Sciencemadness Discussion Board

The trials & tribulations of Thorium production

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Dan Vizine - 4-4-2014 at 12:06

As I understand it, in 2015 the US government will move to more tightly control the buying and selling of radioactive materials by requiring that buyers and sellers have a license. I haven't researched it myself, this is what I was told by the supplier that I buy most of my chemicals from on eBay, a reliable former chemist.

So I guess the time to move on my dream of producing thorium metal is now. The only thorium material I can access in a reasonable amounts currently is thorium nitrate tetrahydrate (and I have), the universal thorium salt. According to the literature this material can be calcined directly to thorium dioxide. And I'm sure it can, but I have purity concerns.

Alternatively, based on work done by the government, it appears that a better route will be treating aqueous thorium nitrate with ammonia to a pH of seven or eight. This will give me thorium hydroxide which can be calcined with a greater expectation of achieving high purity thorium dioxide.

Since I'm talking about thorium dioxide, those of you who have explored these same dark synthetic passageways probably already realize that I have opted for the straight calcium reduction route for 1 h @ 950 degrees Celsius.

The other methods that I have discarded include electrolysis of molten thorium halides (primarily because of the difficulty of obtaining the tetrafluoride), the magnesium reduction of the tetrachloride (because I am not confident that I can completely separate the residual magnesium from the thorium-magnesium solid solution) and calcium reduction of the tetrafluoride (for both reasons).

The reaction vessel is a 304 stainless steel pressure container from Whitey. It's rated to 1800 PSI but I don't really expect significant pressure to accompany this reaction. Of course it will scale significantly after an hour at 950 C, but it only needs to last for one or two trials. From past experience though, after cleaning the surface scale off this reactor, it will still be quite serviceable for my other needs. I won't be pumping it up to 1800 PSI anytime soon (or ever).

I've tried to make a detailed accounting of the daughter products that I need to worry about, primarily radium and radon. All of the reactions will be done outside, because, well that's obvious...

The jar which has been sealed forever probably contains some radon. Simply opening that outside will certainly be enough to allow it to dissipate safely. A larger amount of radon is undoubtedly trapped in the crystal lattice and it will be freed upon the first dissolution. Given the exceptionally long half-life of thorium, yes, there will be radium, but is it enough to worry about? Well let's put it this way... Thorium nitrate and thorium hydroxide or dioxide mixtures were used, as everyone already knows, as mantels in camping lanterns. Am I willing to risk exposure to something that was a commercial product forever? Yes. To put this in perspective, when I think of some of the horrible cancer hazards I've worked with in my lifetime, including bis(chloromethyl) ether, this is just another one. However, it does have unique features. I am used to being able to destroy my cancer hazards by reacting them, not so with thorium. I also appreciate the formation of "hot spots" caused by the inhalation of radioactive particles, how this greatly concentrates the effective radiation received by a tiny bit of tissue. The obvious answer here is to work outside, wear a respirator and observe good chemical hygiene.

The product from the reaction is expected to be a coarse metallic powder which can be compacted to form "solid" bodies of sorts. This is usually the first step taken along the route toward sintering. Instead, I'm going to produce the compacts at a pressure of about 40 tons/sq inch (this works quite well with platinum powder and thorium is softer, similar to copper, and annealed copper, at that) for remelting.

I found a person with an inert gas arc-melting furnace who will melt this material for a fee of a few hundred dollars an hour. My concern here is what to use as the hearth plate. Ideally it should be thorium dioxide ceramic. I still need to think about this.

Anyway, why have I started this topic if I haven't done the experiment yet? Well, I hope to take advantage of the collective smarts of this group to point out what I've missed. This synthesis seems to be worth all possible preparations prior to beginning.










[Edited on 4-4-2014 by Dan Vizine]

elementcollector1 - 4-4-2014 at 12:43

While I have not worked with thorium, why not show all of us a good time and start from thoriated tungsten welding rods? :D
1800 PSI is probably good, although I'd be careful all the same - these types of reactions can be explosive at times.
Be sure to watch for potential double salts - I have no idea if 'thoriates' exist, but it's entirely possible, which would make reaction with ammonia a no-go.
Just a thought, after the recent propylene carbonate RT electrolysis research - might thorium be possible through this route? I know not everything is soluble in propylene carbonate, but it would certainly save on setup costs...

blogfast25 - 4-4-2014 at 12:46

Hi Dan,

I have some sources indicating the calciothermic reduction of UO<sub>2</sub> was abandoned because of poor quality of the metal obtained, largely because of U's great affinity for oxygen, resulting in brittle metal with high oxygen content. Similar reports exist for similar oxides like zirconia and titania (indeed these metals are produced in anaerobic conditions, if pure, malleable metal is what you want).

I believe the situation will be similar for ThO<sub>2</sub> + 2 Ca.

I understand the difficulty of preparing anhydrous ThF<sub>4</sub> but would personally gun for magnesiothermic reduction of that fluoride.

I've been working for some time on ZrF<sub>4</sub> + 2 Mg and am preparing the fluoride by pyrolysis under argon of (NH<sub>4</sub>;)<sub>2</sub>ZrF<sub>6</sub>. I wonder if a similar Th salt could exist?

UF<sub>4</sub> + 2 Mg is tried, tested and used but of course Th's MP is much higher than that of U...


[Edited on 4-4-2014 by blogfast25]

blogfast25 - 4-4-2014 at 12:49

EC1:

He has access to thorium nitrate: no need to mess with thoriated electrodes.

Dan Vizine - 4-4-2014 at 13:04

This isn't a Goldschmidt or "Thermite" reaction, in fact I think it's endothermic which is why we have to cook it at 950 C.

The ammonia reaction was worked out by ORNL. It will work and it's easy. Still kicking myself hard for letting 100 g ThO2 for $75 slip away on eBay.

I neglected to mention that the reaction is going to be performed at about 500 mm in argon. Part of the reason I bought the commercial cylinder is because I want it sealed, I mean really sealed. I have a T sized cylinder of UHP argon in the basement that I use for preparing ampoules of group 1 metals (although shiny silver barium is going to be mine, dammit!).

The magnesiothermic reaction is nice because it makes a solid metal blob but you have to distill excess magnesium out to get sponge. I am wary of my ability to do so efficiently or even know if I have.

[Edited on 4-4-2014 by Dan Vizine]

[Edited on 4-4-2014 by Dan Vizine]

blogfast25 - 4-4-2014 at 13:08

Quote: Originally posted by Dan Vizine  
This isn't a Goldschmidt or "Thermite" reaction, in fact I think it's endothermic which is why we have to cook it at 950 C.

I neglected to mention that the reaction is going to be performed at about 500 mm in argon. Part of the reason I bought the commercial cylinder is because I want it sealed, I mean really sealed. I have a T sized cylinder of UHP argon in the basement that I use for preparing ampoules of group 1 metals (although shiny silver barium is going to be mine, dammit!).

Thanks, guys!


No, I'm pretty sure it's exothermic but I'll get back to you on that.

Certainly the magnesiothermic reductions of both ZrF4 and UF4 are strongly exothermic.

Argon may help but it's the presence of oxide itself that leads to oxygen in the metal (at least in the case of UO2).

blogfast25 - 4-4-2014 at 13:14

Standard HoF of ThO2 = - 1226.4 kJ/mol
Standard HoF of CaO = - 635 kJ/mol

So, standard heat of reduction = - 44 kJ/mol, barely exothermic.

This also means that your equilibrium constant (at least at RT) is fairly close to one. That would explain why poor quality metal would result.

Quote: Originally posted by Dan Vizine  
The ammonia reaction was worked out by ORNL. It will work and it's easy. Still kicking myself hard for letting 100 g ThO2 for $75 slip away on eBay.



Did you mean the precipitation of hydrated thoria with ammonia? Or the whole thing, including the recuction? The precipitation bit is the 'walk in the park bit'.


[Edited on 4-4-2014 by blogfast25]

elementcollector1 - 4-4-2014 at 13:18

I know he has a source - I was just proposing some inane ramblings as usual.
Once he gets Th(OH)4, wouldn't HF or NaF be relatively easy to obtain? After that, thionyl chloride or maybe heating with a few equivalents ammonium chloride might be possible for obtaining anhydrous ThF4.

Dan Vizine - 4-4-2014 at 13:21

Hi Blogfast,

You're the thermodynamicist between the two of us, and you may be right. However no exotherm of any importance occurs during the reaction.

The flourides are expected to be exothermic in reduction, that much is clear. In fact, that's the problem!

The temperatures generated are too extreme for my reactor, which will handle the Ca/ThO2 OK. I don't want to get a lot of iron, nickel and chromium in there as well. I'd need to go to a Mo liner which is not possible due to reactor geometry.

blogfast25 - 4-4-2014 at 13:22

Quote: Originally posted by elementcollector1  
After that, thionyl chloride or maybe heating with a few equivalents ammonium chloride might be possible for obtaining anhydrous ThF4.


You've got your chlorides cap on. We're talking fluorides here.

blogfast25 - 4-4-2014 at 13:26

Hi Dan (or should I say 'Zan' ;) ):

If I have time I'll try and work out a value for K at 950 C. Personally I'm sceptical: at low values of K, your metal will be riddled with residual ThO2. And there will be unreacted Ca too...

Agreed that there will be no noticeable exotherm but that creates the other problem...


[Edited on 4-4-2014 by blogfast25]

Dan Vizine - 4-4-2014 at 13:26

The chemistry to obtain the halides is well documented. I am trying to avoid soluble species because that means evaporation and evaporation means carry-over and carry-over means spreading the contaminated areas.

The hydroxide allows virtually quantitative Th recovery and a "clean" filtrate.
I'm still debating the best calcination method to minimize dusting.

Damn, that was fast...outed already. Oddly enough, universities have contacted me because of forum posts here. I might as well just attach my real name. If I'm doing something wrong, the use of a user name won't hide me. And besides, I don't think I am doing anything I need to hide. As a life-long chemist, I apply all precautions possible.

[Edited on 4-4-2014 by Dan Vizine]

blogfast25 - 4-4-2014 at 13:31

Quote: Originally posted by Dan Vizine  
I am trying to avoid soluble species because that means evaporation and evaporation means carry-over and carry-over means spreading the contaminated areas.



Which I why I'm kind of glad I 'missed' an opportunity to buy some decent Uraninite some years ago. I'd be too tempted to prepare the metal and have the hazmat smurfs drag me off to gaol... :(

[Edited on 4-4-2014 by blogfast25]

[Edited on 4-4-2014 by blogfast25]

Dan Vizine - 4-4-2014 at 14:59

Blogfast,
ORNL investigated the ammonia reaction in great detail as they wanted tailored thoria particles. The Ca reduction was/is a practiced production method.

