Ammonia Soluble Hexachloropalladates (IV)

[kadriver]

I ended up making several more additions of hydrochloric acid and hydrogen peroxide with some med-low heat.

It really fizzed up when I added the H2O2, but I could tell that more of the Pd black powder was dissolving because the solution began to get so dark that I could not see through it even when held up to the light.

 

[kadriver]

It got to the point where I could not tell if there was any black powder in the bottom of the beaker, so I poured off the solution into another clean beaker.

Sure enough there were some particles of Pd black powder that were still un-dissolved. I worked on this all day to this point adding fresh HCl and H2O2.

 

[kadriver]

I rinsed down the sides of the beaker containing the un-dissolved Pd black powder with fresh hydrochloric acid.

Then I put the cover on and added a little fresh H2O2 - the remaining Pd black powder dissolved right in front of my eyes in just a minute or two.

then I added this back to the main solution.

 

[kadriver]

I evaporated off much of the liquid before I went to the next step

Then I made up some fresh saturated ammonium chloride solution and added drop by drop to the dissolved Pd black solution and got another surprise.

I was expecting just a little Pt orange powder (if any) to precipitate out. But there was much more platinum in those "Pd blacks" that I expected.

 

[kadriver]

I filtered out the orange Pt powder and will save it until I get a good quantity then burn it in a quartz dish.

The filtrate should be my palladium - more to follow.

kadriver

 

[lazersteve]

Have you performed a stannous test for Pt on a sample of the newly formed orange salt?

Steve

 

[kadriver]

No, I'll get some of the orange powder out of the filter and dissolve a little in water and check - but what else could it be?

kadriver

 

[RaoOvious]

Kevin,

By the look of your salt you have most probably made Palladium Tetrachloropalladate (II) with some Pt salt (NH4)2PtCl6.(If Pt is in sol.).The reason for this is your solution is extra-concentrated.It is very normal in successive precipitation of Pt & Pd.

To solve this you would have to rinse the filtered salt with water back to the filtrate,add some ml's of HCl,heat and concentrate it to 20ml/gram or at a con. level where it doesn,t form this thick and fluffy salt upon cooling(Normally it would range from 20-10ml/gram).

If there is any platinum then it would precipitate as fine orange/yellow powder not like this fluffy and thick Palladium II salt.And then you can proceed for Pd as per usual route.

 

[freechemist]

Kadriver writes:
I have had this beaker sitting on one of my shelves for months containing Palladium dissolved in nitric acid. The palladium came from mixed black PGMs, I extracted the Pd using dilute nitric acid, then evaporated it to remove most of the liquid. I did a stannous test and it is loaded with palladium, the standard test solution on the left contains 100mg Pd dissolved in 100ml liquid.

The brown stain on the left corresponds to the reference-solution, containing 1g Pd/liter. The stain on the right shows clearly, that Pd and Pt are present. The Pd-concentration in the sample-solution seems to be much higher, than 1 g Pd/liter. The Pt-concentration, as indicated by the strong orange coloration of the paper, concentric around the dark-green Pd-stain, seems to be quite high, too. One can distinguish between Pd and Pt by washing the stains on/in the paper with copious amounts of distilled water. The Pd-stain (dark green) will disappear slowly, being washed out completely, whereas the orange Pt-stain will stay back on/in the paper.

RaoOvious writes:
Make sure that there is no trace of nitric acid(water washes and Ph neutral) before washing the Pd black with dilute HCl,otherwise some of the Pd black would again go into the solution.

In my practice, this was never a problem. In contrary, a too low electrolyte/acid-concentration can lead to peptization of such PGM-blacks, making their filtration more and more cumbersome. Assuming a rest-wash-solution-pH of 2 for the last filtration step, and a volume of 5 ml liquid means, that a maximum-amount of 5*10^-5 moles HNO₃ is available, to oxidize a maximal amount of 5*10^-5 gram-atoms Pd-metal to Pd(II), corresponding to a maximal possible loss of 5.3 mg Pd, in an experiment like presented here, by Kadriver.

