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12AX7
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Alternatives to aqua regia?
(Fleaker: this is of course nothing against you, just experimental, well maybe a little as insurance if your PtCl6 doesn't come.  )
I have (had) one catalytic converter. It came from a 1980s Nissan, so probably isn't too bad. My understanding is most, if not all, converters are
built on a cordierite (magnesium aluminosilicate, a reasonable refractory and insulator, very thermally stable) honeycomb substrate, with a coating of
porous alumina bonding colloidial PGMs to it.
Last week, I busted the honeycomb out of the casing and ground up about half of it. For the last week, I've had it soaking in ~30% H2SO4, presuming
to dissolve the Al2O3 which the PGMs are trapped in. Little seems to have been done, as a fragment of unbroken honeycomb that's been soaking still
supports flameless ignition when preheated and given a propane-air mixture.
Even if the Al2O3 hasn't dissolved, I still have to find a way to get the PGMs out of the remaining cordierite. I don't have any nitric acid to make
aqua regia, so it occurred to me I might make a solution of chloric acid instead. So, I took a sample of the crud off the filter and added 31% HCl
cut about half with water, which appeared to react somewhat, raising the temperature about 10 degrees. I then boiled the suspension for about 10
minutes, adding single crystals of NaClO3 until reaction stopped. The addition of a crystal caused immediate release of green gas, which smelled of
chlorine rather than chlorine dioxide. Even so, I kept the flask out of my line of sight until it dissolved. Swirling the flask appeared to absorb
the gas from the airspace in the flask well enough.
Now that the solution is cooling and has settled, I see it is sort of green-orange-reddish, which I would associate with chloroferrate(III) ions.
Question: how much Fe2O3 is in a typical catalytic converter ceramic oxide analysis?
I wasn't expecting to see much PGM in here (there's what, a few grams in total in the *entire* unit?), but there should still be enough to electrowin
a thin coating from this solution -- if any has dissolved.
Tim
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Rosco Bodine
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Maybe try muriatic acid plus ammonium nitrate .
Some added urea might help .
This might help you pass the time while it is dissolving ,
pondering the physics involved here .
http://www.youtube.com/watch?v=boqUUPMT6Gc
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not_important
International Hazard
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The platinum and palladium chlorides are dark red-brown in colour.
SFAIK there's no intentional iron in the catalytic converters, just incidental in the ceramic raw materials, that which gets picked up in the
processing of the ceramics, and any acquired by erosion and corrosion of the engine and exhaust system.
Bubbling chlorine into water containing the suspended metals will dissolve them, as will generating chlorine by some chemical reaction. Alternatively
a nitrate salt can be added to aqueous HCl to make aqua regia.
I doubt that 30% H2SO4 at near room temperature will do much to the cordierite or alumina. However as the metals are deposited on the surface of the
ceramics there should be much problem removing the metals. The acid soak may have removed some of the iron contamination picked up during operation
of the engine.
The mixed alkali chlorides or the platinum metals have fairly low solubility, ammonium chloride is used to precipitate some of the group in various
processes. This might be the best way to isolate the platinum group from other stuff in solution. Alternatively a reducing agent could be used to
convert them to the free metals.
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vulture
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30% sulfuric acid isn't going to do squat to either annealed alumina or platinum.
Try H2O2 and HCl.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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12AX7
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Don't have anything better than 3% H2O2.
Surely a few bits of chlorate does as well?
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Dr. Beaker
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If you have access to mercury you can try extracting these metals as amalgams.
no need to say that precautions should be take to avoid mercury intoxication
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Eclectic
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NaNO3 + HCl.
Ammonium ion is probably not a good choice for this mix.
[Edited on 11-10-2007 by Eclectic]
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Fleaker
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Don't bother with mercury, it won't work with platinum.
I'm surprised you didn't just ask me about this privately.
You don't want ammonium cation in it just yet.
