Mixed Black PGM Powders

[lazersteve]

The data I compiled in the chart I posted above is from several very early chemical text that clearly states plain ammonium chloride will precipitate Pd from nitric solutions.

In Hoke she is assuming we have mixed PGM solutions, in these cases the solution is denoxxed to allow partial separation of the Pt and Pd. Since your solution is primarily Pd in nitric solution you shiould be fine with NH4Cl only. Make sure the Pd solution is very concentrated (blood red, burgundy wine color) before adding the saturated solution of ammonium chloride (37.2 g/100mL @20C). Remember that adding ammonium chloride to water will produce a cold solution (endothermic), so less than the above stated amount of NH4Cl will dissolve in the given volume of water. I typically make up a large bucket of saturated NH4Cl solution to keep in the lab with excess NH4Cl crystals in the bottom to assure saturation. Allow this mix to sit for sometime before using as the salt does not instantly dissolve, before use it should still have solid crystals in the bottom. Make sure you don't add any solids to the Pd solution when precipitating. It's fine to perform the ammonium chloride addition at room temperature or below.

You should try a small sample of the cold concentrated solutions (Pd nitrate and ammonium chloride) to be certain you will get precipitates when they are mixed. If your sample does not precipitate a brick red (or lighter towards yellow) salt as soons as you add the solutions together, one or both of the solutions is not concentrated enough.

If you Pd salt precipitates as a bright yellow color, it is very pure and does not need to be repurified. If it is darker colored towards brick red it needs purification.

Pure Pd Colored Powder:

Dirty Pd Colored Powder

If the color is darker than the first photo, repurify it.

Keep me posted on your progress.

 

[kadriver]

GSP:

I try to keep things tidy to aid my work - but yes, I do a little prep work before I shoot the pictures such as wiping off the surfaces and laying down paper towels.

It makes for a better shot and excludes clutter. Thank you for the compliment.

Steve:

I'll do a small test batch using the amounts and procedures outlined above. If I need to concentrate the main Pd solution, then I will just heat it on low and evaporate some of the excess liquid before precipitating.

Thank you for guiding me through the process.

kadriver

 

[kadriver]

Hello:

I performed an experiment on a small test batch of my main palladium nitric solution to see if I could get a precipitate.

First, I filtered the solution with fine filter paper.

 

[kadriver]

Then did a stannous chloride test...

 

[kadriver]

I made a saturated ammonium chloride solution using 50ml distilled water and a little over 20 grams of ammonium chloride.

Upon adding the ammonium chloride, the beaker chilled and the powder was not dissolving very well so I added a little heat.

Once the heat was added (two five second periods in the microwave) nearly all the powder went into solution and the resulting solution was clear.

Edit to add a picture

 

[kadriver]

I poured 50ml of the palladium solution into a 250ml beaker.

Then, using a disposable pipette, I drew off the ammonium chloride solution about 3ml at a time an began to add it to the palladium solution.

At first I could see a light colored precipitate start to form. I added about 25ml of the saturated ammonium chloride solution to the palladium solution.

The solution turned cloudy, but I did not see any red precipitate.

 

[kadriver]

I concluded that the palladium solution was probably not concentrated enough.

So I added a small teflon stir bar and placed the beaker on the hotplater stirrer on low heat to evaporate some of the liquid.

It took a while (about 2 hours), but I got what appears to be brick red precipitate.

I guess the next step is to repeat this experiment but first evaporate the palladium solution down with low heat before adding the saturated ammonium chloride solution.

Thanks for looking - any comments or critique always welcomed.

kadriver

 

[lazersteve]

Great work.

You can evaporate the Pd solution to 1/2 or less of it's original volume then repeat the test, you may need to heat the solution to get the brick red precipitate to form. Typically a saturated solution of Pd is so dark red you can not see through it.

Use DMG to scavenge the last of the Pd from the dilute pale yellow solution. This yellow Pd(DMG)2 can be added to the brick red precipitate and the mixed colored powders treated as described in the Purifying Dirty Pd post cited above.

The final resulting bright yellow Pd salt is then calcined, treated with zinc-acid, or base-hydrazine to get a very pure Pd sponge.

You are showing other members a perfect example of the processes related to recovery and purification of Pd, thank you for your dedication to the forum.

Steve

 

[RaoOvious]

As always great to see those visuals and inputs of Steve along together...Keep up the good work...

 

[kadriver]

Hello:

The precipitate looks a bit over-cooked with a slight crust and very little liquid.

I began the next steps by making a 15% ammonium chloride solution by adding 30 grams of ammonium chloride to 200ml distilled water.

I preheated the water in the microwave for about 40 seconds - it was not boiling, but very warm to the touch.

I added the ammonium chloride to the heated water and it dissolved quickly and completely.