@Greyish solution after cementation and intensive washing of Pd:

This greyish colour/turbidity may well be caused by small amounts of residual, unreacted zinc-powder, reacting slowly with water to very small particles of insoluble zinc-hydroxide, Zn(OH)₂. Thus it is not necessary, to filter. Chance is, that this turbidity disappears on addition of some diluted acid.

@Kadriver:

As I can see from your last posts, you're on a very good way. First, dissolving residual zinc with diluted HCl, followed by filtering, washing, drying. This leaves you with a weighable amount of raw Pd-powder, and you know now much better, what you are working with.
You already have dissolved the Pd-black in HCl/H₂O₂, which should leave you with a solution containing mainly Pd(II), together with some Pd(IV).
Contrary to you, I am not surprised, to see how much Pt you are precipitating. SnCl₂-testing to me shows clearly the presence of quite a lot dissolved platinum.
In order to clarify my comments I have collected some of your fotos in the attached pdf-file.

 

[kadriver]

Thanks for each of your responses - by posting the pictures one can see the progress and the mistakes I make as I go. This is the reason I post many photos of my experiments with the platinum metals - and I greatly appreciate the inputs given by each member who responds. The forum can watch as I grow (or fail) as a novice PGM refiner.

I picked out a small piece of the salt from the filter and put it in a spot plate.

Added a few drops of water to see if it would dissolve - it did, so I drew the test sample up in the pipette and expelled it back into the cavity to get it dissolved completely and to mix thoroughly.

 

[kadriver]

I dipped a piece of filter paper into the mixture and then added a drop of stannous chloride - it turned brown which would indicate Pd.

Then I placed a drop of Pd standard solution (100mg per 100ml liquid = 1 gram per liter concentration) in the cavity to the left of the test sample.

Placed a drop of Pt standard solution (100mg per 100ml liquid - 1 gram per liter concentration) in the cavity to the right.

Then added a drop of stannous chloride to each sample in the spot plate.

After doing these tests I believe that the salt in the filter is NOT platinum, but mostly palladium with very little, if any, platinum.

I plan to re-dissolve the Pd salt from the filter back into the rest of the filtrate with distilled water, then concentrate it through evaporation again.

The last evaporation was down to about 20ml or so.

This time I'll only take it down to 40ml, then add the concentrated ammonium chloride to get any Pt (if present) to precipitate out.

I'll be following the procedure given by RaoOvious above.

I'm glad I was instructed to test it otherwise I would have just assumed it was Pt salt (which is was NOT as per the sample test results).

Thank you!

kadriver

 

[lazersteve]

I suspected you may see that you had precipitated Pd and not Pt, this is why I suggested you do the stannous test on the orange salt.

When I precipitate Pt from mixed PGM solutions it is typically a bright orange color if contaminated with Pd:

Iridium contamination will give a brick red colored Pt salt:

Rh contamination gives a yellow green color (top left filter):

and lastly, nearly pure Pt with will be canary yellow:

As a general rule, the lighter yellow and denser the Pt salt (see note in post below), the higher the purity.

Notice that all of these salts pictured above are dense and do not have any transparency to the crystals. The transparency is typical of precipitations done with highly saturated ammonium chloride solutions which naturally tend to entrain other PGMs in the crystals.

Your test results is a prime example of why you must always test regardless of what you believe you have produced.

Keep up the great work Kevin, your posts are a prime example of what makes the forum great.

Steve

 

[lazersteve]

Lou pointed out to me via PM that Pt ( and PGM salts in general ) are more fluffy as the purity increases, therefore they are technically less dense.

I incorrectly used the term density above, when in fact I was referring to the difference in appearance between relatively pure PGM salts and those that have a large excess of crystallized ammonium chloride in them. These entrained salts have a slightly transparent crystal color and look slushy as opposed to packing 'densely' and clumping into the filter with a consistent color throughout as seen in my photos.

