Sciencemadness Discussion Board

Dissolution of tungsten in H2O2

Stibnut - 13-3-2016 at 15:15

I found some 4% ThO2 welding rods online and I've been dissolving them in 20% H2O2 to extract the ThO2. It looks like things are going well so far - they seem about half-dissolved after 4 weeks and I just changed the H2O2 because it appears the old stuff has completely decomposed. I collected some of the resulting solution and discarded the rest.

There's a yellowish precipitate on the bottom of the container, and the solution is yellow with a smell that resembles a cross between an organic solvent and bleach. Some of the precipitate is probably acrylic paint from the orange marking on one side of the rods; it is difficult to dissolve in water but dissolves well in isopropanol. The solution itself is a nice pale yellow color.

What do I likely have in solution, and is the tungsten solution supposed to be yellow? I can't seem to figure out whether tungsten in H2O2 forms tungstate or some more complicated tungsten ion. And is the smell likely just dissolved paint or is there something more interesting going on?

I really should have clipped the paint-covered ends off so I'd have a pure tungstate (or other tungsten ion) solution, although I think I'll be able to wash the ThO2+yellowish precipitate with isopropanol or ethanol and recover the ThO2 with reasonable purity.

annaandherdad - 13-3-2016 at 15:41

If you have a geiger counter it is a good way to find out when and how you are concentrating the thorium.

annaandherdad - 13-3-2016 at 15:47

That was a thoughtless reply.

If the rods are reasonably old, ten years or so, then you'll have a fairly complete decay chain present, thorium->lead, and you'll have nearly equal activity of every daughter product in the chain. But the different daughter products have different chemistry, so they there will be chemical processes that will separate them. Thus, the radioactivity will not necessarily follow the thorium, not all of it, anyway.

phlogiston - 13-3-2016 at 15:55

Since Th-232 decays nearly exclusively via alpha-decay your geiger counter will not detect it. The radioactivity that you measure with the GM will come mostly from the daughters.

[Edited on 13-3-2016 by phlogiston]

Stibnut - 13-3-2016 at 16:57

Actually I was wondering what happened to the tungsten - is it dissolved as the tungstate or as some bigger ion? And is the solution supposed to be yellow and have a funny organic solvent/bleach smell, or is this just dissolved paint from the painted end of the welding rods?

The thorium dioxide is visible as a white powder and it definitely shows up on a Geiger counter. When I was changing the H2O2, I got a small sample of the ThO2 (didn't weigh it but maybe 100 mg), washed off the tungsten/paint precipitate with isopropanol, and put it in a microcentrifuge tube. Using a Geiger counter I measured about 4 times the background. I should have several grams of the stuff when I'm all done.

blogfast25 - 13-3-2016 at 18:47

Quote: Originally posted by Stibnut  
When I was changing the H2O2, I got a small sample of the ThO2 (didn't weigh it but maybe 100 mg), washed off the tungsten/paint precipitate with isopropanol, and put it in a microcentrifuge tube. Using a Geiger counter I measured about 4 times the background. I should have several grams of the stuff when I'm all done.


What do you plan doing with it?

blogfast25 - 13-3-2016 at 18:50

Quote: Originally posted by annaandherdad  
That was a thoughtless reply.

If the rods are reasonably old, ten years or so, then you'll have a fairly complete decay chain present, thorium->lead, and you'll have nearly equal activity of every daughter product in the chain. But the different daughter products have different chemistry, so they there will be chemical processes that will separate them. Thus, the radioactivity will not necessarily follow the thorium, not all of it, anyway.


With a half-life of 1.4 x 1010 years, 10 years should not yield much by way of daughters. To tired to calculate it now, though...

[Edited on 14-3-2016 by blogfast25]

Stibnut - 13-3-2016 at 19:45

Quote: Originally posted by blogfast25  


What do you plan doing with it?


What I'd like to do is reduce it to thorium metal. I'm not sure how difficult that will be though - I'm rather new to amateur chemistry.

