Ammonia Soluble Hexachloropalladates (IV)

[9kuuby9]

Thank you RaoOvious

 

[freechemist]

Hi kadriver,

Thanks for sharing your experiments, especially the pictures, staying in sharp contrast to a lot of photographic "artwork" shown up in this forum. Up to now, I have three comments regarding your posts:

1.) The title of the thread is simply wrong, because a salt like "ammonium hexachloropalladate(II)" doesn't exist. What you mean is ammonium hexachloropalladate(IV). The roman ciphers in the name stand for the oxidation-state of palladium in the respective compound, and this is IV (+4) in the only sparingly soluble (NH₄)₂PdCl₆, ammonium-hexachloropalladate(IV), containing Pd(IV). There exists a chloro-complex-salt of Pd(II) too, ammonium-tetrachloropalladate(II), (NH₄)₂PdCl₄, which is much more soluble in water, and as a solid, forms dark brown, needle-shaped crystals.

2.) In your last post from August 1st you ask for a flocculant: "Is there a flocculant that I can use to get this to settle quickly and not interfere with the reactions?" - To me it is not clear, what you mean by "this": the title-compound to be precipitated or the freshly washed, acid-free Pd-black? - Anyway, (NH₄)₂PdCl₆ usually forms well formed, easily filtrable crystals, and a flocculant is not needed.
Pd-black, especially, if washed free of acid and/or dissolved salts tends to peptisize in water, that means, it seems to form sort of a colloid, settling only difficultly. According to my experience, in this case, it is sufficient, to add one tenth of the suspensions volume 32% HCl (muriatic acid), and give it, constantly stirring (e.g. with a magnetic stirring bar), a short boil during a few minutes. Usually the finely suspended Pd-black coagulates and becomes filtrable much better.

3.) For safety-reasons I, personnally, would not precipitate (NH₄)₂PdCl₆, but the corresponding potassium-salt instead, K₂PdCl₆. Doing this, you never will have issues with NCl₃ and/or potentially explosive chloramines.

 

[kadriver]

Freechemist;

Thanks for the insight. I got the information for the title by looking back through some older posts and transposing the information from these old posts. I am still a newbie beginner and do not have these terms memorized yet.

My goal is to form the Pd salt that is readily soluble in ammonia. Would that be the (NH4)2PdCl6, ammonium-hexachloropalladate (IV)?

I want to avoid forming the Pd salt that is sparingly soluble in ammonia. Would that be the ammonium-tetrachloropalladate(II), (NH4)2PdCl4? I can see where I made a mistake with the roman numerals. It appears that the title should have the (IV) instead of the (II).

Maybe one of the moderators would kindly change the title, if it can be done. What should the title be?

I have saved all the rinse water and some fluffy dark grey material has begun to form in the bottom of the beaker.

With respect to "this" in line item two of your post, I was referring to the suspended material in the rinse water. I was wondering if there is something that can be added to the rinse water to get the suspended material to settle quicker.

Steve has offered a solution in the form of a tissue plug in a funnel. I have never used a "charmin plug" so here is another opportunity to try something new.

I also want to try your suggestion as an experiment to broaden my knowledge, so I'll divide the wash water and do both operations. I have a hotplate stirrer so it should be no problem.

I seem to remember a fault with using the potassium - it damages the fused quartz dish during incineration - if my memory serves me correctly. But I will do some more research and take the warning seriously - thank you.

kadriver

 

[lazersteve]

Kevin,

I have plenty of natural Sylvite (KCl) on hand and can send you a few pounds for free if you need them. Let me know via email and I'll get the KCl right out to you.

Steve

 

[kadriver]

I have done several more washes using distilled water and the pH has finally gotten to pH7 neutral.

The last pH test was a seven, but I did one more wash for good measure. I think I have done a total 7 washes - with the final wash being number 8.

I let each wash settle for at least 6 hours before decanting, testing pH and adding more distilled water for the next wash.

Notice the dark grey fluffy material that has coalesced in the bottom of the full beaker.

kadriver

 

[kadriver]

This is a shot of the 8th rinse after settling overnight.

The pH test was back to an acidic state of about pH6.

Don't know how that happened.

 

[kadriver]

The next step is to dissolve the residual zinc out of the black palladium with dilute HCl.

I scooped out a small portion of the Pd black powder from the main container and rinsed it into a small beaker with distilled water.

I added about 10ml distilled water to the small sample of Pd black, then added about 1ml of concentrated HCl.

The reaction began immediately with bubbling as the HCl attacked the bits of zinc.

I let the reaction continue until there was no more bubbles, then I added about 1/2ml more HCl and let it sit for another 1/2 hour.

Then I did a stannous test to make sure none of the Pd had dissolved.

 

[kadriver]

Before committing the entire batch to a dilute HCl treatment, I chose to see what would happen with a small test sample - because this is my first time doing this and did not know what to expect after adding dilute HCl to dissolve residual zinc.

My curiosity satisfied, I poured the test sample back into the main batch, rinsing all the Pd black out of the test beaker and into the main batch.

Then I added about 100ml or so of distilled water and about 10ml of HCl to the main batch, stirred, and got the same result as with the test sample.

