Seperating Ag as AgCl from Pd(NO3)2 in a nitrate solution

I Leeched Ag & Pd with 35% Nitric acid then I cemented them both With Copper.

The cement was washed several times and then digested in 35% Nitric acid.

The Solution was saturated with Ag and Pd. after filtration their has formed a plateau like yellowish type of crystals and some remaining black powders which was presumably Pt.

Then I added HCl to the filtrate to precipitate Ag as AgCl. I stirred the solution to ensure full precipitation of the AgCl (aside from the small soluble amount of AgCl in the solution)

When I was decanting and filtering the resulted solution, I noticed small needle shaped crystals; Which when described look like stalagmites. Emerging needles from a plateau like base which where colored orange-brown. (very fragile crystals)

After much of the solution was decanted from the AgCl containing vessel, I doubled the volume with distilled water and I also Added HCl. After much stirring and settling, The needle shaped crystals did not dissolve. Could this be some insoluble Palladium salt?

Quite the situation, Since it very hard to separate the two compounds from each other. NH4(OH) is also out of question since their is over 1 kg of AgCl present in the containing vessel.

Any help and or suggestion is appreciated! :mrgreen:

What was your source material?

What you are describing sound much like PbCl2

NaCl (salt) will precipitate the silver as silver chloride while leaving the Pd in solution.

needle shaped crystals sounds like lead chloride.

Lead chloride can be removed from silver chloride.

Boiled in a solution of water lowering the heat below boiling (keeping the solution as hot as possible), giving it time to let the fluffy silver chloride settle, decant the clear solution into a cooling jar, lead chloride will crystallize out of the clear solution as needle like white lead chloride salts.

Lead chloride is not very soluble at all in cold water but becomes pretty soluble in boiling hot water, silver chloride is insoluble in hot or cold water.
The lead chloride gives no color to the boiling water or the lead chloride dissolved in the water.

If you have a large batch of silver to clean up, the water from the cooling jar can be reused to collect more silver (once cooled and the PbCl2 settles out of solution), in this case using more than one cooling jar to keep the process going, and to lower the amount of waste water generated from the process.

When I was decanting and filtering the resulted solution, I noticed small needle shaped crystals; Which when described look like stalagmites. Emerging needles from a plateau like base which where colored orange-brown. (very fragile crystals)

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If these needle-shaped crystals were colored orange-brown, they consisted certainly not of lead chloride (PbCl₂), which is colourless.

Then I added HCl to the filtrate to precipitate Ag as AgCl. I stirred the solution to ensure full precipitation of the AgCl (aside from the small soluble amount of AgCl in the solution)

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In recovering palladium from mixed Pd/Ag-solutions in aqueous HNO₃, I always used an "inverse procedure", that means, I added the mixed Pd/Ag-solution slowly to an excess of hot (nearly boiling) aqueous HCl (1 part 32%HCl; 1 part water; v/v), constantly stirring the mixture, thus slowly precipitating AgCl, and forming at the same time soluble chloro-complexes of Pd(II), PdCl₄^2-, and, maybe, also some Pd(IV), PdCl₆^2-. Per gram-atom (mole) of Pd, I always calculated 9 moles of HCl (50% excess on quantitative, theoretical formation of PdCl₆^2-), in addition to 1 mole of HCl per gram-atom of silver to be precipitated. During addition of the Pd/Ag-solution to hot hydrochloric acid, NO_x was evolved constantly. After complete addition, the mixture was boiled under reflux, until no more NO_x was visible. It was then set aside to cool down and settle down AgCl. After decantation/filtration, AgCl was thoroughly washed with diluted, warm HCl (ca. 5-10 g HCl per liter). The combined filtrate and wash-solutions were treated further to recover Pd as solid red K₂PdCl₆ or as the yellow (NH₃)₂PdCl₂.

Wonderful explanation freechemist, I really enjoy and appreciate reading your responses. :mrgreen: I will use your outlined process for future processing.

So the Key here is to convert the Pd(NO3)2 into soluble chloro complexes of Pd(II) and Pd(IV) while precipitating Ag as AgCl to avoid the formation of insoluble Palladium nitrate salt(s).

How do you suggest to process AgCl mixed with insoluble Palladium nitrate salt(s)?

So the Key here is to convert the Pd(NO₃)₂ into soluble chloro complexes of Pd(II) and Pd(IV) while precipitating Ag as AgCl to avoid the formation of insoluble Palladium nitrate salt(s).

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Personally, I woudn't talk of Pd(NO₃)₂ and/or of soluble/insoluble palladium nitrate salts. The term "palladium, dissolved in a halide-free, acidic medium", like aqueous HNO₃ matches reality much better. Metallic palladium, even in massive form, can be dissolved quite easily in excessive sulfuric acid/water mixture, using HNO₃ only to oxidize the metal, in an only slight excess over an assumed stoichiometrically needed amount. This way, highly concentrated solutions of Pd(II) in a halide-free, aqueous sulfuric acid medium can be obtained.

The key-step in separating Ag from Pd in combined HNO₃-solution consists in delivering sufficient chloride to the mixture, that soluble chloro-complexes of Pd and solid AgCl are formed quantitatively, and this is best done by adding the combined Ag/Pd-solution to an excess of hydrochloric acid.

How do you suggest to process AgCl mixed with insoluble Palladium nitrate salt(s)?

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My suggestion, without garanty for real functioning: Mix the solids with a sufficient amount of a conc.HCl/water-mixture (1:1;v/v), to get an easily stirrable suspension. Heat and boil the suspension, constantly stirring, under reflux, until no more NO_x is evolved. Then proceed like already described in my first post on the subject.

Some further notes on separting AgCl from "palladium, dissolved in a halide-free, acidic medium", like aqueous HNO3 and HCl.

As per freechemist's Suggestion; I went ahead and mixed the solids with con/HCl water mixture (1:1). Heated the mixture up to 110C° and Stirred the Suspension using a glass rod. it's quite hard to stir the Suspension since it settles fast with a conc./HCl water mixture. A magnetic stirrer would not work in this case since the fluffy AgCl is too thick and easy settling. after a half our of stirring, some of the Complex Palladium salt dissolved. But the majority still remains. I think that this method would be able to successfully separate the two salts from each other but Only As per freechemist's Suggestion; Key here is that the mixture is heated well and stirred constantly. As of my lack of stirring I did not successfully separate the two salts but some of it.

I went ahead and washed the AgCl to a degree where it's filtrate changed from a dark Red-Orange to a light pinkish-yellow. after a good wash I doubled it's volume in Distilled water and added 1/10 Concentrated Sulfuric acid. (1 Sulfuric acid and 10 Distilled water ratio) after a good Stir I added a Iron plate to convert the AgCl salt into elemental Silver. the usual washing, From here I'll dissolve the elemental metals (the small amount of Pd included) in Nitric acid And separate the two elements as per freechemist's outlined process.