Iron fines

Iron fines are the free metallic iron that isn’t incorporated into agglutinates, encased in glass, or deposited on the surfaces of mineral and rock particles. There’s not a lot of it in any given scoop of regolith but iron fines could be very important to Lunar Homesteaders. A simple magnet might be all we need to “mine” this resource.

Most of the iron fines originated as impactors. Rocky and metal meteoroids (large and small) hit Luna and vaporize. Some iron is ejected out into space, some is converted to nanophase iron, some become trapped in glass, and a very small amount ends up in the regolith.

 

Availability

• Native Fe in Lunar soils is 10X greater than in the rocks the soils were derived from. Meteoroid impacts only contribute 1% to Lunar material, with meteoroid iron contributing a fraction of that 1%. The majority of this iron is from auto-reduction of FeO in minerals during impact strikes (4).  This means nanophase iron.
• Apollo 16
  • (3 highland samples) = 0.15% (by weight) FeNi (74 micrometer – 1.0 mm)(2, pg 157)
  • Apollo 16 soil – 0.4% – 0.5% Fe-Ni metal (mean composition of 5..6% Ni and 0.36% pct Co) (6)
  • Meteoritic components in Apollo 16 regolith could be 0.7% to 1.7% of the total mass (3)
• Apollo 14 (2 mare samples) = 0.05% (by weight) FeNi (74 micrometer – 1.0 mm)(2, pg 157)

• Meteoroid particles contribute 0.17±0.08% (equivalent weight) to Lunar soil. (5)
• It’s been estimated that if Apollo samples are typical of the average Lunar regolith there could be at least 7 BILLION metric tons of accessible FeNi metal in the top 10cm over the entire Lunar surface (Space Resources: Vol 3 Materials, 157).

 

Particle sizes

• Meteoroid particles are predominately >330A in size. (5)

 

Chemical composition

• Impacts spread material over a wide area. It is very difficult to determine if an iron particle came from an impacting body, was already on the surface, or was created due to the impact.
• Free metallic iron can come in several chemical varieties. Chemical composition can vary by site and between samples in the same site. Varieties can include:
  • Fe⁰
    • Most elemental iron is native but some could have come from impacting bodies.
  • FeNi
    • There’s a lot of overlap between meteoroid and native metallic iron. Nickel (Ni) and cobalt (Co) contents of native iron metal can vary from 0%-50% for Ni and 0%-8% for Co. This falls within the range of iron-nickel asteroids. (1, pg 151)
    • The extracted iron could be 99% pure FeNi powder (2, 157).
  • Fe plus other elements (trace amounts only)

 

Physical properties

• Varies as chemical composition can vary.

 

Mechanical separation

Not needed for this phase of the project.

 

Refining

Not needed for this phase of the project.

 

Data

Concentrations (percent weight) of metal (FeNi) in Lunar soils (74 micrometer – 1.0 mm)(2, pg 157)

• Apollo 16 (3 highland samples) = 0.15%
• Apollo 14 (2 mare samples) = 0.05%

 

Total (Fe⁰) in combined Lunar samples (highland and mare) is 0.54±0.18% (equivalent weight) (5).

• 0.20±0.10% (equivalent weight) of combined Lunar samples was nanophase iron (40-330A), mostly in agglutinate glass

• 0.17±0.08% (equivalent weight) was meteoroid particles (predominately >330A)
• 0.17±0.08% (equivalent weight) was from source material (predominately >330A)

 

Concentrations, sizes, and origins of metallic iron (Fe⁰) in 79 Lunar Soil Samples. (5)

• Total (Fe⁰)
  • 0.54±0.18% (equivalent weight) of Lunar soil is Fe⁰.
  • Fe⁰_TOT = Fe⁰_RM + Fe⁰_MM + Fe⁰_SM
• Fe⁰_RM
  • Concentration of metallic iron produced by exposure-induced reduction of ferrous iron
  • 0.20±0.10% (equivalent weight) of samples
  • 40-330A in diameter
  • Predominately associated with agglutinate glass
• Fe⁰_MM
  • Concentration of metallic iron produced by metallic phases of micrometeorites involved in forming agglutinates
  • 0.17±0.08% (equivalent weight) of samples
  • Predominately >330A
  • 70% (equivalent weight) of total Fe⁰ in samples was Fe⁰_MM

 

Resources

1. Lunar Sourcebook
2. Space Resources: Vol 3 Materials
3. Iron Isotope and the Origin of Nanophase Iron in Lunar Regolith
4. The Lunar Dust Problem: From Liability to Asset
5. Origins and size distribution of metallic iron particles in the lunar regolith
6. The nature of the meteoritic components of Apollo 16 soil, as inferred from correlations of iron, cobalt, iridium, and gold with nickel

 

Not used but relevant

Handbook of Iron Meteorites (http://evols.library.manoa.hawaii.edu/handle/10524/33750)