# PGM black melting problem



## eh_arien (Apr 19, 2015)

Hi everybody , 
I'm a chemist I've been working on refining of cats and chemical catalysts for about 1 year .
I reduced the black pgm by aluminum from the pregnant solution and tested by XRF , showed 90% pgm content in total (Pd+Pt+Rh) and smal amount of copper and lead 
but when I try to melt it with oxy/fuel torch there are some white smoke coming off and I see a huge weight loss , from a 60 grams black powder I got 35 one time , another time I made palladium sponge from a red ammonium hexachloropalladate , it was 50 grams after melting with copper became 100 grams alloy but only 14% by weight was palladium !!! 

Doed anybody know what is happening here ?


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## Lou (Apr 22, 2015)

You need to calcine the material at 800*C before attempting to melt.

Probably helps to clean up any aluminum residual with dilute NaOH or HCl, rinse til neutral with water.

Also, melt with oxy hydrogen in an a Wesgo melting dish for these small quantities.

Don't know why you'd add copper or lead.


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## eh_arien (Apr 23, 2015)

thanks for answering , is it important for the material to be extra pure and sponge form before melting ? or all pt , pd , rh can be melted all together ? because it takes me more time and cost to further process the material . I added copper to stop the powder to be blown away .
is it just because the way that I melted that I lost too much or there are some other impurities that can be hidden from XRF, maybe salts or oxides ? i konw it's better to use oxy hydrogen but it doesn't matter if it is not shining


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## kurtak (Apr 23, 2015)

eh_arien said:


> . I added copper to stop the powder to be blown away .



Try melting it with silver instead - silver has a lower melt temp then copper so acts as a better "molten metal solvent" to bring down the melt temp of the PGMs which should then give you a better homogenies metal bar

Then (if you live in the U.S.) try contacting this company :arrow: https://thegoldcenter.com/ 

They claim they will pay out on all the metals (Ag & PGMs) based on an XRF read out (a lot of places wont pay on the Ag unless it over a minimum)

I have not done business with this company - only talked with them 

Kurt


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## Lou (Apr 23, 2015)

Actually, don't try melting it with silver. That causes issues down the line with Pd/Pt extraction and any refiner that gets it in will be ticked. I hate high silver PGM feeds. I imagine that company uses some sort of energy dispersive XRF. It will not give an accurate reading unless calibration standards that roughly match that matrix are used. 


Best thing for you to do is to clean it up like I said you should do with dilute muriatic or a couple molar caustic to remove the aluminum. Then rinse very well, then dry and heat to 900C. Then it would be easier to melt with a slightly oxidizing flame. The Pd and Rh will throw sparks but the platinum won't.

You will get more money if they were separate, but the difficulty in separating those elements is probably more than you want to attempt at this point especially given the small quantity.

Some refiners prefer the material as powder, so it can be ground up, sampled, and then done on ICP/AA. I don't melt any PGMs coming in unless there's obvious organic contamination or they're bulk solids that need copper and granulation.


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## eh_arien (Apr 23, 2015)

I was selling this black pgm powder directly to a small company they were taking a xrf test and was paying me 10% below and no payment for rhodium , after about 1 month when the quantity rised to 100 grams each time , they told me when they try to melt this powder they lose a lot , and they stoped working with me unless I make a homogeneous bar , I tried the melting myself and the same thing happened . I lost half of the material 
since I haven't done any icp -aa -aes or -ms test , I don't know how much impurity can possibly be there , have you ever done this tests on any pgm black sample from car catalyst directly cemented without any further purification ? what was the result for you ? I have lots of cats waiting , if I lose half of the material as impurity it doesn't worth to refine them .
by the way I live in belgium


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## Lou (Apr 23, 2015)

Typically, auto cat samples are milled, sieved, homogenized and a portion taken for pre-treatment (oxidation to de-coke, then N2/H2 to reduce the PGMs to a leachable form). 



The white smoke is alumina. You need to remove the aluminum! Do the treatment step on the cemented powder like I suggested to clean it up! That'll help


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## eh_arien (Apr 23, 2015)

of course I will , I use aluminum pieces for cementing (not powder ) and since the solution stays acidic there is no aluminum residue but there can be some tiny amount of aluminum chloride inside pgm black , what makes me very confuesed is that , is it possible , that half of my pgm black be something that can not be detected by XRF ? I will get access to an induction furnace in 2 week to see if there is a change or not .


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## butcher (Apr 23, 2015)

Carbon can also make the platinum volatile, (even carbon from a torch), as Lou pointed towards when he said to use a slightly oxidizing flame.
What type of torch are you using and how are you using it?

Heating the powders too hard too fast (to melt), before the powders have been calcined where salts are driven off by heat, can be another cause of loss.


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## kurtak (Apr 24, 2015)

Lou said:


> Actually, don't try melting it with silver. That causes issues down the line with Pd/Pt extraction and any refiner that gets it in will be ticked.



Lou

I am confused by your above statement 

The reason I am confused is I had two refiners (Mid State & EnviroChem) tell me to melt my PGM sponge with silver (I have not actually sold any of the PGMs I recover from other processing) That was what they told me when I asked them if they would buy it as sponge (recovered from solution with zinc) because I had no way of melting it (at that time which was about 3 years ago) They said they would not take it as sponge so to melt it with silver

Also - in this Johnson Matthey video (at 5:40 - 6:40 into it) they talk about producing 2 feed stocks from their smelting process that then goes to their leaching process :arrow: http://www.jmrefining.com/video-page 

One feed stock is silver based which contains primarily Pd & Pt as the PGMs --- & the other feed stock which is iron based containing all 5 PGMs (not sure which of the 6 is missing here)

Also most all refiners I have talked to will take (& pay out) on dore bars of silver that contain Au &/or PGMs (assay fee goes up according to number of metals you want to account for)

Also - as I mentioned in my other post some refiners will pay on the PGMs (&/or Au) but only pay on the silver if the silver meets a minimum (for dore bars) 

So as you can see I am a bit confused here :?: 

Kurt


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## Lou (Apr 24, 2015)

Just because that video says something doesn't mean it's the truth. No one's going to walk you through their plant and tell you everything as it's done.