Here's an old thread with a prime example of what I was referring to:

Entrained PGM salt photos thread

and a sample photo from the thread:

Entrained PGM salts

Note how the salt appears glass like and not 'densely packed' as the photos I posted above.

Thank you for correcting my terminology Lou, it's good to know someone is keeping me straight! :wink:

Steve

 

[RaoOvious]

This time I'll only take it down to 40ml, then add the concentrated ammonium chloride to get any Pt (if present) to precipitate out.

I'll be following the procedure given by RaoOvious above.

Kevin thus you have precipitated (NH4)2PdCl4 with minimal amount of Pt salt as already enumerated above.After concentrating this Pd salt with the filtrate, in fact you do not need to put in more NH4Cl as it is already present in the mix.

What you have to critically evaluate is concentrating it to around 20ml/gram,let it cool and see if there is orange/yellow fine grain Pt salt appearing without the thick and dense Pd II salt,if yes you are good to go for filtration of Pt salt,if orange yellow Pt salt is appearing with the usual suspect thick Pd II,then you would have to dilute it a bit with 50/50 Distt.water/HCl and give it heat until thick Pd II salt disappears,and then go for filtration.

If at any concentration level there is no indication of orange/yellow fine grained Pt salt then you can safely concur that there is no Platinum or its in mil or micro grams,then you can straight away go ahead for chlorine addition without filtration for Palladium Precipitation.

But as per your elegant pictorial presentation,I guess you would have some orange/yellow fine grained Pt salt at some level,around 15-20 ml/gram concentration level.The rule of thumb is the more concentrated your Pt,Pd solution after addition of conc. NH4Cl is,the more chances there are of appearing and mixing of thick brown needle shaped Pd II salt with your desired orange/yellow Pt IV salt.

For clarification purposes have a look at the pic where the grains are free and fine and are not interlocked(except here the salt is of Pd not Pt,just for grain finess purpose) like Pd II or you can call form ur beautiful yellow Diammine Pd II salt which you did last year.

I hope this would help,anyways keep up the great series.

Rao

 

[kadriver]

I over - concentrated my solution by evaporating it too much and formed the ammonia insoluble (NH4)2PdCl4 upon adding the concentrated ammonium chloride.

Since I have 2.3 grams of Pd black powder as weighed in earlier in this post, then I should only concentrate my solution volume down to 20 x 2.3 = 46ml.

I was thinking, "the more concentrated the better". But this is not the case. The 15ml to 20ml per gram of Pd black powder concentration factor is a critical number.

I'll give this a go as soon as I get some time freed up. More to follow.

kadriver

 

[RaoOvious]

Kevin,

This pictorial presentation might help you in the current scenario.It show separation of Pt (IV) salt in a combined solution of Platinum and Palladium.Specially the color of Yellow Pt. (IV) salt,this is how should be yours' at that stage.

Further I would be uploading further pics of the situations where thick brown needle shaped Pd (II) is also precipitated when precipitating Pt. (IV) or when concentrating the Pd rich solution(for Pd IV salt precipitation by introducing Chlorine gas) after clean separation of Pt.(IV) salt from the combined solution.

 

[RaoOvious]

Continued..................

 

[kadriver]

Great photo presentation RaoOvious - thank you.

I got behind on some things but I am starting to get caught up.

I still have the Pd salt in the filter, will re-dissolve and then re-concentrate and watch for the fine Pt salt to form.

These photos will help as a reference.

kadriver

 

[kadriver]

I got some time so I continued the process here.

I removed the filter paper, now dry, with the Pt/Pd salts and rinsed all that I could into a 1 liter beaker.

There were crystals of ammonium chloride on the filter paper from the previous precipitation that rinsed into the beaker with the Pt/Pd salts.

 

[kadriver]

This is a photo looking straight down into the 1 liter beaker.

Some of the salts did not dissolve - you can see a pile of the salts collected in the center of the bottom of the beaker.

I did not add any HCl, just distilled water.

After reviewing the instruction I see that I was supposed to add "50/50 distilled water/HCl"

I'll add some HCl when I get back to the shop and see if the salts will dissolve.