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kilowatt
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[*] posted on 4-10-2008 at 06:51
Thorium Separation From TIG Electrodes


I would like to prepare anhydrous thorium (IV) fluoride for a magnesium alloying agent. Starting with thoriated TIG electrodes, the easiest way I have found to digest these is with electrolysis in a solution of sodium hydroxide, forming sodium tungstate. I am not familiar enough with thorium chemistry to be able to tell what this process will result in, but I would assume the tungstate can easily be precipitated with ammonium chloride as ammonium paratungstate. Am I correct to guess that thorium would precipitate out (either un-altered as oxide, or as sodium thorate) as the tungsten matrix is dissolved into the alkali? If it too dissolves, does anyone know how to separate it from the tungstate?

There is then the matter of preparing thorium oxide from the process and then preparing anhydrous thorium fluoride from the hydrated variety obtained by adding HF to thorium oxide. I've been looking at some patents, but there is really little information out there on the alkaline chemistry of thorium or of the lanthanides or other similar metals.




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[*] posted on 4-10-2008 at 10:20


Yes, W or Th have opposite behaviors in acidic/basic solution. You'll end up with a precipitate of Th(OH)4 or hydrated ThO2, provided you keep it carbonate-free. That will be soluble in HCl, HNO3, and slightly soluble in dilute H2SO4; the various hydrated thorium sulfates are soluble at 1 to 4 grams per 100 cc water. Filtering that solution, then adding ammonia will reform the hydroxide; treating that with hydrofluoric acid will form ThF4.4H2O which has low solubility in the acid. Getting anhydrous ThF4 is a bit trickier, mixing the hydrate fluoride with a several-molar excess of "ammonium bifluoride" NH4F.HF then slowing heating that to 200 F, and finally pulling a vacuum to remove excess ammonium salts, would do the job.


Why the fluoride over the chloride?
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[*] posted on 4-10-2008 at 13:44


What is the concentration of thorium in your TIG Electrodes?
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[*] posted on 4-10-2008 at 14:04


Thanks, I just happen to at one point have purchased some reagent grade ammonium fluoride. Ammonium bifluoride could be prepared by adding a mole of HF to it if I am not mistaken.

I am not sure the exact reason for using thorium fluoride over chloride, but it probably has much to do with its fusibility. All the patents and info regarding preparing the alloy specify a low melting mixture of thorium, lithium, and magnesium fluorides, which is added to the magnesium melt at around 700°C. The excess magnesium metal reduces the thorium fluoride under the conditions and thorium metal enters the alloy while magnesium fluoride enters the fused saline layer which apparently has fairly low viscosity allowing easy separation as the magnesium alloy is poured off. I have not been able to find a phase diagram for thorium chloride in such a system, but at least one of the patents has a full ternary phase diagram for the fluoride system.

I do have a concern that the fused saline mixture will attack or admix with the crucible (aluminum oxide for now, but silicon carbide in the future once I have a larger closed furnace).

At kclo4: The thorium oxide (not actual thorium) concentration is 2% in the most common variety. For example a package of 10 1/8" diameter x 7" rods would have around 5.3g of thorium oxide, enough to make about 1lb of the magnesium alloy. Such a pack of rods normally retails for about $30 but can be had for an order of magnitude less if one looks hard.

[Edited on 4-10-2008 by kilowatt]




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[*] posted on 4-10-2008 at 14:32


Spent TIG rod nubs may be even better, although you don't know if they contain Th or Ce, Zr, etc.; you'd have to ask the weldors what they use, or what the company buys.

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[*] posted on 4-10-2008 at 16:25


this is news to me.
how dangerous are thorium salts to work with.
they are radioactive to my knowlage.




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[*] posted on 4-10-2008 at 16:36


Thorium salts are extremely dangerous if they end up inside the body, just like uranium salts. However the radioactivity is a non-issue as long as careful steps are taken to avoid ingestion, since it is only very slightly radioactive. Thorium is indeed used in plenty of commercial applications, which are entirely unrelated to its radioactivity. For example these magnesium-thorium alloys are highly castable, quite strong and creep resistant to 250°C. They are normally used in aerospace applications. TIG electrodes are available in 1%, 2%, and 4% thoriated varieties as well as ceriated, lanthanated, or pure tungsten.



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[*] posted on 4-10-2008 at 16:42


what about skin contact ?

sorry stupid me ;) you can touch welding rods so
only solubles are prob. I need want the oxide my self.

[Edited on 5-10-2008 by Ephoton]




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[*] posted on 4-10-2008 at 16:46


Soluble thorium compounds (like thorium fluoride) can be absorbed through the skin, but insoluble ones are quite safe to handle (thorium metal, thorium oxide).



