Assaying Platinum

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golddie

Well-known member
Joined
Jun 3, 2009
Messages
515
I have been looking in the forum for this and I couldnt find anything.
Should I dissolve the platinum in AR
then precipitate with ammonium chloride
then dry the metal and weigh the difference

I thought about following the
Platinum slide show
by steve.
but what is denoxx the filteration solution.
 
here are some things to concider while you are waiting for an answer to you question,from another member, as I do not know details of the materials you are assaying, or your process.

assay's are usually done in a melt with flux .
and may work better than wet methods were if working with small amounts some may get lost in solutions filters etc.

platinum is pretty much insoluble in cold Aqua regia,

platinum will dissolve in hot > 150 deg Aqua regia with time,


denoxx Usually refers to eliminating the nitric acid from aqua regia, usually by heating to evaporate the nitric acid from solution, heating to a thick syrup (not salts)

caution here the nitric will concentrate in solution till it azeotropes, and at this point it can foam over (boiling values out of pot) as it seems the majority of it want's to come out all at once, slow heating and paying close attention here is important, I watch for solution to start to bubble small foam just before this point, and lower heat at this point untill most of NOx fizzes out at this point, then I raise heat again.

to this thick syrup a little HCl is added you may see brown NOx fumes, evaporate thick again, repeat HCl and evaporation for total of three time's to insure Nitric has been eliminated, sometime's I use a couple of prills of urea to see if there may be nitric left if so they fizz when solution is hot,
(a trick Harold teach's is to use a button of gold to help use up nitric he would keep note of added amount and recovered amount as he was refining metal's for customer's), of course adding gold trick you would not use in an assay.

some people use urea to denoxx, but I feel this just complicates your solutions.

others can give you better solutions to the question you are asking about assay, details of your material, and to what you have done up to this point would be helpful to get proper answer.
 
Lets say a jeweler brings me a sample for assaying.
The material is in fillings form.
The materials that are most likely to be in that mixture is
Pt,Pd,Rh,Silver ,Gold,Iridium Copper,and Nickel.

Here is how I would assay this
I would wrap it with lead with 20 times its weight
Since the melting point of the metal that is the toughest
I would pre-heat oven to
Rhodium Rh 3571 f 1966 c

****Do you need a special oven here ****
cupel it
roll it
Now you are left with
Pt,Pd,Rh,Silver ,Gold,Iridium

put in dilute nitric
Now you are left with
Pt,Pd,Rh,Gold,Iridium


put in AR
Now everything is in th solution
Pt,Pd,Rh,Gold,Iridium

Drop GOld first with SO2

collect


Now everything is in the solution is
Pt,Pd,Rh,Iridium

Pt with
sodium chloride

Pd with sodium chlorate crystals


Rh with zinc or maybe Magnesium powder


--------------------------------
QUESTION

1) What happens to Iridium
2) How accurate would this assay be
3) If anyone has a different way maybe they can post it here

Thanks
 
That assay would be dead in the water, for numerous reasons. The most glaring problem is that the temperature is far too hot--your lead would all evaporate! If you're after accurate PGM, do ICP or use gold or silver as the collector.
 
Hi Lou
Thanks for your input.
ICP looks like an expensive machine
So Ill try

gold or silver as the collector.
Click to expand...
Exactly what you mean I dont know.
I assume its the wet method
What Ill do is
It would be a good thing if I can give the amount of each metals in this assay
For example if I can tell the customer the percentage of the amount of each metal

First step would be to
Get rid of copper and nickel first

If I use nitric then I cant know the amount of silver in this in this assay.
Also the platinum groups will come down with the silver.

How about HCL
I looked in my books and I dont know the effect HCL has on copper and nickel.

Should I drop the gold first with SO2

This to be is a brain twister
For most it is probably elementry

Go ahead and give us your opinion
Thanks
 
I thought about the the post steve had with the order of the sequence of metal that droped other metals or something like that
I would like to know the location of that thread and would that chart help in this case
 
golddie said:
I thought about the the post steve had with the order of the sequence of metal that droped other metals or something like that
I would like to know the location of that thread and would that chart help in this case
Click to expand...

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=60&t=559&p=53747&hilit=electromotive+series#p53747

GoldSilverPro

Silver Part 2 - CEMENTATION

Here's a very incomplete list of metals as they appear in the electromotive series.

Magnesium Mg
Aluminum Al
Zinc Zn
Chromium Cr
Iron Fe
Cadmium Cd
Nickel Ni
Tin Sn
Lead Pb
Hydrogen H
Copper Cu
Silver Ag
Palladium Pd
Mercury Hg
Platinum Pt
Gold Au

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=60&t=559&hilit=electromotive+series
 
Hi Buthcer and Barren
Thanks for your help
For starters how about removing the base metals with dilute nitric
Then you will also drop the silver but you can cement silver with copper and weight the difference for calculating the percentage of silve in this batch.

Also I have heard in the forum people saying to remove the base metals
Can someone tell me a bit about that
 
PreciousMexpert said:
Hi Buthcer and Barren
Thanks for your help
For starters how about removing the base metals with dilute nitric
Then you will also drop the silver but you can cement silver with copper and weight the difference for calculating the percentage of silve in this batch.

Also I have heard in the forum people saying to remove the base metals
Can someone tell me a bit about that
Click to expand...

