Lunar Iron Characterization

This is where I’m going to analyze the data I’ve gathered. All this info is on other pages. I’m going to try to keep this page easy to read so I’m not including sources here. You can look at the data in the appropriate sub-categories.

General Lunar iron info

• Iron, in some form, is present in every Lunar sample. Sometimes it’s just a trace amount and sometimes it’s substantial.

• The iron presence (by percent weight) of “average” soils ranges from 4.7% to 10.9% for highland samples and 14.3% to 19.8% for mare samples. It’s unclear if soil is all regolith or actually soil (<1 cm).
• The type of iron available, its composition, and its concentration vary widely between sites and between samples at the same site.
• High energy impacts spread regolith across significant distances. Samples taken from a particular area may have originated tens or hundreds of kilometers away.
• Homesteaders have to be prepared to process a wide range of materials with variable (and unpredictable) iron content.

 

Types of iron

Lunar iron comes in two basic types with several sub-types each.

• Lunar free iron – Metallic iron that isn’t bound in a solid chemical solution (minerals). Doesn’t require a chemical process to extract the iron. It will probably require a heat process though.
  • This is the most valuable type of iron as we way not have to do much to get it.
  • Magnetic and electrostatic separation should be enough to extract the metallic particle from the regolith.
  • All Lunar samples had the presence of iron metal grains but never more than 1% by volume.
  • Lunar free iron can be used immediately – It’s already in metal form and doesn’t have to be chemically refined (not sure about this). It is often encased in glassy agglutinates though. We’ll have to find a way to free the iron particles. Some of the particles are very fine and we might not be able to recover them.
  • Regolith simulants don’t do a good job of accurately representing the nanophase iron particles in Lunar samples.
  • Types of free Lunar iron:
    • Nanophase iron (np-Fe⁰)
      • Abundance
        • Found in almost all samples. Found as metallic particles in agglutinate glass and as metallic particles deposited on individual soil grains. The majority of the metallic iron particles are in the agglutinates and not on the rims.
        • Soil particles 2 – >100 nanometers had concentrations of 0.33% Fe⁰ by weight.
        • Smaller particles have more nanophase iron (as rims).
        • Lunar regolith can contain up to 50% dust sized particles (<50 micrometers).
        • Mare regolith is more likely to have more nanophase iron than highland regolith (a high of 1% by weight vs. 0.7%).
      • Physical properties
        • Grain sizes between 1-10 nanometers for rim nanophase particles. Grain sizes between 10-100 nanometers for nanophase particles in agglutinates.
        • 40% of all metallic iron in samples is 4-33 nanometers.
        • Super-paramagnetic.
          • Increasing soil maturity also increases the amount of nanophase iron in the soil. This makes the soil more magnetic in general and can overwhelm the magnetic properties of the source material. This could make it harder to separate out the iron.
        • Melting point Fe⁰ = 1538°C, 2800°F, 1811 K

• • • • • Specific heat capacity = 0.450 J/(g °C)
        • Low level microwave radiation (2.45 MHz) can melt fine soil (<50 micrometers) to 2000 °C in two minutes.

• • • • Chemical composition
        • Mostly pure elemental iron (Fe⁰) but some iron isn’t fully reduced and some nanophase iron particles are alloyed with nickel and other elements.
    • Iron fines
      • Abundance
        • The highlands most likely have more iron fines than marias. The highlands have been hit more frequently and therefore will have more meteoroid iron.
        • It doesn’t really matter though because the abundance of iron fines (much less than 1% by weight) anywhere is too low to make them worth hunting down.
      • Physical properties
        • Hard to determine because of the variety of chemical compositions.
        • Particle sizes can range from nanophase size to who knows.
      • Chemical composition
        • Can be anything from elemental iron to FeNiCo (with 50% Ni and 8% Co) to iron alloyed with other elements (trace abundance only).
        • Maximum sampled FeNiCo = (50% Ni)(8% Co)
    • Agglutinates – Not a type of iron but most of the free iron (nanophase and fines) is contained in agglutinate particles.
      • Abundance
        • Agglutinates are present in almost all samples. Agglutinate abundance can range from 5-65% in soil, with an average of 25-30%.
      • Physical properties
        • Typically smaller than 1 mm.
        • Fragile and easy to break into smaller particles.
        • Are usually sharp and jagged.
        • Other physical properties are difficult to define since agglutinates are composed of many different components.
      • Chemical composition
        • Complex. Can be composed of any type of mineral particles, rock particles, iron of varying composition, and glasses of varying composition.
        • The rocks and minerals generally reflect the source soil they are found in.

