# Stuck to crucible



## markqf1 (Jul 15, 2009)

I have a crucible that "got overheated" and now has a glob of material stuck to the bottom.
Material includes pt, pd, rh.
Any ideas on how to recover it?
Could I mix up some ar in the crucible and put it on a hotplate?

Mark


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## EDI Refining (Jul 15, 2009)

Just a suggestion, dont know if its a proper way of going by it:

Have your AR in a large beaker, use a hotplate to speed reaction, then put the crucible in the solution. After PGM are dissolved, clean the crucible with h20 and dry at low temp


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## Noxx (Jul 15, 2009)

If you heat the button with MAPP gas for example, you might be able to soften the borax. Use a pair of tweezers to grab the button.


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## markqf1 (Jul 15, 2009)

It's quite a bit more than a button.


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## lazersteve (Jul 15, 2009)

I've used a long shank screwdriver and a gentle tap with a hammer to dislodge buttons from the bottom of deep crucibles in the past. Be sure to support the crucible against the force of the blow so the energy of the strike goes to the button, not the crucible wall.

Be careful as this may also break your crucible.

Steve


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## markqf1 (Jul 16, 2009)

Thanks for the suggestions guys.
The crucible is toast anyway so worst case, I'll break it into pieces.

Mark


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## qst42know (Jul 16, 2009)

Is there an easy to remove metal that could be added to reduce the melt temp of PGMs? 

I would guess you are not getting it hot enough. 

What type of torch are you using for the platinum group?


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## goldsilverpro (Jul 16, 2009)

I like Noxx's idea best. The slag should melt fairly easy and release the button.

Is that a clay assay crucible? If so, you can gently tap around it and break the sides away until only the bottom inch, or so, of the crucible remains. If you're careful, you won't break the bottom - the ball end of a small ball peen hammer works pretty well - wear safety goggles. That will make it easier to work with the torch. I have used this technique several times on a new assay crucible to torch melt gold, when I didn't have a clean melting dish.

Or, just break everything away from the button. Once the button is out, you can tap away the slag or pieces of crucible stuck to it with the back of a stainless spoon or about a 3/8" steel rod about 6" long. After tapping, rinse it under running water while rubbing it with your finger.


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## markqf1 (Jul 16, 2009)

Thanks for the suggestion.
I used Steve's method and managed to save the crucible for another day.
It did come out with a little of the crucible still stuck to it.
Mark


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## markqf1 (Jul 16, 2009)

qst42know,
I done it in a furnace at about 1250C.
It was a mistake I won't make again. :lol: 

Mark


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## Lou (Jul 16, 2009)

Big enough crucible there Mark? 

I hope you'll fill it up one day.

Seriously though, as a general rule one should never try to physically dislodge material from any crucible you plan on handling (while hot) ever again. Most clay and/or assay crucibles are cheap enough to be considered disposable. 

Trying to dissolve it out with aqua regia will take a very, very long time, most likely days or weeks depending on the size of the button and just how high a noble alloy it is.

My question is: what PGM melts at 1250?


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## markqf1 (Jul 16, 2009)

Excellent question Lou!
I suppose none. :lol: 
This wasn't an attempt to melt anything.
I had alot of material including some salts, some clammed up filters, some black powders, some stuff I dropped with cabisol contaminated zinc, some metal fragments, some sand, and I'm sure some alumina.
My thought was to "clean it up" which, I intended to do at about 500C.

Well to make a long story short, let's just say I won't try it again. 
Sometimes, trial and error teaches us alot.  

Mark


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## Lou (Jul 16, 2009)

Ok, well the thing about PGM salts it that you only want to calcine them if and only if they are free of other metal salts (spectroscopically pure). Ammonium is the ONLY cation that should be present and there's no reason to heat beyond a dull red heat.This is also true of the actual metal sponges (i.e. platinum sponge should never be heated if you suspect it has salt in it). The obvious reason is that there will losses due to volatilization. Many people forget that platinum and a chloride, bromide, or iodide salt will react forming a platinum compound which might just get up and go out of your calcination dish.

Another suggestion I might give is that you acquire a Pyrex crystallization dish. This is what I use when heating precipitates--it allows you to spread an even amount of material over a large surface area. The best way to burn *filters **is in a heated quartz tube with oxygen then go after it with an aqueous or gas phase method.

The only ways to remove alumina from a mixture of platinum and other PGMs are a.) thermal cycling to change crystalline structure, then dissolution into HF (something you are quite familiar with), b.) heating with concentrated bases in a silver dish, c.) high temperature chlorination in a tube furnace. That's really about it. Alumina is pretty darn inert. A hot, concentrated and dangerous solution of sodium or potassium hydroxide will remove the Cab-O-Sil (fumed silicon dioxide, aka quartz sand) and any residual zinc, forming silicate and zincate respectively.


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## markqf1 (Jul 16, 2009)

I knew you would have the answer Lou.
Now, in your opinion, how would you process the stuff that I collected from the crucible?

Mark


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## Lou (Jul 18, 2009)

Add copper or silver to the crucible, melt and hold (hoping that it would all dissolve). Cast an anode and have at it electrolytically. Get the anode slimes and process conventionally, or more preferably with gas phase extraction/refining.

Let me make one thing clear to everyone who reads this thread: You should NEVER, ever consolidate platinum group metals (by that I mean melt them and make buttons/shot/pieces) if it can at all be avoided. NEVER melt your processed platinum/palladium/rhodium sponge unless you are sure you are done with it!! It is murder to dissolve bulk platinum, so don't attempt it!


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## markqf1 (Jul 20, 2009)

Thanks for the advice Lou.
I had alot of "contaminated " stuff that ended up in the mix.
It would have been nearly impossible to process it all individually so, I Decided to burn everything that would burn.
I accidentally cooked it alot longer and alot hotter than I had originally planned.

Sometimes it is hard to ignore my wreckless intentions. :lol: 
This has cost me alot but, has taught me alot. 

Since then, I have made quite a few improvments to the button.
After a couple of different treatments, It seems what I have left is a mass of undissolved powder containing rh tainted with some sand,alumina, a lead-palladium alloy that has proven to be slow to dissolve and alot of lead sulfate.
I will introduce it to a little hf tommorrow and then maybe try the furnace with the addition of some copper to get me better access to whats left.
I've managed to salvage quite abit of pt, maybe all of it.

Any ideas ?
I'll see what hoke says.

Mark


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