Can you make deuterium-depleted water through a freezing method?

Deuterium-depleted water (DDW) is sold commercially by some companies. It is apparently manufactured by fractional distillation, which leverages differences in boiling points of heavy and light water. 


My question is this: can DDW be manufactured through a freezing method? Heavy water has a freezing point of 38.8 °F and normal water of 32 °F. If a jar of water were kept in a water bath of say a constant 35 °F, wouldn't the heavy water freeze and sink to the bottom of jar, allowing the DDW to be siphoned off of the top? I am surprised there appears to be no discussion of the merits or demerits of this idea anywhere on the internet. 




Not easily. For all practical purposes, $\ce{D2O}$, $\ce{DHO}$ and $\ce{H2O}$ behave the same -- including complete miscibility. Though some small fraction of the liquid that freezes first would be enriched in $\ce{D2O}$, and to a smaller extent in $\ce{DHO}$, it would still be composed largely of $\ce{H2O}$. 


According to [Wikipedia, the Girdler process](https://en.wikipedia.org/wiki/Girdler_sulfide_process) is the most energy efficient means of separation.


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To clarify, the objective is not to obtain heavy water. It is to obtain light water. So it is not an issue if the ice contains only some deuterium, but mostly light water, as the point is that the liquid water now has less deuterium than it did before. 


I actually just got a reply from a DDW manufacturer who said the following:


"Deuterated ("heavy") water has a higher freezing point than ordinary water, there is indeed a fractionation slightly above zero Celsius, but it does not mean that all heavy water will be frozen. 


By holding the temperature at let’s say 1°C, you can get some ice that contains D2O or DHO in a higher concentration than in liquid because the freezing point for H2O is lower.


This way you can reduce the D-concentration of the water with 8-10 ppm in one step. If you wish to achieve further decrease you have to freeze this water in further steps.


According to our knowledge, fractional distillation is the best way to produce DDW in large scale."


This same manufacturer says that home water distillers can at best reduce deuterium concentration by 1 or 2 PPM per pass, which is much less efficient than commercial evaporative methods. But an 8 to 10 drop in PPM from a freezing method (per pass) is considerable (if true), as the early clinical trials in this field suggest that even drops of say 20ppm are potentially clinically significant.


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I would say. Diffusion rates play a role. The closer the surface of ice formation is to the freezing point of deuterium water. The purer the deuterium ice will be. The process will be slowed because of this but a purer form of deuterium depleted water would result. Since I have no experience this is speculation on my part. With the formation of ice some heat would be liberated and a natural form of convection would occur. 


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