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Palladium is the most common of the platinum group metals (PGM). It is the only member of PGM that is dissolved in nitric acid by itself. It is a steel white metal with a melting point of 1554.9 °C (2830.82 °F). Just like silver, molten palladium can dissolve several times it's volume of oxygen so care should be taken when melting palladium.
Palladium and nitric acid
Palladium can be dissolved in nitric acid.
Palladium and hydrocloric acid
Fine particles of palladium can be dissolved by straight hydrochloric acid.
With an added oxidator HCl can dissolve palladium without problem. For example palladium catalyst on alumina substrate was completely dissolved by a solution of 7% HCl and 5% H2O2 at 60°C for 2h and a liquid to solid ratio of 10 to 1. The palladium chloride was reduced to palladium by a formic acid solution. (ref 3)
Palladium and sulfuric acid
Palladium can be dissolved in hot concentrated sulfuric acid, giving PdSO4, a red water soluble salt.
( Main article List of palladium compounds )
Palladium forms a lot of different compounds thanks to it's rich chemistry. Common oxidation states are +1, +2 and +4. Palladium is used in many applications as a reagent or as catalyst. Left over products, reagents and catalysts is a good source of material for the refiner.
- Palladium hydride actually hydrogen absorbed into the palladium crystal lattice. It can be troublesome to refine if you don't know how. Discussed in a thread on GRF.
- Palladium nitrate can be separated from a silver nitrate solution by raising the pH to 6.5 while heating (not boiling), palladium nitrate is transformed into Pd(OH)2 and other hydroxides that can be filtered off. The palladium hydroxide can be redissolved in hydrochloric acid and the silver filtered off as silver chloride.
(ref 2, 10)
Palladium and sulfite
If a palladium(II) solution close to neutral pH is mixed with sodium or potassium sulfite it will form a complex salt only sparingly soluble in water.
Na2Pd(SO3)2.2H2O respectively K2Pd(SO3)2
Boiling the salt in excess aqueous sulfuric acid - no halides, nor nitrates may be present! - it decomposes to metallic palladium, NaHSO4, SO2 and water. (ref 4)
Reduction of diammine-palladium(II)chloride (yellow palladium salt) can be done in a couple of ways. For example by calcining (see below) or by reduction by formic acid (ref 5)
(NH3)2PdCl2 + HCOOH => Pd(metal) + CO2 + 2 NH4Cl
Calcining palladium salts
3 (NH3)2PdCl2 => 3 Pd(metal) + N2 + 4 NH4Cl + 2 HCl (ref 5)
When melting palladium avoid using a melting dish with quartz in it, it can form palladium silicides. Use a MgO or ZrO2 melting dish.
(Main article Palladium refining)
This is a short overview of how palladium metal can be refined.
- Digest palladium metal in nitric acid.
- Add NH4OH to pH 1-2 and filter
- Add NH4OH to pH 10 and filter, removes iron and nickel
- Add HCl to pH 6.5-7 and filter, removes AgCl
- Add HCl to pH 3, a yellow palladium salt will precipitate
- Cool the mixture and collect the precipitate in a filter, rinse with 1% HCl in DI water.
- Liquids goes to the stock pot for reclamation of left over values
- Reduce the diammine-palladium(II) chloride with formic acid, calcining or other method of choice
- Wikipedia : Palladium
- Webelements : Palladium
- GRF : Picture of palladium sponge
- GRF : Palladium precipitation
- GRF : Purifying Palladium Precipitated from Dirty Solutions
- GRF : Great thread with lots of pictures
- GRF : Palladium silicides when calcining Pd salts
- (2) GRF : Lou on separating palladium from silver in a nitrate solution
- (3) Recovery and separation of palladium from spent catalyst
- (4) GRF : Palladium from nitrate solution
- (5) GRF : Reduction of diammine-palladium(II)chloride (yellow palladium salt)
- (6) GRF : 4Metals method for producing >999 palladium powder
- (7) GRF : 9kuuby9 shows pictures of 4metals process on refining palladium concentrates
- (8) GRF : Lazersteve - Purifying Palladium Precipitated from Dirty Solutions (with pictures)
- (9) Hoke page 177 : PART III. REPURIFYING PALLADIUM
- (10) Modern Electroplating 12 : Palladium Electroplating by Joseph A. Abys, a great paper on palladium, its chemistry and plating.
- Science Madness : Refining of palladium and platinum
- Salt lake metals : Palladium compounds