From "The Handbook of Preparative Inorganic Chemistry" by Brauer.

II. REDUCTION OF THE OXIDE WITH CALCIUM

Th02 + 2Ca = Th + 2Ca0
264.1 80.2 232.1 112.2
A) PREPARATIVE PROCESS
The process is based on the reduction of very pure ThO2 with distilled Ca in the presence of anhydrous CaCl2 heated to 450°C.
The CaCl2 melts at the temperature of the reaction, affording a liquid reaction medium. The heavy Th product settles to the
bottom and is thus protected by a layer of melt. The apparatus is either a steel bomb capped with a threaded conical lid (cf. the paper of Marden and Rentschler) or the simpler welded steel tube described under method I for the preparation of Ti. The charge, which is made up of four parts of Th02 , four parts of CaCl2 and three parts of ground Ca, is vigorously shaken in a closed bottle to achieve the most complete mixing possible. The bomb is filled rapidly, sealed and heated for one hour at 950°C. The tube is then cooled and opened; the resultant pea-sized reaction product is gradually added to water (about two liters per 40 g. of starting Th02 ) with vigorous stirring to prevent a local temperature rise. After the calcium has completely reacted with the water and the evolution of gas ceases, stirring is stopped, the supernatant liquid is decanted, and the solid is washed four times with two-liter portions of water, vigorously shaking each time for 5-10 minutes. The decanted supernatants are low­-concentration suspensions of dark, fine Th. Finally, 200 ml. of water is added to the remaining heavy residue, followed by 25 ml. of conc. nitric acid (vigorous stirring). The odor of acetylene is noticeable, and if the ThO2 used in the preparation was made from thorium nitrate which contained some sulfate, the odor of H 2S will also be present. After 10 minutes, the solution is diluted tenfold, the product is allowed to settle, the supernatant is de­canted, and the acid treatment is repeated once or twice. After thorough washing with water (twice, two liters each time), the product is suction-filtered, treated with alcohol and ether, and dried in vacuum at 300°C. Under favorable conditions, the relatively coarse, dark gray powder is obtained in 90% yield.

The addition of CaCl2 is can be seen to be advantageous.

According to another source: "The powder [from the Ca reduction] may be compacted and sintered to give massive metal that is very ductile"

So, here's hoping this is better than patent information!


[Edited on 4-4-2014 by Dan Vizine]

blogfast25 - 5-4-2014 at 02:34

Dan,

I've found my own references to the process, so that's settled.

Can you elaborate a bit on scale and how you plan to hold the reactor at 950 C?

Dan Vizine - 5-4-2014 at 11:43

A former obsession supports the current. At one point I used to enjoy building machines from parts. I needed to cast metal parts, so I built an 1100 C metal melting furnace out of some FeCrAl wire from two discarded space heaters and ceramic fiber board, etc. A cheap PID controller from eBay, a high current SSR and a heatsink teamed with a K thermocouple completed the set-up.

I may make a hole through the furnace top to allqw the reactor to be connected to an external rod agitated by hand or an old air powered windshield wiper motor from a truck. Like on a Kugelrohr.

The reactor is SS304, about 10% Ni. People often think that stainless steels, especially austenitic ones, are good choices for high-temperature work and metal melting. Like the austenitic SS RA330, which resists scaling to 2100 C. RA330 has high Ni, like 35 to almost 40%, I think.. But the higher the Ni, the worse the resistance to liquid metals. Molten calcium cracks RA330, but I believe I'm fine with SS304. So, I'll accept the exterior scaling that occurs.

The belt sander, btw, will be used to powder Ca if it does so without grit contamination. That may be optimistic, so I may need to use a file. Microscopic examination should tell.

All final chemicals were purchased last night, HNO3, Aq. NH3 and CaCl2 dihydrate USP grade.


1100 C Furnace (Small).JPG - 87kB PID Controller with SSR and Heatsink (Small).JPG - 54kB 6 Inch belt sander (Small).JPG - 36kB




[Edited on 6-4-2014 by Dan Vizine]

Dan Vizine - 5-4-2014 at 11:54

The other pics:



Top of Furnace (Small).JPG - 91kB

75mL 304 SS (Small).JPG - 114kB

The reactor has a 75 cc capacity. I'll put a hole in the furnace roof.



[Edited on 6-4-2014 by Dan Vizine]

blogfast25 - 6-4-2014 at 03:40

Fantastic. Please do report on your progress here. I for one would love to write about it.

Dan Vizine - 6-4-2014 at 08:33

Blogfast, I'm planning to do exactly that. The reactions will wait until it's warmer here in New York as everything is to be done outside as much as possible.

Thanks for your many thoughtful comments. I'm surprised that this is still mostly a dialog, though. I was really serious about wanting the input from any or all others involved in similar projects.

Sensible precautions I've not mentioned, hazards I've not thought through, preferred ways of doing things? All comments are invited. This needs to work perfectly the first time.

blogfast25 - 6-4-2014 at 09:26

Quote: Originally posted by Dan Vizine  

Sensible precautions I've not mentioned, hazards I've not thought through, preferred ways of doing things? All comments are invited. This needs to work perfectly the first time.


Avoiding particulate matter is the obvious thing to do but you're already taking that seriously. I think there are far worse things to work with than thoria and thorium.

Look forward to get the full report!

EC1:

For ThF<sub>4</sub> (anh.) one of the routes is pyrolysis of NH4ThF<sub>5</sub>, as I thought. Not incredibly hard either, 300 C. Rather heavy on the NH4HF2 though...

elementcollector1 - 6-4-2014 at 09:30

Problem is, only a handful of members here have done anything like this, and even then the projects usually weren't so similar that they could be easily compared.
blogfast25: Ah, so pretty much the fluoride equivalent. Seems about right, but don't these usually have to be run for 4 hours under vacuum or some other long time?

blogfast25 - 6-4-2014 at 09:38

Quote: Originally posted by elementcollector1  
blogfast25: Ah, so pretty much the fluoride equivalent. Seems about right, but don't these usually have to be run for 4 hours under vacuum or some other long time?


As with all reactions, rate depends strongly on temperature but with a reported decomposition temperature of 300 C,

NH4ThF5 === > NH4F + ThF4

... should proceed quite swiftly, at say 500 C.

Vacuum is one option, to protect the fluoride from:

ThF4 + O2 === > ThO2 + F2, which is thermodynamically favourable.

As coincidence would have it my latest batch of (NH4)2ZrF6 is just drying, as I'm writing this. I will be pyrolysing that in a stream of argon (instead of vacuum), hopefully next weekend.

In all cases the starting material must be bone dry.


[Edited on 6-4-2014 by blogfast25]

Dan Vizine - 11-4-2014 at 18:55

How is ThF4 separated from the NH4F? Can NH4F be removed by sublimation?

What's the ZrF4 for?

elementcollector1 - 11-4-2014 at 18:57

If this is anything like the chloride, the NH4F decomposes into NH3 and HF, which are both hygroscopic. Given enough starting NH4F, this should remove all the water from your chloride, rendering it anhydrous.

Dan Vizine - 11-4-2014 at 19:13

So, what do you do the reaction in, nickel? Or can other reactors be used if everything is dry and continually purged by inert gas during HF evolution?

Chemosynthesis - 11-4-2014 at 19:35

Quote: Originally posted by elementcollector1  
If this is anything like the chloride, the NH4F decomposes into NH3 and HF, which are both hygroscopic. Given enough starting NH4F, this should remove all the water from your chloride, rendering it anhydrous.

This is valid, just as with the chloride.

I don't have this in hand, but check out J. Chem. Phys. 37, 2311 (1962); http://dx.doi.org/10.1063/1.1733003

I am interested in adopting that article and J. Inorg. Nuc. Chem., 1962, Vol.24, pp. 387-391 for another project.

blogfast25 - 12-4-2014 at 05:01

Quote: Originally posted by Dan Vizine  
How is ThF4 separated from the NH4F? Can NH4F be removed by sublimation?

What's the ZrF4 for?


Pyrolysis of NH4ThF5 === > ThF4 + NH4F

The NH4F fumes off, like NH4Cl does, leaving behind the dry ThF4. The NH4ThF5 is obtained by dissolving freshly precipitated Th(OH)4 in hot, concentrated NH4HF2,

The ZrF4 will be for a magnesiothermic reduction.

[Edited on 12-4-2014 by blogfast25]

Dan Vizine - 12-4-2014 at 07:51

How is the ammonium zirconium fluoride decomposed? Or, more specifically I guess, what is the reactor made of?

Lambda-Eyde - 12-4-2014 at 08:03

I'm surprised to see this hasn't been posted yet (I think?). Pleased to see you're back, Dan/Zan. Looking forward to reading more.

Attachment: Production of Thorium Powder by Calcium Reduction of Thorium Oxide.pdf (159kB)
This file has been downloaded 1218 times


Dan Vizine - 14-4-2014 at 16:17

Thanks for this incredibly useful reference.

My Th will have several hundred ppm Ni, I see. Not a major concern. If I end up at >99% I'd be ecstatic, and quite satisfied @99% and not at all disappointed if I break 98%. These are modest goals given past work.

Dan Vizine - 15-4-2014 at 15:56

Say hello to my little friend.

[img][/img]

elementcollector1 - 15-4-2014 at 16:47

You stop that. :D

[Edited on 4-16-2014 by elementcollector1]

annaandherdad - 16-4-2014 at 11:10

Hi, Dan, just a couple of things about thorium. If your supply has been sitting around for a few years since it was prepared (thorium nitrate in your case), say 10 or 15, then it will have an equilibrium population of the entire chain of decay products. This is quite unlike uranium, which requires thousands of years to reach equilibrium. The bottleneck in the case of thorium is radium 228, with a half-life of about 6 years.

So if you transform your sample of thorium chemically, in particular, if you do anything to purify it, then you will be throwing away all the daughter products, some of which are interesting. For example, you could repeat what Curie did with uranium, by isolating radium; the difference is that your isotope of radium has a 6 year half-life, so its activity will gradually disappear on a human time scale. Another interesting isotope is radon 220, with a half-life of less than a minute. It gives some spectacular effects in a cloud chamber, see the youtube video on this by bionerd23 (https://www.youtube.com/watch?v=Efgy1bV2aQo), which is one of the coolest scientific videos I've ever seen. But to get this radon, you must start with thorium that has been left undisturbed (not purified chemically) for roughly 5 or more years.

Actually, I have to correct that. If you take a sample of thorium that has been sittiing around for a long time and purify it chemically, you'll get a mixture of thorium 232 and thorium 228, the latter of which has about a 1 year half-life. So the small amount of thorium 228 will start its decay chain, and produce some radon after a while. But this will only last a couple of years.

