# yellow palladium salt



## arthur kierski (Aug 13, 2011)

i usually reduce yellow pd salts to black pd , with formic acid.
yesterday i did the same process and the solution with the yellow salt was not reduced to black pd---
could some member tell me what went wrong? and what could be done with the yellow salt ?
thanks 
Arthur


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## bhupesh17 (Aug 15, 2011)

hi,i m bhupeshmulik frm india
u are using formic acid for reduction of pd salt,i will tell u right procedure.
u first take yellow residue in a beaker(it should be completely acid free,means before taking yellow residue u wash residue with water)add first few formic acid in a beaker then add water to neutralise formic acid till upto yr water and formic acid solution ph is 7(dip ph paper in water and by adding water in formic acid check the colour of ph paper,and now u add ammonia slowly because of exothermic acid base reaction takes place.(exceptional case for formic acid that u r adding acid into water).now u will get black residue at the bottom of cleared white watery transperent solution.
advice =u better try hypophosphoRUS acid and tell me results.no any addition of chemicals.


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## arthur kierski (Aug 15, 2011)

thanks bhupesh for your explanation----i will doit and then tell you if i reached good results-----i used to use hidrazine which is not more allowed here in brazil
regards
Arthur


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## freechemist (Aug 17, 2011)

Hi Arthur, 

To reduce diammine-palladium(II)chloride (yellow palladium salt) to the metal, principally there exist several different methods, the most simple one being calcination at temperatures up to at least 800oC, using a porcelain dish or crucible, covered with a loosely sitting lid. Heating has to be done not too quickly, because decomposition begins at much lower temperatures (ca. 300oC), under emission of white fumes of HCl and NH4Cl. The according reaction is: *3 (NH3)2PdCl2 => 3 Pd(metal) + N2 + 4 NH4Cl + 2 HCl*. Holding the decomposed mixture for about 2 hours at 800oC assures complete reaction to palladium-metal as a greenish-blueish-gray metal sponge.

A different method involves reduction with formic acid, which has to be done very carefully, the reaction being quite difficult to control. Formally reaction occurs according to the following equation: *(NH3)2PdCl2 + HCOOH => Pd-metal + CO2 + 2 NH4Cl*. The active reduction reagent is not formic acid (HCOOH) itself, but it's anion, HCOO(-), which is obtained by deprotonation of the acid, which can be achieved, but only in small quantities at the beginning, through the complexed ammonia-molecules in the yellow palladium complex-salt. The formiate anion formed slowly in the mixture is oxidized to CO2 and a second proton, H(+), which is neutralized by the second NH3-molecule contained in the yellow complex salt. The actual reduction reaction in a simplified form thus can be written as follows: *Pd(II) + HCOOH + 2 NH3 => 2 NH4(+) + Pd-metal + CO2*. Mixtures of yellow palladium salt and aqueous formic acid solution do not react at room temperature. Heating to at least 80oC, up to nearly boiling some times, is necessary to onset reaction, but once begun, reaction can become very violent, such, that even a quite large reaction vessel can become too small for containing the reacting mixture, resulting in a mess of spilled palladium-black, starting material and salt-solution. Therefor I propose to you the following procedure:
1.) Suspend the yellow palladium salt in sufficient water, to obtain a theoretical concentration of 20 to maximum 50 grams Pd in 1 liter. Heat the suspension to nearly boiling under constant stirring (mechanical stirrer or magnetic stirring bar).
2.) Under constant stirring and heating, add no more than ca. one tenth of the required amount of formic acid to the hot suspension. Wait until reaction has onset, clearly visible on sudden upfoaming and formation of palladium-black (stay patient, sometimes much time is needed).
3.) Only after subsiding of this first reaction, add the rest of formic acid in small portions, waiting after every addition on subsiding of the newly ongoing reaction. Usually an excess of formic acid over the stoichiometrically calculated amount has to be used, because formic acid, together with water vapour, is volatile, and secondly because a Pd-catalyzed side-reaction, producing hydrogen-gas and hydrogencarbonate uses up some formic acid (formiate). At the end of the total reaction, addition of more formic acid does not cause more upfoaming of the now totally black mixture.
4.) If the palladium black does not settle down quickly after having stopped the stirrer and heating, add a few milliliters of a strong mineral acid (HCl; H2SO4) until the mixture shows a clearly visible strong acidic reaction (pH-paper), stir and heat again and let settle again after a few minutes boiling. If necessary repeat the acid-treating. Usually a well coagulating Pd-black is obtained, suspended in a colourless, waterclear solution. To be sure of complete reaction, test the clear solution by addition of a few drops of DMG-solution.
5.) Work up by decantation/filtration, washing with plenty of water, drying and/or calcining.

Regards, freechemist


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## Lou (Aug 18, 2011)

The greenish blue gray powder is a mix of PdO and Pd. PdO forms readily at 800*C.

Do it as safely as possible in hydrogen.


Lou


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## freechemist (Aug 23, 2011)

Hi Lou, 

Melting palladium-black in an induction furnace can become very cumbersome through losses in Pd as fumes of very finely divided palladium-dust. Therefor we decided, to sinter the Pd-black formed in our refining process, before finally melting it. Preliminary experiments, done with lots of a few hundred grams of Pd-black showed soon, that a temperature of 800oC was necessary - and sufficient - to alter the finely divided black powder to quite massive, but still porous greyish chunks of metallic Pd, which then could easily be melted in an induction furnace. Sintering experiments at significantly lower temperatures (ca. 600o to nearly 700oC) in contrary, produced greenish-blue, dark grey powders, evidently being mostly oxidized material (PdO?), comparing weights of incoming and outcoming materials. At higher temperatures, finally at 800oC, this weight-gain was clearly inversed, leading to the above cited greyish chunks of sintered material. Later on this phenomenon was used specifically and successfully in the working up of spent up industrial Pd-catalysts, such as 5% or 10% Pd on activated charcoal, to recover metallic palladium.

Regards, freechemist


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## Lou (Aug 23, 2011)

Ah yes you are right. PdO dissociates at high temp. I meant merely that there should've been no green color if it is to have been fully reduced.

Oxygen is difficult to remove from Pd, it's best to melt under argon at reduced pressure.


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## soonaar (Aug 25, 2011)

hi
I want to know the exact method to recover all that three metals viz. Palladium, Gold and Silver for one and same liquid mixture of aqua regia. 
thanks!


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## samuel-a (Aug 25, 2011)

soonaar said:


> hi
> I want to know the exact method to recover all that three metals viz. Palladium, Gold and Silver for one and same liquid mixture of aqua regia.
> thanks!



START HERE


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## Nadeem (Jan 1, 2023)

bhupesh17 said:


> hi,i m bhupeshmulik frm india
> u are using formic acid for reduction of pd salt,i will tell u right procedure.
> u first take yellow residue in a beaker(it should be completely acid free,means before taking yellow residue u wash residue with water)add first few formic acid in a beaker then add water to neutralise formic acid till upto yr water and formic acid solution ph is 7(dip ph paper in water and by adding water in formic acid check the colour of ph paper,and now u add ammonia slowly because of exothermic acid base reaction takes place.(exceptional case for formic acid that u r adding acid into water).now u will get black residue at the bottom of cleared white watery transperent solution.
> advice =u better try hypophosphoRUS acid and tell me results.no any addition of chemicals.


Vry nice infomation bro 
Thnks a lot


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