Sciencemadness Discussion Board - Thorium Separation From TIG Electrodes

Thorium Separation From TIG Electrodes

kilowatt - 4-10-2008 at 06:51

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.

not_important - 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?

kclo4 - 4-10-2008 at 13:44

What is the concentration of thorium in your TIG Electrodes?

kilowatt - 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]

12AX7 - 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.

Tim

Ephoton - 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.

kilowatt - 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.

Ephoton - 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]

kilowatt - 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).

Ephoton - 4-10-2008 at 16:53

thanx kilowatt.

not_important - 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.

Ephoton - 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.

chloric1 - 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.

kilowatt - 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]

kclo4 - 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?

not_important - 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.

blogfast25 - 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/MgF2/ThF4, 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 ThCl4, because MgCl2 has a much lower MP (714 C) and would definitely be easily removed as 'liquid slag'. Perhaps the real reason for choosing ThF4 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 ThF4 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 ThCl4 or thoria, thanks...

Interesting post...

[Edited on 6-10-2008 by blogfast25]

watson.fawkes - 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.

blogfast25 - 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?

kilowatt - 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:

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]

blogfast25 - 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?

kilowatt - 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.

UnintentionalChaos - 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.

kilowatt - 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]

blogfast25 - 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?

kilowatt - 7-10-2008 at 08:42

Ok here's basically a summary of everything:

I've only done one experiment before with a 3/32" pure tungsten rod in 25% NaOH connected to a 9V battery. The diameter had notably decreased within some seconds, and had reduced by several hundreds of an inch (maybe half the original diameter) within some minutes; I did not record exactly. The electrolyte was at room temperature and a great excess of NaOH was used. The continuous setup I used for the platinum/tungsten alloy had a water-cooled cell consisting of a small jar sealed inside a larger one, with holes being drilled in the larger jar for the water lines. I used a variac connected to a step-down transformer (I re-wound a microwave oven transformer to output about 10V max at high current) and a single stud diode as a rectifier. I used a graphite cathode and anode mount; the anode mount wore down much faster than the highly resiliant alloy. My water-cooled cell ran at about 40-50°C but this just depends on the flow rate and the cell power, and isn't too important. For digesting the thoriated tungsten rods I would just use the rods as both anode and cathode and use either 60Hz AC (probably at around 5V) or a timed relay to reverse the polarity every few minutes.

I can't find much solubility data for sodium tungstate. One MSDS states 41g/100g H2O at 0°C. I would start with plenty of water to dissolve the entire batch. I would add to that enough saturated NaOH solution to react all the tungsten with about twofold molar excess based on Na2WO4. Thorium oxide or hydroxide should simply collect at the bottom of the cell (according to not_important, not me). After it is filtered you could check the solution with a geiger counter to make sure there is no thorium left, but I don't have one. Heat the thoria precipitate to a high temperature to obtain dry ThO2 and weigh to make sure it is close to the calculated amount. If there is no thorium left in solution, the tungstate can be precipitated as ammonium paratungstate by adding ammonium chloride. Copious amounts of ammonia will be evolved at this stage as the excess NaOH is neutralized. If there is any soluble thorium left in the solution, it could be acidified by adding hydrochloric or nitric acid (though H2SO4 could work too, but not as ideally due to the low solubility of thorium sulfate). The acidification will precipitate WO3 hydrate, so the thorium will remain in solution, which after filtering can be boiled down or precipitated, likely by adding NaOH. A peroxide method was also mentioned.

[Edited on 7-10-2008 by kilowatt]

not_important - 7-10-2008 at 09:21

Thorium hydroxide is soluble in solutions of alkali carbonates, forming complex double carbonates; sorry not hard numbers on how soluble but some double carbonates can be isolated. H2O2 will precipitate thorium from mildly acidic solutions of its salts, redissolving it takes addition of something that destroys peroxide (like iodide or stannous compounds).

