# problem with platinum salts



## lazylightning (Jul 30, 2008)

Hi,

So I have a solution that tested positive for Pd and Pt using the stanous chloride. I neutralized it via boil-off and proceeded to add ammonia chloride to it while hot, filter and repeat. I got many different colored salts, starting with a deep red at first. Then orange, then fine orange and fine yellow crystals. Later when I diluted it a bit I got really light yellow large crystal precips. I went through nearly two kilo's of ammonia chloride ( I ran out) and I'm still getting precips and the solution is still a dark green color.

When I take any of the crystals and dissolve them in a minimum few drops of water or HCl, my stanous test shows nothing. Stannous works with known test solution. My red crystals make a yellow solution that can stain the paper towel itself light brown where there is no stanous but there where the stanous is its a nice white color- nothing. Any ideas?


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## Oz (Jul 30, 2008)

The first question that comes to mind is other than Pt and Pd what was your starting solution. Second is what was the source of PMs? It may give clues if there is contamination of other elements.


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## Lou (Jul 30, 2008)

More details please.

Did you add ammonium chloride solution, or the powder itself?
How much PGMs were you expecting in grams? Of what kinds (Pt, Ir, Ru, etc)?


Try adding HCl to the paper towel that has soaked up some of your dissolved precipitate. See if it also doesn't clear up.

I would like to see some photos.


I'm fairly certain I gave complete procedure for separating Pt, Pd, Ru, Os, Ir, and Rh to you already. I suggest you look it up!


Lou


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## Oz (Jul 30, 2008)

In case you don’t have a camera do these look familiar?


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## Lou (Jul 30, 2008)

Oz, good work my friend! That is what it should look like! Oddly enough, I find that the closer your platinate precipitate is to a nice canary yellow, the better quality it will be. Just something I noticed.


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## Oz (Jul 30, 2008)

Lou,
Thanks for the kind words!
Maybe I’ll do a re-processing of some platinum precipitate for chuckles to see just how much cleaner a yellow I get.


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## lazersteve (Jul 30, 2008)

Lou,

I'm been striving to get that illusive canary yellow Pt you have talked about. I finally made some, but I had to use the PtCl2 powder you sent me to get there.

Typically I get the stuff from my cat extractions to come down canary yellow with a tint of green (Rh). The most common Pt precipitates I see are orange. They all test the same to stannous chloride.

Do you have any suggestion for repurification of the orange salts to make them yellow? I know how to repurify the red Pd salt to nice yellow salt, but not the Pt salt (aside from incineration and redissolving the black metal in AR).


Steve


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## Lou (Jul 30, 2008)

It is hard to get that particular quality ammonium hexachloroplatinate because it is often contaminated with Pd and Rh which impart a darker colour to it. When it is canary yellow, your Pt will always assay 99,95% at the _minimum_.

While I don't have a surefire way to cheat your way out of a repurification step, I do have some helpful pointers for getting a purer product. Really it is dependent upon how much Pd and Rh are present and to a lesser extent others in the platinum group.


Keys to improving your purities:

Use high quality ammonium chloride.
Use a saturated solution of ammonium chloride and do the reaction quite warm (say 60C), then heat to 80 or so. Then let it cool slowly. Once it is at room temperature, put the solution into an ice bath. Filter and rinse with cold saturated ammonium chloride. This will rinse many of the undesirables right out.

If you're hell bent on getting it yellow, you can recrystallise it from a saturated ammonium chloride solution (saturated at room temperature, you must heat to dissolve the (NH4)2PtCl6. You add your powder until it will no longer dissolve in the solution, boil for a while, and then let it slowly cool. It should start crystallising almost as soon as the heat is off. Add a little hot distilled water, just a bit, and then seed it with some pure product. It will start to crash out and as it cools you will get a large crystalline product. Chill in ice solution and filter. It should be fairly pure in this case. Keep in mind this only works for removing at most .5-.75% of impurities from the finished platinum. 

So heavily contaminated stuff will not work.

Remember to keep all the filtrates that have Pt and reuse them.


Lou


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## lazylightning (Jul 31, 2008)

Hi! I think I understood pretty well how to do it. Something is strange though. I heat it to about 80C and add four tablespoons of dry ammonia chloride to the 400 - 600 ml solution that tested positive for Pd or Pt. It did not test positive for Rh. The solution no longer tests positive for Pd or Pt and neither does the dissolved precipitate. My known gold is a very concentrated solution and it makes a big dark purple fuzz relief spot on the paper towel when dried, perhaps my stannous works because the gold solution is too concentrated? Perhaps I'll try to thin it out and retest that stannous.

