Claims about asteroid mining talk about how many resources are on each asteroid, with claims of "trillions of dollars" of raw materials. Ignoring the cost of getting to the asteroid, have previous missions turned up evidence that these materials are actually minable? For instance, it may be true that there is lots of iron, but if that iron doesn't appear in deposits that can be easily processed and extracted it doesn't matter at all.
There have been no sample return missions from M-type (metallic) asteroids. Their composition has been estimated from spectroscopic data and radar albedo. The IR spectra of these asteroids was matched with meteorites showing similar spectra, and the asteroids were assumed to have the same composition as the meteorites. But meteorite spectral matching with asteroids is problematic, so chemical analysis of meteorites does not necessarily correspond to the composition of asteroids with similar spectra.
Using near-infrared spectroscopic analysis, this paper https://iopscience.iop.org/article/10.3847/PSJ/ac235f concluded that “the amounts of Fe, Ni, Co, and the platinum group metals present in 1986 DA (a near-Earth asteroid) could exceed the (Earth) reserves worldwide.”
However, they did not describe the ore mineral types. The mineral type is essential for assessing the challenges of extraction. For instance, nickel is usually present as nickel sulfides. On Earth, these are extracted by froth flotation. This requires water and gravity which are both in short supply on asteroids.
Iron ore is usually mined as iron oxide. A strong reducing agent (such as charcoal or coke) is needed to reduce iron ore to metallic iron. Typically, 630kg of coke is required to make a ton of steel. https://corsacoal.com/about-corsa/coal-in-steelmaking
Methods for refining ores on Earth have been optimized for Earth conditions. Water and coal are commonly used because they are readily available. In space, electrochemical reduction is a promising alternate technology.
Earth has a highly oxidizing atmosphere. Many oxide ores were formed by atmospheric oxidation of exposed rock in the 2.2 billion years that Earth has had an oxidizing atmosphere. The metal-rich asteroids have obviously not had the same exposure to oxygen.
Assay data is needed before buying asteroid mining stocks.
Iron? Maybe, but...
The first material being considered for mining (you may be surprised to find out) is water. The processes for mining water are generally well known and benign (ice has a very low crushing strength and high content of desirable volatiles) so it's not unreasonable to extract water from just about any form we can find it in. But there are also many other prospective mining feedstock options, with various chemical compositions and physical properties, including carbon, nitrogen, iron, nickel, sulfur, and platinum-group metals. The processes of mining any of the above may include drilling, blasting, cutting, and crushing.
Extraction may involve chemical or physical processes such as thermal decomposition of minerals and salts to release water vapor, Mond process chemistry, electrolysis and many more techniques.
Fabrication also may require heating, distillation, microwave sintering, or removing contaminants with other compounds.
Getting equipment to do all this up there really does add up. But it's not impossible. Just expensive.
However, the cost analysis of feasibility is done by comparing the cost of end-to-end retrieval of the material against its so-called "up-mass" (mass that needs to be lifted from Earth into high lunar orbit). The cost of returning an asteroid to the same high lunar orbit was estimated at \$2.6B (15 years ago, and perhaps under-estimated) and that'll get you a 7 m asteroid with an up-mass of roughly 500,000 kg. It was also estimated that each kg currently costs about \$100K. That's $50B. So if the asteroid mining technique only costs \$2.6B for the same amount of material, then by Grabthar's hammer, what a savings! right?
Note: I don't personally find this tantalizing because the Earth-market value of this material is still zero -- it's water. And the practical use of water in space-faring is in growing crops, keeping people alive, radiation shielding and making rocket fuel. But it doesn't directly have any business value. It's largely the government funding lunar or Martian exploration that would be the consumer of such water - trying to save money on lifting water from Earth to the moon. I'll bet my money on the Artemis mission's endeavour to extract ice from craters at the moon's south pole. Still - it costs a lot to get water to the moon, so if we can make use of in situ water, that's preferred! Now, if there were a way to get the material all the way back to Earth to be used by existing companies, and if we could get rarer metals, that would be amazing too! But I'm not yet aware of any feasible plans to do so.