As for radium, if you separate that chemically, you actually get a mixture of two isotopes, one with a half life of 6 years, the other only a few days. So after such separation, the activity will drop by 1/2 over a few days; then over a year or so it will build up again as the equilibrium decay chain is established, this time starting with radium 228 (here the bottleneck is thorium 228).

I bought some thorium nitrate with the intention of using it to get some radon 220 as in bionerd23's demo, but I'm thinking better of it now. If you'd like to have it I'd be glad to give it to you (I think you'd have to be in the US).

Dan Vizine - 18-4-2014 at 10:15

Since the cost of materials acquisition has to stop somewhere, I will not have instruments appropriate to measure the emanations from my sample.
Heretical as it may sound, I will gladly forego radium. Everybody draws the line somewhere, mine tends to be about where I can no longer assess the dangers. Polynitroalkanes, pyrophorics, potent alkylating agents, liquid HCN, etc. Bring 'em on. Things of microscopic size that I can't detect but that are as dangerous as Ra, that's a whole 'nother story as they say.

I'd rather isolate a pound of ricin (NOTE: G-man, this is just an example, so if your software found my ricin remark, rest easily.) than isolate 10 mg of Ra.

annaandherdad - 19-4-2014 at 19:06

Yes, I think you're right, you wouldn't want to do this without a geiger counter. But I might say the same thing about your project for production of thorium metal. You're going to have those decay products in your sample of thorium, and if you do anything to purify the thorium chemically, such as making thorium metal, the decay products are going to be there in your waste.

The thorium decay chain is *much* more favorable than the uranium chain, insofar as the danger of the decay products is concerned. You'll have radium, all right, but it will be nanograms, not milligrams. Also, unlike the radium isotope you get from uranium, this one has a half-life of only 5 years.

In equilibrium, which you will probably have with your thorium sample, the total activity (in Bequerels) of each of the decay products will be the same as that of your thorium. In other words, the amount of radium will be so small that the number of decays you get from it will be the same as from your thorium. Given the long lifetime of thorium (1.4 x 10^10 yrs), a mole of thorium will have maybe 10^6 Bequerel. The radium in the decay products will have the same activity.


Dan Vizine - 19-4-2014 at 20:07

Annaandherdad,

It's midnight and I'm heading to SF in the morning. I very much appreciate the content and intent of your remarks and I want to continue this discussion as soon as I can find the time to do it justice.

Dan

annaandherdad - 28-4-2014 at 08:03

I've been thinking about the chemistry of the thorium decay chain for some time, but haven't done anything because of various worries (not only mine, but my wife's too). But maybe I will, some day. In the meantime, you might be interested in some of my reflections on the subject.

First of all, to put the radioactivity of thorium into perspective, Th232 has a half-life of about 1.4x10^10 years, or a 1/e life (the "lifetime") of this divided by ln 2=0.7, or about 2x10^10 years = 6 x10^17 sec. This means that a mole of Th232 produces about 10^6 decays/sec, due to the initial decay Th232->Ra228. This is 10^6 Bequerel/mole, or roughly 4000 Bequerel/gm. This compares to natural potassium (with it's .01% of K40) that has an activity of 35 Bequerel/gm.

The actual activity of a sample of natural Th is 10 times as much as this, because of the decay of the daughter products. Measuring activity in Bequerel gives just a rough measure of the radiation, because the different decays are of different types (alpha, beta, gamma), and have different energies. For example, the decay Ra228 -> Ac228 produces a beta particle (electron) with quite a low energy. But measuring activity in Bequerel is at least a place to start in thinking about the radioactivity.

If you chemically purify natural thorium, you will get a mixture of Th232 and Th228, with one atom of Th228 for every 7x10^9 atoms of Th232. This number is the ratio of the half-lives of the two isotopes (1.4x10^10 years vs 1.9 years, my data comes from the wikipedia article). The total activity of thorium prepared in this way is twice the activity of pure Th232, that is, about 2x10^6 Bequerel/mole, because both the Th232 and Th228 produce the same rate of decay. As time goes on, however, the activity will increase, as the daughter products are created and start decaying themselves. Of course, no one prepares pure Th232, because there is no point in separating the isotopes and it would be a lot of trouble.

If you wait long enough, such a sample of thorium, chemically purified at t=0, will produce 10 x the activity of pure Th232, that is, about 10^7 Bequerel. This is the same activity (in Bequerel/mole of Th) that you would see in a sample of thorium ore, that did not contain any radioactive substance apart from the thorium decay chain. Here "long enough" means several multiples of 5.7 years, the half-life of Ra228, the daughter product in the thorium chain with the longest lifetime, and the factor of 10 comes from the fact that there are 10 radioactive daughter products of Th232. In equilibrium, every daughter product produces the same activity (in Bequerel), and the molar fraction of each daughter product is the ratio of the lifetime of Th232 to the lifetime of the daughter. So, for example, in such a sample, the number of moles of Ra228 would be 2x10^9 times less than the number of moles of thorium, and, of Ra224, you would have 1.4x10^12 times less. These ratios again are the ratios of the lifetimes. Ra228 and Ra224 are the two isotopes of radium that occur in the thorium decay chain.

One conclusion from all this is that if you're not afraid of the radiation from a sample of thorium, you shouldn't be afraid of the radiation from the daughter products. Of course, you have to be aware of the types of radiation involves, and physical characteristics (radon is a gas, etc).

The two most interesting things to do chemically to a sample of thorium are to separate the thorium from its daughter products (purify the thorium), and to separate the radium. The other daughter products have lifetimes that are too short to make chemical separation very interesting. Presumably you could separate the radium by precipitating the sulfate. I assume radium sulfate is even less soluble in water than barium sulfate. The actual quantities of radium are very small, so one could worry about whether the radium sulfate might remain in solution (say, after adding sodium sulfate to a solution of thorium nitrate), that is, in spite of the low solubility, since the molar fraction of radium is so small. I'm not too sure about this, but I had the impression for discussions on this forum earlier that if one added some barium nitrate, and then precipitated the sulfate, that the radium sulfate would precipitate along with the barium sulfate. Of course, the Curies did something like this in their work, and it would be useful to learn in more detail what they did.

The radium produced in this way would be a mixture of the isotopes Ra228 and Ra224. It would have less activity than the original sample of thorium (because the other daughter products and the thorium itself would have been rejected), but it could be much more concentrated. Practically speaking, in a home lab you'd be talking about nanograms of radium mixed in with milligrams (at least) of barium.

Now would this be a horribly dangerous thing to keep around your home? Not if you measure it in terms of total activity; it would be less than the activity of the thorium you started with. Only the concentration would be different. You could contaminate your lab if you spill it, but, again the total activity of the contamination would be about the same as that of your original thorium, and, in any case, the radium activity would decay with a half-life of about 5 years. Obviously you wouldn't want to wait 50 years to use your lab again (to wait for the activity to decrease by a factor of 1000), but at the same time it's not like you're running a danger of contaminating your entire neighborhood for a million years.

This is quite different from what you'd get (following the Curies) if you separated the radium from natural uranium, because that isotope of radium has a half-life of 1600 years. I read somewhere that Marie Curie's cookbooks (that she used at home) are so radioactive that they have to keep them in a lead box. And they will have to continue to do so for a long, long time.

I was interested in separating the radium for the purpose of producing radon. More about radon later.


Dan Vizine - 1-5-2014 at 11:18

Judging from the physical characteristics of the bottle, which include the old Fisher embossed cap, the font used in their certificate of analysis, the look of the label material and other indicators, this bottle is probably at least 40 years old. Old enough to guarantee that we are talking about material with an activity on the order of 10exp7 Bq/mol. So, 1 pound of the tetrahydrate represents about 8.2 x 10exp6 Bq.

I'd like to look at this in comparison to the ICRP occupational radiation exposure guideline which is 50 mSv/yr. Unfortunately, it's difficult to find a figure* for the number of nanoSv per unit time per Bq internalized (committed effective dose equivalent) for thorium nitrate. Although it's surely going to be lower for the nitrate that the dioxide, right now I don't have any idea what the rough magnitudes are. Maybe it would be instructive to just to do the calculation with the value quoted for K 40 which is five nano Sieverts over 50 years per Becquerel ingested just to ballpark it? I realize that the K value is for ingestion, whereas the thorium daughters will be primarily inhalation dangers so this has limited value...maybe very little....

(5nSv/Bq) (453 g) ( 4 x 10exp4 Bq/g) = 91 x 10exp6 nSv = 91 mSv = 9.1 rem/year. A bit less than twice the 5 rem/yr that ICRP allows. All in all, if the 5nSv/Bq isn't wildly divergent for my material (I'll look more), the risk for simply standing next to the contents of the bottle is acceptable. After that, it's all a matter of chemical hygiene (mostly).

With regard to the radium sulfate, just as you surmised it has somewhat lower solubility than barium sulfate in keeping with periodic trend. However the solubility, just taking your nanograms figure at face value, wouldn't exceed the solubility product constant with the volume of solution that I will have.

One of the more potentially challenging aspects will be adequate cleanup. Just one of several examples....there are many steps where metallic thorium is being triturated in water. The water from the washes, which is decanted (prior to filtration), contains the fines that have proven troublesome (fires, explosions) for experimenters to dispose of due to the nature of very finely divided thorium. I probably will not try very hard to capture this material for reprocessing. More likely I will simply solidify it with concrete.

*I take that back. It was easier than I thought. Now to try and decipher it....


[Edited on 2-5-2014 by Dan Vizine]

MrHomeScientist - 1-5-2014 at 13:27

So many damn units for radiation, and I've never been able to figure out how to convert between them or what any really means. I have similar problems with the million ways to express gas pressure. :mad:

Anyways best of luck preparing thorium! I've been reading this thread with excitement. The closest I'll probably come is obtaining thorium oxide from thoriated welding rods - I already bought the rods, and there's a couple methods outlined on the forum. I briefly considered a "thorium thermite" using the oxide, but even if that is possible thermodynamically it sounds like a pretty horrifying radiation risk.

Dan Vizine - 1-5-2014 at 18:16

The units of radiation dosage are enough to make your head swim. It's so damned much work just to wade through.

Speaking of hypothetical thorium thermite, my primary concern is avoiding airborne everything. I am still kicking myself for missing the ThO2 that was on eBay. Now I have to be concerned about radon trapped in the crystal lattice when I dissolve the nitrate, the residual ThO2 that will remain in sintered glassware, and the problematic drying of the precipitated ThO2. The last one is the worst. Think about it. How do you best dry a water moist material without millions of microscopic pops creating a certain amount of dust? It has to be absolutely dry. So dry that I can calcine it at 800 C for 8 or 10 hours prior to reaction. If you don't, adsorbed CO2 ends up as C in the product.