Yes you can remove the base metals with dilute nitric. It is faster than HCL, HCL/Peroxide. It is also more expensive and time consuming if you have to make your own nitirc rather than purchase it.

I try to process my items using reclaimed AP soultion and a crock pot or on a hot plate in a glass coffee pot. I will generally start off a batch with reclaimed solution and heat(about 100 to 140 deg). I try not to add peroxide to solutions to reduce the chance of disolving some of the PM's. I have found that on the hot plate the sloution will turn clear on the bottom of the container up to about 1/3 of the volume. When it does this I just adjust the heat up some or turn it off completely and stir the solution and the process will continue. I also find that a little bit of new HCL is to be used just to up the concentration some more of the solution. I use this for CPU's, fingers, and pins with solder. Pins with no solder and larger plated items I will do in a cell.

I would not use this for karat scrap or filled items. For thesse I would do in dilute nitiric.
 
By using gold or platinum as a collector you will collect all of the PGM's in one bead and you can decide where to go from there. If you add a relatively large (10 x the expected Pt content) silver charge, the Pt and Pd will go into the nitric when parting in nitric. There are methods to part in different acids to separate the Pt from the Pd.

If you add gold as a collector you are doing it to facilitate the Pt dissolving in the aqua regia so you can boil off the nitric and drop ammonium chloroplatinate in a classic method.

If you have all of the metals you listed, Rh, Ir, Pt, Pd and Au Lou is right ICP is the way to go, gravimetric assays for multiple PGM's are the most difficult assays to perform, and when you're buying, you can lose more than you gain if you screw up.

Some of the guys who post here have XRF machines, I don't recall who has what (maybe if those that have an AA or ICP or XRF said so in their profile we could be more helpful) Anyway if you have an XRF you could produce a assay bead by cupellation with the added benefit of a gold or silver collector, and run an XRF assay and do the math to calculate what was in the original sample.
 
Hi 4metals
Thanks for your help.
I had written this reply befor your post

Hi Barren
Thanks for that reply
Now I have removed the base metals and I am able to give a Percentage of the silver amount

I am left with
Pt,Pd,Rh,Gold,Iridium

Gold I will drop with SO2

Pt with Ammonium Chloride

Pd with sodium chlorate

Rh with zinc or Magnesium powder.

I dont know what to do with Iridium
Maybe someone can tell.

Would this be a proffesional assay.
Thanks
Click to expand...
 
Hi Barren
In this list does it mean that
copper
can drop all those metals
that are below it
Thanks


Magnesium Mg
Aluminum Al
Zinc Zn
Chromium Cr
Iron Fe
Cadmium Cd
Nickel Ni
Tin Sn
Lead Pb
Hydrogen H
Copper Cu
Silver Ag
Palladium Pd
Mercury Hg
Platinum Pt
Gold Au
Click to expand...
 
in the series, copper will replace gold in solution, they kind of exchange places, the copper would have to be in metal form (still having all its electrons), the metal copper will donate its electrons to the gold dissolved in the acid (poor gold lost his when he got dissolved), when the gold gets these new electrons it will become metal gold (just in brown or black powder form), now if we drop a beer can in this copper solution beside fizzing, the aluminum will donate its electrons and copper precipitates, well now we have an aluminum solution, well just for fun lets put a Iron bar in there guess what the Iron wants to keep all its electrons in this solution it is selfish and will not donate them to the aluminum solution as aluminum is more electronegative, and higher in series than Iron is.
 
If I dont want to have the Pt and Pd in nitric
Will weak nitric dissolve Palladium

I can also try
HCL
or
HCL/Peroxide
to remove the base metals

Once this is done

Everything goes into AR
Pt,Pd,Rh,Gold,Iridium

I will drop the gold with SO2

Now i have
Pt,Pd,Rh,Iridium

Like you said 4metals
We should have a list of those people that have
AA or ICP or XRF
machines

But still it would be a good lesson if we can figure out this puzzle
 
quote(If I dont want to have the Pt and Pd in nitric
Will weak nitric dissolve Palladium)
platinum will not be dissolved in nitric,unless alloyed with at least 8 times it weight in silver, palladium can, silver will also, if tin or solder eliminate them prior to using nitric.
HCl will precipitate the silver from nitric, copper will replace the palladium.
it may help more and save us all time if we know exactly what it is you are processing their source, and the state they are in powder or chunks of metal. powders would need good inceneration, jewlery sweeps usually also get a good wash in hydroxide, ( Harold has good post on technique).
base metals should alway's be eliminated first.

qoute(Once this is done
Everything goes into AR
Pt,Pd,Rh,Gold,Iridium )

no everything won't nessarily go into aqua regia, gold and palladium can in cold aqua regia, platinum if aqua regia is very hot, Rh, would need special treatments usually done in pre-melting processes, or cooking with chemicals (bisulfate fusion). Ir will be left undissolved

(I will drop the gold with SO2)
SO2 gas. if the platinum group are suspected I would choose ferrous sulfate to precipitate the gold.

(Now i have
Pt,Pd,Rh,Iridium)
we can only hope to have alot of these metals including gold and silver.

this I would not do for an assay, I would look for a good assayer to work with, you need to keep customers they can be bread and butter.

http://pubs.acs.org/doi/abs/10.1021/ja01975a002

http://chestofbooks.com/reference/American-Cyclopaedia-10/Platinum.html
 

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