From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: aluminum (was Re: Lunar SPS and other ideas...)
Date: Mon, 27 Mar 2000 15:44:58 GMT

In article <8bmhsl$lme$1@nnrp1.deja.com>, gbaikie  <gbaikie@hotmail.com> wrote:
>> ...you can do electrolysis on molten regolith, getting mixed metals at
>> one electrode and oxygen at the other...
>
>I would think that you would at least crudely attempt to sort the
>regolith before electrolysis...

Unfortunately, there isn't any simple way to do really effective sorting.
So much of the regolith, at least in many areas, is bits of breccia --
composites formed when random fragments are half-melted together -- that
there's not a lot of mileage in simple physical sorting.  (For example,
the commonly-proposed idea of using magnetic separation to extract
metallic iron falls down because a lot of the iron is small particles
embedded in other things.)

What might well be worthwhile is trying to pick regolith with favorable
average composition -- it does vary.  Neither the variation nor the best
choice for electrolysis is understood in detail, mind you.

>are you saying it's workable to simply
>dump it into a pot (or forget the pot) and pump electricity through the
>regolith and capture oxygen?

Basically, yes.  There have been quite a few experiments using Earth
materials with roughly lunar compositions, although I'm not sure it's ever
been tried on actual lunar soil.  You get fairly pure oxygen at the anode,
and mostly iron and silicon at the cathode.  With the right conditions it
can even be moderately efficient.

The gotcha is that molten silicates are *very* corrosive; few things are
fully inert to them.  The choice of materials for the container needs
work, although there are some preliminary results indicating that well-
chosen ceramics might do.  The choice of materials for the electrodes,
especially the anode, needs *lots* of work.
--
Computer disaster in February?  Oh, you |  Henry Spencer   henry@spsystems.net
must mean the release of Windows 2000.  |      (aka henry@zoo.toronto.edu)

From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: aluminum (was Re: Lunar SPS and other ideas...)
Date: Mon, 27 Mar 2000 15:54:27 GMT

In article <8bmvbb$2t7$1@nntp.Stanford.EDU>,
Jonathan Stone <jonathan@DSG.Stanford.EDU> wrote:
>But potlines need electrodes. How easy is it to come by high-purity
>carbon on the moon?

Not very, alas -- it's one of the handful of volatile elements that are in
very short supply there.  Also, although it's the normal choice of
electrode for aluminum production last I heard, for some reason it isn't
typically mentioned as a possible electrode for electrolytic oxygen
production on the Moon -- perhaps it's not stable in silicate melts? --
and that might mean you'd have trouble with impure feedstock.  (As others
have noted, bauxite concentrations generally form by aqueous processes
that aren't going to occur on the Moon.)
--
Computer disaster in February?  Oh, you |  Henry Spencer   henry@spsystems.net
must mean the release of Windows 2000.  |      (aka henry@zoo.toronto.edu)

From: malloy00@io.com (MA Lloyd)
Newsgroups: sci.space.tech
Subject: Re: aluminum (was Re: Lunar SPS and other ideas...)
Date: 27 Mar 2000 18:15:07 -0600

henry@spsystems.net (Henry Spencer) writes:

>Not very, alas -- it's one of the handful of volatile elements that are in
>very short supply there.  Also, although it's the normal choice of
>electrode for aluminum production last I heard, for some reason it isn't
>typically mentioned as a possible electrode for electrolytic oxygen
>production on the Moon -- perhaps it's not stable in silicate melts?

Because it reacts with the oxygen forming CO and CO2, which is fine
for Al production on Earth, since the carbon's cheap (I think it's mostly
petroleum coke) and it lowers the energy required, but is a disaster
if you want the oxygen, or don't want to supply about as much mass of
carbon as you extract aluminum....

--
-- MA Lloyd (malloy00@io.com)