precipitation of ammonium hexachloroplatinate

[cdepace]

I have been trying to get this reaction to happen for sometime with no positive results. Is there a pH range which should be established before the reaction will take place. My process is as follows:

Decan the Cats
Grind the Cats using a Ball Mill
Roast the Cats
Aqua Regia --> Boil down 3x to expel HNO3
Add approx. 3x volume in water
Filter
Add approx. 50g of NH4Cl and heat
Then ... Nothing

I am confident that my leaching process is sound, because using electrochemical laws, I was able to coat a copper wire with the platinum. Any help, comments or direction would be greatly appreciated.

Thanks

By the way, if this is wrong forum i am sorry, but does anyone know where approx. how much pgm's are lost in cat over time, maybe like an amount / yr. I understand that this is hard to answer, but if someone could estimate it would be a great help. Sorry if this question is wrong forum

 

[samuel-a]

I see no mention of testing with stannous chloride...

How do you know there is Pt in your leach?
If you are unfamiliar with testing, you can start here

PGM's solutions will not perform when too diluted. After de-nox, keep the solution concentated.
once cold, add NH4Cl ----> No yellow precipitation, no Platinum. it's simple.
then add Na/K chlorate or hypochlorite solution and watch if any red Pd salt is being precipitated.

 

[Harold_V]

Aqua Regia --> Boil down 3x to expel HNO3

Refrain from making reference to evaporation by discussing boiling. That is not acceptable terminology on this forum. One DOES NOT BOIL to evaporate---that is the source of lost values.

If you mean evaporation, that's what you should say.

Do not put a number sequence on the elimination of nitric by evaporation. It does not magically disappear after three evaporations. It may take five, and it may take one.

Harold

 

[freechemist]

Precipitation of ammonium hexachloroplatinate occurs only, if the concentration of dissolved platinum is fairly high (at least several grams per liter). With rising temperature the solubility of ammonium hexachloroplatinate is rising too. Thus, heating will not help in the precipitation process. After my experience, a honeycomb-type-catalyst, once dismantled and milled down to a fine powder, yields a maximum of about 1-1.5 grams of PGM's (mainly Pt and some Rh) per kg of dry powder. Leaching with AR yields copious volumes of highly diluted PGM-solutions, containing also a lot of dissolved base metal (mainly Al), originating from the powdered ceramic base material, it's concentration being much higher than the Pt-concentration, making concentration of PGM's to a practicable value by evaporation nearly impossible. The only way to recover platinum would then be by reduction to Pt-metal, which can be accomplished with zinc-dust, or, probably, by elemental gaseous hydrogen, if a certain amount of finely divided platinum- and/or palladium-black is already present in your leaching solutions. An alternative reduction-method is the reduction with sodium borohydride (NaBH4)-solution. NaBH4, even as an aqueous alkaline solution ("VenMet") is commercially available. The following Link gives you a list of suppliers and products: http://www.buyersguidechem.com/AliefAus.php?pnumm=392685484825.

- And, don't forget, testing with stannous chloride will let you detect dissolved platinum down to concentrations of a few milligrams per liter.

Regards, freechemist

 

[HAuCl4]

freechemist: How about the cheap sodium formate?.

 

[freechemist]

For several reasons I think that sodium formate will not be useful, amongst them mainly the one, that you have to bring big volumes of acid to a pH value of at least 3-4 to give quantitative reduction a chance. So for me, the conditions given, sodium formate, even if much cheaper, is no option.
Besides, in my earlier refining-times, I once was lucky to obtain on demand, answering an add in a chemical related journal, a whole liter of "VenMet"-solution (20% Na BH4 in a 20-30% NaOH-solution) as a free sample.

Regards, freechemist

 

[HAuCl4]

Interesting. Thanks. I always get freebie chemicals from customers surpluses, throwaways, etc. Definitely the way to go if one only process stuff sporadically like me.