This is a goldmine, well, not literally. Still, I wonder if this could be a paradigm shift with other elements, and if so how many???
Scientists crack a 20-year nuclear mystery behind the creation of gold
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Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#32This is a goldmine, well, not literally. Still, I wonder if this could be a paradigm shift with other elements, and if so how many???
This isn't Reddit
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#33Earlier quoted context omitted.
Could you use a centrifuge to separate the elements instead of vaporizing it?
You cannot use a centrifuge to separate solid iron. Using a centrifuge with liquid iron would create a gradient of concentration of the heavier elements dissolved in it, but that would not be enough to separate them. All that could be done with a centrifuge with liquid iron would be to obtain an iron alloy enriched in heavy elements. However, I doubt that it would be possible to make a centrifuge for liquid iron that…
Iron and platinum have different melting points. If you melt the alloy, then spin it to concentrate the platinum, couldn't you coax the platinum to separate out as solid clumps by adjusting the temperature?
Alternatively, there are differences in magnetic properties that could be exploited...
This isn't my field, so I'm just spitballing. I bet if you can get the cost of launch and interplanetary transit to be low enough for people to really start tinkering with asteroid mining though, someone will crack the metallurgy issues...
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#34Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#35Earlier quoted context omitted.
Since you didn't show your math, I did a quick calculation. .45J/g/C specific heat of iron means .45MJ/tonne. 1811K to melt iron means 815MJ/tonne. 3.6kWh/MJ, so 226.4 kWh should melt 1t of iron.
Yes, but melting is just the beginning of the process. Even your computation is incomplete, because it is not enough to heat iron until the melting temperature, you must also provide the additional latent heat of melting. Similarly for boiling iron, after heating to the boiling temperature there is an additional latent heat of vaporization. There is still no easy way to separate platinum-group metals from liquid iron…
> gold has about the same vapor pressure as the much more abundant iron, nickel, cobalt and germanium, so it would be impossible to extract it from iron by vaporization
Magnets!
Will fill in the details of this idea later.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#36does anyone else experience an “eyes glazing over” effect when you read things like “Heavy elements such as gold and platinum are forged under extraordinary conditions, including when stars collapse, explode, or collide”? It seems totally beyond possible in scope and scale to validate something like this, even if you managed to get up close to one of these events it would still be too big and powerful to follow what…
It is quite difficult to validate if you only consider the most direct of means like smashing two stars together and then physically going out and picking up the pieces. There are other means to validate that type of thing though. Trying to come up with those means is a lot of fun. Can you think of any?
I'm ignorant on the subject, but when you boil it down isn't this all about throwing things at each other?
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#37Earlier quoted context omitted.
Yes, but melting is just the beginning of the process. Even your computation is incomplete, because it is not enough to heat iron until the melting temperature, you must also provide the additional latent heat of melting. Similarly for boiling iron, after heating to the boiling temperature there is an additional latent heat of vaporization. There is still no easy way to separate platinum-group metals from liquid iron…
> gold has about the same vapor pressure as the much more abundant iron, nickel, cobalt and germanium, so it would be impossible to extract it from iron by vaporization Magnets! Will fill in the details of this idea later.
You’d have to deal with the Curie Point of the metals.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#38Earlier quoted context omitted.
All the other precious metals are less than 1 ppm compared to iron, but platinum is more abundant, and by weight it is about 6 ppm in iron. The advantage of an asteroid is that its entire metal core has 6 ppm of platinum and a fraction of a ppm of gold, while on Earth the quantities of ore containing such amounts of precious metals like a half ppm or a quarter ppm of gold are much smaller. There certainly exists no "…
I assume those abundances in asteroids are actually the abundances in iron meteorites, right?
Those are the average abundances in the iron that forms the asteroid metallic cores, which are exposed in a few asteroids, presumably because of ancient collisions.
The asteroids where such cores are exposed, instead of being buried under huge amounts of rocks, like in the planets, are those that are targeted for mining.
The iron meteorites are pieces detached from such asteroid cores, so they provide samples of their composition.
Some meteorites, the so-called chondrites, come from small bodies that have never aggregated into bigger asteroids or planets since the formation of the Solar System, so they have a chemical composition close to the average composition of the Solar System.
Other meteorites have been detached from big bodies, like asteroids, planets (e.g. from Mars) or from the Moon.
These meteorites are either made of rocks, when they have been detached from the surface of such bodies, or made of an alloy of iron, nickel, cobalt, germanium, some times also silicon, together with other metals that are present in much smaller quantities, when they have been detached from exposed asteroid cores.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#39Earlier quoted context omitted.
Heat exchangers for metal vapors at temperatures of a few thousand kelvin would be a significant technical challenge. A heat exchanger needs fluids between which heat can be exchanged. Besides the fact that it would be very difficult to have pipes for fluids at such temperatures, it would not be so easy to efficiently heat the fluid more than it was heated by the recovered heat and then control somehow a fluid jet to…
working fluid? the same hot iron vapour is used to heat the incoming molten iron, no heat exchanger is perfect so the preheat would inevitably be a few percent short of the target temperature, the remainder is just the energy you supply to negate any heat lost through insulation (space is large, so one could use a ridiculously large insulation) not that any of this matters, since chemical methods would be much more e…
Chemical methods would be much more efficient, but they would need huge amounts of chemicals that do not exist on asteroids, so they need to be brought from elsewhere.