Silver is a nuisance element in PGM circuits. Them telling you to melt it with silver is just a way of them saying they want you to take the melt loss on powders. Most people who prepare powder/sponges of the metals are doing it with aluminum or zinc and have elementary knowledge. On outbound high purity sponge lots, gas and loss-on-ignition are held at tight specifications, so when I ship a 100 ounce lot of fine contained metal, it weighs just slightly heavy to account for the fraction of a percent you lose on melting the platinum. If I get upset over a 0.1 % variation in melt loss, how would you feel if you took a 10% melt loss (or more, see that thread about melting PGM powders)?

And I wasn't questioning on who takes what silver dore wise, just whether or not they really can pay out. 

I don't know most all refiners you've talked to, but I'll say most all of the refiners that aren't Heraeus, JM, Metalor and perhaps a very few number of other smaller entities do not even have the analytical capabilities to reliably/honestly payout upon all six (Pt/Pd/Au/Ag/Ir/Rh).

JM obviously is used to dealing with those materials (hell, they're used to dealing with just about everything) so they have something worked out. It also all depends on silver content, high silver feeds where silver is the collector/solvent means nitric acid digestion, and palladium is going to follow. Even platinum potentially! 
For me, Ag/Pd/Pt/Au means 1. digesting the Pd/Ag, precipitating the silver and washing Pd assay off, digesting the Au/Pt and any Pd residue, combining the Pd liquors, deNOx, de-golding, removing the platinum and palladium together as mixed salts, then separating the salts out with some clever yet finicky chemistry. It's a drag. Lot of people can do dental gold well, but the Pd/Pt portion are the dog.

End of the day, I guess my perspective is that of the guy actually doing it. I don't like silver or gold in my PGM feeds but the most integral part of refining is getting a diverse range of materials squeezed into a form that fits into the refining circuit.


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## eh_arien (Apr 26, 2015)

At the moment I'm trying to make different sponge samples to test with induction furnace . There is something that makes me very confused , lead is completly insoluble in rich chloride solution like aqua regia but I always get 2-5% lead in all of my xrf tests which is not normal .


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## Lou (Apr 26, 2015)

Get some proper calibration samples and maybe this won't be an issue.


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## eh_arien (May 19, 2015)

thanks lou , would you please tell me how much calcination in 900oC is important before tring to melt palladium-black and platinum-black .( does it help the material to stick together ? and for how long should it stay in 900oC) because I always skip this step and think that would be the mistake . even in hokes book it's not mentioned that you may lose too much material even if you use oxy-acetylene . because I always get fumes when I try to melt palladium-black , my powder is free of acid and chlorides ( I wash it several times with acid ,base and water at the end and test with litmus paper) only traces of lead and iron would be present


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## Lou (May 20, 2015)

Here's what you do:

remove excess zinc and any alumina with hot 30%+ NaOH.

Rinse until neutral on litmus, then calcine at 800-900C to sinter the material together. 

Then you can melt with O2/H2 flame in a Wesgo melting dish.

Lou


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## eh_arien (May 28, 2015)

I tried so much to find a furnace to incinerate the pgm black powder before melting but no success yet , meanwhile a professional suggested me a technic to reduce the loss , he told me to solve the borax in warm water and pour it on the powder in crucible then start to heat with reducing flame until in sinter a little bit then open the oxygen more and more until it melts , I tried this with a oxy-propane torch I didn't have access to hydrogen . the result was much more better from 3 grams , I got 2.5 grams the loss was 16% . the powder showed 80% pd , 10%pt , and after melting it was the same under XRF . 
can you please tell me your experiences on melting of pd black ? I still look for a furnace to incinerate the powder before melting to see if it improves the result


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## Lou (May 28, 2015)

Did you follow my procedure? You need to get the junk out of there. 

All the borax is doing is melting and encapsulating the grains so you don't blow them away with the flame. Your torch technique is probably sloppy. Always start slow and sinter the material so the surface area is less so less PdO sparks off.

Typically you briquette the Pd or Pt black then melt in zirconia crucible in an induction melter.


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## eh_arien (May 28, 2015)

yes I did it as you said , several times wash first with hydrochloric and then with sodium hydroxide solution and then with water until the water becomes neutral , I tried to find a furnace for calcination but unfortunately couldn't , so I directly tried to sinter the material with reducing slow flame I saw no smoke and just little bit of sparks but still lost 16% , what is your experience and what do you suggest ?


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## Lou (May 28, 2015)

Did you know the material was perfectly dry?

This is what you need:
http://www.ebay.com/itm/Thermolyne-Barnstead-FA1630-1-Heavy-Duty-Muffle-Furnace-240V-5-5x13x5-/371321120141?pt=LH_DefaultDomain_0&hash=item567476a58d

Get an alumina dish to calcine in and you're good to go.
Failing that, try making it into pellets with a press and die. 10 mm pellets need about 25 tons. 


FYI, 

I don't ever melt Pd black on inbound lots--usually dry sample and dissolve. The material when refined and made into Pd sand is sold as a product. Typical loss on melting for 9999 Pd sand is <0.25% if melted under vacuum.

Lou


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