platinum +silver

arthur kierski · Nov 19, 2010

i am receiving a ball containing pt and silver(300grams)
how can i separate the pt from ag?
i heard that in this special case nitric acid will dissolve pt and it becomes almost impossible to recover from the nitric solution
thanks for any help and advice

Arthur

4metals · Nov 19, 2010

Generally if the silver content is 10 times greater than the platinum content, the platinum will pass into the nitric when dissolving. This is a fire assay trick to remove gold from platinum by adding excess silver.

You can recover the silver in a silver cell and recover the platinum in the slimes in the anode bag.

HAuCl4 · Nov 19, 2010

What is the % of Pt vs Silver?. If it is less than 10%, the easiest is to run it through a cell like 4metals says. If you don't have a cell then you can also:

1-Use sulfuric acid for digestion of the silver. The Pt stays as black powder. If there is Palladium some of it dissolves, some stays with the Pt depending on %.

2-If you insist in using nitric acid, you can drop the AgCl with table salt, filter the solution clear of AgCl, and then cement the Pt with a copper bar. But the AgCl will likely retain some Pt unless washed very carefully.

If it is more than 10% then make it less than 10%!. :lol:

4metals · Nov 19, 2010

The parting with sulfuric acid is also a valid option, it is used in the fire assay attached.

Oz · Nov 19, 2010

I do not recall Arthur ever mentioning a silver cell so he will probably go with nitric. If that is the case, after removing any undigested Pt from your nitric digest I would add HCl (not salt) to precipitate your silver as the chloride. After separating your silver chloride, wash it well as it will want to drag down Pt from your solution. Add your washings to your solution and filter well one more time to get as much as possible of your silver chloride removed.

At this point you have Pt in AR and it depends on if you want sponge or salts of platinum. For sponge, cement with zinc,(if you are concerned by traces of silver chloride you can do a wash with ammonium hydroxide then rinse here) then wash solids in HCl to remove any traces of excess zinc. For salts, reduce to syrup with HCl additions to remove nitric then precipitate with ammonium chloride for your ammonia hexachloroplatinate salt.

The above is based only on having silver and platinum in this mix, if there are other traces modifications may be needed. If there is not enough silver you could be left with platinum solids from your nitric digest that have trapped silver, the same as you would with a gold/silver inquart that was too low in silver.

Wish you the best Arthur.

arthur kierski · Nov 19, 2010

i do not have a cell-----i do not know the % of ag and pt in the ball------i will try to find the percentages------most likely i will digest the ag with sulfuric ------thanks for the informations
Arthur

arthur kierski · Nov 19, 2010

thanks Oz,i received your thread when i was answering the other members.
by the way,it is only ag and pt(no other precious metals)----perhaps i will have more details tomorrow.
i received your e-mail about the rich chinese city----very interesting
thanks
Arthur

Oz · Nov 19, 2010

Its always a pleasure Arthur, I like your tenacity and ethics.

I am curious as to what compelled you to take the sulfuric digest route though. Hot sulfuric is more hazardous and slower than the nitric and you still need to be sure you have less than 10% platinum. I also know nitric is inexpensive for you.

I'm not being critical, but I am curious.

Corrected typo, I wrote silver where it now says platinum

arthur kierski · Nov 19, 2010

Oz,you are very kind in your comentaries.

i chose sulfuric because i was afraid nitric would dissolve some platinum and that would be dificult to recover from the nitric solution--------i read this in george gadjas book and this stayed in my mind ( i read this 10years ago)
by the way,i think that the ball is 80 to 90%ag-----i suppose 1to2ounces of pt-----
surely as you mentioned i have all nitric i need at a very cheap price---and probably i will use it because of my experience with nitric
thanks again
Arthur

Oz · Nov 19, 2010

Well I can understand if you wished to avoid the digestion of your platinum but it is not difficult to recover from the nitrate. You are familiar with AR and removing silver chloride as well as nitric from solutions. I see the logic either way. I personally would still take the nitric route, but I also run silver cells and I never really cared for cementing silver out of sulfuric either.

Let us know how you choose to proceed and how it works out for you.

4metals · Nov 19, 2010

Arthur,

One of the best things you can do with George Gajda's book, Gold Refining, is to burn it. It is full of partial information and unnecessary steps, better books have been written.

I'm surprised you don't have a silver cell, you've mentioned silver scrap many times on the forum.

Oz · Nov 19, 2010

4metals said:
One of the best things you can do with George Gajda's book, Gold Refining, is to burn it. It is full of partial information and unnecessary steps, better books have been written.

I have never read George Gajda's book, but one of the best books ever written on refining is this forum. It has very knowledgeable people with many years of hands on experience, as well as all the typical mistakes as they happen and the solutions to them.

lazersteve · Nov 19, 2010

Arthur,

I agree that either 35% nitric acid or the silver cell are the best processes for this task.

The cell would be the most direct route in my opinion. Setting one up is very easy and it doesn't have to be large to work.

If using nitric be sure to flatten and roll (using a mill if you have one) the ball out to increase the surface area that is exposed to the acid. This will speed the digestion reaction.

