PGM recovery diff method.

[lazersteve]

Wash bottle.

Steve

 

[kjavanb123]

Lou,

Thanks for your complete review on Pt refining. in your step 1 cementing with zinc, do I need to dissolve the soda ash first before cementing with zinc? or just directly zinc into the AR pregnant solution?


Also this method works if all 3 elements are mixed or does it work if only 2 of them are in the solution?


Thanks
Kev

 

[Lou]

Complete review on PGM refining? I'm almost positive that you're being sarcastic with me; please desist. Sorry if I seem disparaging, but it's no easier than saying "I want to be a master woodworker or mason or star athlete".

You don't need to use soda ash. In fact, keep it out unless you have pH papers (if you do, get the pH to 2-3 and then start with zinc additions). Most importantly, remove the nitric acid from your solution. If you do not, it will take much more zinc to reduce the PGMs because the nitric will preferentially be reduced to laughing gas and other nitrogen oxides and not ever transfer its electrons to the platinum.

This method works well for any metal less active than zinc. This includes copper and iron.

 

[kjavanb123]

Lou,

I tried your method this morning and I think i was lost at step 2 and on lol. Here is some
slide show for you all.

Per your last instruction, tried to remove the nitric in solution using evaporation method,


Tried the stannous test as I progressed each step of denoxx-ing and adding HCL to solution
View attachment 3

I am guessing this is syrup enough
..

After 2nd addition of HCL to solution and make it syrup again, I added soda ash to the soltuin


Cementing with zinc, added to solution, then added the NaOH to remove the zinc.


Forum won't allow more than 5 pics, so I just tell you what happenee then
Added nitric acid and it turned to yellow, not brown as I guess there was no Palladium. and still have some zinc or NaOH fizzling in the solution
I went ahead and added sulfuric acid slowly..it bubbled and turned into canary yellow with some white residue.

Here are my confusions.

1. the original solution which was concentrated AR, I added sulfuric acid, does that remove the NoXXX? verses HCL-CL solution which would react with soda ash and zinc and black powder would produce, i didn't see that reaction with AR. what is the problem here?

2. in step 2 of ur instruction, addition of NaOH to remove the zinc, NaOH should be mixed with warm water first then pour it to solution?


Thanks
Kev

 

[Lou]

Let me be clear: after you've cemented the PGM-bearing solution with zinc, filter or decant the solution to remove the colorless supernate. Then add some fresh water to the precipitate, stir, let it settle, and repeat. This removes excess acid and zinc chloride. After that, use a 20% weight/volume solution of lye to dissolve the excess zinc (this solution can be used multiple times if you're patient and sparing on the zinc turnings). Do this warm but not boiling. Look (through your goggles!!) and see if there are any bubbles of hydrogen being produced. If not, the zinc is removed as soluble sodium zincate. Pour off the lye solution and then you can add nitric acid to remove the palladium. Remember, nitric removes palladium and lesser base metals that may have been cemented. Hot, concentrated sulfuric acid removes the rhodium and also palladium (that's why you use the nitric acid to remove the palladium in the first step). The platinum is not affected by either sulfuric or nitric acid or combinations thereof. It should be pretty pure, but you can redissolve it in aqua regia or in cold to room temperature HCl to which you add small additions of hydrogen peroxide.

3.) Add nitric acid and the solution will turn yellow then deep brown as the palladium dissolves. [<1h]

If yours didn't go brown during the nitric addition, that means it's not very concentrated. The fact it went yellow means that the palladium was dissolving--if it didn't go green, then there's no copper but iron may still be present. I prefer small additions of nitric acid, and decanting and rinsing until color is no longer produced. Then it gets the same treatment for rhodium, except sulfuric acid is used and caution taking it in heating it and decanting. It's better not to rinse. You can always leave them altogether and separate conventionally, running bromate hydrolysis on the impure platinum yellow.


Lou

 

[kjavanb123]

Lou,

Thanks for your clearfying the instructions. I was wondering what happens if I add concentrated sulfuric acid to the AR pregnant solution at the begining.

H2So4 + H2PtCl6 ----> ?

or if addition of H2O2 at the begining would that releases the nitric?

20% weight/volume? can you plz give me some example? sorry no chemistry background here.

Thanks
Kev

 

[Lou]

Keep the sulfuric out of it except for removing rhodium from platinum (AFTER the palladium is removed).

