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Relatively pure iron has more uses and potential value than nickel-iron alloys. Separating those nickel-iron alloys commonly found in meteorites and expected to be common in asteroids (Kamecite, Taenite) into their elemental components appears to be difficult. The viability of asteroid mining depends on the economics and finding relatively pure iron (and other relatively pure materials) would change the economics, by greatly simplifying the refining process. Is there any evidence of relatively pure iron in asteroids (evidenced in pure iron meteorites) or basis for expecting to find it?

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    $\begingroup$ Relatively pure iron is not very useful for construction, it is too soft. An alloy of iron and carbon is needed with the right amount of carbon, it is called steel. Too much carbon makes the alloy brittle, too less makes it soft like pure iron. But meteroite iron was used in history: "The iron found in iron meteorites was one of the earliest sources of usable iron available to humans, before the development of smelting that signaled the beginning of the Iron Age". $\endgroup$ – Uwe May 18 '18 at 22:22
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    $\begingroup$ Making alloys is easier than unmaking them. Carbon can be added and all kinds of alloys are possible beginning with pure iron - useful alloys that are not possible beginning with nickel-iron; separating iron from nickel has to be done first. Of course there is demand on Earth for nickel-iron alloys - but the demand is much less than for iron. $\endgroup$ – Ken Fabian May 18 '18 at 22:31
  • $\begingroup$ I checked and Egg Rock is 8% nickel, oh well ;-) 1, 2, Who discovered “Egg Rock”? The Curiosity rover or people? $\endgroup$ – uhoh Feb 27 at 14:37
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Finding macroscopic (i.e., big enough to actually use) pure-iron meteoroids appears to be extremely low-probability. Certainly the bulk composition of the metals in Earth (good references here, here, and here) and metallic meteorites is iron plus nickel, a siderophile, and a few also-rans, like sulfur and oxygen, and other siderophile metals like cobalt.

Pechersky et al indeed documented cases of nearly-pure iron crystals or quasi-spherical nodules in meteorites, but these have dimensions in microns (10-50 microns) and are embedded in the much more common taenite or kamecite, or occasionally schreibersite (an iron-nickel phosphide). I can't imagine that sorting through a crushed sample, looking for microscopic grains of not-quite-pure iron, is any less cumbersome than electrochemical smelting of taenite or kamecite, and the yield (iron produced per ton of ore processed) of the smelting would be much greater.

Supernova explosions and white dwarf explosions spew large amounts of both iron and nickel into the interstellar medium, and these go on into the next generation of stars and the planets that form with them. Much of the iron comes from the decay of unstable nickel nuclei generated directly in the explosion, so they are tightly associated. Since nickel is a siderophile, when they are melted during incorporation into a planetary body and subsequent differentiation the nickel essentially dissolves into the iron and the two sink together into the core. Even if pure-iron meteoroids did exist (almost certainly tiny! dust from supernova explosions and such!), when they are incorporated into a planetary body and they sink to the core they become just another part of the iron-nickel solid solution in the core melt.

According to Pechersky et al the production of the nearly-pure iron nodules might be a process that occurs as the melt is initially solidifying, or it might occur after parent body disruption, as the original minerals decompose from the iron-nickel solid solution.

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  • $\begingroup$ My internet searches didn't lead me to Pechersky et al. Informative answer, thank you Tom. $\endgroup$ – Ken Fabian May 18 '18 at 22:38
  • $\begingroup$ @KenFabian You're welcome! Always glad to be helpful. $\endgroup$ – Tom Spilker May 19 '18 at 0:13
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Between the orbit of Mars and Jupiter, you can find the Asteroid Belt. The total mass of all of the asteroids is about 4% that of the Moon. About 10% of the mass is thought to be M-type (metal-rich) asteroids.

Some of the asteroids like 16 Psyche are made up of mostly metals like iron and nickel. NASA is planning a mission, Psyche to explore this minor planet in 2022, which arrives in 2026. After this, we would have a better idea of the viability of using an asteroid as a source for construction material.