Thorium sulfate s a mess. It can crystalise with 0, 2, 4, 6, 8, or 9 H2O. The anhydrous sulfate is soluble, up to 25 weight percent at 0 C, but the solution soon deposits the 9 or 8 hydrate; the 8 hydrate slowly changing to the 9. The 9 hydrate is stable below 43 C, the 4 hydrate between that and 100 C, the 2 hydrate above 100 C. Increasing temperature reduces solubility of the tetrahydrate but increases solubility of the other hydrates. In grams per 100 g water, the 9 hydrate is 0,74 @ 0 and 3,0 @ 40; the 4 hydrate is 4,0 @ 40 and 1,9 @ 55 C. Interchange between the various hydrates tends to be slow, along with the low solubility making the sulfate less than attractive for use during purification.

The simplest way of separation, in my opinion, would be as follows. Use recently boiled water for making solutions. Make up alkali hydroxide solutions by first making a very strong solution of Na or K OH, and letting it sit without exposure to air until any suspended solids settle, the carbonates have lower solubility in the concentrated hydroxides, then carefully pouring off the clear solution for diluting to the needed strength.

Electrolytic dissolution in alkali, or H2O2 + alkali, should leave the thorium as the very insoluble hydroxide/oxide along with small amounts of unreacted tungsten and trace impurities. Filter and wash with dilute hydroxide and then boiled water.

Now comes an annoying part. Reports from several people indicate that the thorium may or may not be in a form easy to dissolve; apparently differences in the manufacture of the rods or slow crystallisation from solid solution may give a difficult to dissolve oxide.

First attempt to dissolve the thorium containing precipitate in warm to hot moderately strong HCl, adding a few drops of HNO3 or H2O2. If you're swimming with it, HNO3 will work in place of HCl. Expect a small amount of tungstic acid to remain as a solid, filter the solution and save the solids as well as the filtrate. Precipitate the thorium with NaOH, wash with dilute NaOH, aqueous ammonia, boiled water, then alcohol, and acetone, let dry. Weigh the solid to determine the recovery of thorium as Th(OH)4.

If the precipitate from acid treatment was large or if thorium recovery seems low, the solids from the acid treatment can be processed in several ways. One is fusion with a bisulfate or mix of Na2SO4 and (NH4)2SO4, keeping it molten with occasional stirring for 5 or 10 minutes, then pouring onto a stone slab or iron plate, crushing the solid, boiling with an excess of 5 to 10 percent NaOH for some minutes, filtering and treating the solids with acid as above. Alternatively the precipitate can be treated with hot HNO3 plus a little HF or soluble fluoride, then the Th precipitated with hydroxide.

If carbonates were an issue during the original dissolving of the rods, one approach that could be taken is the following. Estimate the amount of NaOH remaining, add an equivalent of that of ammonium chloride or sulfate as a solution. Boil gently until no more ammonia is given off, ammonium carbonates are not stable in hot solutions and are driven off as NH3 and CO2 along with the steam.

blogfast25 - 8-10-2008 at 07:30

That was detailed, thanks. I hope kilowatt will keep us informed of any progress...

kilowatt - 8-10-2008 at 08:44

Progress comes slower than usual during the school year, and my usual is slow enough. I will try this next time I'm home though.

jshine - 4-4-2011 at 21:42

I'm curious if anyone has attempted the procedure outlined in 2006 by "not_important" to determine whether it works and, if so, how well? It's very detailed and makes sense based on what little I know of the chemistry of thorium & tungsten, but it would be great to get experimental verification of what works & what doesn't.

Any experiences would be appreciated.

IPN - 25-9-2011 at 06:07

In an attempt to obtain some thorium compounds from welding rods I did an experiment in dissolving tungsten in a sodium hydroxide/sodium nitrate melt (I have loads of alkali nitrates available, but not much hydrogen peroxide and I don't like electrolytic methods). I decided to try pure tungsten first so I don't have to worry about thorium contamination before I get the procedure perfected. So 27g (0,147mol) of relatively pure tungsten (not welding rods) in the form of short 3mm thick rods was placed into a ceramic pot with 24g of sodium hydroxide pellets and 100g of coarse sodium nitrate. The amounts weren't really calculated as I couldn't come up with a balanced reaction. I just took a good excess of oxidizer and half the amount of hydroxide in moles.

Mixture was slowly melted using a gas portable stove and stirring with a steel rod. Few minutes after the reaction mixture had become completely fluid a very vigorous reaction kicked in heating the mixture instantly into orange glow and shattering the ceramic pot while lots of steam or some other white vapour was generated (I was expecting this to happen so I had the pot in a steel pan, containing the melt). No visible red gasses were seen (did it outside and it was pretty windy so can't be sure). After the reaction had slowed down the melt formed a light green/white solid cake with visible pieces of tungsten. This was carefully drowned with water and left to sit.

