Continuing from Part 1 of this tutorial you have been told to remove the flask off the hot plate and allow it to cool back to room temperature and settle for about one hour.
Next step is to filter the resulting solution free of any solids.
And test it for precious metals presence with Stannous Chloride Test solution or with DMG test for Palladium.
Positive for Palladium presence.
C. Palladium and Silver cementation.
When done filtering, solution may vary in color from yellow green to deep burgundy and now contains dissolved precious metals, mainly Palladium but may hold as well Silver chloride, Gold and on rare occasions Platinum.
Solution will hold with those precious metals traces of un-dissolved base metals such as Nickel, Barium, Lead and Tin but not to the point of harming the recovery process.
Locate the filtered solution on hot plate with low-medium heat and start adding Aluminum (Al) or Zinc (Zn) chunks/shavings, those metals are very reactive to Acid solution so be careful and add few pieces at a time, let them react all the way to completion before adding more.
You bill be far better served using Zinc rather the Aluminum since Al tends to linger and stick to the precipitate.
Soon you will notice a color change in the solution and black precipitate swirling in the beaker, the black precipitates composed of all metals located lower the Al/Zn on the reactivity series.
After a few Al/Zn addition, you should perform Stannous Chloride test before each new addition so that you could tell if all of the precious metals have been precipitated.
If you are unsure of your test you can keep adding Al/Zn until solution turns clear with no color (Zn) or with light yellowish tint (Al)
Once done with Al/Zn addition, allow the solution to settle at least 12 hour (over night)
D. Palladium and Silver separation.
Once settled over night, with a pipette or a syringe, siphon (do not decent) the liquid as much as possible without disturbing the black solids.
Liquid will go to your waste solution container.
Add just enough HCL 32% to cover the black powder.
And start dripping Nitric Acid drop by drop (literally), add a drop, mix and wait for a reaction (fizzing and bubbling) let the reaction subside before adding the next drop and so on until the black powder is completely dissolved.
The idea behind this method is to use only the needed amount of Nitric Acid so that you could avoid the need of neutralizing it later.
The reason for the second Aqua Regia dissolution of the Palladium is to get rid of any other non precious elements that may have been in the first Aqua Regia digestion.
Perform another Stannous Chloride Test to approve Palladium content in solution.
Let the solution settle over night, any white solids at the bottom of the flask can be a combination of Silver Chloride, Titanium Dioxide and Aluminum Oxide (if Al is used).
Once settled over night, filter or siphon the solution to a dark sealed storage container.
You are now done with the Palladium recovery out of the Monolithic Ceramic Capacitors and prepared a Palladium Chloride solution ready to the Refining process. Congrats!