# Problem Droping the Platinum out of Aqua Regia



## Anonymous (Jun 11, 2008)

We mixed silver (50gr.) with platinum(29gr.) Placed it in Nitric Acid got rid of the silver, and then placed the remaining dust in to the Aqua Regia.Platinum disolved in the solution boiled twice and added Hyrochloric acid to get rid of the nitric and then put in the ammonium chloride to drop the platinum sponge out.
Which it did but we were excpecting a lot more to come out, we only got 6.70gr pure Platinum out. Any Idea where the rest of the Platinum could be???


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## Harold_V (Jun 11, 2008)

rob said:


> We mixed silver (50gr.) with platinum(29gr.) Placed it in Nitric Acid got rid of the silver, and then placed the remaining dust in to the Aqua Regia.Platinum disolved in the solution boiled twice and added Hyrochloric acid to get rid of the nitric and then put in the ammonium chloride to drop the platinum sponge out.
> Which it did but we were excpecting a lot more to come out, we only got 6.70gr pure Platinum out. Any Idea where the rest of the Platinum could be???


Yep! 

In your silver :!: 

Assuming you recovered the silver with copper, you can recover the platinum by parting the silver in a silver cell. It will report in the slimes. 

Did you heat the nitric solution? Was your silver solution blue/green, or was it quite dark green? If you recovered the silver with copper, given enough time the platinum will have cemented out, too. It usually comes down last, and leaves a dark trace in the silver. If you recovered the silver as silver chloride, the remaining solution should still be dark green, or even leaning yellow, depending on how much copper was mixed with the silver. Test the solution with stannous chloride----do not trust the color of the solution to be the final indicator.

"But, platinum won't dissolve in nitric", you're inclined to say. 

That's true----it won't. But all the rules change when platinum is in the presence of silver. It does dissolve, albeit slowly. In this case, because you had it finely divided, I expect a great deal of it dissolved. That's one of the reasons I liked to use silver for inquartation. It becomes the carrier of the platinum group, which normally isn't recoverable in small amounts in large volumes of solution. See Hoke for more information on this subject. 

One other thing to consider. The platinum group of metals often will not precipitate totally, and will occasionally refuse to precipitate at all (solution is often too dilute). Be certain you test the remaining (chloride) solution to insure you got complete precipitation. If you did not, it may be required to extract the platinum with zinc, then re-process. 

If you would like a full recovery, keep your solutions as concentrated as you can. When you have a cylinder of platinum that is well concentrated, the moment you introduce ammonium chloride, it will flash brilliant yellow, with a virtually complete precipitation, assuming you have enough ammonium chloride present, and you have properly evaporated. 

In the future, if you desire to process platinum, do not alloy it with silver. In the solid state, it will dissolve in AR if heated, although it takes quite a bit of time. That way you don't lose any to other metals. 

Harold

edit: removed one word that did not belong in the second large paragraph.


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## Anonymous (Jun 11, 2008)

Hi Harold
I hope you are well. Thank you once agin for helping me out.
The Silver (50gr.) in the Platinum (29gr.) was pure silver. 
And yes we did Heated the nitric acid.
After we filtered the solution from the black dust (platinum) the liquide was a dark green colour. Which we still have. I was going to use salt do get the silver out.
The Black powder we placed it in the AR and after that we boiled it twice and then we added water 3 times the volume of the solution which was,
1.5L of solution + 4.5L water.After that we added the ammonium chloride.

There was no copper used at all.

So what do you suggest I do with this Nitric acid solution I have???

With the AR chloride solution Should I just drop in zinc like you suggested and then re-process. What happens when I drop zinc in there and how much Zinc do you think i should put in there???

Once again thank you to everyone who is willing to help.
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## Harold_V (Jun 11, 2008)

rob said:


> The Silver (50gr.) in the Platinum (29gr.) was pure silver.
> And yes we did Heated the nitric acid.
> After we filtered the solution from the black dust (platinum) the liquide was a dark green colour.


Bingo!

Pure silver in a nitrate solution is virtually colorless (a pale yellow at the worst, and blue only if there is copper present). It is dark green because you have dissolved platinum included. 



> Which we still have. I was going to use salt do get the silver out.



In this case I'd recommend you use HCl instead of salt, then rinse the silver chloride well, until there is no color rinsing out. The remaining solution should be yellow, lighter or darker, depending on the degree of saturation. 

Evaporate the solution to eliminate nitric, then you should be able to precipitate the platinum with ammonium chloride. The use of HCl instead of salt is to eliminate any problems you may have with the salt in evaporation. It is more than desirable to keep the solution as concentrated as possible. The presence of free salt may make that impossible. 



> The Black powder we placed it in the AR and after that we boiled it twice and then we added water 3 times the volume of the solution which was,
> 1.5L of solution + 4.5L water.After that we added the ammonium chloride.



As I mentioned previously, the degree of concentration is important with the platinum metals, at least for platinum and palladium. I have no experience with the others. Keep your solutions as concentrated as you can, so you can achieve full recovery. If you can dilute only one volume, that would be very good. In this case, if you had a grand total of 6 liters of solution, I'm surprised you got any reaction at all. I would have had no more than a half liter of solution after filtration, to which I would have introduced the ammonium chloride. I repeat----keep your solutions as concentrated as you possibly can-----otherwise you won't achieve good recovery. Knowing how dilute yours was, I have no doubt, you left some platinum behind. Is the remaining solution yellow?



> So what do you suggest I do with this Nitric acid solution I have???



See above. The values can be recovered quite easily. 



> With the AR chloride solution Should I just drop in zinc like you suggested and then re-process. What happens when I drop zinc in there and how much Zinc do you think i should put in there???



If you choose the zinc route, I suggest you combine all of your solutions once you've precipitated the silver as chloride. That would include all of the rinses. By now it will be very dilute. You may not have to evaporate, assuming you don't have too much free acid present. An ounce of zinc should be adequate, but an excess does no harm. Use zinc flour if you have it at your disposal. Stir the vessel well, then sprinkle the zinc in the solution. The conversion should be quite rapid. Test the solution with stannous chloride, and add more zinc until you get no reaction. 

Allow the material to settle well, then decant the barren solution. Get the remaining solids in a beaker, then introduce HCl, which will dissolve the remaining zinc. That should leave you with fairly pure platinum, but any base metals that may have been present will possibly still be there, so I'd recommend you re-dissolve the black powder in AR. 

This time, when you filter the solution (after evaporation) keep it as concentrated as you possibly can. It should be a dark yellow color, even leaning towards brown. You'll find it precipitates much better, and possibly completely. Use an excess of ammonium chloride----it does no harm. My practice was to use about 25% more than necessary, which I dissolved in hot water. As you likely know, the water turns cold upon dissolution of the ammonium chloride----so don't start with cold water. Takes too long to dissolve.

Let us know!

Harold


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## Lou (Jun 11, 2008)

Those are essentially perfect instructions and I have nothing to add. I must stress that it is imperative that you keep the solutions as concentrated as possible, that is important advice!



Lou


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## Lino1406 (Jun 12, 2008)

2.9g at 0C
6.7g at 20C


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## Lou (Jun 12, 2008)

You mean the ammonium hexachloroplatinate.


Looking at those numbers, it's obvious why smaller volumes means better recovery. 

A little trick is to add some ice cold ethanol to a solution containing (NH4)2PtCl6. It will help get a second crop of crystals.


Lou


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## Lino1406 (Jun 12, 2008)

Complete recovery


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