it will only dissolve the Ag at the very surface of the W/Ag matrix & that is because your nitric/D-water solution cannot penetrate past the very densely compacted W to get at the silver deeper (beyond the surface) of the W/Ag matrix
Therefore - kinetic energy is "required" in order to get the nitric to penetrate past the compressed W & dissolve away the Ag compressed deeper in the W/Ag matrix
So - to provide this kinetic energy you MUST LITERALLY BOIL the W/Ag matrix in the nitric AND it takes MANY hours of BOILING to "fully" penetrate the matrix & leach ALL the silver out of that matrix
To put this somewhat in perspective - depending on the batch size - &/or the size of the pieces of the W/Ag matrix it can take anywhere from a "full" day (24 hours) to as much as 4 - 5 days of BOILING the matrix in nitric
Example; - the points out of household circuit brakers are only about 4 or 5 mm square or round & about 2 - 2.5 mm thick
If you put about a 1/4 kilo (250 - 300 grams) of these very small points in a beaker you have to BOIL them in the nitric for
"at least" 24 hours to get "all" the silver leached out of them --- increase the batch size will increase the time of BOILING them in the nitric --- increase the size of the matrix (such as larger industrial points) will increase the BOILING time
Example; - a kilo of the larger industrial points will take 2 - 2.5 days of BOILING them in the nitric & even then you will likely need to test them to see if all the silver is leached out (to be explained later in this post) & if not may need to BOIL them in the nitric for another day or 2
This is why I asking the OP for pics of his "shavings" --- if they are more then 1 mm in thickness he will likely need to bring the leaching up to a FULL BOIL to leach all the silver out --- if they are less then 1 mm in thickness he can likely get away with less then a full on boil but will still likely need to bring it up to a "simmering" boil - once the initial reaction from dissolving the silver at the "surface" of the matrix dies down in order to get "all" the silver leached out
Again - pics of the material the OP has would help in getting him headed in the right direction as leaching the silver out of the sintered W/Ag is "not" as simple as putting it in a beaker with 50/50 nitric/D-water &/or applying "a bit" of heat (though that "may" be the case IF the shavings a small/fine enough)
Now then - so how do tell when all the silver is leached out of the W/Ag sintered matrix (when talking about larger pieces like contact points)
As the Ag leaches out of the W matrix the W becomes soft & black - so with small points like household circuit brakers you can use a glass stir rod to see if they will crush apart all the way to the center - if only an outside layer of black W brakes of - leaving a "grey" harder center - you are not done boiling them in the nitric
With the larger industrial points you are better served to fish some of the points out of the beaker to see if you can snap them in half - if you cannot snap them in half they are not even close to done - if you can snap them in half then you want to look at the broken edge & if they are fully black to the center & soft & easy to crush then you have most (if not all) the silver leach out - if on the other hand they do brake in half relatively easy but you see some gray color in the center of the brake you are not done leaching them & need to boil them some more
Also - though the vast majority of the W will go undissolved - due to high temp of "boiling" in the nitric along with the kinetic energy of the boiling "some" W will go into solution however that is not a problem as that small amount of W will stay in solution when you recover the Ag from the silver nitrate
And as a final note; - generally sintered W/Ag runs "about" 30 - 40 % silver with 60 - 70 % tungsten
Kurt