It would also be really cool to use it as a radioisotope generator for some of its decay chain. If there's some way to extract radium from thorium, I could have a source of Ra-228 and daughters. If lead can be extracted, then I'd have Pb-212, which produces a nice spike on a gamma spectrum and lasts long enough to be played with (10.6 hr), albeit obviously in tiny quantities.

Quote: Originally posted by blogfast25  
Quote: Originally posted by annaandherdad  
That was a thoughtless reply.

If the rods are reasonably old, ten years or so, then you'll have a fairly complete decay chain present, thorium->lead, and you'll have nearly equal activity of every daughter product in the chain. But the different daughter products have different chemistry, so they there will be chemical processes that will separate them. Thus, the radioactivity will not necessarily follow the thorium, not all of it, anyway.


With a half-life of 1.4 x 1010 years, 10 years should not yield much by way of daughters. To tired to calculate it now, though...

[Edited on 14-3-2016 by blogfast25]


Actually 10 years is enough to see detectable amounts of the entire thorium series. The first decay has a half-life of 14 billion years, but after that, none of its decay chain has a half-life in excess of 5.75 years (Ra-228). Unlike uranium, the whole decay chain does occur in detectable quantities on a human timescale.

I have a relatively cheap gamma spectrometer that I bought from Russia on ebay. I used it to detect some of the gamma-active daughters of Th-232 - namely Ac-228, Pb-212, and Tl-208 - in the welding rods before I put them in the H2O2. The whole series is definitely there. If I do manage to extract them and look at them in isolation, I'll definitely post about it in Radiochemistry.

blogfast25 - 14-3-2016 at 08:42

On reducing Th compounds to metallic Th, there's already a very long thread here:

http://www.sciencemadness.org/talk/viewthread.php?tid=29927&...

For much smaller quantities, I'd go ThF4 + 4 Li.
Quote: Originally posted by Stibnut  


Actually 10 years is enough to see detectable amounts of the entire thorium series. The first decay has a half-life of 14 billion years, but after that, none of its decay chain has a half-life in excess of 5.75 years (Ra-228). Unlike uranium, the whole decay chain does occur in detectable quantities on a human timescale.



Over 10 years, conversion of the originally present Th-232 to the first daughter would amount to about 0.00000005 %. So while the whole decay chain may be detectable by counter, somehow isolating these would require methods where macro-chemistry simply doesn't apply.

annaandherdad - 14-3-2016 at 08:59

Stibnut---yes, you were more explicit in making the point I was trying to make. blogfast---yes, the absolute quantity of daughter products is very small, but the activity, measured in Becquerel, is almost the same for all the daughter products in the chain. So the total activity is that due to Thorium 232 times the number of daughter products (plus one, for the thorium itself).

You are right that normal macrochemistry doesn't apply, but, for example, you can co-precipitate radium sulfate with barium sulfate.

phlogiston---when I was fooling around with these ideas a while back I seemed to find that some tables of decay products list only alpha (for a certain decay) when in actuality there is certain probability of alpha plus gamma. That is, after the alpha is emitted, the daughter nucleus may be left in an excited state, which then decays via gamma. I'm not sure whether this applies to the decay of thorium 232, however, or what the branching ratios are.

And by the way, to say that the activity of every daughter product is the same (after the decay chain asymptotes to equilibrium) says nothing about the nature of the decay (alpha, beta, gamma, neutron) or its energy.

The fact that the thorium 232 decay chain equilibrates with a time scale of about 5 years makes some interesting possibilities for radiochemistry, that one does not have with the uranium decay chain.

blogfast25 - 14-3-2016 at 09:18

Quote: Originally posted by annaandherdad  

You are right that normal macrochemistry doesn't apply, but, for example, you can co-precipitate radium sulfate with barium sulfate.


Co-precipitation is indeed an often used isolation method in micro-radiochemistry. But how do we know it wouldn't co-precipitate other daughters too?

careysub - 14-3-2016 at 09:25

Thorium-232 does emit some fairly low energy gammas directly accompanying the alpha decay, with a probability of 0.26% and 0.02%

γ-ray energy(keV) Intensity(%)
-----------------------------------
63.81 0.26
140.88 0.02



http://wwwndc.jaea.go.jp/cgi-bin/nuclinfo2010?90,232

https://www-nds.iaea.org/sgnucdat/a3.htm

Energy level diagram:
http://www.orau.org/ptp/PTP%20Library/library/DOE/bnl/nuclid...

