Lunar-Calcium

Lunar Calcium
Dave Dietzler

From:
http://www.epa.gov/osw/nonhaz/industrial/special/mining/minedock/id/id4-cal.pdf

(Quote) “As shown in Exhibit 1, high calcium limestone, CaCO3, is quarried and calcined to form calcium oxide. As
shown in Exhibit 2, the calcium oxide is then ground to a small particle size and dry blended with the desired amount
of finely divided aluminum. This mixture is then compacted into briquettes to ensure good contacts for reactants.
The briquettes are then placed in horizontal tubes, i.e., retorts, made of heat resistant steel and heated to 1100-
1200oC. The open ends of the retort protrude from the furnace and are cooled by water jackets to condense the
calcium vapor. The retorts are then sealed and evacuated to a pressure less than 13 Pa. After the reaction has been
allowed to proceed for approximately 24 hours, the vacuum is broken with argon and the condensed blocks of about
99% pure calcium metal, known as crowns, and calcium aluminate residue are removed.” (Unquote)

We don’t have limestone on the Moon. Calcium oxide can be obtained by sulfuric acid leaching of anorthositic regolith that might have to be melted, quenched and ground first to break down the crystalline structure of the anorthite grains and filtering out silica and most of the calcium sulfate than forms. The silica and CaSO4 can be separated electrostatically. The CaSO4 would then be decomposed purely with heat or by heat and carbon to get CaO.

This CaO would be ground fine and mixed with aluminum ground fine and briquetted. Thus, we need aluminum by some process to get calcium metal. We will also need grinders. Perhaps Al2O3 (emery) or SiC will be used for grinding wheels. Alternatively, we can melt the aluminum and spray it under pressure with an inert gas, probably helium 4 obtained by volatiles harvesting, from a nozzle to get a fine mist of Al droplets that cool by radiation and also by the cooling effect of the gas and are collected. This might be done in a helium filled inflatable, since we wouldn’t want to waste helium into the vacuum. Calcium oxide won’t melt until 2500 C. so we would have to grind it. Fortunately it is not that hard.

Retorts could be made of cast highland regolith that forms a glassy material with an m.p. of about 1500 C. or ceramics from molten silicate (“magma”) electrolysis that have an equally high m.p. Since my thinking is that this would be done at Mt. Malapert we won’t have access to cast basalt, but future bases in or near the maria will. Vacuum will be free on the Moon. When we remove the calcium from the retorts we won’t have to break the vacuum because the tubular retorts will be surrounded by vacuum. Cooling for the retorts to condense the calcium might be a problem. If we make them long and shield them from the Sun they might cool enough by radiation alone to condense the calcium. Heat on the reduction end would be supplied electrically. It’s always possible to drill coolant passages in the condensing end of the retorts and pipe helium or nitrogen thru that goes to a space radiator shielded from the Sun by foil.

We might also get CaO by destructive distillation of anorthite in the vacuum at temps. over 2000 C. If we can only get CaAl2O4 this way we could leach that in H2SO4 to get CaSO4 and Al2(SO4)3 that are easily separated by filtration.

The CaSO4 would of course be decomposed with heat or heat+carbon to CaO, CO and SO2. Some CaSO4 would be used as is-it’s plaster.

Calcium metal could be used for bus bars out in the vacuum. It can’t be used indoors because it react rapidly with oxygen and moisture in the air. It is a lighter conductor than copper. It could sublimate in the vacuum so the bus bars would be coated with aluminum or a ceramic. Calcium is fairly soft and could be extruded into wires that are coated with vacuum vapor deposited aluminum to prevent sublimation in the vacuum.

CaO reacted with an excess of carbon in an arc furnace at 2000 C. will form calcium carbide, CaC2 and CO.

CaO + 3C ==> CaC2 + CO

CaC2 will react with water to form acetylene for oxyacetylene welding and cutting. Since we wouldn’t want to lose carbon and hydrogen in the form of CO2 and H2O from acetylene combustion this kind of welding and cutting would only be done indoors. Out-vac we would use electric metal arc welding and cutting, and/or lasers and electron beams.