tubelectric
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Heavy water (deuterium oxide) enrichment
Just some speculation... How difficult would it be to separate some heavy water from standard tap water? Or make some water with even a moderate
concentration of D2O, let's say 10%.
Since the concentration of deuterium oxide(s) in natural water is relatively low (150ppm?) a lot of water is needed. But if one could process an
ordinary household swimming pool of water, he should, in theory, be able to get at least a few grams of enriched heavy water...
Which method would be the easiest way for enrichment? The difference in the boiling points is about 1.5 kelvins which makes distillation pretty
difficult. Distilling large amounts of water also requires quite a lot of energy.
Electrolysis is another possible method but what is the key characteristic that allows heavy water separation? I think I once read a paper saying that
the threshold voltage (below of which no electrolysis occur) is slightly higher for D2O than H2O but I didn't find the accurate values. According to
wikipedia the voltage is about 1.48V for "water" and I guess the difference is just some millivolts.
[Edited on 13.11.2012 by tubelectric]
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phlogiston
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Do not expect pure light water to come over as a single fraction at a distinct temperature. The vapour is just slightly depleted in D, whereas the
remaining water will be slightly enriched and the boiling point of the solution will be slightly raised.
Similar for electrolysis.
Yes, it takes large amounts of energy, which is why it is typically done where electricity is cheap. The Norwegians, for instance, profit from clean
abundant hydroelectric power.
There are also chemical reactions that have a strong isotope effect, enabling separation. Look up the Girdler sulfide process if you're interested.
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kristofvagyok
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Quote: Originally posted by tubelectric  | | Which method would be the easiest way for enrichment? The difference in the boiling points is about 1.5 kelvins which makes distillation pretty
difficult. Distilling large amounts of water also requires quite a lot of energy. |
Chem industrial methods for home applications usually work really bad. Distillation of hundread of liters water is not cheap and how could you
determine the DHO content of the water?
We've got several liters of impure D2O, approx 95% and it is not good for anything what we need for (NMR spectroscopy), cause the 5% of normal water
kills the spectra. The production of pure D2O from our "impure" is also not easy, so you could think about it that how hard is to make some from tap
water.
Here is what we currently use, directly from Sigma:
But, if you want to make some, then electrolyse some water what has some NaOH in it.
A better thing is to buy it from ebay, or get a neutron generator and use it 
Also, the second most easily obtained deuterated organic solvent, the benzene-d6, it is prepared by adding benzene to D2O (or DHO) with catalytic
amount of sulfuric acid. The carbon likes the deuterium more that the oxygene does, and every hydrogen of the benzene will be substitued by deuterium
in a few days. I think that this is the most easy method for making some "isotope chemistry" home.
I have a blog where I post my pictures from my work: http://labphoto.tumblr.com/
-Pictures from chemistry, check it out(:
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phlogiston
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Kristof, I don't think there is actually any preference of the benzene for D over H. The H's are simply rapidly exchanging with the D or H from the
water around, and if you use an excess of heavy water, the H's from the benzene get diluted into the heavy water, leaving mostly D's on the benzene.
[Edited on 14-11-2012 by phlogiston]
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zed
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D2O's Mp suggests some form of freezing out might work. Of course, as a prerequisite it would be nice to start with a D enriched water. Some
waters are naturally higher in the material.
Comets are especially tasty. Some estimate 20x standard concentrations therein.
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kristofvagyok
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Heavy isotopes form stronger covalent bonds than their lighter counterparts; for example, a carbon-deuterium bond is stronger than a carbon-hydrogen
bond.
I have a blog where I post my pictures from my work: http://labphoto.tumblr.com/
-Pictures from chemistry, check it out(:
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