In the whole Earth the abundances of the elements are similar to the averages of the Solar System, with the exception of some volatile elements, most of them being non-metals, which have been lost in space during the condensation of the Earth and also later.
However the Earth is made of layers with different chemical compositions and many elements are concentrated in layers that are too far from the surface to hope that we will ever reach them. So in the accessible part of the Earth, close to the surface, those elements are seriously depleted.
Some asteroids, unlike the Earth, have never been melted. In that case their composition is homogeneous, similar to the averages of the Solar System. Other asteroids are broken parts from the cores of bigger planets, so they have a composition like in the Earth at very high depths.
However, in the latter kind of asteroids the useful metals are dissolved as tiny percentages in an iron-nickel-cobalt-germanium alloy. This will make their extraction incredibly energy-consuming. On Earth such metals have been separated during millions of years from their surrounding minerals and they have been accumulated as native nuggets or metallic sulfides that are very easy to process for their final separation and purification.
With the alloy that exists in planet cores and asteroids nobody has demonstrated an efficient separation method yet. The laboratory methods used for such separations use huge amounts of water and acids and they will be impossible to implement on an asteroid. Carrying raw metal from asteroids, which is almost completely iron, would also increase the costs tremendously.
So it is absurd to even consider asteroid mining before demonstrating a method that can extract the metals from iron at the mining sites and with a minimum consumption of energy and of non-recyclable reactants.
However the Earth is made of layers with different chemical compositions and many elements are concentrated in layers that are too far from the surface to hope that we will ever reach them. So in the accessible part of the Earth, close to the surface, those elements are seriously depleted.
Some asteroids, unlike the Earth, have never been melted. In that case their composition is homogeneous, similar to the averages of the Solar System. Other asteroids are broken parts from the cores of bigger planets, so they have a composition like in the Earth at very high depths.
However, in the latter kind of asteroids the useful metals are dissolved as tiny percentages in an iron-nickel-cobalt-germanium alloy. This will make their extraction incredibly energy-consuming. On Earth such metals have been separated during millions of years from their surrounding minerals and they have been accumulated as native nuggets or metallic sulfides that are very easy to process for their final separation and purification.
With the alloy that exists in planet cores and asteroids nobody has demonstrated an efficient separation method yet. The laboratory methods used for such separations use huge amounts of water and acids and they will be impossible to implement on an asteroid. Carrying raw metal from asteroids, which is almost completely iron, would also increase the costs tremendously.
So it is absurd to even consider asteroid mining before demonstrating a method that can extract the metals from iron at the mining sites and with a minimum consumption of energy and of non-recyclable reactants.