Then, after the reaction completes, I need to break the reaction cake into pea-sized pieces and hydrolyze them by throwing them into water, where the unreacted Ca will bubble and spew. I need to watch the temperature so as to avoid the re-oxidation of Th. At this point, things become easier.....

Anyway, thanks for the well wishes. This will undoubtedly take a while to play out. I kind of picture setting a lab up outside in the warmer weather. Since I live in the Buffalo area, that probably means June.

The Volatile Chemist - 1-5-2014 at 19:04

Side Note: Could you separate out different isotopes of thorium, or other many isotoped elements, by electrolysis, like they do for water? Higher isotopes less likely to be electrolyzed first?

Dan Vizine - 1-5-2014 at 20:04

No, the kinetic isotope effect is large enough for H/D to do this, not for larger atoms. Also, for H/D there is a mechanism to remove products out of the reaction mixture that you wouldn't have for a metal.

The Volatile Chemist - 2-5-2014 at 12:06

Quote: Originally posted by Dan Vizine  
No, the kinetic isotope effect is large enough for H/D to do this, not for larger atoms. Also, for H/D there is a mechanism to remove products out of the reaction mixture that you wouldn't have for a metal.

So the method wouldn't even work for odd isotopes of lithium...? huh.

Dan Vizine - 2-5-2014 at 13:36

The % by which they vary in weight becomes small quickly. But even if it could work in principle, you still have the real world problem of separating the product.

It works well for water + heavy water because of two reasons. The first is that the isotopes differ greatly (% wise) in mass. But the second is just as important. When you electrolyze water the products leave as gasses. How are you going to do that separation cleanly with a high temp. lithium cell? Of course, that's not to say the alternative is clean either.

Li-6 and Li-7 were traditionally separated (enriched is more accurate) by multistage distillation. A single stage isn't nearly enough though, because the masses are close. The difficulty in separating these nuclear species, together with the incorrect assumption that Li-7 wouldn't fuse, led to a disastrous "Hydrogen" bomb test in the Pacific called "Castle Bravo". We expected 4 or 5 Mt and got 15 Mt by mistake. That remains the largest nuke the US ever detonated.


[Edited on 3-5-2014 by Dan Vizine]

annaandherdad - 3-5-2014 at 16:48

I found an old article on the solubility of radium sulfate (attached). It is very interesting. The most interesting points are these:

1. When precipitating radium as a sulfate from a mixture containing radium and barium (with the barium typically in great excess), the fraction of radium in the precipitate is the same as it was in the solution.

2. The solubility of radium sulfate does not follow the law of mass action, in other words, there is no equilibrium constant. In particular, the solubility of radium sulfate in water and in dilute sulfuric acid of various concentrations is about the same, whereas the law of mass action would predict a massive suppression in the solubility of radium sulfate in the presence of sulfate ions. The article does not discuss other situations of interest, such as the solubility of radium sulfate in solutions of sodium sulfate, nor does it provide more than speculation as to why the law of mass action is not followed.

3. The solubility of radium sulfate at 25C in water is 8.2x10^-8 gm/cc (the units they used). In view of point 2 above, there is no point in trying to calculate an equilibrium constant.

The article is an early one on the subject, and no doubt a lot of later research has been done. The article leaves a lot of questions unanswered. But for me the main point is that if one wanted to precipitate radium from a sample of thorium (say, thorium nitrate), it could be done with high efficiency by adding some barium salt and then some dilute sulfuric acid.

Probably someone on this forum has knowledge that goes way beyond what I know or what is in this article; I'd be glad to hear any good information.

Attachment: Lind.Underwood.Whittemore.JACS.XL.465.1918.pdf (524kB)
This file has been downloaded 529 times


annaandherdad - 3-5-2014 at 17:42

The units of radiation exposure are certainly confusing. I haven't tried to study them in detail, because the details involve various fudge factors to convert energy deposited into an equivalent biological effect. But before the fudge factors are applied, one is talking about energy deposited per unit mass of tissue. So a Sievert is one joule/kg (then adjusted by fudge factors), and a rem is 100 ergs/gm (again, adjusted). 1 Sievert = 100 rem. The annual exposure that people get from natural sources (cosmic rays, radon, etc) is about 300 millirem/yr (3 milli Sievert), as I recall from the days when I worked in radiation, and you maybe double this from medical procedures.

I've been looking at an article on the internal radiation exposure to the human body. This is it:

http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyw...

I've been playing with the numbers in this article. They are measuring the gamma rays produced by K40 decay in a human body. They estimate 140g of K in a human body of 70kg, the nominal value they use. Due to the content of K40, this translates into 4,400 Bequerel (they cite this as 266,000 decays per minute). The say that 89% of the decays are beta decays with a maximum energy of 1.33MeV. When I work this out, it comes to 8.4x10^-10 J/sec = 1.2x10^-11 J/kg-sec, assuming 70kg body, which is 3.6x10^-4 J/kg-year, or nominally 36 millirad/year. But the article quotes the value of 16 mrad/year. Now I believe the rad is 100ergs/gm, before any biological effect fudge factors are applied. But the article says that the beta decays of the K40 exposes the human body to only 16mrad/yr. So did I make a mistake? Maybe the difference is accounted for by the fact that the 1.33MeV quoted is the *maximum*energy per beta decay; since some energy is carried off by the neutrino, the *average* energy deposited in the tissues would be less, maybe bringing the number down to 16mrad/yr. I'm just guessing about this.

Anyway, if I do the same type of calculation for thorium, adding up all the energies of all the 10 decays of the 10 daughter products, I get 6.8x10^-6 J/sec-mole, or in a 70kg body (assuming you ate a mole of thorium), you'd have 9.7x10^-8 J/kg-sec-mole, or 0.29 J/kg-year-mole, or 0.29 Sieverts/year-mole (unadjusted for biological fudge factors), or 29 rad/year-mole. This is a lot more radiation than you'd want to get in a year, but then you probably wouldn't be eating a mole of thorium.

One could work harder on these numbers and get some better estimates. Given that the starting point is energy deposited per mass of tissue, obviously there is no effect if no energy is deposited. A lot of the energy released by thorium and its daughters is alpha radiation, which won't deposit any energy into your body if you don't eat it or breathe it.


annaandherdad - 5-5-2014 at 16:45

Found this article on thorium deposits in the US. I go back to the area in North Carolina where there are placer deposits of monazite, but I never knew they were there.

http://pubs.usgs.gov/circ/1336/pdf/C1336.pdf

The Volatile Chemist - 6-5-2014 at 06:41

Wow on the thorium deposits! I doubt there's anything radioactive in Ohio, but I go with my family to the Carolinas every so often... Is there a section of SM just for gaining hard-to-find regents from deposits? There should at least be a post for it -- I'll look.

annaandherdad - 6-5-2014 at 09:57

Yes, and it looks like monazite is a good source of rare earths, too. See:

http://en.wikipedia.org/wiki/Monazite

Given the interest in rare earths, makes me wonder if someone is looking anew at those placer deposits. I'm also wondering if it's possible to go out there with a pie pan and pan for thorium, without getting shot at, I mean.

annaandherdad - 6-5-2014 at 10:07

Another article on thorium production and consumption in the US:

http://minerals.usgs.gov/minerals/pubs/commodity/thorium/690...

elementcollector1 - 6-5-2014 at 10:07

Sigh... The only good deposits near me are in Idaho, and these just appear to be random placers - not exactly a good place to start looking. Still, I'll keep this map in mind if I ever get the opportunity.

annaandherdad - 6-5-2014 at 10:19

The last article I posted says that since new regulations were implemented in the US for disposing of thorium, the production of rare earths from domestic monazite has virtually ceased. Monazite also sometimes has uranium in it, which as far as I'm concerned would be undesirable. Still, if I could get my hands on several kg of it, it certainly would be tempting to process it.

IrC - 6-5-2014 at 12:57

Quote: Originally posted by annaandherdad  
I'm also wondering if it's possible to go out there with a pie pan and pan for thorium, without getting shot at, I mean.


Plenty of places, especially on BLM land where you or elementcollector1 could pan on a weekend camping trip along a stream without worrying about someone bothering you. Get an empty 5 gallon plastic paint bucket, a shovel, and a couple items from Garrett: http://www.garrett.com/hobbysite/hbby_gold_pans.aspx

http://www.garrett.com/hobbysite/1650200_14in_sifter_classif...

http://www.garrett.com/hobbysite/1650400_super_sluice.aspx

Set the screen on the bucket and fill it from the stream bed using the shovel, and the pan repeatedly filled with water is used to wash it down into the bucket. When you have a decent amount of finer material in the bucket use the pan in the stream filling it half full from the bucket and washing this material down to black sand. You pie pan will lose most of the black sand. The ridges in the 15" Garrett pan were designed with much experimentation to keep the sand as you wash out the rest meaning many times less work to collect what you want than the smooth pie pan. In one day of fresh air outdoors you could fill the bucket with black sand. Don't forget to look for Gold flakes and small diamonds in the black sand as well.

In the 80's I worked in R&D all week in Phoenix, waiting to spend my weekends 90 miles North just below Prescott, Az working my two Gold placer claims. Great way to get the hell out of the city every week even if only for a little while. I ran a small sluice box and used a pan to process the output from it. For your purpose panning would do as well, since you do not need to process large amounts looking for Gold.

pan.jpg.bmp - 900kB

annaandherdad - 6-5-2014 at 14:41

IrC, thanks a lot! That's some really useful information. I'll have to see if any of those thorium placer deposits in North and South Carolina are on public land. Also, my daughter is really interested in going to into the Sierras to pan for gold, although she might lose her enthusiasm if we actually did it.

IrC - 6-5-2014 at 15:09

http://www.blackcatmining.com/mining-equipment/mini-sluice.c...

mini-sluice.jpg - 80kB

Something like this would provide pounds of black sand with relatively easy work, you set it up on the side of the stream to allow water to run through it as you shovel in gravel from the stream bed. You remove the carpet from the sluice every so often and wash it inside your 5 gallon paint bucket half full of water. This way you clean the carpet, the black sand settles to the bottom of the bucket. Put the carpet back in the sluice and run it again. Eventually you carefully pour the water out of the bucket leaving pounds of black sand in the bottom to take home and process. They have a page of tutorials: http://www.keeneeng.com/resources.html

Actually a lot of weekend fun as a hobby. I ran a 3.5 inch dredge and recovered about 14 oz Gold in 83 on my weekends. Was a nice way to get fresh outdoor air and sun to combat stress from the work week.

http://www.blackcatmining.com/

This place has about the lowest prices. You use the pans to work the output from your sluice box, not really required if the black sand is your goal instead of Gold obviously. Would be a fun camping outing for you and your daughter. There are more places you can find to do this with no problems than you may think. Without worrying about the 'guy with a shotgun' you mentioned earlier. Many do this as a hobby.