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  • $\begingroup$ Construction or other materials for use in space offer the potential for reducing costs of space based projects, but the bottom line is surely the overall profitability of those projects - I would think from material resources delivered to Earth markets. $\endgroup$ – Ken Fabian May 18 '18 at 23:47
  • $\begingroup$ @KenFabian Unfortunately, right now there's no material we use on Earth that would be less expensive to get from space than to produce from Earth resources (mining, etc.). If we get a practical He3 fusion reactor some time in the future that might change, but for now mining asteroids for materials for use on Earth just isn't economically viable. BUT ... if we get a thriving space construction industry going in LEO and/or lunar orbit, it might be cheaper to bring materials from near-Earth asteroids than to launch them from Earth's surface. Aerocapture aeroshells made of silicate slag? $\endgroup$ – Tom Spilker May 19 '18 at 0:27
  • $\begingroup$ @TomSpilker - I tend to agree - giant leaps rather than small steps required. Yet I think the successful exploitation of space resources for use on - for sale to - Earth is a crucial economic threshold on the way towards permanent human occupation of space. Nickel-iron may not be the best source of iron to make steel alloy - but it is extraordinarily abundant. $\endgroup$ – Ken Fabian May 19 '18 at 2:45
  • $\begingroup$ @KenFabian Indeed! If we start building large structures in the asteroid belt, the primary structural material might be iron-nickel alloy. If it's strong enough, it's right there - just use it! Skip the energetically expensive step of separating the nickel out. $\endgroup$ – Tom Spilker May 19 '18 at 3:47
  • $\begingroup$ If we would build large structures in the asteroid belt, we should think also about the risk of collisons with asteroids. There are a lot of unknown objects without orbit data there. Tracking those objects will be much more difficult than tracking of satellites and debris in LEO. $\endgroup$ – Uwe May 19 '18 at 9:56
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I have very good information for you!

I confirm that there is pure iron in space because I have a 99% iron meteorite.

Pure iron meteorite

This samples weight 42,38g, and the fusion crust is no longer visible because I have several acid tests, before knowing that it should be kept.

This is the certificate of analysis.

Translation:

Mr Siliman showed me four meteorite samples.

Two samples contain more than 99% of iron, with small amounts of manganese and cobalt.

By Dr Albert Sotto, doctor of chemistry.

Certificat of analysis

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    $\begingroup$ Welcome to Space Exploration! Please translate this post into English, as all posts on this site must be in English to allow voting and moderation to work properly. $\endgroup$ – Nathan Tuggy Mar 2 at 19:37
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    $\begingroup$ I think I know the English, but lack edit privileges. The answerer should do the edit. $\endgroup$ – Oscar Lanzi Mar 2 at 23:41
  • $\begingroup$ @OscarLanzi I think to be an answer this needs some explanation of context and relevance, also in English. Imperfect English is okay, others can edit then. $\endgroup$ – uhoh Mar 3 at 0:06
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    $\begingroup$ @Siliman - thanks for the translation to English, and for your participation in an English speaking site; I admit sites in other languages would be missed entirely by me. Can you provide more information about the meteorites that were sampled and analysed? Were the samples all from different meteorites? Was the iron content homogenous within the 99% iron meteorites? Do you know of other meteorites showing similar iron content? (Knowing what proportion are high Iron is a guide to how common they might be as asteroid material. Theories of asteroid formation could also be affected). $\endgroup$ – Ken Fabian Mar 5 at 2:16
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    $\begingroup$ @Siliman - thank you. I would expect there are ways to confirm the meteoric origin although they may not be readily available to the average researcher - trace elements and isotope profile perhaps. Finding high iron content asteroid material that would require minimum processing should be of interest to those proposing asteroid mining ventures. I still doubt precious metals are going to be found except well mixed in NiFe - and hard to refine - but Iron is an important industrial metal; IMO it will be basic commodities being economically viable that will make Asteroid mining work. $\endgroup$ – Ken Fabian Mar 15 at 5:13

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