I then used the 15% ammonium chloride water to rinse the sides of the beaker.

 

[kadriver]

Steve, thank you for your comments - I am enjoying the experience.

kadriver

 

[kadriver]

I then set up a filter and filtered the brick red powder.

I used the 15% ammonium chloride solution to wash the sides of the filter paper and to rinse the powder out of the beaker into the filter.

I also added about 9ml 15% ammonium chloride water to rinse the powder in the bottom of the filter and waited for the filter to run dry.

 

[kadriver]

After allowing the powder to run dry in the funnel, I removed the filter paper.

I opened the filter and spread it out on some paper towels to dry.

I will allow this powder to dry completely and add it to the rest of the powder later on.

kadriver

 

[kadriver]

I'll test the filtered solution with DMG, recover any Pd/DMG precipitate, and add to the brick red powder before purifying.

 

[kadriver]

Rather than repeating the experiment with another 50ml, I elected to go ahead and slowly evaporate the main Pd solution since I got the desired result from the first experiment.

The Pd main solution must be highly concentrated before adding the ammonium chloride to precipitate out the Pd.

I began by transfering the main Pd solution to an open container to facilitate the evaporation process.

I then moved everything outside since I do not yet have a suitable fume hood.

I placed the container on low heat to concentrate it before adding the ammonium chloride.

kadriver

 

[RaoOvious]

way to go kad.....keep em coming

 

[lazersteve]

Kevin,

No need to let the brick red powder dry fully. Slightly wet PGM powders are safer as they do not get airborne when handled and cause allergic reactions if they get in your eyes, lungs, or on your skin.

Rinse brick red salts and Pd(DMG)2 with water directly into beaker and dissolve in 10% NH4OH with lots of stirring.

Slimey or colored solids left in the ammonia solution is fairly normal. Filter these out until the solution is 100% transparent and free of particulate. Add >30% concentration muriatic acid to the ammonia solution with stirring until pH shifts acidic. Don't breath the thick white fumes (ammonium chloride vapors) when mixing.

Steve

 

[Lou]

Palladium isn't nearly as dangerous as platinum, but still, exercise good chemical hygiene.


You want to precipitate the palladium with ammonium chloride and sodium chlorate in the cold and make sure there isn't an excess of free chlorine (you can risk NCl3 formation). Also, you want to be over 50 g/L Pd but not overly high (200 g /L) because of drag down with other elements. Your solution should be largely Pt free. Pt and Pd are very difficult to separate if you don't have an ORP meter and are doing it conventionally and not using DMG (even then, precipitate the Pt first, rinse well, and then go after the Pd). DMG is for scavenging Pd, not for practical refining because it is so porous/fluffy/high in surface area, it will retain a lot of other PGMs and base metals.


I've attached two photos of what yours should look like. This precipitation was done at ~70 g/L and as you can see from the raffinate, it's possible to get very, very nice results (how many mg Pd+2 do you really think is left in solution per liter?). This is how yours should look kadriver--you've done everything right to this point. This material was pure enough it needed not the ammonia treatment and was calcined in the hood and then post-reduced with H2 in the tube furnace.


A note about the ammonia treatment:

when at first you do it, you may see a pink then fleshy precipitate appear--keep adding ammonia and let it digest. You really don't want the pH above 10, so it's easy to rush over much. Most of the gunk will precipitate at 2. I do two filtrations on it: 1 at pH 10, 1 at pH 8. Then take to pH 2-2.5 and filter again. The hydroxide cakes will hold up significant Pd; consider this a polishing step after your Pd is already 99%.

Just because it is nice and yellow doesn't mean it is pure, as the other PGMs can readily contaminate it and leave no visible trace. It will not remove Pt well unless the solution volume is high and the Pt content is less than 0.2%, and then Pd begins reporting appreciably. I am NOT (let me be emphatic here) a believer in using zinc EVER to reduce fine palladium produced from this procedure and disagree with Steve wholly on that. I am fine with it for platinum, because the zinc distills off at 1800C (probably into the lungs). If you want to reduce it, caustic soda and formic acid, 65-80*C. It is the best way to reduce palladium from the diammine. It gives a nice, easily filterered open pore precipitate, much like proper hydrazine application with ammonium hexachloroplatinate.

 

[lazersteve]

Lou,

There is no need for sodium chlorate in his precipitation reaction because he is precipitating from a nitric solution.

Steve

 

[Lou]

Oh yes, I see that now. Didn't read it all the way.

Advice still stands.

From a nitrate solution it is possible, and preferred although that makes an inferior precipitate. It is preferred because it's safer and in his case, easier than syrupizing into a chloride and less manipulation. It is not advisable to add ethanol/DMG/DMSO (any organic) to a concentrated nitric acid solution, especially when hot. Therefore, ammonium chloride is a good avenue for this particular instance.