Watch a few vids on how to operate the gear before you go out: http://www.youtube.com/results?search_query=Sluice+Box

http://www.youtube.com/watch?v=F6KRHey8Ors

http://www.youtube.com/watch?v=4OR1MlXneFo

Edit: forgot to add a couple Gold panning vids:

http://www.youtube.com/watch?v=ZqpxZ9p3hao

http://www.youtube.com/watch?v=W2db-nGQgWo

Don't forget to pick a couple nicely shaped lightweight shovels.


[Edited on 5-6-2014 by IrC]

elementcollector1 - 6-5-2014 at 15:18

Used to gold pan as a hobby, so I have everything but the sluice...
14 oz?! Where were you, Yukon?

IrC - 6-5-2014 at 15:48

I had 2 placer claims outside Prescott, Arizona back in those days. Eventually moving from Phoenix in the 90's I could not keep up the yearly filing and assessment work so someone came in and filed over me. Turned out to be a mining company that searched county courthouse records looking for claims with out of date paperwork so they could grab them forcing the owner out. I mean if you were a day late these people jumped on it. All over Arizona, and most other states they have people looking. Then around 94 Clinton repealed the 1873 mining act so it no longer mattered.


Dan Vizine - 8-5-2014 at 08:14

Quote: Originally posted by annaandherdad  


They estimate 140g of K in a human body of 70kg, the nominal value they use. Due to the content of K40, this translates into 4,400 Bequerel (they cite this as 266,000 decays per minute). The say that 89% of the decays are beta decays with a maximum energy of 1.33MeV. When I work this out, it comes to 8.4x10^-10 J/sec = 1.2x10^-11 J/kg-sec, assuming 70kg body, which is 3.6x10^-4 J/kg-year, or nominally 36 millirad/year. But the article quotes the value of 16 mrad/year. Now I believe the rad is 100ergs/gm, before any biological effect fudge factors are applied. But the article says that the beta decays of the K40 exposes the human body to only 16mrad/yr. So did I make a mistake? Maybe the difference is accounted for by the fact that the 1.33MeV quoted is the *maximum*energy per beta decay; since some energy is carried off by the neutrino, the *average* energy deposited in the tissues would be less, maybe bringing the number down to 16mrad/yr. I'm just guessing about this.


When I repeat your calculations I get the same answer within rounding errors...
0.89(266000 dis/min) X (1 min/60 sec) X (1.33 MeV/dis) X (1.60x10E-13 J/MeV) X (1/70 kg) X (31500000 sec/yr) X (100 rad/J kg) X (1000mrad/rad) = 38mrad/yr

Your reasoning re. average vs. peak MeV/disintegration is the only logical answer. This shouldn't have been glossed over, it leaves you scratching your head.

I haven't looked at the related Th calculations yet, but lunchtime is almost over. They will get looked at this evening, hopefully. Right now, it's 70 F outside and so it's time to get this starting material broken up and divided into a few lots.

Update: What a nicely behaved free-flowing solid. There were loosely consolidated clumps that broke easily. The resultant material resembled the fine granular NaOH (formerly sold by Red Devil) in terms of density and texture. Very easy to be neat when weighing and transferring.

If no other stuff comes up, maybe I'll get to the first reaction this weekend. Still debating if I want to use my sintered glass or buy something disposable...guess I'm off to eBay to see what's available....




[Edited on 8-5-2014 by Dan Vizine]

annaandherdad - 8-5-2014 at 14:58

And while we're on the subject of thorium, there is the story of Thorotrast.

http://en.wikipedia.org/wiki/Thorotrast

Gives interesting information about what happens to you (and your life expectancy) if you eat thorium oxide.

annaandherdad - 8-5-2014 at 16:46

Dan, I didn't see your answer sooner. I'll do so as soon as I can.

Dan Vizine - 11-5-2014 at 09:36

Robert,

I was doing some calculations on the daughter products just to see the magnitudes and ranges involved.

Only 1/2 pound of the pound was mine. The MW of the nominal tetrahydrate is 318.12, so the ~1/2 pound (actually 227 g) is 4.30*10E23 molecules.

I calculated average lifetimes from the half-lives.

I derived the # of atoms of each species by multiplying 4.30*10E23 by the ratio of its half-life to that of 232Th. From that I derived the average number of disintegrations per second and the number is 9.5*10E5 for all daughters except 212Po which shows 6.1*10E5 per second and 208Tl which shows 3.4*10E5 per sec due to branching in the decay chain.

All of the disintegration/sec figures are self-consistent except for the parent 232Th. I can't find my error. I get 6.8*10E5 here. Essentially all atoms are 232Th, so there are 4.30*10E23. The half-life is 1.4*10E10 years, or 4.4*10E17 sec for an average lifetime of 6.3*10E17. Dividing # molecules by average lifetime of the 232Th in them, gives me 6.8*10E5 which is only about 72% of the activity of the daughters(?!).

Some of the abundance figures were interesting though:
about 246 trillion 228Ra atoms
about 30 billion 228Ac atoms
only about 76 million 220Rn atoms
while for 212 Po, if i did this correctly, only 1 atom exists, on average, for 3 msec/sec. For the other 997 msec, on average, 0 atoms of 212Po exist.
The amounts are truly tiny.

I found it perplexing that the entire decay chain (and the others) consists of only one of two things, either alpha or beta emission. Other processes, like positron emission, don't seem to make notable contributions I guess?

Is it valid to multiply the activity times the sum of the energies for all steps of the 232Th --> 208Pb chain (42.6 Mev) to get the total radiated energy? Meaning 9.5*10E5 disintegrations/sec times 42.6 Mev/disintegration times 1.6*10E-13 J/MeV?



[Edited on 11-5-2014 by Dan Vizine]

annaandherdad - 11-5-2014 at 18:29

Dan, I can't do justice to your message tonight, I'm giving an exam tomorrow and it isn't ready yet. Just wanted to mention some things I learned.

Some of the alpha decays in the thorium decay chain are accompanied by gammas. The wikipedia article I was looking at (on decay chains) just gives the total energy of each decay, without breaking it down.

http://en.wikipedia.org/wiki/Decay_chain#Thorium_series

I don't know which ones, but a little research would find the answers. I also heard that the reason they use Americium (I think it's 242) in smoke detectors is that it is an alpha decay that is free from gammas, so the radiation is confined to the small ionization chamber.

I have a clunky old yellow geiger counter from the 60's, it has a shield that you're supposed to remove in order to allow it to detect beta particles (otherwise the shield blocks them). It never detects alphas; with the shield up it only detects gammas. It works, and registers counts when I open my little bottle of thorium nitrate, but the sound is pretty faint and I'd like to get a better one. bfesser has some reports of a good, modern geiger counter. At some point I want to invest in one.

As for the beta decays, I gather from the wikipedia article that they're all electron emissions; the little arrows are all to the northeast on the chart of nuclides. These could be accompanied by gammas, too, I don't know.

The decay of K40 is more complicated, there there is a certain branching ratio for electron absorption and for positron emission.

Dan Vizine - 12-5-2014 at 06:41

Hi Robert,

As I understand it, there is an inevitable gamma ray component to these decay chains for two related reasons;

1) Bremsstrahlung from beta decays

2) Need for the nucleus to throw off energy after alpha or beta emission perturbs it

Here is the breakdown of the energies/step

232Th-->228Ra 4.1 MeV
228Ra-->228Ac 0.05 MeV
228Ac-->228Th 2.1 MeV
228Th-->224Ra 5.5 MeV
224Ra-->220Rn 5.8 MeV
220Rn-->216Po 6.4 MeV
216Po-->212Pb 6.9 MeV
212Pb-->212Bi 0.6 MeV
212Bi-->212Po 2.3 MeV
212Po-->208Pb 9.0 MeV
208Tl-->208Pb 5.0 MeV

A lesson I have learned, and recently re-learned, about radiation: It's never as simple as it seems, even on the rare occasions that it seems simple.....

Is gamma ray production from Bremsstrahlung proportional to the ke of the emitted particle? It seems it would have to be.



[Edited on 13-5-2014 by Dan Vizine]

annaandherdad - 13-5-2014 at 06:54

Hi, Dan. When you computed the activity (decays per sec) of the daughter products, you multiplied the number of atoms times the lifetime, right? And the lifetime is the half-life divided by log 2=0.69. I suspect your 72% is actually 69% = log 2.

Also, it's Th(NO3)4(H20)4, right? That's what wikipedia says, I don't have my bottle with me right now. I get 552 for the molecular weight.

In any case, you've got a substantial fraction of a mole. Here are my results for the amount of each daughter species, in units of mole (daughter) per mole (parent 232 Th):

228 Ra 4.09 x 10^-10
228 Ac 5.07 x 10^-14
228 Th 1.36 x 10^-10
224 Ra 7.08 x 10^-13
220 Rn 1.25 x 10^-16
216 Po 3.27 x 10^-19
212 Pb 8.64 x 10^-14
212 Bi 8.19 x 10^-15
212 Po 4.32 x 10^-25
208 Tl 1.48 x 10^-16

Notice that on average, there is less than one atom of 212 Po for every mole of 232 Th.

And I get an activity of 9.41 x 10^5 Bequerel/mole for the parent 232 Th (in my earlier post I estimated this at 10^6).

On to bremsstrahlung.

Dan Vizine - 13-5-2014 at 08:16


Hi Robert,

My replies in blue:
When you computed the activity (decays per sec) of the daughter products, you multiplied the number of atoms times the lifetime, right? And the lifetime is the half-life divided by log 2=0.69. I suspect your 72% is actually 69% = log 2.
Actually, I didn't. I mistakenly divided by average lifetime. Oops.

Also, it's Th(NO3)4(H20)4, right? That's what wikipedia says, I don't have my bottle with me right now. I get 552 for the molecular weight.
Yes, it's nominally the tetrahydrate.I feel [slightly] less silly about this error. I referenced the American Elements website to get an anhydrous MW of 246.04 (image attached), and ignoring common sense, I added 4 mol H20 (72.08) to get 318.12.

Notice that on average, there is less than one atom of 212 Po for every mole of 232 Th.
Yes, even in my flawed calculations I got that result. That was rather fascinating.


Well, I should adjust my numbers to see if they jive with yours.



Anhyd. Thorium Nitrate.gif - 12kB

[Edited on 13-5-2014 by Dan Vizine]

annaandherdad - 13-5-2014 at 13:22

Hi, Dan, on thinking about gamma rays I'm trying to separate what I know for sure, what I've just learned recently, and what I think is right based on general principles but where I could be wrong or have an incomplete picture. So with that disclaimer, here's what I think I know about this situation.