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[*] posted on 4-10-2008 at 16:53


thanx kilowatt.



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[*] posted on 4-10-2008 at 20:13


Inhalation is the greatest danger for thorium, in part because industrial processing for concentrating thorium in ores had the dioxide as their major product, and working with large quantities of powder generally result in dust in the air. It's also the major danger because it seems to be the best absorption route, generally 0,0% to 1,0% of orally ingested thorium compounds are absorbed, the oxide isn't significantly absorbed through the skin and the radiation from it is blocked by the dead keratinised cells of the outer epidermis.

So protect yourself from breathing any dust or mist, and avoid skin exposure to the soluble compounds.
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[*] posted on 5-10-2008 at 04:16


I am thinking of making it impregnated on a pumice for a catalist so I guess I will have too use the soluble salts anyway.

I don't need a lot though so this source looks like a winner too me.

it is very important I think to understand its dangers beforehand.

yet again thankyou.




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[*] posted on 5-10-2008 at 05:08


The sodium tungstate generated alone would justify the investment into the rods. Have you priced sodium tungstate recently? Ridiculous! Buy the way, are you sure anodic dissolution in alkali is enough to oxidize tungsten? Never tried this myself.



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[*] posted on 5-10-2008 at 15:23


Yeah I've tried the anodic digestion on pure tungsten rods before, with 25%w/w NaOH and a 9V battery. It worked startlingly quickly. The oxygen forms a layer of WO3, and we know that this quite readily reacts with NaOH, so more WO3 can be formed. However when I tried it with a real setup on some 2% platinum tungsten alloy, it took weeks to even have a visible effect. I suspect however on thoriated rod it would work just as quickly as on pure tungsten.

[Edited on 5-10-2008 by kilowatt]




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[*] posted on 5-10-2008 at 18:21


Quote:
Originally posted by chloric1
The sodium tungstate generated alone would justify the investment into the rods. Have you priced sodium tungstate recently? Ridiculous! Buy the way, are you sure anodic dissolution in alkali is enough to oxidize tungsten? Never tried this myself.


Hmm, whats useful about Sodium Tungstate? Just it being an oxidizer for some organic things I guess?
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[*] posted on 5-10-2008 at 18:54


Tungstates themselves aren't great oxidisers. But they and heteropolyacids based on Mo or W form a range of catalysts including oxidation catalysts.
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[*] posted on 6-10-2008 at 07:39


Quote:
Originally posted by kilowatt

I am not sure the exact reason for using thorium fluoride over chloride, but it probably has much to do with its fusibility. All the patents and info regarding preparing the alloy specify a low melting mixture of thorium, lithium, and magnesium fluorides, which is added to the magnesium melt at around 700°C. The excess magnesium metal reduces the thorium fluoride under the conditions and thorium metal enters the alloy while magnesium fluoride enters the fused saline layer which apparently has fairly low viscosity allowing easy separation as the magnesium alloy is poured off.


That fusibility would definitely have to come from the ternary system LiF/MgF<sub>2</sub>/ThF<sub>4</sub>, because the latter two have melting points (resp. 1,263 and 1,111 C) that exceed even the boiling point of liquid magnesium. LiF MP is 848 C ...

In a certain sense, it would be more logical to use ThCl<sub>4</sub>, because MgCl<sub>2</sub> has a much lower MP (714 C) and would definitely be easily removed as 'liquid slag'. Perhaps the real reason for choosing ThF<sub>4</sub> over the chloride is related to the latter's poorer thermal stability (just guessing here)? Fluorides are definitely more expensive and hazardous to prepare, even if this one can actually be prepared aqueously, without F2 or anhydrous HF...

kilowatt, are the patents and ternary system available online? Reduction of ThF<sub>4</sub> with Mg would be a method (almost certainly at least) to prepare lump thorium. The same reduction of the chloride would also be possible but probably requires a bomb-type reactor to avoid the slag from boiling off...

Personally I didn't even know that some TIG electrodes contain thorium and that it can be relatively easily extracted from them. Perhaps we should keep quiet about it, before they ban them too, as they did the thoria based lantern mantles? ;)

I'm definitely looking out for some of these electrodes but wouldn't be keen on using HF, I'll stick to either ThCl<sub>4</sub> or thoria, thanks...

Interesting post...