20% w/v means 200 g of NaOH per 1000 mL of water.


Lou

 

[goldenchild]

Very little has changed save for induction melting, instrumentation, S/X and perhaps some finer points in the aqueous chemistry. One thing that has certainly remained the same: people who refine platinum group metals do not like newcomers. They will not like you refining them. They don't like those who talk about refining them (incidentally, Gilchrist was well respected for his chemistry, not for his mouth). There are not many names in the game so to speak and most roads lead to Rome. Ponder that when you go to sell your first 10 ounces of fine metal!

Lou,

I finally got to thoroughly read this thread and what you said here reminded me of some pictures I once saw. I was able to find the article. I was wondering(without giving any trade secrets away) how long it would take a large scale refinery to accumulate the amount of Pt in two of the pictures. One being the guy holding the huge block of Pt and the other of the bucket of Pt sponge. Also, on average how long does it take to get scrap of say jewelry from jewelry, to sponge to melted bar?

Here is the link. Its 2nd and 4th post.
http://www.pricescope.com/forum/rockytalky/virtual-tour-of-precious-metal-refinery-t41704.html

 

[Lou]

Incoming scrap jewelery (say bands) have to be sorted, weighed, melted, shot, digested, filtered (to remove Ru and Ir), precipitated, calcined, assayed (if you use ICP-AES, you assay here), or melted and then assayed with XRF as the bulk. Large ingots like that are often not cast--it's rare to see one so big. Often one makes more 950 (usually Ru based, because Ir is so soft and doesn't take a Rh plate well) or 900 alloy and sells as casting grain, wire, or other fabricated goods. The alloys work harden much more than the Pt, so they have to be annealed. Time can be from 3 days of good work under the best conditions to weeks if you're making value-added product. It really depends on what you're set up to do. Most important in refining Pt is having it down to the right size. If you don't have it down to a high surface area material on an incoming refining lot, it'll take a very long time (dissolving massive platinum is about as frustrating and quick an endeavor as hand-chiselling one's own granite monuments with a spoon.

Platinum bars are poured from zirconia crucibles that are "double bagged" inside an alumina crucible. The heavy wall alumina bears the weight of the ZrO2 crucible containing the Pt. Zirconia looses its strength after a few heats and must be replaced fairly often. Usually you have a "starter" plug or heal of platinum that soaks up the power because most melters are 10-12 kHz and won't heat powders for crap. Same thing for gold powder--most of the heat goes into the graphite or SiC crucible and melts it by conduction! It's a different story if you put a cylinder of gold in there. When the Pt plug melts you can add the sponge platinum. I much prefer to have not melted the material but have the sponge sit upon the bulk metal and heat, that way any moisture is steamed off.

Pd is much of the same, except atmosphere control is more important as it is considerably more gassy than platinum.

Because quantities of Rh are so small, it is always more convenient to torch melt by hand with oxyhydrogen on a magnesia block while wearing shade 12s or 13s and averting your eyes. Shade 10 is good for platinum or quartz working.


EDIT: It's quicker to refine jewelry platinum rather than raw platinum concentrates (that's involved!) because all impurities are generally known and it's a fairly simple separation to rid it of the Ru, Ir, or Co.

Lou

 

[HAuCl4]

Had missed this nice thread. Thanks for the panoramic view and the descriptions Lou!.

Fascinating and unprofitable for 99.99% of people including myself, that's how I'd describe PGM refining!. :lol:

 

[kadriver]

Fascinating and unprofitable for 99.99% of people including myself, that's how I'd describe PGM refining!. :lol:

Great way to have fun learning something new though - I am having a blast!

I want to thank Lou for posting this process. It is straight toward and practicle for a new guy like me.

I am printing the pages of instructions to keep at my shop for reference.

kadriver

 

[HAuCl4]

It can become an addictive hobby!. Beware!.

 

[kadriver]

6.) What's left is mostly pure platinum. Digest in HCl to which hydrogen peroxide is carefully added at room temp. then boil the solution once to rid it of chlorine. [<3h]

Good luck, have fun, and don't get anything on your skin!

Lou

I am new to PGM refining and plan on using this process - can I use HCL/Cl instead of HCL/H2O2 to dissolve the black powder in step 6? Is there an advantage to use H2O2?

Thanks - kadriver

 

[lazersteve]

Both work fine, no salt formation with peroxide.