One reason for gamma rays in radioactive decay is that an alpha or beta transition typically takes one nucleus into an excited state of another, which then decays by an electromagnetic transition to its ground state. In this situation, the gamma ray comes off with a definite energy (the difference in the energies of the two nuclear levels). It's also possible that a cascade of transitions and gamma rays will be followed to reach the ground state, instead of a single transition.

Another mechanism for the production of gammas in radioactive decay is bremsstrahlung, as you say, but based on what I know I believe gamma rays by this mechanism should be less frequent and of lower energy than those described in the previous paragraph. In addition, these gammas (or x-rays, photons by whatever name you want to give them) will come off with a continuous spectrum of energies.

Bremsstrahlung is a somewhat confusing name, because it's used for different types of physical processes. One if them is when a high speed, light particle, typically an electron or muon, is passing through matter. When the particle passes close to a nucleus it is accelerated by the nuclear electric field, and emits radiation (typically one photon) as a result. The energy of the photon follows a distribution; most of them have only a small fraction of the energy of the particle, but the distribution has a significant tail extended to higher energies, so that occasionally the charged particle loses almost all of its energy, which is converted into the energy of a single photon. Bremsstrahlung is the dominant mechanism for energy loss when relativistic electron pass through matter. Electrons from beta decay are typically relativistic when they are created.

This is probably not the kind of bremsstrahlung you are referring to, although in beta decay the ejected electron will undergo bremsstrahlung if it passes through matter (as it usually does). You are probably referring to the fact that in beta decay the ejected electron may be accompanied by a photon, which can be thought of as the radiation produced when the electron is created accelerated out of the nucleus (getting a big push from the nuclear electric field). Based on what I know, this type of event (beta particle plus photon) should be exceptional, that is, more rare than a beta particle without a photon, because producing the photon requires a higher order of perturbation theory and the probability involves an extra factor of the fine structure constant (1/137). In any case, when a photon is produced, it has a spectrum of energies, from zero all the way up to the maximum energy released in the beta decay.

So based on all of this my guess would be that the majority of the most energetic gamma rays from decays such as in the thorium chain will be from nuclear transitions following alpha or beta decay, with a discrete spectrum.

There are other mechanisms for the production of gamma rays in radioactivity, for example, positron emission will be followed by the annihilation of the positron with an electron.

As I related, a friend of mine told me that smoke detectors use 241 Am (in an earlier post I guessed that it was 242, it's actually 241) because their alpha emission is not accompanied by a gamma ray. According to wikipedia, however, that's not quite correct, the alpha decay 241 Am -> 237 Np is accompanied by a gamma ray in a small percentage of the cases. My friend may be right, however, that the low number of gammas is one reason this isotope is used in smoke detectors, that is, not much radiation escapes from it. Wikipedia says there is 37KBq in a smoke detector.

Dan Vizine - 15-5-2014 at 19:45

Hi Robert,

The former mechanism is the one I meant for Bremsstrahlung, which roughly translates to "breaking energy". This was the gamma source I wondered about.

But, there isn't much need to wonder about the hazards too much, a wealth of thorium related work has been published over the last 60 - 70 years.

I've assembled a body of information that indicates the relative dangers of 232 Th and 238U. The results also clearly show the different natures of the the radiological hazard.

In the following passages it is instructive to remember that the alpha particle causes the highest ionization per unit length of path, it is this radiation which is of greatest concern in considering radiation inside the human body. Externally only the beta and gamma radiations are cause for concern.

In the processing of thorium materials, decay products fall into several columns of the periodic table and therefore behave chemically in different ways. Because of the short half-lives of many of the later decay products, the chemical problem is essentially one of handling two elements, thorium and radium.

When thorium is separated from other isotopes in the decay series, the thorium fraction has only a slight alpha activity. There is no beta radiation and only a slight amount of gamma radiation (from the 0.09-MeV gamma rays which emanate from Th-228 decay). More on the efficiency of separations to follow.

However, the activity from the Th-228 side of the chain is quickly re-established. A first equilibrium state is reached in about 36 days (10 half-lives of Ra-224). Activity then declines, as Th-228 decays faster than it is replenished by decaying Ac-228. About 3 years after separation, the activity is lower than at any other time except immediately after separation. From this point, activity increases until the second equilibrium state is reached in about 60 years.

After chemical transformations occur, non-thorium fractions contain Ra-228, which has as one of its decay products the strongly active Th-228. An example of the acute radiotoxicity of some of the isotopes involved can be found in the work on Th-228 by Finkel and Hirsch. They state that Ra-228 is as toxic as Po-210, Pu-239 or U-233. The 20- to 30-day LD50 for these alpha emiters fall between 36 and 58 microcuries/kg and indicate a toxicity within the first month after injection twenty times as great as that for Ra-226. The 20- to 30-day LD50 value for Ra-224 was estimated at about 1000 microcuries/kg of body weight. On the activity basis, these LD50 values suggest that when thorium is separated from the radium isotopes, Ra-228 constitutes the main health hazard.

For purposes of better understanding the relative radiological hazards, thorium is often compared with uranium. While the two are considered to be about the same order of hazard, the nature of the hazards differ.

While the decay rate of Th-232 is only one-third that of U-238, the number of alphas emitted per disintegration of Th-232 is, except for brief periods of time after separation, three times that of U-238. The total energy of the alpha radiation from thorium is 36.2 MeV. The total energy from U-238 plus U-234 is only 9 MeV.

It is the Th-234 and Pa-234 found with the uranium which account for the beta activity in natural uranium. The beta radiation from uranium in equilibrium with Th-234 and Pa-234 exceeds that from thorium in equilibrium with all of its daughters. Beta dose rates in contact with infinite sources would be approximately 240 and 115 mrem/hr for uranium and thorium, respectively. On the other hand, thorium gives considerably more gamma radiation than does uranium. Uranium dose rates from infinite sources have been estimated at about 10 mr/hr in comparison with 50 for thorium.

So, the results are a little surprising. Now I want to try to apply the thorium dose rate conversion factors to roughly quantify risk.



[Edited on 16-5-2014 by Dan Vizine]

Dan Vizine - 17-5-2014 at 09:49

"So, the results are a little surprising. Now I want to try to apply the thorium dose rate conversion factors to roughly quantify risk."......wow, the arrogance...

Quantifying risk is more complicated than I ever imagined. I see a certain similarity between just trying to get a very basic understanding of this area and the actual process of nuclear fission, they are both an ever-broadening series of branches.

Every thing I pursue, be it effective dose, absorbed dose, kerma, infinite sources or whatever, inevitably ends up in it being defined in terms of many others variables. Usually, I need to look up definitions of a number of these which are, in turn, being defined in terms of several others variables...etc.




[Edited on 17-5-2014 by Dan Vizine]

Dan Vizine - 27-5-2014 at 13:45

So many details....

powerful stirrer for the Th(OH)4 : check (It's a re-purposed Buchi stirring motor)

stirrer.jpg - 74kB

Dan Vizine - 29-5-2014 at 10:31

Some suggested practices, collected from the internet:

Chemical SOP’s – Uranium & Thorium

Specified Hazards

a) Both uranium and thorium emit alpha particles, which have a relatively large kinetic energy but due to the (relatively) high mass and charge they will not penetrate the epidermal layer of the skin. Since keratinized epidermal cells do not have a nucleus and are relatively metabolically inert, they are basically immune to damage due to ionizing radiation. Therefore the outer layer of skin is an effective shield for alpha particles (the one exception is the eye where viable metabolically active cells are at the surface). Damage from alpha particles occurs when they are injected, ingested or inhaled such that the alpha emissions interact directly with viable tissue. If that occurs, alpha particles will cause approximately 20 times as much biological damage, per unit of energy absorbed, as gamma rays or beta particles. It is important to ensure that airborne concentrations of uranium be minimized as far below the ACGIH (2006) limit of 0.20 mg/m3 of air as possible and that designated areas are cleaned when contaminated – this prevents the spread of contamination. Problems can best be avoided by careful control of any finely divided material and by good hygiene practices.

b) Uranium is more toxic than lead [1], and is radioactive. Uranium exposure can lead to kidney damage and disease, lung fibrosis and malignant neoplasm formation in the lungs, hematopoietic system damage and leukemia. Thorium [2] should be treated in a manner similar to uranium.

Activities which could produce airborne particles of uranium/thorium must be performed using the proper equipment.

The following ppe must be worn:
i. Air purifying respirator.
ii. Unvented goggles, if respirator is not full face.
iii. Tyvek suit with booties
iv. Thin walled nitrile gloves

Only use the following personal protective equipment once, check it for contamination and then dispose of it:
• Thin walled nitrile/ latex gloves
• Tyvek suit with booties
• Respirator cartridges (APR, R100 or better)

Decontamination procedures for elastomeric respirator and goggles: (elastomeric respirators and unvented goggles must be decontaminated prior to storing them.)

1. After removing respirator from face, discard respirator cartridges as contaminated radioactive waste.
2. Use two respirator cleaning wipes (alcohol free), one to wipe the exterior of the respirator and the other to wipe the interior. Use another wipe to clean the goggles. Be sure to wipe all surfaces. Used wipes must be disposed of as radioactive waste.
3. Disassemble the respirator in accordance with manufacturer recommendations.
4. Wash all parts of the respirator, and the goggles in the mild soap solution/warm water solution prepared before you began clean-up. Do not dump water in tub down the drain.
5. Rinse washed goggles and respirator components in the sink and set them on paper towels to air dry prior to storage.
6. Set tub of water aside and let the water evaporate from the tub. Once evaporated use the Geiger counter to determine if interior of tub is contaminated. If tub is contaminated then clean it using a respirator wipe, then use the Geiger counter again to determine if contamination exists. If the tub won’t wipe clean then note that it is contaminated on the label of the tub. Store the tub in its designated area.


Work Area Decontamination Procedures
1. Use a HEPA vacuum to collect any loose contamination.
2. Use a damp cloth and bucket of mild soap solution and water to wipe contamination that the HEPA vacuum did not collect from contaminated surfaces. Then use the Geiger counter to determine if radioactive contamination is still present. Repeat process until area is cleaned up, or it is determined that such work is futile.
3. Set bucket of water aside in a designated are and let the water evaporate. Once the water is evaporated use the Geiger counter to determine if interior of bucket is contaminated. If bucket is contaminated then clean it using a damp towel and then use the Geiger counter again to determine if contamination is still present. If the bucket won’t wipe clean then note that it is contaminated on the bucket label. Store the bucket in its designated area.
4. Towels, rags, and other such items used to clean up need to be disposed of as radioactive waste.