It would be impossible to bring millions of tons of acid and of water, so if an acid would be used it would have to be regenerated, e.g. by the electrolysis of the iron-nickel-cobalt salts, which would also need a lot of energy.
Designing a process that could regenerate and purify the acid in a closed cycle, with no losses of any fluids, due to the difficulty of replacing them, would be a very difficult task. Nothing remotely similar has ever been achieved. On Earth, any such methods use at least vast amounts of water and air that are not recycled.
Also, any chemical methods would need to be performed inside a perfectly sealed installation.
Vaporizing iron and the other more volatile metals with an electron beam could be made in a partially open vessel, in the vacuum from the surface of the asteroid. The main difficulty would be to ensure that the metal vapor goes in a certain direction and not omnidirectionally, to avoid its condensation all over the installation.
When vaporizing metals in vacuum with an electron beam, you do not pass through a liquid phase, but the metal is vaporized directly from solid pellets. This method ensures a high efficiency of conversion between electrical energy and heat that is actually used for vaporizing the iron, instead of being lost in the environment.
Thus there would be no molten iron to be preheated, even supposing that there would be materials suitable for a heat exchanger working at such temperatures.
Moreover, even if one would first melt the iron in a closed vessel, heat exchangers transfer heat well only between dense fluids, i.e. liquids, supercritical fluids or at least gases at high pressures. The liquid iron qualifies, but not the iron vapor, from which transferring the heat would be bad. Better heat transfer could be achieved if the iron vapor would condense inside the heat exchanger, but for that a means to ensure a high enough pressure for the vapor would be needed, but that may be difficult to ensure without preventing its advance in the pipes. Liquid iron can be pumped with magnetohydrodynamic pumps, but for pumping iron vapor there is no easy method. Perhaps one could ionize the vapor, to be able to move it with electric fields.
A heat exchanger working at a temperature so high would tend to have a very high heat loss, due to radiation. It may be difficult to ensure that you recover more heat than the extra heat that is lost.
In any case both the attempt to use chemical methods or the attempt to make a heat exchanger for iron vapor would be engineering challenges that require solutions far beyond everything that has ever been done on Earth.
By contrast, vaporizing metals in vacuum with an electron beam is a routine technology on Earth. The only big challenge is that in normal vaporization installations the vapors go in all directions. On Earth this is not a problem, because everything around is covered with some thin metallic foil, on which the vapors condense. After that the metal foil is dumped if the evaporated metal is cheap, or it is sent to metal extraction by chemical methods if the metal is precious and it must be recycled.
On an asteroid, in order to avoid the deterioration of the installation, one needs either a method to move the useless vapor in a certain directon, e.g. by ionization and then moving with an electric field, or perhaps by making iron foil and covering the installation, and then working in batches, where one vaporizes an iron pellet, so-that the platinum-group metals remain in the pellet holder and the volatile metals are deposited on the iron foil, which is then dumped and the cycle repeats.
This is the only method that could be done with existing technologies, with minimal improvements over them.
However, it would not be worthwhile, as the cost of extracting thus platinum-group metals from an asteroid would be many times greater than on Earth.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#40Earlier quoted context omitted.
You cannot use a centrifuge to separate solid iron. Using a centrifuge with liquid iron would create a gradient of concentration of the heavier elements dissolved in it, but that would not be enough to separate them. All that could be done with a centrifuge with liquid iron would be to obtain an iron alloy enriched in heavy elements. However, I doubt that it would be possible to make a centrifuge for liquid iron that…
Iron and platinum have different melting points. If you melt the alloy, then spin it to concentrate the platinum, couldn't you coax the platinum to separate out as solid clumps by adjusting the temperature? Alternatively, there are differences in magnetic properties that could be exploited... This isn't my field, so I'm just spitballing. I bet if you can get the cost of launch and interplanetary transit to be low eno…
Different melting points are easy to exploit only when metals do not mix in liquid state.
Even when metals do not mix in solid state, but they mix in liquid state, that usually cannot be used for separation, because the liquid solution will become solid at a temperature different from the melting temperatures of the components and lower than them, and the solid alloy will consist of the component metals intimately mixed at the level of microscopic crystals, so you cannot separate them (this is called an eutectic alloy, like the lead-tin alloy used for soldering, where by solidifying it you do not obtain separate lead and tin, but just a non-separable alloy, and by remelting the solid alloy you obtain a liquid solution, where again, the metals cannot be separated).
If the metals also mix when solid, the solid metal is a solid solution that does not melt at any of the melting temperatures of its components, but at an intermediate temperature, and the metals cannot be separated regardless whether the alloy is solid or liquid.
Here, in asteroid cores, the precious metals are present in a very small proportion, so they form either a liquid solution when molten or a solid solution when solidified.
The melting temperatures of platinum et al. do not matter, the melting temperature of the alloy is slightly lower than that of iron, corresponding to that of an iron-nickel alloy. The other alloying elements are in quantities small enough that they have negligible influence on the melting temperature.
In conclusion, differences in melting points can only very seldom be exploited for metal separation and they cannot be used for the iron alloys of planetary or asteroid cores.
You can exploit only either the difference in boiling points or the differences in chemical reactivity with acids or oxidizing agents.