Large Volume vs. Small Volume CAT Processing

[skippy]

Kurt, it's good summary of a lot of stuff you have put together here. I think your idea of sodium hydroxide fusion with silver is interesting. Even the very best leaching seems to top out at low ninety percent recovery of Pt and Pd, and 75-85% Rh recovery. Downside: Melting with any flux leaves a strongly alkaline waste that will need to be disposed of too. Hazardous waste. Neutralize it?
Plasma smelting the whole business needs no flux and leaves a pretty inert slag.

Lou, any elaboration on why you say the sodium hydroxide is less effective? Does it not totally flux alumina silicates?

 

[kurtak]

Sorry for the delay in getting back to this but was very busy this week end & for the next few day - an uncle of mine recently died - he was an electric motor repair man all his life & was the kind of guy that never threw anything away - so I along with other family are working this week to clean up so the estate can be settled --- me being the scrap man in the family have been given the task of dealing with all the scrap - have hauled in about 40,000 pounds of motors (yes 20 ton) & there is more plus tons more of other scrap - dumpsters full

Will try to post again in the next day or two

Kurt

 

[Lou]

NaOH attacks Pt/Pd.

 

[kurtak]

As I stated in my original post of this thread --- "& though I learned a lot I can't claim I know everything - so I don't know everything - which means I don't have all of the answers - which means this thread is about sharing what I did learn"

Due to the total lack of information concerning smelting CATs I did put a great deal of time into research looking for what would work as a flux for smelting CATs (what would dissolve the ceramic substrate) including searching the forum & speaking with the two major "industrial" chemical suppliers in my area & "at that time" NaOH was the only thing I could come up with

In our trial runs - which were small smelts made for comparison of recovery of smelting vs. leaching (bread loaf vs. bread loaf or straight edge vs. straight edge etc.) we did see a better recovery in smelting - but even that better recovery did not justify our further pursuing the attempt to process CATs on a large scale (which is my intended purpose in posting this thread - that trying to process CATs on a large scale is really beyond the reach of the home/hobby refiner - whether leaching
or smelting)

I will go back & edit a note into my post concerning your advise to use cryolite as the flux

Also you have made mention of copper being used (by the big boys) as the collector metal - according to this video by Johnson Matthey they have two types of feed stock that goes from the smelting process to the chemical processing - silver based being one & interesting enough an iron based one - http://www.jmrefining.com/page-view.php?pagename=Video-page&language=

In my understanding (which I admit to be limited) silver serves as a better collector metal (sponge effect & the need for better circulation when using copper) so I am most certainly interested in reference to using copper instead of silver (I am always open to leaning something new)

Kurt

 

[arsenic123]

Thank you for this awesome post. Can you please give in a nutshell what exactly should be used as collecting material and flux. You said you will edit the post for cyrolite but I didn't see the changes and why borax will be inefficient. Can you please write in a nutshell only for smelting.

Thank you

 

[kurtak]

arsenic1

you need a flux that will "dissolve" the ceramic substrate - borax &/or soda ash will not do that - cryolite & NaOH will - however based on what Lou posted NaOH will also react with the PGMs thereby leading to PGM loss

silver or copper can be used as the collector metal - you need to be sure that your flux runs very fluid so you get really good circulation in the crucible if you use copper

Kurt

 

[madelyn]

Thanks for the great detailed post on this kurtak!
A few questions ?
1. What type of furnace were you experimenting on? As I went through the effort of learning how to build my own small induction furnace for more than 3 years now just for the purpose of smelting cat material, just waiting for my celem capacitor this month so that I can start melting. This would give a good stirring on the melt mix to my knowledge as the induction furnace magnetizes the metal with frequincy.
2. How did you load and unload the crucible ? As the slag freezes instantly when the same heat energy is not overall and because it does not conduct heat like metal.
3. What was the temperature you mentained during the melt?
4. What was the quantity of of meterial you loaded the crucible with evrytime?

Thanks again in advance and I think everyone working on refining cats appreciates this a lot!

 

[rhwhite67]

Try a sodium bisulfate roast at 1700 degrees f for 2.5 hours then pour the roasted materials into a mold. Crush them and disolve the now water soluable Rh Pt and Pd in boiling DI water. Acidify with HCL and precipitate or use AR and cement out the PGMs over time using copper powder. It will not get all of the PGMs out but a high percentage and plain clay assay crucibles work just fine. The other option is to carefully pour the roast directly into a large stainless steel pot of warm water.

You can also precipitate the metals directly from the water with ethanol. they precipitate as a white to redish powder. Dissolve with DI and HCL to convert the PMs to their chl formas and precipitate the PD with Sodium Chlorate, Pt with AmCl, then precipitate the RH using magnesium powder.

Had good luck with this in a black sand material I was processing. It might work for CATs. The sodium bisulfate when molten in th eroast will infiltrate the voids in the CATs and should convert the PGMs to a water soluable sulfide form. In my case it worked to grab even the microscopic Au in the material I was roasting.

 

[goldenchild]

rhwhite,

What vessel do you roast the material in?