You can make a cheap aqua regia with an alkali nitrate and concentrated hydrochloric acid.
Hot hydrochloric and sulfuric acids will dissolve away the substrate material. You won't get much Pt, not enough to be worth your time.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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evil_lurker
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NaCN under heat and pressure is whats needed.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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12AX7
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The only nitrate I have is about 100g Ba(NO3)2. This thead isn't about making aqua regia per se: read the subject.
Tim
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Eclectic
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12AX7, do you have a picture of the core support ceramic? Would it be useful for technochemistry applications?
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12AX7
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It could be. I don't have a picture, but it's not hard to describe: it is a grid pattern (square, not honeycomb per se), 0.1mm thick walls and 1mm
spacing (so I've heard; I haven't measured it). This grid is extruded in a very straight prism, and the ends (as manufactured) are quite flat.
If nothing else, I can take the leftover ground up crud, mix with some clay and make firebricks.
Tim
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not_important
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I did say that most ways of generating chlorine in the solution will work, it's just that aqua regia works and is well documented; nitrate salt + HCl
is satisfactory because the goal is to isolate the precious metals rather than performing a full analysis of the material.
So anything that makes chlorine, or is a strong enough oxidiser and there is a source of chloride ions, will work. Making chloric acid just seems a
bit risky, although you did it in a conservative fashion that should be OK. But you're still potentially have some HClO3 around, which would bother
me.
An alternative uses bromide and oxidisers, including bromine itself. See the attached patent.
Attachment: US5304359A1.pdf (411kB)
This file has been downloaded 980 times
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Eclectic
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Re. Core Material: So you could cut plugs with a diamond grit core drill and use it as catalyst carrier in a tube furnace? Or is the orientation
wrong? Harbor Freight has some small diamond core drills really cheap this month.
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chemrox
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| Quote: | Originally posted by vulture
Try H2O2 and HCl. |
Tell me about H2O2 and HCl. I tried this as a glass cleaner because I'd read aabout it here. It released some chlorine right away, started bubbling
and got very hot in the next few minutes. The fumes were choking and I vacated the area after getting the stuff under my (somehwhat inadequate) hood.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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UnintentionalChaos
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What proportions did you mix them in? An excess of HCl would reduce the newly formed HOCl and outgas chlorine.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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12AX7
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As far as chloric acid goes: on addition of NaClO3, there was some ClO2 apparent, but over time, it decomposed to several more Cl2's.
The container, with lid, was opened a few hours after addition, revealing a heavy blanket of green gas which could literally be "poured" out of the
container. Yeah, I think there's just a little chlorine in the mix! The stifling smell was exclusively chlorine, no obvious ClO2 present.
So as long as there's something like elemental chlorine in solution, stuff like platinum is going to get into solution?
Tim
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vulture
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| Quote: |
Tell me about H2O2 and HCl. I tried this as a glass cleaner because I'd read aabout it here. It released some chlorine right away, started bubbling
and got very hot in the next few minutes. The fumes were choking and I vacated the area after getting the stuff under my (somehwhat inadequate) hood.
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Duh! That's the fracking point of the mixture! If you got improper safety measures in place, don't blame the method, blame yourself.
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So as long as there's something like elemental chlorine in solution, stuff like platinum is going to get into solution? |
Well, you need something that's strong enough to oxidize the palladium and something to complex it. That's why aqua regia works, NOCl oxidizes and Cl-
works as a ligand.
[Edited on 11-11-2007 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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12AX7
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| Quote: | Originally posted by vulture
Well, you need something that's strong enough to oxidize the palladium and something to complex it. That's why aqua regia works, NOCl oxidizes and Cl-
works as a ligand.
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(And platinum, and whatever else is in there...)
So the question is, how does NOCl compare to Cl2?
Tim
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vulture
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From what I could gather, palladium metal is attacked by the following:
Conc. HNO3, Aqua Regia, HCl/Cl2, HCl/Br2, HBr/Br2, NaOCl solution, KCN solution, Br and Cl2.
