# Acid leach of converter beads and electrowinning



## alancj (Apr 17, 2010)

Hi all, a few years back I obtained 40 lbs of cat beads off ebay, and I'm now just getting around to trying to get the PGMs out. I originally tried some test batches of 250 grams, with a couple different methods, but this was a while back and my record keeping was crap... 

What I'm doing now is an acid leach solution based on patent #7,166,145 B1 "Recovery of Precious Metals" http://www.freepatentsonline.com/7166145.html

Basically I used 2 liters of solution; 100 ml of con. sulfuric acid, 75ml of HNO3 and 75ml of HCL, plus 45 grams of ammonium chloride and 2 packs of sodium bromide salt (pool chemical, 112g), the balance filtered water. 

The solution fumed nicely with brown and purple gasses 

This covered about 4 lbs of cat. beads in an old crockpot, and was cooked on high (basically boiling) for 3 hours.

This was then electrolyzed with two carbon gouging rods at 6v and ~6 amps. The idea here (according to the patent) is that electrolysis of the solution will (presumably) drive out the metals and be plated onto the cathode as metals, as well as regenerate the leach so it can be used again. I got a black powdery deposit on the cathode (negative electrode), the anode seemed to be unaffected. 

I did this again, reusing the leach solution after adding additional HNO3 (50ml) and HCL (75ml). (the patent implied that electrolysis regenerates the solution, but I don't see how it is going to return acid gasses and nitrogen oxides that have escaped from the solution, despite being covered. I also feel that adding more bromide salt would be necessary, given that the acid and heat would cause it to escape) I did this in a 4l glass wine jug in a double boiler arrangement with 5lbs of cat beads and increased solution volume to cover beads. This was heated for 3 hours, and I used a rubber stopper, sitting on top of the neck, to hold back excessive evaporation of "nasty's", but to prevent any pressure build up.

I electrolyzed the solution again, for several hours, this time with a stirring motor arrangement to get a better deposit on the cathode. (I did some reading and basically the better the solution mixing the lower the PGM concentration levels will be and the faster they will be removed as well as making a better deposit on the cathode.) 

This time the cathode had a more flaky deposit, not black powder as before, but slightly shinny. I wouldn't say it was a slam dunk, "wholly crap that looks like platinum glitter" type deposit, but it was encouraging. 

Both times the leach was electrolyzed straight out of the reactor, with no filtering or settling done aside from removing and rinsing the beads with a bit of water (I returned the rinse back to the leach solution.)

The big question I have is how to test this to see if the black powder I scrapped off the cathode is or contains any PGM's. I also would like to be able to test the left over beads to see if there was complete/decent recovery. Basically I have no Idea if anything I'm doing is working, and I don't want to go and do another 8 batches and find out it's not working. 

I was thinking that if it was metal powder, I could just heat it with my oxy/acetylene torch and if I get a shinny bead then all is well. But I have nothing to melt it on, and nothing to use as a flux or even know if I need a flux. I read that carbon should be kept away from platinum when melting... but I was planning on burning the paper I collected it on.

If anybody has any information that could help, like any knowledge of the electrowinning stage, testing, and experience with acid leaching, I would be very grateful. The patent was very sketchy on that part, and I'm more assuming that the dissolved metal ions are supposed to come out on the cathode and in the form of free metals. 

So here is a picture of the stuff I've scarped of the the cathode from two runs.


Thanks!
-Alan


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## alancj (Apr 17, 2010)

Prolog:
I paid 200 for the beads, which was probably not a great deal, but at today's prizes I think 8-10 grams recovery of platinum and I would break even. I'm not planning on selling it or making money, I just wanted some platinum for other projects and thought it would be fun to recover it from some converters. 

I don't know if that amount is really feasible from 40 lbs of beads. What do you all think? 

The two other methods I tried was dissolving the substrate in molten sodium hydroxide and filtering out the undissolved stuff (after putting the solidified mass in water) and treating with AR and also just treating it with AR directly. I was making my nitric acid in a tinny little 250 ml retort so I didn't like using much nitric acid. I should have bought a 1 litter one  I don't see 'em for sale anymore on ebay. 

