# Black solution appeared after cementation of acidic solution containing at least Pt and Pd



## nahan (Apr 9, 2018)

Hi friends

I have dissolved some ore by pyrometallurgical process followed by resulting a hydrochloric acid solution containing Pt and Pd analysed and detected by atomic absorption, along with many other base metals like Fe, Co, Mn, Cu, Ni, etc. so, when I try to cement Pt and Pd by copper wire from my orange colored acidic solution, a very black solution is appeared as if I have dropped black ink inside the solution and even after a week, no detectable black precipitate but a black solution is observable, and a white precipitate is gathered at the bottom of the solution.

1-What should be this very black color, which seems not to be filterable as a distinct black precipitate?
2-Is this a colloidal Pt, Pd, or even any other PGMs like Rhodium (which I saw in a paper indicated that Rh could be precipitated from acidic solution by Cu powder as a black precipitate)?
Any comments will be appreciated.


Nahan.


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## Lino1406 (Apr 9, 2018)

Traces of silver, silver chloride


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## nahan (Apr 10, 2018)

Are you sure about silver? How can I separate it from the solution? 

Nahan.


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## Palladium (Apr 10, 2018)

Centrifuge!


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## nahan (Apr 10, 2018)

Thank you Palladium! I will try it.
Only a problem remains! Where did Pd and Pt go ??


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## kurtak (Apr 10, 2018)

Are you using heavy pieces of copper (like copper buss bars) copper wire - or copper powder to do your cementing ?

Are you using some kind of agitation such as a bubbler (if using heavier copper) or stirring (if using powder) ?

The agitation needs to be vigorous 

PGMs - without agitation - tend to create a "thin" passivation layer on the surface of the copper that prevents the PGMs continuing/completing the cementing process

"Traces" of silver chloride can cause the same passivation problem - which agitation may - or may not over come

Kurt


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## Iggy-poo (Apr 10, 2018)

Sometimes, boiling the solution gently, will cause the fine precipitate to coagulate into clumps that will readily precipitate. Try a small sample to determine time and rate.


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## kurtak (Apr 10, 2018)

Iggy-poo said:


> Sometimes, boiling the solution gently, will cause the fine precipitate to coagulate into clumps that will readily precipitate. Try a small sample to determine time and rate.



If you have a colloid problem you are better served using a flocculant --- with an acidic solution you need to use an organic polymer floc

Edit to add; - although heat sometimes works - I have had better luck freezing solutions which again only works "sometimes"

Kurt


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## nahan (Apr 10, 2018)

Thank you Kurt!
I used thin copper wire so that after a week almost all of the wire was dissolved. In addition, sometimes vigorus agitation was performed so, passivation could not be a problem in my work. 

As Iggy-poo stated, gentle heating seems to be efficient to coagulate the black solution but first of all, it should be cleared that really what is the black matter (as solution)? Silver may be a propre candidate as Lino 1406 stated, cause silver is lower than copper in the electromotive series but some other elements like Pt, Pd or Rh are in the same position which I think could appear as black precipitate/matter during the cementation so, could the black matter be rhodium? platinum? gold? or even a non-precious metal??


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## kadriver (Apr 16, 2018)

Palladium said:


> Centrifuge!



I experienced the same thing. I ran it in my cetrifuge for 10 minutes and it was still black as ink. But I did have some black powder that settled. and I was able to get that.

Where can I get some "floculant" to see if I can get this black ink to clear up and come down?

Thanks
kadriver


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## kadriver (Apr 16, 2018)

nahan said:


> Hi friends
> 
> I have dissolved some ore by pyrometallurgical process followed by resulting a hydrochloric acid solution containing Pt and Pd analysed and detected by atomic absorption, along with many other base metals like Fe, Co, Mn, Cu, Ni, etc. so, when I try to cement Pt and Pd by copper wire from my orange colored acidic solution, a very black solution is appeared as if I have dropped black ink inside the solution and even after a week, no detectable black precipitate but a black solution is observable, and a white precipitate is gathered at the bottom of the solution.
> 
> ...



Here is a quote from freechemist on this colloid suspension and a possible way to solve the problem

freechemist said:
"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."

kadriver


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