 

• Mineral iron – Elemental iron bound in a solid chemical solution (minerals). Requires at least one chemical and/or heat process to extract the iron. There are several minerals that are of interest when it comes to iron.
  • Ilmenite (FeTiO₃)
    • Abundance
      • Ilmenite is the most abundant oxide mineral found in Lunar rocks.
      • Apollo 11 and Apollo 17 mare basalts are up to 15%-20% ilmenite by volume.
      • High-Ti mare basalts contain the highest concentrations of ilmenite.
      • Most samples contained <2% ilmenite. Two percent is still OK though.
    • Physical properties
      • Melting point = 1367 °C
      • Paramagnetic
    • Chemical properties
      • Mostly FeTiO₃ but up to 6% can be MgTiO₃.
      • A simple heated hydrogen reducing atmosphere should cause the Fe and TiO₂ to fall out as slag. We’ll have to figure out a process to recover the iron.
  • Pyroxene
    • Abundance
      • Pyroxene is the most abundant dark mineral at the surface.
      • Mare basalts show the highest abundance of pyroxenes.
      • Highland rocks show the least abundance of pyroxenes.
    • Physical properties
      • Hard to define as there are so many varieties.
      • Paramagnetic
    • Chemical properties
      • Hard to define as there are 20 different varieties. Only a few have the iron we are looking for.
      • Pyroxene is going to be more difficult to work with than ilmenite or olivine, even though it’s more abundant.
  • Olivine
    • Abundance
      • Mare basalts also have the highest concentrations of olivine.
      • Still just a few % by volume according to one paper and up to 35% in mare in another.
    • Physical properties
      • Fayalite melting point = 1025 °C
      • Forsterite melting point = 1890 °C
      • Magnetic = ???
    • Chemical properties
      • Fayalite (Fe²⁺₂SiO₄) and forsterite (Mg₂SiO₄) are found together in olivine.
      • Most olivine is composed of 25-50% fayalite (the one we want).

• • Spinel
    • Abundance
      • Second most abundant opaque mineral (after ilmenite).
      • Found in all mare basalt samples (up to 10% by volume) and some highland samples.
      • Often found with ilmenite and metallic iron.
    • Physical properties
      • Magnetic = ???
    • Chemical properties
      • Several varieties.
      • Primarily looking for ulvöspinel (Fe₂TiO₄).
  • Armalcolite
    • Abundance
      • Minor mineral found in very small quantities in high-Ti rocks.
    • Physical properties
      • Unknown but from what I could find I think it’s probably non-magnetic. And therefore not what we’re looking for right now.
    • Chemical properties
  • Troilite
    • Abundance
      • Found in all samples at less than 1% by volume.
      • Found with ilmenite, spinel, and metallic iron.
      • Might be more abundant in mare regolith.
    • Physical properties
      • Non-magnetic. This is a non-starter as magnetic separation is critical to my plan. Maybe electrostatic separation would work though.
    • Chemical properties

 

My thoughts on Lunar iron

Basically, we’re going to have two different types of Lunar iron to work with.

The first type is the free metallic iron. This is the stuff we’re going to go after first. We’ll use magnetic and electrostatic beneficiation to separate the metallic iron from the mineral iron. What we’ll end up with is a mix of very small iron particles encased in glass, iron fines, mineral and rock particles with an iron film, agglutinates, and dust. We’ll have to figure out how to extract just the iron from this mess. That will leave us with iron particles of varying sizes and composition. We’ll have to decide if we can use the iron in this form of if we need to refine into a more uniform product. Figuring out how to extract and use Lunar free metallic iron is crucial to the formation of a Lunar Homestead.