-Alan


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## skippy (Apr 17, 2010)

Sounds like a good little test you've got going on. 

As far as regeneration, the electrolysis should generate some bromine from the bromide in your solution, although you're right, I don't see it regenerating the nitric acid. 

For testing your extraction, you've done a nice sized test so you should be able to separate your metals and weigh them (if you have or can get access to a decent scale). I know you've done the electrowinning, but I would also check the electrolyte for unprecipitated values with stannous chloride, and if there are any values I would either try to further electrowin them out or cement them out. Then I would redissolve these metals by refluxing in hot AR for a few hours and then selectively precipitate the Pd and Pt. The rhodium will remain undisolved, but you can take the residue from the AR digestion and do a bisulfate fusion on it to put the Rhodium into solution. You could then cement it out. 
Then I would do a hot AR leach on your extracted beads and do the same selective precipation to see what you left undissolved/unrecovered from your previous leach. I think the hot AR leach should be acceptable for establishing whether your extraction was satisfactory. If you find a lot of values in the AR leach of the pre extracted beads, then you would know your technique needs some tweeking. Lazersteve has a great video on PGMs that includes the selective precipitation, that should help get you up to speed, but here's a good post on this if you need to know how to separate them right away 8) http://goldrefiningforum.com/phpBB3/viewtopic.php?f=51&t=6638&p=59148&hilit=chlorate#p59096

I wouldn't worry about melting your metals, it would make a nice button of mostly pgms, but it wouldn't tell you how well you extracted what metals, which is the crux of the matter isn't it?


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## alancj (Apr 19, 2010)

Thanks for the input. I do have a triple beam lab scale, .1 gram graduated. I don't have anymore nitric acid unfortunately, I used the last of it renewing the leach for the second batch. Is the poor man's AR (nitrate + HCL) any good for dissolving PGM's? And could I use that for the testing? I just don't know if the extra stuff gets in the way or not. I have plenty of nitrates: calcium, potassium, ammonium, and a bit of sodium.

If not I probably could distill some more acid. Or, (gasp!) buy some.

Now I have a question about processing catalysts in general... In the reading I had done a few years ago I remember people saying that you need to roast the beads first, presumably to remove carbon deposits. Then some said it was unnecessary. Is there a consensus on that?

I also wonder how well boiling with AR dissolves the PGM's, if it gets into the pores of the catalyst and truly scavenges it all. This is where I thought the idea of dissolving the alumina in sodium hydroxide and treating only the filtrate seemed like a good idea.. every last bit of the metals would be freed up to be exposed to the AR for dissolution. It is, however, an extra step and a pain.

Is the video you are referring to the one Lazersteve is selling?

For now I've filtered the insolubles from the leach solution and bag and tagged the things I will need to test. I plan on testing 4 things: insolubles in the leach, spent cat beads, leach itself, and of course what I scraped off the cathode. There does seem to be a deposit on the anode after the second run I did, I wonder what this is? Oxides of some metals?

I just noticed the spot prices ticker... at 1684 a troy ounce what I have could be worth 1k if it is even .1% by weight platinum. I better not get my hopes up, but I'm feeling better about it. 

As for melting the metals, it would be nice to be able to do once I get them separated. If this all works out nice I suppose I could buy some more converters and separate more; call it investing 

Thanks, Alan


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## Platinum (Apr 19, 2010)

I got a used Platinum Mill for sale. :shock: :shock: :shock: 

Just kidding.


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## alancj (Apr 19, 2010)

oh boy, those are getting rare... I hear they don't make `em any more. I'll pay you double!

Seriously though, did the platinum mill use a similar scheme I'm working on?


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## goldsilverpro (Apr 19, 2010)

The longest thread we every had, I think, was on the Platinumill - 25 pages
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=51&t=1316&hilit=platinumill

The guy selling them was on the forum for awhile.


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