[1] LD50 oral for Pb (in Pb- acid Batteries) is 500 mg/Kg). For rats the LD50/21 days was 6 mg of uranium ore per kilogram body weight (6mg U/kg). This is comparable to the ORL-RAT LD50 for diarsenic pentoxide (As2O5) which is 8 mg/kg—meaning that it would only take 600 mg (0.6 g, about half the mass of a dollar bill) of ingested As2O5 to kill off a 75 kg human. The only plus is that U oxides are mostly insoluble. The RfD for uranium (soluble salts) is 0.003 mg/kg/d based on body weight loss and moderate nephrotoxicity in rabbits
[2] Animal studies: LD50 value: thorium nitrate: 48mg/kg (IVN rat); thorium oxide: 400mg/kg (IMS mice); LC50 value: No information available. Annual limit of intake (human) : 200 Bq;

All of the above simply validates my suspicion that drying the hydroxide and calcining it will be the most difficult step to do cleanly.

[Edited on 29-5-2014 by Dan Vizine]

blogfast25 - 29-5-2014 at 11:47

Interesting, Dan. Makes me think about the use of DU in armour piercing conventional tank munitions again...

Dan Vizine - 29-5-2014 at 17:27

Apparently there's more laying around than I realized. A current estimate is that it may take $300 M to clean up the DU in Iraq.

blogfast25 - 30-5-2014 at 10:13

If it is more toxic than lead, using it in an application that pulverises it into open air and into a human environment may have been slightly irresponsible, to say the least.

But I've a feeling you won't find the military carrying out any environmental impact studies...

[Edited on 30-5-2014 by blogfast25]

Dan Vizine - 31-5-2014 at 07:15

I've been giving the prolonged high temperature calcination step the most thought of all. I see it as clearly the most hazardous by a large margin. This is the step most likely to cause aerosol formation (this and the hydrolytic work up with decomposing Ca causing bubbling), which is really the only thing I fear in this prep. My thinking has radically changed as this project has progressed. I'm much less worried about gamma emanations than the feeble ("I can even go through a sheet of paper") alpha particles. This is the exact same reason that plutonium is so toxic.

I had considered two large silica melting crucibles shaped like bowls. Put them together like a clamshell and heat. But in what? My furnace? I'd rather not contaminate that. So......?

Then this mullite process tube appeared on eBay for only $20. It is 2 inches in OD and a foot long. Wrapping it with Super Kanthal A-1 wire will allow the 900 C that I need, easily. The cool, open end of the process tube can be fitted with an exhaust tube which will carry all effluents to a mineral oil trap.




Mullite tube.jpg - 15kB

[Edited on 31-5-2014 by Dan Vizine]

Dan Vizine - 31-7-2014 at 12:34

Finally found some time....

To a stirred, clarified, room temperature solution of thorium nitrate tetrahydrate (227 g, 411 mmol) in distilled H2O (2.5 L) was added 28% aqueous NH3 (317 mL, 285 g, 4.60 mol) in one portion. The temperature of the resultant white slurry was found to rise slightly (~35 C). Stirring was continued under ambient conditions for 1.0 h and then the precipitate was collected by filtration and washed in succession with distilled H2O (3 x 500 mL), dilute aqueous NH3 (0.6 M*, 5 x 500 ml) and additional distilled H2O (5 x 500 mL). The filtrates were combined for disposal. The bright white solid was allowed to air dry in preparation for calcining.

* Prepared by dilution of 103 mL 28% aqueous NH3 to a volume of 2.5 L with distilled H2O.


2.jpg - 988kB

blogfast25 - 2-8-2014 at 04:38

Thorium hydroxide, you don't see that everyday.

Looks like you're inching forward. Stay safe!

sbreheny - 2-8-2014 at 17:21

Dan - I hope that you have some radiation measuring equipment and that you are taking precautions. 227g of Thorium Nitrate is going to be emitting quite a bit of radiation. I have a 10g sample which, if I recall correctly, registers about 10mR/hr on my Geiger counter at a few inches away. I know that this is probably way off because of the lack of proper calibration, etc., but it's enough that I wouldn't want to spend much time around it (30 hours would be 1 year's worth of natural background radiation). Much worse would be if you were to inhale even a tiny amount of dust or droplets of solution. Sean

Dan Vizine - 7-8-2014 at 12:00

This thorium hydroxide (or hydrated thorium dioxide) is an absolutely wretched material. The washings took four days to complete, filtration was very slow and difficult. This will dry to a fairly voluminous solid. My only hope of using my original reaction vessel for the reduction is if calcining densifies it.

The solid is still in the funnel mainly because I haven't decided on the best way to air dry it yet. This outcome was pretty much the next to worst case scenario, only a gel could have been worse.

In the meantime, I built another "disposable" furnace for calcining. The picture is of the first run to 1200 C (just to see if it could).

I'm trying to use disposables as much as possible. The filter funnel is a 1000 cc Nalgene HDPE bottle fitted with a porous polyethylene filter disk about 1/2 thick.

funnel.jpg - 823kBFurnace.jpg - 1MB

careysub - 7-8-2014 at 13:32

Quote: Originally posted by sbreheny  
... I have a 10g sample which, if I recall correctly, registers about 10mR/hr on my Geiger counter at a few inches away. I know that this is probably way off because of the lack of proper calibration, etc., but it's enough that I wouldn't want to spend much time around it


But only for the part of your body that was a few inches away from it. Don't tape it to your pillow.

Quote:
(30 hours would be 1 year's worth of natural background radiation)


Or 120 hours if you live in Denver (they seem to be doing okay, despite getting 800-900 mRem more than the 'average').

Dan Vizine - 7-8-2014 at 14:55

Quote: Originally posted by sbreheny  
Dan - I hope that you have some radiation measuring equipment and that you are taking precautions. 227g of Thorium Nitrate is going to be emitting quite a bit of radiation. I have a 10g sample which, if I recall correctly, registers about 10mR/hr on my Geiger counter at a few inches away. I know that this is probably way off because of the lack of proper calibration, etc., but it's enough that I wouldn't want to spend much time around it (30 hours would be 1 year's worth of natural background radiation). Much worse would be if you were to inhale even a tiny amount of dust or droplets of solution. Sean


Sean, The relative hazards of this have been considered for months. Every reasonable step is taken to avoid contamination.

I even let the radiation angle dictate the chemistry. The "hydroxide" step was only done to get rid of the most important contaminant, radium. I could have calcined the nitrate directly. The aqueous nitrate was sparged with air for an hour (outside) just to be rid of radon.

I've spent quite some reading about the long term dangers of trace thorium dioxide ingestion/inhalation and I've concluded that I can live with the dangers.

Is anybody else surprised that a pound was sent to me and it was not specially wrapped. Nevertheless, it didn't, apparently, set off any radiation detectors anywhere.

Dan Vizine - 20-8-2014 at 15:43

Well, at least you catch a break now and again. The extremely bulky bright white solid has dried down to a dense, friable off-white solid of only 15 - 20% of the original volume. Tomorrow I'll finish drying to constant weight at 80 - 90 degrees C.

The process tube and the reactor will still be suitable.

Hopefully, calcination, grinding & sieving (in a glovebag) will be done early next week.

Source of Thorium

careysub - 21-8-2014 at 07:09

Today it appears the cheapest (and quite readily available) source is 2% thoriated tungsten welding rods, at a thorium cost of $10/g.

Lots of Alibaba offers though for thorium nitrate, some in ridiculous quantities (minimum order one metric ton), but the price is $10/kg. Other offers sell in gram amounts with a listed price range of $1-$100 per gram (one gram minimum). I wonder how much you would have to buy to get the $1/gram price.

I shudder to think about the importation issues of a kilogram of thorium these days.

Dan Vizine - 21-8-2014 at 14:25

The import difficulties are so great that one website selling elements had a buy lined up from GB, but had to scuttle the whole thing just because of these issues.

I've never seen anyone who claimed to have actually gotten the thorium out of thoriated tungsten.

There is a world of difference between "so-and-so sells thorium" and "I can buy thorium". Almost as big as "it's in there, and I want to get it out." This is the easiest way to get it that I see (well, it could have been easier if I had been able to buy ThO2).

[Edited on 21-8-2014 by Dan Vizine]

careysub - 21-8-2014 at 17:25

Quote: Originally posted by Dan Vizine  
...
I've never seen anyone who claimed to have actually gotten the thorium out of thoriated tungsten.
...



I see some on this thread:
http://www.sciencemadness.org/talk/viewthread.php?tid=395

The H2O2 dissolution of tungsten seems to work rather well. The only question was whether the small amount of insoluble residue was pure thorium, or had some tungsten phosphate.

I think dissolving the residue in hot conc H2SO4 to make soluble thorium sulfate (tungsten resists sulfuric attack) would eliminate any possible tungsten admixture.

[Edited on 22-8-2014 by careysub]

Dan Vizine - 22-8-2014 at 14:57

But then you are left with thorium sulfate, not the metal. And if you want the metal you need to do further processing. In my view, it's just better to start with reagent grade materials than stack successive steps, each with its own handling peculiarities (and then you have to face the expanded decontamination of additional equipment).

If I could have started with ThO2, I would have.

After drying at 90 degrees C for a total of 15 h and pulverizing, 127 g (103 %, TY= 103 g) of a very heavy white powder was obtained. Most likely residual water. On the plus side, any of the conceivable impurities, water, ammonium nitrate, residual thorium nitrate, all pyrolyze to gasses and/or ThO2.

Hope to calcine Monday.

blogfast25 - 23-8-2014 at 05:18

I see a plan coming together.

careysub - 23-8-2014 at 08:52

Quote: Originally posted by Dan Vizine  
But then you are left with thorium sulfate, not the metal. And if you want the metal you need to do further processing. In my view, it's just better to start with reagent grade materials than stack successive steps, each with its own handling peculiarities (and then you have to face the expanded decontamination of additional equipment).


The remark about making the sulfate was only in the case that an insoluble tungsten compound actually is present, as postulated in the old thread (it does not clarify if their really was excess material on careful weighing). It was proposed on the thread that the contaminant (if it exists) might be tungsten phosphate.

I just checked and tungsten phosphates are soluble, so I suspect the peroxide dissolution gives a decent grade of thorium oxide directly. This makes it easier to obtain from this route than preparing it from thorium nitrate (say).

careysub - 23-8-2014 at 09:49

Quote: Originally posted by IrC  
http://www.blackcatmining.com/mining-equipment/mini-sluice.c...



Something like this would provide pounds of black sand with relatively easy work, you set it up on the side of the stream to allow water to run through it as you shovel in gravel from the stream bed. You remove the carpet from the sluice every so often and wash it inside your 5 gallon paint bucket half full of water. This way you clean the carpet, the black sand settles to the bottom of the bucket. Put the carpet back in the sluice and run it again. Eventually you carefully pour the water out of the bucket leaving pounds of black sand in the bottom to take home and process. They have a page of tutorials: http://www.keeneeng.com/resources.html

Actually a lot of weekend fun as a hobby. I ran a 3.5 inch dredge and recovered about 14 oz Gold in 83 on my weekends. Was a nice way to get fresh outdoor air and sun to combat stress from the work week....

