Platinum & Silver in AR - which to precipitate first?

[Brett Novak]

Hi folks - sorry for the hiatus - have been diligently working away on the gold stuff and am back to working with platinum.

Material is 2 part platinum and silver - NOT alloyed, rather Platinum coated in silver sleeve for a medical application. (it's actually close to about 6:1 by weight Platinum to Silver Ratio) I've been boiling in nitric and then fire cleaning (there's also molybdenum present) but getting mixed results, so was thinking of trying to clean a batch with AR. (Getting between 80 and 85% platinum purity)

I know I can get the silver out with HCL or Copper, but I'm wondering, should I drop the Platinum 1st with Ammonium Chloride, or second?

Harold has a great post here - Platinum Thread - but I think that's a how to recover rather than a how to start - maybe I'm reading it wrong?

BTW - Molybdenum really wreaks havoc on glassware - you get a nasty yellow sludge at the surface level that needs to be scraped off with a razor blade

 

[Xing]

if there is Cl ion, silver will come out, so NH4Cl will react with Pt and Ag i think.

 

[Brett Novak]

well, me being the idiot that I am... apparently (At least according to the interwebs) AR doesn't dissolve silver - so I guess it's sort of self-separating with the material I'm using. Which makes sense, since I have pieces of the sensor wire still floating in the boiling AR!)