 

[NobleMetalWorks]

You can use a specific flux, and a smelting process to actually break the alumina silicates or Zeolites that the precious metals are bound to. This will liberate the precious metals and allow recovery.

Smelt/Flux to crack alumina silicates, homogeneous melt, pour into a cone mold, knock off the metal tip, re-melt and pour into grain, process with acids.

Scott

 

[im1badpup1]

I think you could improve leaching to around 98.5% on a few kg scale. on hundred kg it drops to about 94%

Il explain a few things. Size of the particle to be leached DOES matter. We all know the intention is the PGM coatining is intended to stick EXPOSED on the honeycomb surface, or it simply wouldnt work as a catalyst totally encapsulated.

So the smallest particles are totally encapsulated or the last bits of the particles that are actually stuck arnt accessable.

I want to talk about the poor rhodium yields compared to other PGMs a moment. The rhodiums accessable, its just not been leached efficiently. Theoretically its gettable to as least as efficent recovery as the Platinum and Palladium.

Ever looked under a microscope at whats going on? imagine a hair follicle, the hair is your PGM. Theres plenty of contact to attack the hair stem. Once you reach the pore theres a gas bubble forms with a meniscus, thats your problem for getting the remaining %s. You have no contact. Put a dry foot scrubbing pumice stone in water and observe this.

A fine grind to micron size will expose almost all PGMs, but the powder creates its own problems.

Heat and pressure is a partial solution. more heat gas bubbles expand, less gas. more pressure shrinks them, youre right inside the 'pore' now. Agitation helps
When youre plat palladium and rhodium recovery balances its probably as good as youll do.
About 98.5% on each.

I think thats still possibly unacceptable compared to smelting recovery.
I saw a post on using oxone, which was going to be my suggestion on a second leach, to try extract the last %s of hardest to get values. I didnt know it could be done in as harsh an enviroment as the poster elaborated on though

Somebody smart in the industry could probably combine a sulfidic ore with a flux and collect the cat PGMs in a button killing 2 birds with one stone.

I recently read a benchtop leach exceeding the 98.5% total recovery but attempts to scale up to half and ton batches yields dropped to around 94% total..

Even with that high a recovery in the mining industry what was missed the waste would still be considered an ore, itd be over 10ppm values. So their recovery rates in comparison are probably 99.5%.

Perhaps a dry process would squueze more PGMs but chasing 1-2-3% in anything but a professional laboratory isnt really feasable

In fact the molten salt reaction extracts 99.9% of all pgms https://patents.google.com/patent/US5238662A/en

description of molten salt reaction http://www.platirus.eu/news-and-events/selective-chlorination-molten-salt-reaction/

 

[samuelbaldwin010]

Ether copper or silver can be used as your collector metal & although copper is much cheaper then silver (there by making it a considered collector metal choice) silver is "by far" the better choice for your collector metal - this is due to what takes place in the crucible during smelting as well as the properties of the two metals them selves

First lets look at what we are trying to accomplish in the smelting - we are trying to collect a "VERY" small amount of PGMs from a "VERY" large amount of ceramic matrix in which the PGMs are literally locked up in - we are talking "less" then 10 grams of PGMS per kilogram of ceramic (so that is .00X kg PGMs per kg CAT material) so the first thing that needs to happen in the smelt is to dissolve away the ceramic to unlock the PGMs for collecting which of course is served by the NaOH (sodium hydroxide) as your flux (your not melting the ceramic - you are actually dissolving it in a reaction as the NaOH becomes molten)

It is important to understand that you want a finely granulated well mixed load (flux/CAT material/collector metal) going into your crucible to insure optimum collection of your PGMs - this includes having a fine granulated collector metal - the finer & more homogeneous the mix of the load going into the crucible the better the collecting of the PGMs is served & you want plenty of collector metal (the more metal in contact with the ceramic matrix the better the collecting)

The melting point of NaOH is very low (318 C) where as the melting point of your metals is very high which is why you want fine granulated collector metal well mixed in your load - NaOH is also "very" fluid when it becomes molten (although it becomes thicker as it dissolves the ceramic) so if you use large pieces of collector metal they would simply fall to the bottom of your crucible as the flux begins to melt without being molten to collect the PGMs

Its not that finer metal melts at a lower temp (though this is true in a "small" way) its that it takes less energy to melt a small piece of metal as opposed to melting a large piece of metal & your heat (energy) starts at the walls of the crucible & works its way into the center of the load - so you want your metal to start melting at the wall so it can preform the task of collecting as the melting moves towards the center of the load

There are a couple of reasons why silver is a far better collector metal then copper - first is that lower melt point metals act as a solvent to higher melt point metals there by lowering the melt point of the higher melt point metal - molten metals also act like a sponge in that they actually suck metal in (you can watch this happen if you have ever moved a large pool of molten metal around in a melting dish to pickup a non-molten bead in your dish)

Also lower melt point metals are "more fluid" then high melt point metals & the more fluid the better the sponge effect - another words the more fluid the better they are at collecting & this is what makes silver a better collector then copper

The melt point of copper is 1084 C & the melt point of silver is 961 C which is 123 C (or 221 F) lower then copper so it melts before copper to become the collector & it is more fluid - "much" more fluid which means a better sponge effect for collecting

Having good circulation in the crucible during the smelt is also important so I will cover that next

Kurt

I was reading your post, great information and very informative and very detailed explanation.
I really appreciate the fact you took the time to write this and share it with the community.
I have learned alot from reading it. So I would like to thank you for your wisdom and time.