There was fizzing and bubbling as the dilute HCl dissolved the last little bits of zinc that were too small for me to remove with tweezers.

I let the dilute acid sit over the Pd black powder for about an hour, adding a few drops of HCl to see if a reaction fizzed up - there was no more reation so I concluded that all the zinc was dissolved.

 

[kadriver]

I rinsed the black powder several times with distilled water.

The powder was very clean looking and settled quickly after each rinse.

The wash water was clean after each rinse - I did four rinses to ensure all the dissolved zinc was removed before going to the next step.

It there a reagent that can be added to the rinse water to precipitate the zinc? this would be a great test to ensure that all the zinc has been removed.

 

[kadriver]

This dilute HCl treatment really cleaned the Pd black powder up nicely.

It was fluffy and stuck together and settled very quick after washing.

 

[kadriver]

I got a clean dry 250ml beaker and weighed it to get a tare weight - I wrote the weight on the side of the beaker with a marker.

Then I transferred the Pd black to the 250ml beaker, rinsing all of it from the large 1 liter beaker.

 

[kadriver]

I poured off the rinse water, then gave it a few more rinses to make sure that the powder was nice and clean.

It settled and clung together so well that I could pour these rinses off very easily.

 

[kadriver]

Next I drained off all the water that I could and dried the powder in the beaker over low heat in my fume hood.

I then weighed the beaker with the dried Pd black powder to get the total weight of my product.

The tare weight of the beaker was 118.4g and the weight of the beaker and the dried black powder was 120.7g

The total weight of the Pd black powder was therefore 2.3 grams (120.7g - 118.4g = 2.3g).

 

[kadriver]

I then calculated the chemicals needed for the next step using the number 2.3g of Pd black powder.

I was instructed to use 5ml of a 90/10 solution of HCl/H2O2 for each gram of Pd black that is to be dissolved.

I wrote down the calculations and snapped a photo (hope my math is right here).

I am using AP (acid/peroxide) to dissolve the Pd black powder to avoid any nitrous compounds to be formed in with the Pd solution.

By avoiding the nitrous compounds I won't have to evaporate and rehydrate with HCl to expel the any excess nitric - because there won't be any nitric to expel.

 

[kadriver]

I set the beaker with the dried Pd black on the heater with the heat OFF.

Then I added the calculated amount of HCl required to dissolve the Pd black powder.

As soon as I added the concentrated HCl it turned orange - I have no explanation for this unless the conc. HCl has dissolved some of the finely divided Pd black powder by itself. I have heard that in this finely divided state that concentrated HCl can dissolve Pd - I hope that is what is going on here.

I added the 10.4ml HCl using a small pipette getting it as close to the amount needed as I could.

I decided to keep going with the experiment after encountering this unexpected color change.

 

[kadriver]

I put a cover on the beaker and then added the required amount of 40% hydrogen peroxide (got it at Sally's Beauty Store Supply for $4) to completely dissolve the Pd black.

I left this at room temp with no heat and let it stand overnight - more to follow.

kadriver

 

[mjgraham]

I have no input on the process but I wanted to say thanks for the photos and steps and info. The photos are great and of high quality, keep up the good work!

 

[lazersteve]

Kevin,

You are doing great.

A few tips:

1. Place a stir bar in the final reaction beaker with the blacks and stir constantly during the dissolution.
2. Heat the reaction to 40C
3. Use the least amount of solution possible for the dissolution, with the lowest possible water content. PGMs precipitate best from concentrated solutions.
4. You could have used the chlorine generator and HCl, instead of 10:1 AP, to dissolve the mixed blacks, increasing the concentration of the resulting solution while reducing the liquid waste generated.

A side note to the process you have chosen:

You also could have used diluted warm nitric acid to dissolve only the Pd from the mixed blacks and precipitated the refined Pd directly from the nitrate solution using any one of several reagents (DMG, SO2, NH4Cl, Formic Acid, Hydrazine, etc. ) without denoxxing. Nitric acid will not attack Pt black ( assuming no chlorine is present), but acid peroxide/chlorine gas will, even at room temperature. If your goal is to put both Pd and Pt back into solution together, then 10:1 AP will work fine. Just remember, your precipitated Pd/Pt salts from the pregnant AP solution will contain drag down cross contamination of the sister metal (Pt/Pd) salt, thus requiring you to refine them both again for highest purity.

Keep up the excellent posts.

Steve

 

[kadriver]

Great tips Steve - thanks.

I did not use chlorine gas because in the next step it (chlorine gas) is used to precip the ammonia soluble hexachoropalladate.

But what I did not think of is the fact that ammonium chloride will be added after the dissolution (where I could have used Cl gas instead of AP) and before the precip of the hexachloropalladate.

Its still all new to me and I am learning by doing as I go, making mistakes but learning from them. Plus others can follow this thread and learn from my mistakes.

kadriver

 

[kadriver]

When I got to my shop the next morning I was surprised to find that most of the black powder remained un-dissolved.

I expected it to be completely dissolved after sitting in the AP overnight (but as Steve pointed out, there should have been stirring and heat added).