🚀 go-pugleaf

* In a message originally to All, Marc Roussel said:
MR> From: mroussel@alchemy.chem.utoronto.ca (Marc Roussel)
MR> Newsgroups: sci.misc
MR> Organization: Department of Chemistry, University of Toronto

[stuff deleted]

MR>      I can give a partial answer to this question.  Most of
MR> the noble
MR> gases (note the spelling) are collected as byproducts from
MR> various
MR> mining processes.  Helium for instance is collected from
MR> natural gas
MR> deposits.  (If the rocks are sufficiently impermeable to
MR> trap natural
MR> gas, they are usually sufficiently impermeable to trap
MR> helium.  The
MR> helium was just part of the initial mixture of gases which
MR> formed the
MR> planet.  Any He in the atmosphere has escaped by now but

I don't think so.  I understand that the helium present in natural gas (wells in
Kansas are a good source) is actually a radioactive decay product from the
actinide elements present in the crust and mantle rocks, which decay by alpha
particle emission (U and Th, principally, and their daughter products).

MR> crust.)  Argon is
MR> present in sufficient quantities in the crust (and is heavy
MR> enough not
MR> to escape readily) that it tends to accumulate in people's
MR> basements;

I think you mean radon (Rn), which is also a radioactive daughter element that
outgasses from igneous rocks, primarily, especially in certain areas in the
eastern US (e.g., the Reading Prong, NW of Philadelphia).

MR> I presume that the other noble gases can be found in similar
MR> ways.

Except for He and Rn, the other rare gases (the term "noble" has fallen into
disuse since Kr and Xe can undergo chemical reactions with fluorine and also
form bonds with oxygen) are extracted from the atmosphere, primarily by
liquefaction.  After the O and N condense out, what is left is a rare gas
mixture, as they all have much lower boiling points than O and N (being
monatomic, their liquids are held together by van der Waals forces only, where
as O and N have dipole moments that help them condense, I believe).  The earth's
atmosphere is about 1% Ar, so Ar is not all that "rare" a gas; the others (Ne,
Kr, Xe) are pretty scarce in the atmosphere (as are He and Rn, which have
already been discussed as to their other sources).  The mixture can be separated
by fractional distillation, as the boiling points of the rare gases are
noticeably different.  Gaseous diffusion would be the hard way!  (It was the
choice for uranium hexafluoride, but the mass difference there was about
.7%--not enough for a significant b.p. difference.)

Roger M. Firestone, Ph. D.
Associate Director, Eng. Svcs.
Maden Tech