There was no Ru or Os left to go into this solution. It was removed and retrieved. I suspect Pd and Pt because this is the solution from the sponge I tried to boil down for four hours with strong AR. That which didn't dissolve I suspect to be Ir, because later when I tried to boil it for hours in conc. sulphuric acid and it was barely phased and the liquid is very blue and does not test positive for Rh.

I forgot to weigh my sample before boiling it in the AR, there may have been about 100 grams or so that went into solution. Maybe 20, hard to say. There was 275 grams before I put it into hot 40%(fuming) HCl for hours to get rid of the base metals. I have 44 grams of what doesn't want to dissolve in anything and I suspect it is Ir.

I'm getting on a plane for a month trip to the Us tommorrow so I guess I'll have to get back to it later on. I'll try to get on line for continuing disscussion ;-)


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## lazylightning (Jul 31, 2008)

more


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## lazylightning (Jul 31, 2008)

Actually it's coming off even more bright yellow than the filterfull in the photo. If it was any lighter a yellow I'd wonder if it was white. If I add some HCl and /or boil off some excess liquid then it starts coming off more orange in color. Strange it will also fluctuate between clear yellow and the next drop is slightly orange and after that bright pure yellow and then slightly orange and so on without changing anything.


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## lazylightning (Jul 31, 2008)

I tried to make a few photos bigger to see the crystals up close.

The source? An ore concentrate leach contaminated with iron and anything else. The Os and Ru were distilled off as oxychlorides in a vacuum rig. The remaining salts were reduced a bit at about 475C under a bit of hydrogen overnight. This baked down mass was chiseled out, ground up and put into hot 40%(fuming) HCl for several hours. Then the remaining solids went into hot conc. AR for four hours (with replentishments of AR). This liquid was boiled down to syrup twice. It tested positive for Pt or Pd with the stannous(liquid in test tube turned yellow). When I added the ammonia chloride to it (until it wouldn't dissolve anymore) hot -80C, after it cooled I had that layer of ruby red crystals. After about four such precipitations it started to give me orange instead of red. Then as I got to yellow I understood that by diluting it a bit, the precipitate would be more yellow and finally pure yellow which I suspect is Pt.


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## lazersteve (Jul 31, 2008)

Lightning,

The Pt salt dissolved in dilute acid should give you a good stannous chloride test for Pt.

Have you incinerated any of the material in the photos?

If so what percentage of the material weight is metallic?

If you are in a hurry, you could dissolve some of the salt in hot water, add a small amount of HCl, and precipitate the metal quickly using zinc dust. Follow it all up with a good HCl wash after filtering and see what you've got.

Once you have the black powder sample you can redissolve it in hot AR and test with stannous chloride for Pt. 

The percentage of the material that is metal could be an indication of what you are dealing with, as well as the reaction to stannous chloride of the test sample.

The crystals are well formed compared to any that I have ever precipitated, mine come down as grainy powders. I have seen excessive amounts of ammonium chloride in the solution form well defined, almost transparent, ammonium chloride crystals also.

Steve


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## Lino1406 (Jul 31, 2008)

1.Stannous chloride test + NH4Cl test
work quite similarly also for selenium, titanium
(see mine "the not-platinum riddle")
2.Changing from orange to yellow -
in platinum - requires change of valence


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## lazylightning (Jul 31, 2008)

Thanks for the good idea. I'll have to try it when I get back in a month. I'll let everyone know then.




lazersteve said:


> Lightning,
> 
> The Pt salt dissolved in dilute acid should give you a good stannous chloride test for Pt.
> 
> ...


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## lazylightning (Jul 31, 2008)

Lino1406 said:


> 1.Stannous chloride test + NH4Cl test
> work quite similarly also for selenium, titanium
> (see mine "the not-platinum riddle")
> 2.Changing from orange to yellow -
> in platinum - requires change of valence



Hi, thanks for the idea. do you have a link to that "the not platinum riddle"? I tried to find it on the forums to no avail. Perhaps I have Os, Ru and Ir but no other pgm's. Anything is possible.

Also, it seemed to me that the orange could be from a mix of Pt with the potential Pd or Rh that might be there too. As I understand, strict control over the ph can let you selectively precipitate.


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## Lou (Jul 31, 2008)

That is ammonium chloride that has entrained some values in its structure. 

You may chose to heat a crystal (after massing it) and then determine how much mass it loses. By this you can determine how much was chloride, and how much is the complex.


Even the best precipitated ammonium hexachloroplatinate will still have 4-5% of ammonium chloride, especially if you did the wash.

I think you should consider reducing values with zinc, and then heating with HCl, then ammonia, then rinsing with water and heating. Add 50/50 solution of nitric acid, and let it simmer until the colour doesn't deepen. 

You have options then, some do a better separation but take more time, are the opposite.

Lou


There's money in there, there's just not very much.


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