Lunar Carbon Supply
Carbon is necessary to produce steel and very little carbon exists on the Moon.  Importation is expensive.  Fortunately, very little carbon is needed to make steel that will contain from 0.15% to 1% carbon and the carbon monoxide reductant gas will be recycled.

Traces of hydrogen, carbon and nitrogen will be mined from the regolith.  Frequently, these concentrations are quoted:  50 ppm H, 100 ppm N, 200 ppm C and 540 ppm S.  But how much carbon can we really get?

The most authoritative figures can be found at: 
http://www.nasa-academy.org/soffen/travelgrant/gadja.pdf
Dr. Kulcinski and his associates at the University of Wisconsin are the experts on helium 3 mining. They have been gracious enough to post large amounts of information on the web for the edification of all would be Moon miners.  I suggest you Google them and read all you can.

Their Mark 3 miner would amass 10 tons and obtain  109 tons H2O, 16.5 tons N2, 56 tons CO2, 201 tons H2, 102 tons He4, 53 tons CH4, 63 tons CO and 33 kg. He3 per year by mining one square kilometer (about 250 acres) to a depth of 3 meters.

This amounts to 15 tons of carbon from the CO2, 40 tons from the CH4 and 27 tons from the CO for a total of 82 tons of carbon.  The CO and CO2 would be shifted to CH4 and pyrolized to get pure carbon.  This would be done by passing CH4 over refractories  heated to 900 C.  When the carbon builds up on the refractories it will be removed with ultrasonic cleaners.

That's enough to make 24,000 tons of 0.33% carbon steel and even more steel of a lower carbon content. 

Numerous volatiles miners would be transported to the Moon by chemical rockets, ion drives, solar sails or tethers and in a few years' time substantial carbon stocks could be stored up. 

Initially, blister steel or crucible steel would be produced from iron fines.  As for direct reduction of silicate minerals with CO gas that would require a long period of development on the Moon.  Pure iron and titanium will be used whenever they can substitute for steel. 

Steel is desirable because it is stronger than pure iron and more easily worked and welded than titanium.

In a DRI "blast furnace" CO will react CO + CO ===>  CO2 + C     This is called the Boudard reaction.  The carbon that forms dissolves into the iron.  That's how we get carbon into the iron without tons of burning coke.  The problem is that some carbon will also get into the slag and that's not where want it.  Fortunately, this problem can be solved by busting up slabs of slag with big motorized tilt hammers, then putting the pieces thru a jaw crusher, then through rod and ball mills to powder it.  We must do this to make cement out of slag anyway.  This heavy equipment must be sand cast on the Moon to reduce upport costs.   Either we cast these machines out-vac and cover the molds with regolith to prevent evaporation or we do it in wetted sand inside pure iron habitat made from magma electrolysis.

Then we must flush the slag powder with hot oxygen gas in a fluidized bed to burn out the carbon and form CO and CO2.  These will be separated by polymeric or C60 nanotube membranes, the CO stored and the CO2 run thru a Reverse Water Gas Shift reactor to convert it to CO.  Eventually, CO2 electrolysis technology might be used:  CO2 + electricity ===>  CO + oxygen. 

The blister steel process does not make much slag nor will much if any carbon be lost into the slag in the steel fluxing furnaces that remove traces of sulfur and silica from the steel.  We will have plenty of steel by the blister steel process to make heavy tilt hammer, jaw crushers, etc. by the time we buld DRI (Direct Reduced Iron) furnaces on the Moon.

We will build the fluidized beds that we use to burn the carbon out of the slag on the Moon from welded ceramic bricks and cast basalt bricks so oxidation of the fluidized bed will not be a problem as it would be in a metal fluidized bed.

By the time we are building huge DRI furnaces to smelt ferrosilite and fayalite primarily and even iron oxide boiled out of highland regolith to get pure anorthite,  we will have numerous robot miners at work producing much more than 82 tons of carbon per year.  If we have 1000 Mark 3 or more advanced miners at work to get 33 tons of helium 3 per year, about enough to sate the USA's energy needs,  we will be mining 82,000 tons of carbon every year.  Even if helium 3 never pans out, we will still mine for volatiles.  Beyond this, we can only look to carbonaceous asteroids and even the Trade Triangle between Earth, the Moon and Mars. Mars has plenty of carbon in it's atmosphere and even more locked up in the CO2 ice of the polar caps.  Mars has significant traces of copper in it's regolith also as we discovered with the Viking landers.  We now know that an ocean covered one third of Mars once.  What if there was life there, just primitive bacteria and plankton in it's oceans?  Could oil have formed?  Oil from Mars could supply the Moon and high Earth orbit with carbon, hydrogen and some nitrogen launched into space by mass drivers atop Olympus Mons or the Tharsis plateau that would then be transported by tankers using solar sails and magnetic sails.  That's really far out. 



   

David A. Dietzler, 2007
to the Damascus Project
to Lunar Resources
Hot oxygen burns carbon out of slag.  O2 is heated by electric coils or solar (not pictured).  Powdered slag is lifted by pressure of O2 through perforations in ceramic plates.  Compressors, valves not shown.  When all slag has had carbon burned out, the pressure is turned off and the powders sifts down to bottom of fluidized bed and is removed thru tap hole.  Cast basalt and ceramic block construction. Block welded together with microwaves or electron beams.
The Pioneer Astronautics COSRS system lost carbon mostly in the form of silicon carbide and this was undone by using extra silica to react with the SiC, but in the lunar DRI (Direct Reduced Iron) that I like to call "blast furnaces" partly just to startle people we have loads of silica to deal with already.  See: Flux

excellent pdf about the Pioneer Astronautics COSRS system:
http://www.lpi.usra.edu/meetings/leag2005/presentations/wed_am/04_berggren.pdf