upcyclist said:
This may not serve Geoff's purposes, but I'm surprised no one mentioned processing cemented silver in a cell*, where Pd (and other trace PGMs) would end up in the slimes.
Due to the fact that Pd is soluble in nitric only some of the Pd stays in the slimes - some of it dissolves into the electrolyte (corrupting the electrolyte) just as copper &/or any other nitric soluble metals - some (including silver) remain behind in the slimes - some goes into the electrolyte --- only metals that are not soluble in nitric remain in the slime without also going into the electrolyte
How the (silver) cell works --- you have to think in terms of a "winning" cell - because that is actually what is going on - the difference is that in the silver cell you are using an (impure) silver anode instead of an inert anode like carbon or platinum plated titanium - but - both the winning cell & the silver cell work on the same principal - which is the "displacement" of the metal dissolved in the electrolyte which causes it to deposit at the cathode as a result of the DC current applied to the cell (positive to the anode - negative to the cathode)
In the winning cell - because an inert anode is used - the metal in the electrolyte is displaced from the electrolyte & deposited to the cathode - the end result being that the metal is removed leaving you with acid that is now free of the metal that was dissolved in it - which in turn means you now have acid that is free to dissolve metal again
And that is what happens in a silver cell - because your electrolyte is made of "silver" in the "first place --- when you turn on the power - silver starts to be displaced "
from the electrolyte" --- which in turn frees up acid that is then able to dissolve metal at the anode - that acid (being nitric) dissolves not only silver - but any metal that is nitric soluble such as copper, palladium, etc.
The result is metal ions being replaced by the acid made free as silver is displaced - BUT - the replaced ions are made up of any metal that is nitric soluble --- therefore you electrolyte SLOWLY begins to "corrupt" --- because this reaction is taking place so slow AND as long as the silver ions are the "predominant" ions in the electrolyte - the silver ions are the ions that continue to displace "
from the electrolyte" --- in other words - the silver continues the be the metal "won" from the electrolyte - as long as they (as ions) dominate the electrolyte
When the electrolyte becomes to corrupted with other metal ions (due to being "dissolved" from the anode) so that the silver is no longer dominating the electrolyte - they also start to displace (or win) from the electrolyte leading to co-depositing of those other metals to the cathode as well as the silver
Also because the reaction of displacement & replacement is taking place so slowly - the free acid that is made available to dissolve metal at the anode is so little - it is also to "weak" to "fully" react with the metal & "completely" dissolve it - so the result is "some" metal being dissolved (to replace ions in the electrolyte as ions are displaced) but some metal also flakes off as "ultra fine" metal resulting in the slimes
In other words - not only the metals that are "not" soluble remain in the slimes - but - "some" metal that "is" soluble in nitric also remains in the slimes - while some (nitric soluble) metal is dissolved allowing metal ion replacement of the electrolyte as metal ions are displaced from the electrolyte
The sort version of the above long story is - the silver cell "does not" work by "transferring" silver from the anode to the cathode thereby leaving everything but the silver in the slimes - rather it wins (displaces) silver "from the electrolyte" which provides free acid to dissolve metal at the anode (any metal that nitric will dissolve) thereby replacing ions to the electrolyte as ions are won from the electrolyte
Sooo - the silver cell is not going to do what Geo wants to do - which is to completely "part" the Pd from the Ag --- the silver cell will give him pure silver "at the cathode" --- as long as he does not allow the electrolyte to become to corrupted that it starts co-depositing - BUT - he will still end up with the Pd mixed with silver - some that is a complex of Ag/Pd nitrate (in the corrupted electrolyte) & some as a matrix of Ag & Pd in the anode slimes --- meaning he is still stuck with "parting" the two metals from each other
So - yes - though he can achieve pure silver by running it in the silver cell - he still has the problem of parting Pd from Ag in the by products of the cell - & the Pd/Ag are now in two places - some in the electrolyte & some in the slimes
Edit to add; - & that is why no one has suggested the silver cell as a solution to what Geo wants to do
Kurt
Just a note here of course and i consider myself sane. However, I will check with my counselor at our next visit. :lol: 