[Edited on 5-6-2014 by IrC]


If anyone decides to sally forth and pan (or sluice) for monazite sand, I am sure they could pick up some cash selling it on eBay, or here (less scrutiny here).

Radioactive minerals go for significant coin on eBay; I don't see anyone on-line anywhere selling it.

Here is an interesting report describing the Carolina deposits:
https://archive.org/stream/monazitethoriumm00kithiala/monazi...

Here is a choice bit:

Quote:

The content of monazite
in the concentrated black sands, however, is small compared with that
of the sluicing concentrates of other sections. The monazite in this
section after being purified seldom shows a higher content than 3.5 to
3.75 per cent ThO 2 . There is considerable magnetite in these sands,
and the bulk of the concentrates consists of ilmenite (titaniferous iron) .


Currently thorium salts (at their cheapest) are going for $10/g. Using that market benchmark, a kilogram of monazite sand concentrate might contain $350 worth of thorium. This is also ten times higher than the concentration of thorium in good ore in the Lemhi Pass formation.

I wonder if a rack of magnets would pull this sand in.

[Edited on 23-8-2014 by careysub]

[Edited on 23-8-2014 by careysub]

Dan Vizine - 23-8-2014 at 22:33

I think that the purity of your material would be highly suspect. I've just inspected a half dozen thoriated tungsten rod MSDS sheets. The % amounts are given to the nearest per cent. No claims of overall purity are made, so what are you starting with really? You only know to the extent they tell you, which isn't much. In fact, most of the brands I looked at actually contained thoria, not thorium. The thorium from this method will beat what you'll get by dissolving welding rods, purity-wise, hands down.

Why not give it a try and we can compare final products by ductility and oxidation resistance?

Dan Vizine - 25-8-2014 at 09:55

Re: Earlier % yield
It should have said "After drying at 90 degrees C for a total of 15 h and pulverizing, 127 g (103 %, TY= 123 g)...."

Calcining is underway @ 1000 C. Expected yield = 411 mmol = 108.5g

At about 400 C, a small amount of brown gas was seen, suggesting a small amount of ammonium nitrate was present. The color disappeared after 10 minutes and water vapor was evolved.

Calcining will proceed for 12 hours.

Calcining.JPG - 73kB

Dan Vizine - 31-8-2014 at 16:42

After a total of 12 hours at 1000 C, the material was recovered from the process tube and finely ground with a mortar and pestle. The resulting off-white, heavy powder was packaged under argon in a 120 mL bottle to give 108 g (99.5%, T.Y. = 108.5 g)of anhydrous thorium dioxide.

The reduction in volume of the hydrated material was dramatic during calcining to the anhydrous dioxide.

A view down inside the process tube toward end of calcining process and the final intermediate:


DSCF2535.JPG - 475kB DSCF2536.JPG - 252kB

[Edited on 1-9-2014 by Dan Vizine]

careysub - 1-9-2014 at 07:24

Quote: Originally posted by Dan Vizine  
...
Since I'm talking about thorium dioxide, those of you who have explored these same dark synthetic passageways probably already realize that I have opted for the straight calcium reduction route for 1 h @ 950 degrees Celsius.
...


You might be able to do this on a small scale without using a reduction bomb, using calcium chloride as sort of a solvent (it dissolves the calcium oxide).

This is briefly described on pp. 6-8 of "Advances in Inorganic Chemistry Volume 31" available on Scribd.

Here is a link to pg. 10 on Google Books that you can scroll up from to get to 6-8:

http://books.google.com/books?id=K5_LSQqeZ_IC&pg=PA10&am...

Since many actinides were never available in 100+ gram amounts (usually kilogram amounts) called for most production-oriented bomb reduction processes, a method that work on the sub-gram scale was needed, and the CaCl2 fluxed DOR process looks like it works pretty well in a stirred crucible.

I think this is interesting because it can be tried out with a small sample.

Dan Vizine - 1-9-2014 at 11:52

Hi careysub,

That is exactly the method I have decided on. I'm attracted to this method because of the unusually high solubility of metallic Ca in molten CaCl2. I hate heterogeneous reactions and the CaCl2 solvent at least makes it somewhat less so. I plan to continuously agitate the reactor during reaction.

The actual reference that I plan to model the reaction on is one published by Fuhrman, N., Holden, R.B. and Whitman, C.I. in the Feb. 1960 J. of the Electrochemical Soc. on pp 127-131. The submission is entitled "Production of Thorium Powder by Calcium Reduction of Thorium Oxide".

My primary deviation from their method is the use of SS 316 instead of the high-chromium, ferritic SS446. As a result, I may pick up more trace iron and nickel than they did (typically 11 - 46 ppm Fe). My primary concern is residual dioxide and so washes will be extensive.

In this study, the reduction is essentially complete. Typically they got from 78 - 91% yields as coarse powder suitable for consolidation. The remaining Th is in the fines separated by decantations. If I can repeat these results I should obtain 74.4 - 86.8 g Th. They typically saw 0.3 - 0.4% residual oxide. If oxide is kept low enough, arc remelted buttons should have a bright metallic surface.

Today, I'm making a furnace roof which is fitted with a porcelain bushing through which the 1/4" SS pipe passes which will provide the head of argon pressure to the reaction vessel as well as agitate it.


[Edited on 1-9-2014 by Dan Vizine]

careysub - 1-9-2014 at 15:48

I wonder if on a small enough scale stirring would not be needed.

Studying the technical history of the Manhattan Project I was interested to read about how they always tried new processes out on a gram scale (or even smaller) before trying 100 g scale reactions (often this out of necessity, first getting only small amounts of pure uranium, then plutonium, etc.).

The metal oxide and calcium chloride can of course be ground together to make an intimate, fine particle mixture; the problem is the calcium - GalliumSource has granular calcium metal, not sure how to get it finer.

Perhaps in a small enough sample diffusion will provide enough mixing (also you can afford to use the calcium in excess - of that helps the reaction).

Ozark Technical Ceramics makes magnesia crucibles with volumes from 1 mL to 25 mL in prices from $15.20 to $35.70 (larger ones too).
http://ozarktech.com/otc-product/mgo-crucibles/

A small charged crucible could be fired in one of those nifty quick-and-dirty tube furnaces you showed, flushed with argon, to observe the reaction with only consuming a small amount of thorium oxide.


Dan Vizine - 1-9-2014 at 16:47

Actually, stirring is apparently not needed, ...well, you decide.....

The authors whose work I'm copying did this work in a stationary, unstirred 5 gallon SS "bucket" with a bolt-on head which was heated by induction. I really don't know for a fact, but I don't think that the "stirring" induced in molten metals by the induction heating process, operates in this reaction mixture.

Most of the other DOR (direct oxide reduction) processes, described in the reference you cited and elsewhere, don't seem to use stirring. Some early attempts used agitation of the reactor but that seems to have been abandoned.

Because of my innate distrust of unstirred reaction mixtures, my reactor will be agitated. I had planned to use an old drive similar to that used on a Kugelrohr (by Aldrich, anyway, the truck windshield wiper unit) but when I dug it out, I found it isn't functional. Agitation will be periodic and by hand, unless I come up with another way.

My calcium is 99.9% pure in large shiny dendritic pieces stored in vacuo in glass ampoules. I plan to clamp it in a vise and file it, while the filings are allowed to drop into a funnel leading to a bottle under continual argon purge. Crude, but I don't know of a better way. It should work well, fingers crossed.

I do need to decide what crucible will be suitable for arc remelting. Beads will be much more commercially appealing than powder or compacts.

Dan Vizine - 2-9-2014 at 17:24

I ended up making the "stirring bearing", in the furnace roof, from a moderately hard ceramic similar to bisque ware.

I welded the required threaded ends onto a 1/4" SS pipe (~12 in. long) which will serve as the means of agitating the crucible as well as the source for the head of argon ( ~ 5 in Hg) to be maintained during the reaction. I haven't leak tested these joints yet. I know from past experience that good looking welds are no guarantee of gas tightness, so here's hoping.

Currently prepping the CaCl2 and Ca for the reaction.

Stirring bearing.JPG - 214kB Assembly.JPG - 156kB

[Edited on 3-9-2014 by Dan Vizine]

Dan Vizine - 3-9-2014 at 20:15

Another detail to address is the final filtration. In keeping with the idea of using disposables whenever possible, I need a set-up which will have a provision for blanketing the final, potentially pyrophoric thorium powder with argon, following filtration, until it can be transferred into a vessel connected to vacuum. The blanketing gas should also be supplied in such a way that it can't fail because of positional variations. It also shouldn't blow in such a way as to potentially kick up any of the finest particles.

I previously mentioned, but didn't explain, my method of funnel construction. I used the material pictured as flat sheets (below) to construct the desired apparatus. It's sintered polyethylene and it's porous. I cut slightly tapered disks of the thicker material (for unsupported applications) to be tightly press-fitted into various cut down HDPE bottles (picture 1) which are fitted with a vacuum-tight hose barb (picture 2). By making one unit a loose fit for another, I can provide an argon blanket which is consistent with the given requirements (picture 3).

One other detail worth mentioning from a safety standpoint is the method of grinding the dioxide so as to avoid exposure. It's cheap and quite effective. I transfer everything into a large Zip-Lock freezer bag and simply work through the bag. It's quite easy if you have a small amount of a well-behaved powder like this one. This, plus a respirator and goggles, along with multiple layers of new lab-grade nitrile gloves and working outdoors, makes me feel that exposure is absolutely held to a minimum. I have disposable, full-body plastic/paper suits, which is certainly overkill, for final operations like pressing the powder into compacts for eventual vacuum arc melting.

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[Edited on 4-9-2014 by Dan Vizine]

Dan Vizine - 7-9-2014 at 14:50

There have been a number of small engineering tasks to take care of to get everything just right. This set up should provide the needed means of suspending the reactor as well as provide the opportunity for agitation. Argon pressure will be applied to the top pipe joint.

Not too many more of these problems left now.


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Radiochemistry Sub-Forum

careysub - 12-9-2014 at 06:25

I think this thread should be moved to the new Radiochemistry sub-forum, as the techniques Dan is discussing are applicable to other actinides, and there is a good discussion on radioactivity and exposure embedded in it.

But since this is Dan's thread, I defer to him where it should be located.

Pok - 12-9-2014 at 07:14

Radiochemistry is more physics - how to separate isotopes and so on. But this threat mainly deals with the chemistry of Th, not its radioactivity. The details about exposure and so on are only side information. Rubidium and Rhenium are radioactive ass well (1/4 of Thorium). But it wouldn't make sense to put their praparation description into the radiochemistry section.

[Edited on 12-9-2014 by Pok]

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