The other type is mineral iron. This iron is chemically bound into the rocks. This iron is going to be much harder to get to but it will probably be much more useful. It’s going to be harder because we’ll have to use at least one chemical reaction (most likely we’ll need several) and a lot of heat to get the iron out. There’s also no ores so we’ll have to process a lot of regolith to get a nice concentration of mineral we’re looking for. Once the iron is out though, it will be pure elemental iron, which we can then use or alloy. There’s also much more mineral iron than free iron. For now I’m going to focus on ilmenite. Olivine, spinel, and pyroxene will come later. Figuring out how to extract and use Lunar mineral iron is the key to opening up the frontier.

The abundance of a particular type of iron doesn’t really matter. The Lunar regolith is a complex mixture and samples from the same site show significant variations in iron abundance and chemical composition. Plus the fact that we haven’t found any concentrations of a particular mineral or metal (ores). Our best option is to come up with a really good way to sort out the various forms of iron that we’re interested in, store them until we have enough for a batch, and then run each type through its own process.

This process gives us several advantages:

• It doesn’t matter what the composition of a particular “shovel full” of regolith is. We sort it, store it, and keep getting more.
• Iron is everywhere so we aren’t necessarily confined to mare sites. Highland sites just need to sort more regolith.
• Waiting until we have enough of a particular raw material (mineral, dust, etc.) means we can optimize the process for that particular material. Batch processes are slower than open processes (think conveyor belts) but aren’t as affected by the variability of the source regolith. Open processes require a steady stream of consistent material to operate efficiently. Consistency isn’t one of the virtues of Lunar regolith.

Coming up with a way to finely sort each raw material is the key.

So, there’s a lot of iron on Luna and in forms we can extract. That’s great. The iron also comes in two flavors, elemental (Fe⁰) and a predominately iron-nickel alloy (of varying and random concentrations) that we can use. That’s great. I don’t see any show stoppers here.

 

Data

Iron presence of average Lunar soils (by percent weight)(Lunar Sourcebook, 346).

• Apollo 11 (mare site) = 15.3%
• Apollo 12 (mare site) = 15.1%
• Apollo 14 (highland ejecta site) = 10.4%
• Apollo 15 (mare site)
  • Mare soils = 16.3%
  • Apennine Front soils = 11.7%
  • Green glass-rich soils = 14.9%
  • Average of all soils = 14.3%
• Apollo 16 (highland site)
  • Cayley Plain Soils = 5.2%
  • North Ray soils = 4.7%
  • Stone Mountain and South Ray soils = 5.4%
  • Average of all soils = 5.1%
• Apollo 17 (mare-highland boundary site)
  • Mare soils = 16.7%
  • South Massif and light mantle soils = 8.8%
  • North Massif soils = 10.9%
  • Sculptured Hill soils = 12.2%
  • Average of all soils = 12.2%
• Luna 16 (mare site) = 16.7%
• Luna 20 (highland site) = 7.0%
• Luna 24 (mare site) = 19.8%

 

Extraterrestrial Materials Processing and Construction (chapter X,M 4.20, 4.28)

• Pure iron (99.9+%)
  • Resistivity = 9.71 10⁸ (m)
  • Conductivity = 0.1030 10^-8 (mho/m)
  • Density = 7.874 10^-3 (kg/m³)
  • Tensile strength (PSI) = 35,000-40,000
  • Yield strength (PSI) = 10,000-20,000
  • Modulus of elasticity (10⁶ PSI) = 28.50
  • Elongation (%) = 28.50
  • BHN Hardness (500 kg load/10 mm ball) = 82-100
  • Conductivity (IAC5) = 17.8

 

Lunar Stratigraphy and Sedimentology (pg 5)

• Composition of Luna – FeO only (units unknown)
  • Bulk – 10.5
  • Crust – 6.6
  • Upper mantle – 12.6
  • Middle mantle – 13.5

 

Iron composition of Lunar regolith (3, pg 238)

• • Mare = 4.4%±0.7% atoms Fe / 14.1% weight FeO
  • Highland = 1.8%±0.3% atoms Fe / 5.9% weight FeO
  • Average = 2.3% atoms Fe / 7.5% weight FeO

It is estimated that 100,000 tons of Lunar soil could yield 150-200 tons of iron (Space Resources: Vol 3 Materials, 281).

 

Resources

1. Lunar Sourcebook
2. Extraterrestrial Materials Processing and Construction
3. Lunar Stratigraphy and Sedimentology
4. Space Resources: Vol 3 Materials