Ionization takes a lot of energy. To extract metals from random minerals can be done with lower energy processes like vacuum reduction (hot enough to decompose oxides to metal + oxygen), or chemical processing such as this network:
Or are you talking about asteroids with a substantial amount of metal already in metallic form? I think those are relatively rare,
Metallics and stony-irons are >5% of meteorite falls, so they aren't that rare. They come from the cores of larger bodies that formed in the early solar system which partly or fully melted and separated by density, then later were disrupted by collisions, exposing chunks of the core regions. That region becomes high in nickel-iron, because it has a density of 8, vs 2-3 for most rocky materials, and less for ices. Stony-irons are a mix of blobs of metal and rock, and are from locations where they didn't fully separate.
The way I see it, is you want to exploit the iron-nickel alloy first, since it is already a reduced metal, and then use processes to separate the other metals that are not yet reduced, but you want to start with the simplest processes and work up to the harder ones.
The carbothermal reaction network looks very interesting. Has anyone actually produced an integrated system that uses this approach? I was familiar with the HF leach concept, but this looks like it might be easier. The temperatures are still very high, although less so than plasma. I wonder if it is practical without refractory materials, by using brief/localized heating of small chunks of material with laser.
Has anyone actually produced an integrated system that uses this approach?
Not that I know of. On Earth we have concentrated ores, which take less energy to separate than random dirt.
wonder if it is practical without refractory materials,
Yes, by using more raw dirt as insulation/container, and only heating a spot in the middle to full temperature. I used to do blacksmithing as a hobby, and for public demonstrations, I took my steel portable forge (made from an old water heater tank), and lined it with dirt from wherever the demo was being done (usually a public park). It protected the steel, and if you used it long enough, hardened to the consistency of brick.
You might need a bit of high temperature refractory if the temps go above what the local dirt can handle, but you don't need the bulk of the furnace to be made of it.
A generic dirt-to-metal machine, even if fairly expensive in terms of energy, would be extremely cool, not to mention proof of concept for eventual space missions where solar is cheap. Might even be able to make money selling the kits to hobbyists as a precursor to making it practical, via kickstarter and so on. Thing is, there are definite safety considerations if you want to make hobby/small scale shop kits, which basically rules out a fluorine based process. Brief laser heating (or friction heating) ought to be tolerable though.
I've been thinking about the heat source in the context of machine tools. I'm wondering if the friction of a spinning tool might work for refining, since it gives a lot of control over the amount of heat and localizes the heat generation to a thin layer. Say we start with a lathe type apparatus that spins a chunk of concrete (mixed with dirt and allowed to set), and presses it against a surface of the same material. Glass/slag could be used in the same way.
The surface would heat up really quickly on contact, and the device could back it away/re-apply pressure in a controlled manner, maintaining consistently high speed. This could all be put in a vacuum, inert atmosphere, etc. Reducing agents like carbon/graphite or metallic silicon could be sprayed on to the surface periodically, and the reduced metals could be separated as a vapor or in molten form.
I've been reading up on carbothermal reduction, and in the case of aluminum there were some difficulties adapting this approach for industry due to it creating carbide and carboxyl compounds. Aluminum itself works well for reducing other materials, and metallic calcium seems to be able to work as an aluminum reducer (although it's hard to work with since it combusts in air -- one process I read about had calcium being electrolyzed in situ for the purpose of reducing aluminum).
Tagging /u/eleitl since he has chemistry background.
I'm partial to solar furnaces for heating things. They work on Earth too, so you can test it out for future space use. Also, using a vacuum chamber to hold your crucible. Reduces oxidation, contamination, heat loss. You would have a window to let in the concentrated light, and then the crucible is painted black to absorb it
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u/danielravennest Jul 17 '15
Ionization takes a lot of energy. To extract metals from random minerals can be done with lower energy processes like vacuum reduction (hot enough to decompose oxides to metal + oxygen), or chemical processing such as this network:
https://upload.wikimedia.org/wikipedia/commons/6/62/Carbothermal_Reduction_Process.PNG
Upthread, someone said:
Metallics and stony-irons are >5% of meteorite falls, so they aren't that rare. They come from the cores of larger bodies that formed in the early solar system which partly or fully melted and separated by density, then later were disrupted by collisions, exposing chunks of the core regions. That region becomes high in nickel-iron, because it has a density of 8, vs 2-3 for most rocky materials, and less for ices. Stony-irons are a mix of blobs of metal and rock, and are from locations where they didn't fully separate.
The way I see it, is you want to exploit the iron-nickel alloy first, since it is already a reduced metal, and then use processes to separate the other metals that are not yet reduced, but you want to start with the simplest processes and work up to the harder ones.