The presence of asteroid metals in great abundance isn't in doubt, primarily in the form of nickel-iron with other metals mixed in. Iron and nickel appear to dominate, with cobalt the next most common element - (from https://www.journals.uchicago.edu/doi/10.1086/625461 )
The average composition, with respect to iron, nickel, and cobalt, of iron meteorites and the metal of stony meteorites has been determined by statistical study of the analyses of 320 meteorites. The average composition of iron meteorites is: Fe, 90.78 ± 0.26 per cent; Ni, 8.59 ± 0.24 per cent; Co, 0.631 ± 0.019 per cent. The average composition of the metal phase of stony meteorites is: Fe, 88.58 ± 0.55 per cent; Ni, 10.69 ± 0.51 per cent; Co, 0.705 ± 0.056 per cent.
But it is the Platinum Group Metal content that causes most of the excitement and the value estimates appear based on analysis of meteorite samples. PGM content varies but higher PGM content is associated with high nickel content and Taenite is the higher nickel content mineral form. However it isn't clear that Taenite will occur on its own and may only occur as crystals and bands within lower nickel Kamecite, ie not readily separable. PGM content appears likely to be reliably at tens of parts per million within the nickel-iron. The preferred refining method would be the (relatively) simple carbon monoxide based Mond/Carbonyl process - which should be able to produce pure iron and nickel from asteroid metal with a leftover rich in cobalt and PGM's.
Ataxite appears to be (?) the type of meteorite that has the highest Taenite content (and therefore most PGM's) but it is a question whether we will find bodies with large amounts of ataxite or alternatives that are higher. As more asteroids get sampled we will know more. (Will Ataxite be the type of nickel-iron sought for asteroid mining?).
In space resource use is significant but the question seems to be asking about mining space commodities for existing Earth markets without positing hypothetical markets for space commodities in space that evade the need to return anything to Earth. Earth will make the equipment and launch it. It is where the investors, creditors and customers are. There is no cutting Earth - or the costs incurred on Earth - out of it.
However, in space resource use appears to be intrinsic and essential to any potential asteroid mining operation - and likely much larger in scale than mining of the primary ore. To be viable the reliance on materials, especially consumables from Earth must be kept to the barest minimum and the largest mass requirements appear to be for reaction mass (or rocket fuels), for in-space transport. Very long life/reliability with minimum ongoing supply from Earth is needed, perhaps solar powered resistojet or arcjet rockets running on asteroid water propellant.
In order to supply water as reaction mass the choice of asteroid matters; metallic ones like Psyche may turn out to have some water but I expect other asteroid types will better suit the need to mine water.
Carbonaceous Chondrites can contain significant amounts of asteroid metal as grains and chondrules within softer, water rich carbonaceous materials and seem a better option both for the physical mining operation and to provide the in-situ resources that minimise need for supply from Earth.
Near Earth Asteroids, that orbit around or inside Earth's orbit would be preferred over Asteroid belt objects beyond Mars, both for less delta-v requirements and for more available solar energy. As long as such asteroids do retain enough water rich carbonaceous material.
The economic viability looks beyond reach currently but achieving a very reliable solar arcjet or resistojet rocket that requires little or no ongoing supply to operate would greatly reduce the costs.
If Starship is successful, then it will be possibly to launch up to 150 tons each launch into LEO. Using Starship to launch our payload into LEO, the next thing we face is the propulsion system we will use to get to the asteroid. There are various propulsion systems, like Hall and NEXT or VASIMIR. After deciding which thruster we will use, the next decision we have to make is the which fuel to use. The fuel should be available at the asteroid so that we can refill the spacecraft there. Hydrogen is very common and is in water ice which can be extracted. Xenon or Hydrogen could be mined and processed on a C-Type asteroid. Once we reach the target (Maybe 16 Psyche),then we should first produce electricity from an energy source. Solar, nuclear and possibly in the future fusion energy would be an ideal energy source. 16 Psyche is rich in heavy metals, so certain elements may be hard to find. Metals can be mined using a centrifugal force to separate the heavier and lighter elements. Electrochemical reactions will be useful, because water ice is H2O so it will be possible to get hydrogen and oxygen which can be used for fuel, air and water.