There will be an equal level of activity of Th-228 which produces rather more gammas:
keV intensity (%)
84.373 ± 0.003 1.17% ± 0.05
131.612 ± 0.004 0.124% ± 0.006
166.410 ± 0.004 0.094% ± 0.007
215.985 ± 0.004 0.226% ± 0.020



[Edited on 14-3-2016 by careysub]

careysub - 14-3-2016 at 10:12

Quote: Originally posted by blogfast25  
Quote: Originally posted by annaandherdad  

You are right that normal macrochemistry doesn't apply, but, for example, you can co-precipitate radium sulfate with barium sulfate.


Co-precipitation is indeed an often used isolation method in micro-radiochemistry. But how do we know it wouldn't co-precipitate other daughters too?


Th-232 decays into Th-228 (T1/2=1.91 years) via Ra-228 (T1/2=5.75 years) and Ac-228 (T1/2=6.15 hours). Th-228 decays into Ra-224 (T1/2=3.66 days).

The Th-228 and Th-232 precipitate together, as does the Ra-228 and Ra-224.

Besides the thorium and radium there are only three nuclides in the entire chain with a half-life longer than an hour (the Ac-228 and Pb-212, at 10.5 hours, and Bi-212 at 1.01 hours), everything else has a half-life of about a minute or a fraction of a second.

If, after performing a precipitation or other separation, you check for radioactivity 4 days later, all daughters will have disappeared, except for those newly generated by the thorium and radium (of which only actinium will be detectable). The thorium will have newly generated Ra-224 detectable, plus all of the later decay products.

[Edited on 14-3-2016 by careysub]

urenthesage - 21-3-2016 at 05:04

Quote: Originally posted by Stibnut  
I found some 4% ThO2 welding rods online and I've been dissolving them in 20% H2O2 to extract the ThO2. It looks like things are going well so far - they seem about half-dissolved after 4 weeks and I just changed the H2O2 because it appears the old stuff has completely decomposed. I collected some of the resulting solution and discarded the rest.

There's a yellowish precipitate on the bottom of the container, and the solution is yellow with a smell that resembles a cross between an organic solvent and bleach. Some of the precipitate is probably acrylic paint from the orange marking on one side of the rods; it is difficult to dissolve in water but dissolves well in isopropanol. The solution itself is a nice pale yellow color.


What do I likely have in solution, and is the tungsten solution supposed to be yellow? I can't seem to figure out whether tungsten in H2O2 forms tungstate or some more complicated tungsten ion. And is the smell likely just dissolved paint or is there something more interesting going on?

I really should have clipped the paint-covered ends off so I'd have a pure tungstate (or other tungsten ion) solution, although I think I'll be able to wash the ThO2+yellowish precipitate with isopropanol or ethanol and recover the ThO2 with reasonable purity.


The yellow salt should be tungsten III oxide. The thoria is virtually insoluble so it shouldnt be too much of an issue. The paint on the tip does not change considerably and will remain with the thoria, you can however burn it off by drying and heating the thoria to a few hundred degrees. Remember that thoria was used in lamp mantles and takes a considerable amount of heat (a few thousand degrees C) to destroy so the paint will burn off.

blogfast25 - 21-3-2016 at 05:39

Quote: Originally posted by urenthesage  


The yellow salt should be tungsten III oxide.


It's almost certainly WO3.H2O2, actually.

http://pubs.acs.org/doi/abs/10.1021/ac60176a021

careysub - 21-3-2016 at 17:45

Quote: Originally posted by urenthesage  
The paint on the tip does not change considerably and will remain with the thoria, you can however burn it off by drying and heating the thoria to a few hundred degrees. Remember that thoria was used in lamp mantles and takes a considerable amount of heat (a few thousand degrees C) to destroy so the paint will burn off.


Just wipe the paint off with a solvent. I used acetone. It came right off.