[Edited on 6-10-2008 by blogfast25]
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[*] posted on 6-10-2008 at 07:46


Quote:
Originally posted by blogfast25
Personally I didn't even know that some TIG electrodes contain thorium and that it can be relatively easily extracted from them. Perhaps we should keep quiet about it, before they ban them too, as they did the thoria based lantern mantles? ;)
A ban is unlikely, considering that thorium is the best additive for this purpose. Alloying metals in TIG tips are specifically there to act as local electron donors, lowering the work function to push electrons off the tungsten lattice. Thorium, an actinide with a couple of 5f electrons, works better on the whole for this than the lanthanides.
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[*] posted on 6-10-2008 at 08:13


Hmmmm... bans are always unlikely until they happen. When the safety freaks get something into their heads, there's usually no stopping them (unless there's a powerful "WT TIG electrode lobby", of course... lol)

Would anodic digestion of these rods be the best and easiest way or would fusing them with an alkali + oxidiser work too? The W would fuse to tungstate and could be separated from the non-amphoteric thoria, could it not?
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[*] posted on 6-10-2008 at 08:24


The patents are, like all patents, readily available. The one I am most specifically referring to is 3026196. On the first page is a phase diagram for the ternary fluoride system, from which the optimal ratios can be seen. This is also discussed later in the patent. I don't know about the chloride, it might work, but it might be too volatile, or decompose at those temperatures like you suggested.

Quote:

A ban is unlikely, considering that thorium is the best additive for this purpose. Alloying metals in TIG tips are specifically there to act as local electron donors, lowering the work function to push electrons off the tungsten lattice. Thorium, an actinide with a couple of 5f electrons, works better on the whole for this than the lanthanides.

Do not fool yourself into thinking that because something is widely used, important, or best suited to a purpose, that this will save it from being banned. Make the no mistake, the only reason these electrodes are not banned is because no one has yet been caught using them to breed fissiles. We can only hope this continues to be the case. Afterall, the thoria lantern mantels were the best for their purpose, iodine tincture is probably the best topical antiseptic (and until recently the most widely used), and ammonium nitrate is the best nitrogenous fertilizer. Yet all these things are effectively banned or heavily regulated. The problem of the "good stuff" or "the real thing" no longer being available because of nanny state legislation is an ever growing phenomena in the western world.

[Edited on 6-10-2008 by kilowatt]




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[*] posted on 6-10-2008 at 10:03


kilowatt:

Ok, got it from freepatentsonline.

That's quite a task you're undertaking there: the reaction taking place at 700 C and under argon takes a bit of engineering I would say from a BYS perspective...

This alloy must worth quite something to you. What do you plan to use it for?
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[*] posted on 6-10-2008 at 17:21


It looks like a very interesting and useful alloy, and since I have a furnace capable of making it, I may as well. I plan to make various lightweight high strength parts with it.



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[*] posted on 6-10-2008 at 23:08


I have a 10 pack of 1/8" diameter by 7" 2% thoriated electrodes sitting next to me. Kilowatt, based on my calculations (currently lacking a scale so my mass is based on a calculated theoretical density) there is about 4.7g of thorium to be recovered as the metal. Not_Important, I take it that the thorium carbonates or hydroxy-carbonate complexes of Thorium are soluble?

I'm not sure where I read it but, I believe that Thorium peroxide can be recovered from a strongly acidified (sulfuric) solution of tungsten and thorium by addition of hydrogen peroxide. If carbonates become an issue, acidification with conc. H2SO4 generating the soluble metatungstate anion and thorium sulfate followed by peroxide precipitation may be a viable route.




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[*] posted on 7-10-2008 at 05:40


Quote:

Kilowatt, based on my calculations (currently lacking a scale so my mass is based on a calculated theoretical density) there is about 4.7g of thorium to be recovered as the metal.

That is correct, remember I calculated the oxide content which is about 88% metal. I just got a 10 pack of 3/16" rods on ebay; they should contain about 10.5 of thorium as metal.

I'm not sure I follow your sulfuric acid route. Metal tungstates form only in alkali solution; if you added acid you'd simply precipitate WO3 hydrate (tungstic acid, more precisely). Thorium sulfate is only sparingly soluble (2g/100mL at 30°C according to wikipedia's solubility table, which is the only source I can find and is sometimes wrong), but if it remains dissolved it could be separated during this step to be precipitated later with peroxide or just boiled to dryness. Backtracking further, all the common acids are very poor at dissolving tungsten in the first place, so I am assuming you are still referring to NaOH electro-digestion as the beginning step?

[Edited on 7-10-2008 by kilowatt]




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[*] posted on 7-10-2008 at 07:37


kilowatt:

Regards this anodic digestion in alkaline solution (of which you wrote that it "worked startlingly quickly"), what's the precise set-up? How much time needed? Need to replenish the NaOH solution and when? The ThO2 hydrate would simply collect at the bottom of the cell, right? Stirring? Temperature?
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