Careful with high concentration peroxide (30%+) as it has a bad habit of delayed reactions. Be sure to wait a few minutes with lots of stirring to be sure you don't form a run away reaction and evertything boils over.

Steve

 

[freechemist]

Hello kadriver,

In his excellent posts about PGM-refining Lou wrote:

6.) What's left is mostly pure platinum. Digest in HCl to which hydrogen peroxide is carefully added at room temp. then boil the solution once to rid it of chlorine. [<3h]

Good luck, have fun, and don't get anything on your skin!

To me the most important paragraph reads: "don't get anything on your skin!" Keep that in mind, if you are inclined seriously to involve in platinum-recovery/refining. Hexachloroplatinates and hexabromoplatinates, in solid form or dissolved, are potent allergens, often showing it's effects after repeated exposures only after a long delay (weeks or even months).

To your question regarding use of HCl/H2O2 or HCl/Cl to dissolve the black powder in step 6:

Definitely Yes! Both methods are functioning well. I personally preferred the HCl/Cl-method, using NaClO3 (sodium chlorate) in place of "Clorox" or NaOCl-solution. Commercially available NaClO3 usually is pure (98% or more), non hygroscopic and well soluble in water, so you can prepare a fairly concentrated solution and add this slowly to your digestion-mixture to generate the chlorine needed to dissolve the black powder. In addition, 1 equivalent of NaClO3 is theoretically able to oxidize 1.5 equivalents of Pt(0) (metal) to the Pt(IV)-state in PtCl6(2-), and thus the amount of sodium added to the solution is much smaller, than using "Clorox" or NaOCl. After my experience addition of some HBr (48% hydrobromic acid), about 10% the volume of the already used HCl, helps to accelerate the dissolution and keep oxidant losses by evaporation/outgassing of elemental halogen (Cl2, Br2) on a low level, especially if using a reflux-condenser on the reaction vessel, because the boiling point of Br2 is much higher than that of Cl2.

Regards, freechemist

 

[Lou]

@freechemist: Halogen and HCl with pressure and heat in a Pfaulder is the way to go.


I omitted several steps earlier on--for instance, and I think everyone here knows, you don't dissolve bulk shot platinum in aqua regia or halogen/HCl. Just doesn't work quick enough. Fine with powders and foils but would never work on BBs or coarse powder.

Used to be that you'd make a 60-75% Pt balance nickel alloy and shot that. That dissolves in aqua regia as fast as gold does. Nickel is kind of looked down on these days...

Today, all the real platinum refining is done with s/x and runs through pretty little tubes. I think freechemist was at MetalorSA in Switzerland, so I'm sure he can confirm

 

[goldenchild]

I omitted several steps earlier on--for instance, and I think everyone here knows, you don't dissolve bulk shot platinum in aqua regia or halogen/HCl. Just doesn't work quick enough. Fine with powders and foils but would never work on BBs or coarse powder.

Used to be that you'd make a 60-75% Pt balance nickel alloy and shot that. That dissolves in aqua regia as fast as gold does. Nickel is kind of looked down on these days...

How about silver? I think I read that Pt will dissolve using only nitric if alloyed with silver.

 

[Lou]

If it's in the right proportion. It's really a troublesome thing that is not easily explained. Anyway, you get your Pt back by adding HCl and forcing the silver out. Unfortunately, some of the silver entraps the platinum...

 

[Dr. Poe]

If it's in the right proportion. It's really a troublesome thing that is not easily explained. Anyway, you get your Pt back by adding HCl and forcing the silver out. Unfortunately, some of the silver entraps the platinum...

When silver is alloyed with platinum in sufficient amounts, They dissolve together into nitric acid. HCl added to the solution precipitates silver chloride, but silver chloroplatinate hangs in solution as white cloud that resists settling. The two can be separated by decanting the white cloud from the silver chloride. Then heating with additional Aqua regia. The silver is released and precipitates as the pure chloride while the platinum remains in solution.
By the way guys, I've really enjoyed this thread. Kudos to you all. Dr. Poe :mrgreen:

 

[Lou]

Plain acidic water alone will decompose silver chloroplatinate.

Specifically though, it is indeed a weird phenomenon.

For those who are interested in a historical work:

http://books.google.com/books?hl=en&lr=&id=sok6AAAAMAAJ&oi=fnd&pg=PA7&ots=rZIrRnk-By&sig=bhq86Xr73VX9V6OpiJj22D6qlUc#v=onepage&q&f=false