Steve

Oz · Nov 20, 2010

The big problem with a silver cell in this case is that first off Arthur does not have one, and this would be the wrong material to learn on. Secondly, even if he had a silver cell, the time frame is longer and recovery accountability of the platinum (the main value) is more difficult in the short term.

I am guessing that Arthur is doing this on a percentage of recovery basis (toll refining), time frame and short term accountability become important. If he has purchased this material outright, by all means he should build a silver cell to process this material. When you own the material or the time frame is not critical to the customer, silver cells rule the day as to platinum group metals in silver.

I should be clear that I have tailored my replies to this thread based on what “I” perceive Arthur's situation is. Arthur, correct me if I am wrong.

arthur kierski · Nov 20, 2010

Oz,you are right-----i will get 30% of the pt----i hope that is more then 2ozs in the ball----the customer uses pt to make lab ware----
thanks Steve for confirming and remind me to flatten the ball
thanks again----when done i will let you know how much pt was in the ball

Arthur

Harold_V · Nov 20, 2010

For what it's worth---my silver always contained platinum and palladium. I'm pretty sure I never allowed the ratio to get anywhere near 90% silver, with the balance platinum and palladium, but I damned well had it high enough that it would isolate the silver from the electrolyte by forming a hard shell of platinum and palladium around the anode. One of them required considerable hand chipping in order to digest the anode. I would recommend highly that this material not be parted directly, and if parting be the choice, to lower the platinum percentage considerably by melting with yet more silver.

One of the tough lessons that will be learned in refining is that parting cells work very best with quite pure metals.

Harold

HAuCl4 · Nov 20, 2010

Thanks 4metals for the (Wichers?) document. You must have quite a collection of documented procedures!.

Oz: I'm not certain that adding HCL instead of salt will work as you suggest (yet it will do no harm), since the Pt nitrate is in a different oxidation state (Insert propeller head joke here) than the required for conversion to Ammonium Hexachloroplatinate. I suggested cementing with copper (or zinc as you suggested for sponge Pt) as that will work every time and it work completely. Of the copper cementing I am certain. As well as the sulfuric route. 8)

And the comment that "it'll be hard to recover Pt from the nitric" or some such is also in Hoke's book, not only Gajda's.

I haven't tried, but if you want to get fancy and experiment: 4metals has posted (in another thread) a detailed sodium formate reduction of silver procedure at pH of 1.5 to 4.(I haven't tried it yet, but others have with repeatable results). After dropping the 9999 silver and filtering, raising the temperature to near boil and pH to 7 and adding more sodium formate it is suggested (I think Lou suggested it), that it MAY drop the Pt, probably quite pure. I haven't done this, ever. I'm a theoretical alchemist. I'm unsure again because the Pt is in the 2 valence state instead of the, more commonly encountered, 4 valence state. I will not know for certain till I or someone else tries, with repeatable results. 8)

Lou · Nov 21, 2010

I've used sodium, potassium, and ammonium formate for in situ reductions of Pt (II) and Pt(IV) when doing organic chemistry as a researcher in college.

A curious thing to note is the shift to a sickly green hue as Pt(IV) --> Pt(II) --> Pt(0).

If there is any nitric free in solution, addition of HCl will quickly a.) precipitate all of the silver, b.) if enough nitrate anion remains (which there should be), it will form an aqua regia and make chloroplatinic acid. Most of these PGMs can be weak to decent Lewis acids, so they'll readily accept electrons/proton.

Lou

lazersteve · Nov 21, 2010

Lou,

Since you first posted about the 'sickly green' reaction in a previous thread, I have tried using zinc to reduce my ammonium chloride PGM salts and found that it works just as you described. It was really no surprise that it worked, it's just amazed me that it worked so well!

The four times I've used zinc and dilute HCl to reduce my PGM salts I was initially worried that I did not see a noticeable reaction with the PGM salt as I added the zinc and it began to dissolve. I stirred and added more zinc as needed and then all at once the color shifted to the drab green color and the PGM salt quickly converted to a nice gray mass.

Here's a snapshot of the final precipitate:

I like this method way better than calcining. The one thing I noticed is that when I melted the resulting metal I got a distinct blue residue on the surrounding firebrick. Do you know what this blue may have been from? I washed the precipitated PGM with dilute HCl to remove any excess zinc, so I'm at a loss as to where the blue came from. The PGM in question was Platinum, and the source scrap was Pt/Ir 90/10.

Here's a shot of the firebrick that was over the top of the crucible showing the blue color in question:

I have not seen this color before when melting Pt metal when the Pt salt is calcined, so I assume it's likely residual zinc. What do you think? I did not see any 'zinc cobwebs' when melting the sponge.

Steve

Lou · Nov 21, 2010

The color is all wrong for any zinc oxide, which ranges from white to yellow depending on the temperature.

I'm at a loss as to what it could be. Positing a guess would be IrO2 as iridium is somewhat difficult to remove completely from platinum without running a Gilchrist. IrO2 also appears blue as a film...

platinum +silver

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