One thought I had though, I am not sure if anyone has thought of this idea I have had, don't think I am the only one to think of it and maybe I am wrong but, couldn't you use hydrofluoric acid to dissolve the Ceramic substrate? I have read that it dissolves porcelain and the like, not entirely certain if it doesn't dissolve the metals or not. Can anyone else elaborate?

 

[Yggdrasil]

I was reading your post, great information and very informative and very detailed explanation.
I really appreciate the fact you took the time to write this and share it with the community.
I have learned alot from reading it. So I would like to thank you for your wisdom and time.

One thought I had though, I am not sure if anyone has thought of this idea I have had, don't think I am the only one to think of it and maybe I am wrong but, couldn't you use hydrofluoric acid to dissolve the Ceramic substrate? I have read that it dissolves porcelain and the like, not entirely certain if it doesn't dissolve the metals or not. Can anyone else elaborate?

It has been discussed briefly and discarded just as fast.
Yes it do but it also dissolves your flesh and even the bones in your body (Short story).
It is the most terrible chemical we can get our hands on.
So no it is not recommended.

 

[eaglekeeper]

It has been discussed briefly and discarded just as fast.
Yes it do but it also dissolves your flesh and even the bones in your body (Short story).
It is the most terrible chemical we can get our hands on.
So no it is not recommended.

You beat me to it.

 

[kurtak]

One thought I had though, I am not sure if anyone has thought of this idea I have had, don't think I am the only one to think of it and maybe I am wrong but, couldn't you use hydrofluoric acid to dissolve the Ceramic substrate?

Per the bold print - yes you could - BUT - only a FOOL would consider doing such a thing !!!

Why - because hydrofluoric is one of the most dangerous acids (if not the most dangerous acid) on the planet

Like 10 times more dangerous then concentrated sulfuric acid

I am not going to right a long post about why HF is even MUCH more dangerous then sulfuric acid - do your own research

Getting even a VERY SMALL amount on you or a VERY SMALL whiff of the fumes will ruin the rest of your life & has the potential to kill you

Let me put it this way --- if I had to make a choice between playing with HF & playing with rattlesnakes - I think I would choose to play with rattlesnakes

Kurt

 

[orvi]

I was reading your post, great information and very informative and very detailed explanation.
I really appreciate the fact you took the time to write this and share it with the community.
I have learned alot from reading it. So I would like to thank you for your wisdom and time.

One thought I had though, I am not sure if anyone has thought of this idea I have had, don't think I am the only one to think of it and maybe I am wrong but, couldn't you use hydrofluoric acid to dissolve the Ceramic substrate? I have read that it dissolves porcelain and the like, not entirely certain if it doesn't dissolve the metals or not. Can anyone else elaborate?

Not while ago, my very good friend passed away. And one of the probable causes of his death is fluoride poisoning through HF vapors.

I think that speaks clearly. Experienced chemist, not another garage cat leaching guy. 10 years of experience with process chemistry.

HF is sneaky killer, it does not smell that awfully as other acids, and the recognition threshold is relatively high. You can whiff HF unnoticed for good few hours, burn your lungs (prolonged development of symptoms, when you realize and develop them - game over) and die from suffocation. It also nicely penetrates the skin, because it is relatively weak acid. It essentially cannot be treated, because aside from wrecking your lungs, it also precipitate all calcium in your body fluids and muscles. Trick is, they cannot give you more calcium, because it will precipitate in your blood directly as CaF2.

 

[samuelbaldwin010]

Okay. I did not realize it was that terrible, I only brought it up since I read about it's use in refining to dissolve bits of glass to clean up impurities in hoke's book. However it made no mention of any of the listed above facts.

This is why I ask questions. I don't think anyone is born with the knowledge of everything. Everyone starts from somewhere. So, now I am aware thanks for everyone's input.

 

[Yggdrasil]

Okay. I did not realize it was that terrible, I only brought it up since I read about it's use in refining to dissolve bits of glass to clean up impurities in hoke's book. However it made no mention of any of the listed above facts.

This is why I ask questions. I don't think anyone is born with the knowledge of everything. Everyone starts from somewhere. So, now I am aware thanks for everyone's input.

I think there should be a warning label to the C.M. Hokes book, that many procedures are not considered safe today.

 

[orvi]

I think there should be a warning label to the C.M. Hokes book, that many procedures are not considered safe today.

Gattermann encouraged his students to smoke while performing specific type of Friedel-Crafts reaction, now known as Gattermann reaction. It uses anhydrous liquid hydrocyanic acid as reagent. HCN gas produced strange taste on the tongue while smoking, serving as an alert of leak or faulty hood even in concentrations unnoticeable by smell...
It was year 1907. We moved far away from this If one was about to plan the synthesis now using liquid HCN, he will be stopped by everyone in the workplace or university, then investigated and in worse case suspended from the position.