I haven't yet worked it up, but just thought I'd report this for now.

EWTH-Th-2 welding rods

cal - 4-4-2012 at 04:17

Quote: Originally posted by IPN

In an attempt to obtain some thorium compounds from welding rods I did an experiment in dissolving tungsten in a sodium hydroxide/sodium nitrate melt (I have loads of alkali nitrates available, but not much hydrogen peroxide and I don't like electrolytic methods). I decided to try pure tungsten first so I don't have to worry about thorium contamination before I get the procedure perfected. So 27g (0,147mol) of relatively pure tungsten (not welding rods) in the form of short 3mm thick rods was placed into a ceramic pot with 24g of sodium hydroxide pellets and 100g of coarse sodium nitrate. The amounts weren't really calculated as I couldn't come up with a balanced reaction. I just took a good excess of oxidizer and half the amount of hydroxide in moles.

Mixture was slowly melted using a gas portable stove and stirring with a steel rod. Few minutes after the reaction mixture had become completely fluid a very vigorous reaction kicked in heating the mixture instantly into orange glow and shattering the ceramic pot while lots of steam or some other white vapour was generated (I was expecting this to happen so I had the pot in a steel pan, containing the melt). No visible red gasses were seen (did it outside and it was pretty windy so can't be sure). After the reaction had slowed down the melt formed a light green/white solid cake with visible pieces of tungsten. This was carefully drowned with water and left to sit.

I haven't yet worked it up, but just thought I'd report this for now.

'EWTH-Th-2 welding rods " These welding rods contain 2% thorium oxide and tungsten only. See MSDS, When the rods are treated with nitric acid the thorium becomes a nitrate and the tungsten does not react with acids. Thorium nitrate is water sol. and tungsten is not. Then heat the Thorium nitrate
to 450-500 to convert to oxide.

Possible thorium exposure!

Dave Angel - 20-8-2012 at 08:28

I wish I had known that TIG electrodes may be 'thoriated' before I ground one into separate electrodes for my spot welder yesterday... It didn't even cross my mind that I might be working with radioactive materials, but in looking to buy a new electrode I've just made this slightly worrying discovery!

Did the work in an open garage, with face shield but no dust mask. This was a red-tip electrode so turns out it was indeed thoriated. Now wondering just how much I've been exposed to and whether there's anything I should, or even, can do? I'm hoping it's one of those 'chronic exposure' hazards and that the small amount from a few grinding operations won't be a significant health hazard....

vmelkon - 20-8-2012 at 09:59

Quote: Originally posted by Dave Angel

I wish I had known that TIG electrodes may be 'thoriated' ....

The packaging should say 2% thoriated. The rods are also color coded (red tipped in your case) so that when they are out of the package, they can still be IDed.

As for the danger, they are only dangerous when you grind the tip to make it sharp like a pencil. It is better to do that outside.

People have been exposed to it for a long time. That's why new rods contain lanthanum or one of the other lanthanides.

Same thing for gas mantles. They use to contain thorium nitrate and cerium nitrate. Now it is yttrium and I think cerium as well.

Good bye thorium!

Poppy - 20-8-2012 at 13:31

Quote: Originally posted by blogfast25

Would anodic digestion of these rods be the best and easiest way or would fusing them with an alkali + oxidiser work too?

Yes nice idea, would powdered TIG rods survive a trip with chlorate in a black powder like fashion?

Dave Angel - 21-8-2012 at 00:15

Quote: Originally posted by vmelkon

Unfortunately the pack was not marked. I remember buying it many years ago from a big chain shop in the UK and whilst they knew it was some sort of welding electrode, it was just a very plain piece of card with shrink wrap. They just put an abitrary price on it and I thought 'why not?' Had I seen the word 'Thoriated' anywhere I would have picked up on it!

I ground it into three pieces with the edge of a bench grinder and ground the tips down a bit. Hopefully not too much dust came off this small operation.

Lesson learned anyway; zirconated electrodes next time, and decontamination of garage the next job!