Before roasting silver or gold that has seen chlorides, I will normally wash them in dilute NaOH solution this forms NaCl salts of any chlorides, which can easily be washed with water, this is a precaution as silver and some gold can become volatile if roasted with any chloride salts.
The nitric will dissolve base metals silver and most of the palladium, silver can be precipitated as a chloride with either table salt NaCl or HCl this will leave palladium in solution, problem is the silver will need converting back to metal before melting (silver chloride is volatile and will burn up most of it as white smoke) silver can be converted with the NaOH Karo syrup method or with one of the acid and metal methods to replace silver from solution.
This will leave most of the palladium in solution. which can be recovered by several methods, cement out out palladium with copper (probably easiest), or zinc (cements out several metals), you can also evaporate the solution down several times adding HCl with each concentration to change the palladium to a chloride, then NH4Cl, and small additions of sodium chlorate to precipitate pd from boiling hot solution (trouble some procedure), or using DMG, dimethyl glyoxime is not only costly reagent, and forms very voluminous solution, for this reason DMG is normally better to test for palladium than a recovery method. and with small volumes you can always just collect palladium in one of your stock pots.
As with the other PGM's what metal you chase after now or try to recover later from the stock pot or silver pot, can be determined of how much of these metals are actually in solution, many time it is easier to keep healthy stock pots and accumulate these metals until you have enough to make a recovery of them, chasing traces will also loose some of the small traces, and you may not have enough to amount to anything recovered, while saving them up in the stock pot letting them accumulate to larger volumes, it may be easier to recover and also you may not loose as much in
the long run.
The Platinum groups are similar in nature to the in that they are hard to separate completely,
they for them most part are more difficult or if not almost impossible to put into solution.
Palladium will not dissolve easily in aqua regia, but it will dissolve into HNO3 alone, or HCl alone fairly easily, (Hoke's speaks of dissolving the palladium in HCl first before adding HNO3 to form the aqua regia to put the other metals into solution with the Pd, otherwise it would be hard to get the palladium to dissolve into the solution with the other metals).
Platinum will dissolve in very hot aqua regia,but can take a long time to dissolve, if powders more easily than the solid metals, but still difficult, gold will dissolve into a cold or barely warmed solution of aqua regia (if not alloyed with silver, or in a high alloy of PGM), gold powders also dissolve much more quickly than solid metals, this gives us a way to dissolve gold away from platinum with out putting much platinum into the solution.
Iridium also dissolves very slowly if at all (incineration can actually help to make it more insoluble depending on previous treatments), you could then cover the powders with adding HCl first, then adding HNO3 ,and heat the aqua regia strongly, to put base metals, palladium, gold, platinum, iridium would dissolve very slowly if at all, Rh is almost impossible to dissolve into this solution.
But then again with most of these PGM's unless you have processes an awful lot of dental gold or jewelry with these metals involved you most likely will not have enough to mess with, so the stock pot method as taught in Hokes book is one way to keep a good little piggy bank.
Keep studying Hokes book, there are different ways you could go about recovery of these metals, and many times the choice you may choose can be decided when you know the conditions you are faced with, or materials and their conditions, as with different situations you face different challenges of recovery, separation, or refining.
