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Scientists crack a 20-year nuclear mystery behind the creation of gold
21–30 of 43 posts
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#22Earlier quoted context omitted.
Platinum is also a peak of element abundance, together with its neighbor elements. So any model of how the elements have been produced must explain why the probability of making platinum and its neighbor elements, osmium, iridium and gold was higher than the probability of making other elements. The existence of other abundance peaks is easier to understand, e.g. the peaks at tin and at lead happened because these 2…
>concentrating one gram of platinum from one ton of iron would be tremendously difficult, requiring a huge amount of energy. melting one ton of iron requires 500KWh, 12 gallons of gasoline, less than $100 on Earth. Or 5 Tesla car batteries fully charged by say 30x30 m solar array in 2.5 hours - cost nothing in space once you got the hardware there. This is why mining in space is going to be a pretty big thing once/if…
> melting one ton of iron requires 500KWh, 12 gallons of gasoline, less than $100 on Earth
The spot price for platinum today is $68, so you'd be losing money doing it.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#23Earlier 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…
Your calculation assumes the heat must be considered wasted, but what prevents a counter-current heat exchange configuration from attaining ridiculously higher efficiencies? not to speak of just using saner approaches like chemical separation (gold and iron are very different chemically)
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#24Earlier quoted context omitted.
Platinum is also a peak of element abundance, together with its neighbor elements. So any model of how the elements have been produced must explain why the probability of making platinum and its neighbor elements, osmium, iridium and gold was higher than the probability of making other elements. The existence of other abundance peaks is easier to understand, e.g. the peaks at tin and at lead happened because these 2…
> in proportions of less than 1 part per million. How much less? I believe most gold produced in the US is from ore with under a half ppm gold (E.g open pit mines in Nevada). Maybe the point there is that we already have practically endless supplies of quarter ppm ore ready for the taking on the surface of the earth. Gold is rare only in so far that the current price reflects the breakeven point of these most abundan…
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 "endless supply" of gold ore with a quarter ppm gold, because the average concentration of gold in the crust of the Earth is a few parts per billion, so the few places where the concentration is as high as a fraction of a ppm are compensated by vast areas where the gold concentration is much less than one part per billion.
While an asteroid may have a lot of iron containing 6 ppm of platinum and a little less than 1 ppm of gold, that is not comparable at all with a terrestrial ore with 1 ppm or a few ppm of precious metals.
The precious metals are the easiest to separate from rocks, which is why one can exploit on Earth ores with a so low content of metal. On the other hand, precious metals are very hard to separate from iron, which is the very reason why in any planet or asteroid these metals end up being dissolved in the iron core.
So the extraction of platinum or gold in so small quantities from iron would be extremely expensive on Earth and much more so on an asteroid, where it is impossible to produce most of the chemicals used on Earth, like acids or cyanides.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#25Earlier quoted context omitted.
> in proportions of less than 1 part per million. How much less? I believe most gold produced in the US is from ore with under a half ppm gold (E.g open pit mines in Nevada). Maybe the point there is that we already have practically endless supplies of quarter ppm ore ready for the taking on the surface of the earth. Gold is rare only in so far that the current price reflects the breakeven point of these most abundan…
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?
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#26Earlier 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…
Your calculation assumes the heat must be considered wasted, but what prevents a counter-current heat exchange configuration from attaining ridiculously higher efficiencies? not to speak of just using saner approaches like chemical separation (gold and iron are very different chemically)
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 transfer efficiently heat to the iron that must be vaporized.
Even if some heat would be recovered from the vapors, the losses due to imperfect heat transfer from fluid to iron might be greater than the recovered heat. Moreover, it is not clear what could be used as the working fluid, because those asteroids are depleted in volatile elements, so any fluid must be brought from elsewhere and any fluid losses would be irreplaceable.
Probably the easiest and most efficient way to heat iron until vaporization would be with an electron beam, but it would not be easy to ensure that the iron vapors do not destroy the installation and they condense in a safe place, from which the iron can be somehow evacuated.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#27Earlier 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…
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 would have a lifetime sufficient to process quantities of the order of one million tons of iron. I do not think that until now anyone has ever tried to make a centrifuge that could work with a liquid metal at such a temperature. Most materials lose their strength at such temperatures, so the risk of breakage for the centrifuge would be extremely high, a risk that is increased by how heavy iron is.
It is also not clear if such an enrichment of the heavy elements would bring a sufficient simplification to further processing steps to make it worthwhile.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#28Earlier 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…
>energy required to vaporize one ton of iron produces .... so you would need a nuclear reactor. it is less than 2500KWh - under $250 of nuclear generated power on Earth. The best - fastest and efficient - way to travel outside planet's LEO that is available today is solar or nuclear powering ion thruster, with only nuclear really beyond Mars. So anyway you come into the asteroid belt with a reactor. A submarine or ic…
You have forgotten many zeros.
If you produce a few grams of a precious metal, that cannot justify the trip until there.
To produce something of the order of one ton, which still seems too low to cover the expenses, you need to process something of the order of one million tons of iron.
With your estimation that could take several years.
In reality the energy consumption would be much greater, because one must cut chunks of iron and transport them to the vaporization installation, then also transport elsewhere the condensed iron.
So you would need a decent number of submarine like reactors in order to achieve an acceptable productivity.
There is no doubt that it would be feasible, but the problem is that at the current prices there would be no way to recover the expenses.
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#29Earlier quoted context omitted.
Your calculation assumes the heat must be considered wasted, but what prevents a counter-current heat exchange configuration from attaining ridiculously higher efficiencies? not to speak of just using saner approaches like chemical separation (gold and iron are very different chemically)
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 efficient
Re: Scientists crack a 20-year nuclear mystery behind the creation of gold
#30Earlier quoted context omitted.
True, but even with that, the amount of siderophile elements like platinum and gold in the crust is much less than in the core of the Earth ("siderophile" means that at the contact between molten iron and molten silicate rock such elements go into the molten iron). Without that impact, it is assumed that almost no platinum-group metals and gold would have remained in the crust.
> Without that impact, it is assumed that almost no platinum-group metals and gold would have remained in the crust. Wow, its wild to think of a counterfactual world without gold. Would those metals have emerged to the crust from volcanism or is that material not sourced deeply enough?
Volcanism at most brings material from the upper mantle, but usually such material becomes mixed with material from the crust, while ascending.
The mantle has slightly bigger concentrations of precious metals than the crust, but the concentrations remain many times smaller than in the core.
The reason is that both the mantle and the crust are made mostly of silicate rocks. The mantle is made of heavy silicate rocks and the crust is made of light silicate rocks, which float on the denser mantle.
The metals that are resistant to oxidation do not mix well with silicates, so they tend to segregate from them, and then, being heavier than rocks, they tend to descend towards the core. If they reach the core, then they dissolve into the melted iron.
When lava is expelled by volcanism, the precious metals contained in it usually separate from the silicates together with metal sulfides and arsenides, which makes them easier to find than if they were dispersed uniformly in the rocks. Other elements that ere much more abundant, for instance germanium and gallium, are harder to mine than the precious metals because they are not concentrated in distinct minerals but they are uniformly distributed in many rocks.