Ammonia Soluble Hexachloropalladates (IV)

[Lou]

Kevin,

The suggestion of dissolving all of the ammine complexes in AR was to save you the step of cementation and introduction of more impurities. A little zinc is probably helpful on the Pd refining side.

When digested in aqua regia, ammonium hexachloroplatinate (palladate, other ammine compounds), the amine ligand or ammonium cation is oxidized away.

Basically, one can reflux in aqua regia any hexachlorometallate, or ammine chloride, and get the respective metal acid. You are oxidizing away the nitrogen.

So, (NH4)2PtCl6 + excess NOCl + H(+) ---> H2PtCl6 + NOX/N2 gases; similarly for Pd.
You can digest Pd(NH3)2Cl2 in aqua regia and get [PdCl4](2-)

It is done when gas evolution stops and no more yellow salt remains to be seen.

Anyhow, your next step is to either to separate the Pd by the chlorate method, or to run a hydrolysis.

 

[kadriver]

Lou, I was wondering what would happen to the ammonium chloride in AR.

How about the nitric from the AR, the zinc take care of that? Should the dissolved yellow Pd salts be de-noxxed by evaporation?

I did not denoxx but just went ahead and added zinc turnings to the filtered Pd/Pt solution.

I was gone all day and did not get to the shop until about 9pm.

This is what the blacks looked like when I got there;

 

[kadriver]

There were still some pieces of zinc in the black powder so I picked them out with tweezers rinsing the black powder off each piece of undissolved zinc with distilled water from a spray bottle.

 

[kadriver]

Then I began to rinse the blacks with distilled water to pH 7.

I did this to ensure there would be no nitric present because the next step is to remove any remaining bits of zinc with dilute HCl. I don't know if this step to remove the nitric with repeated distilled water rinses was necessary or not.

I began the rinses by adding distilled water to the blacks and checking to pH with a pH test strip - it was bright red pH 1 due to the acid present from the AR.

I poured the wash water that contained suspended PGM blacks into 4 plastic bottles about 125ml each.

 

[kadriver]

After carefully weighing each bottle I placed them into the buckets of the centrifuge.

 

[kadriver]

Then I spun then at 1100 rpm for about 10 minutes

 

[kadriver]

The suspended black powder (which usually takes for ever to settle) was all at the bottom of the bottle so I carefully decanted the clear liquid and added the liquid to my PMG stock pot (a 3 liter glass jar I got at the thrift store).

 

[kadriver]

Then I added more black powder to the bottles and spun it again, decanting the clear liquid each time.

I repeated this until all the black powder was in the bottles.

After adding distilled water to the black powder in the bottles and spinning for 10 minutes at 1100 rpm for fives times the pH was up to 4

 

[kadriver]

After each spin I decanted the clear wash water leaving only the black powder at the bottom of each bottle. I then squirted distilled water forcefully into the black powder to rinse it real good.

Then I would spin it again, 10 minutes at 1100 rpm.

I had to use these tweezers to get the bottles out of the buckets because they were flush with the top of the buckets and I could not grab them

 

[kadriver]

It took nine rinses as described above to get the pH to 7 and over a gallon of distilled water.

Like I said before, I do not know if this step (rinsing and spinning to rid the black powder of acid) was necessary or not.

It only took me 3 hours to rinse the powder free of acid.

For those who don't have a centrifuge however, this process would have taken much longer because this stuff does not settle very easily.

My next step is to treat the black powder in 50/50 dilute hydrochloric acid to remove any bits of zinc from the black powder.

More to follow.

kadriver

 

[kadriver]

Kevin,

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.

I went back to the top of the thread and found this statement.

So the washes were necessary.

Tomorrow I'll do the dilute HCl treatment then I'll set up the chlorine generator and dissolve the black powder using chlorine gas to completely avoid any nitrates in the mix.

Cheers!

kadriver

 

[kadriver]

thank you for restarting this thread... I think i am going to be dealing with Pd soon, so i am going to be following this thread closely! thanks again!

I missed this, glad to hear that you are watching.

I've got to learn how to get the PGMs out because I am starting to see a lot more of them now.

One key ingredient to success in ANY endeavor; a strong desire to make it happen. Without this I only operate at half steam or just do enough to get by.

I want to save any Pt that comes out of this until I have enough to do a bromate hydrolysis.

Hope this helps you - I can't wait to get the pure Pd sponge at the end!

kadriver

 

[kadriver]

I decanted the last wash water then added a little distilled water to each bottle.

 

[kadriver]

Then I added an equal amount of HCl to dissolve any remaining zinc particles left over from the cement action process.

There was no reaction, no bubbles at all. I thought there would be a little fizzing as the zinc dissolved.

 

[kadriver]

Just to make sure, I transferred the contents of each bottle to a beaker and added some more HCl and let it sit for about an hour.

I even used HCl to rinse the inside of the bottle instead of water - the HCl was greater than 50/50 concentration and still no reaction at all.

I concluded that all the zinc was gone.

 

[kadriver]

Just like last attempt at the beginning of this thread, the HCl cleaned the black powder nicely.

It was fluffy and settled almost instantly.

 

[kadriver]

I decanted the HCl with a small pipette and then did a couple of washes with distilled water.

Each time the powder clumped together and settled instantly.

I decanted the last rinse and then put it on low heat to evaporate the liquid from the black powder in a beaker with the tare weight of the empty clean dry beaker written in the side of it

 

[kadriver]

After about an hour the powder was bone dry, I did increase the heat to medium towards the end of the evaporation.

The powder looked clean and ready for dissolving in chlorine gas.

 

[kadriver]

I put the beaker on the scale to weigh the black powder, it was 8.2 grams of dry black mixed PGM powder.

 

[kadriver]

I then rehydrated the black powder with a little full strength HCl.