Pt is more resistant it seems. It withstands most acids (including oxidizing ones) up to 100C. HBr, H2O2 (30%), HI and conc. HNO3 get the job done at
100C. From 400C onwards your options expand rapidly: H3PO4, MgCl2, Ba(NO3)2, KOH/K2S, Na2O2, NaOH, NaCN, KOH, KNO3/NaOH, KCN.
Only aqua regia and the halogens (except I2) get the job done at R.T.
Note that this gives you the option to selectively extract the palladium. Saves you cumbersome separations along the road.
[Edited on 11-11-2007 by vulture]
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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not_important
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Problem with that method is that the platinum might shield some of the palladium from being dissolved, and/or the pallidium that does dissolve might
take a bit of platinum with it.
I think that at the stage of getting it off the support it would be better to strip all the PGM off, then convert to the metals or very low solubility
compounds and work with those much smaller volumes.
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12AX7
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Well, the trial sample I boiled in the flask: I electrolysed it overnight, obtaining a small amount of flaky metallic deposit on the cathode. The
solution color still resembles ferric ions.
I am filtering and rinsing the rest of the material which was similarly chlorinated (at room temperature). Pew, doing it outside I might add...
Meanwhile, the remaining K2PtCl6 solution left over from plating those titanium strips (mentioned elsewhere) has been evaporating. I noticed the
other day some small golden crystals on the bottom. Man, that stuff is low solubility. It's probably no trouble at all to evaporate this extract and
see what precipitates, given some potassium ion of course. Any impurity, like FeCl3, is so much more soluble that I should get all the Pt and stuff
out before it crystallizes.
MgCl2 sounds intriguing. How is that? Does it decompose and attack Pt? What oxidizes the Pt then, atmosphere? I happen to have made some MgCl2
hydrate (crystallized and not clumping!!), and as you know, I am not opposed to treating things with fire...
For that matter, fusion with NaOH would work, except that the substrate would gooify, eh?
Tim
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not_important
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Magnesium chloride hydrate will lose HCl long before you reach 400 C. Also most of the listed reagents are pretty aggressive towards most materials
you'd use for containers at the reaction temperatures. I suspect that you'll end up attaching the support ceramic as well, resulting in a lot of
other junk in the solution or forming a precipitate that absorbs some of the compounds you want to reclaim.
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Siddy
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Why not make the nitric acid, if you REALLY cant buy it (photography store), out of sodium nitrate.
Something i really want to know, can old catalytic converters be used for this kind of platinum etc extraction? Wont a lot of the other metals
dissolve with the plat. Is there some easy purification i havent heard of?
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not_important
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The patent I attached specifically gives the recovery of platinum group metals from catalytic converters as an example of applications of the
H2SO4/Br2/Br- dissolution method.
The PGM bearing ceramic material is removed from the metal casing and crushed before extracting the PGM, the only non-platinum-group-metals are going
to be any that were part of the catalyst - generally none - and those picked up from wear and corrosion in the engine - meaning mostly a small amount
of iron. Chemical reduction can easily separate PGM from iron and other base metal compounds, giving a simple and quick concentration of them.
I think that 12AX7 has little nitrate on hand, but ready access to chlorate, thus the question about alternatives to aqua regia. There's no need to
go to the trouble of making nitric acid to make aqua regia for this type of application, adding a nitrate salt to hydrochloric acid works just fine
and eliminates the need for distillation.
12AX7 used chlorate and HCl to make free chlorine in a strong concentration of chloride ions, that mix dissolves the PGM as chloride complexes just as
aqua regia does.
Alternatively the chlorate could be added to a sulfuric acid solution of bromide to generate Br2 for that other method, small amounts of free chlorine
aren't going to hurt and it avoids high concentration of salts in the extraction liquid.
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