Solar furnace for metal extraction - would it work?

[Gigel]

I thought about a solar furnace prototype.

It is like this: light from the Sun is concentrated with a system of parabolic and plane mirrors on the surface of a rock, which is contained inside a vessel. The light and heat is not meant to reach the vessel, only the rock; the vessel could be cooled. The rock can be anything, like granite, basalt or a mineral ore. The light heats the rock to more than 3000 degrees Celsius and the rock materials are effectively vaporised and decomposed into component elements. I.e., the result is a mixture of atomic O, H, C, Al, Fe, Si, Na, K etc., with some compounds still. Now the resulting gases come out of the vessel at high speed and reach a cold surface or cold stream of gases.

The problem is: can the metals be separated from lighter elements in this device? I don't intend a perfect (100%) separation, but still a meaningful one (20-50% would probably do).

Does it need a flux of reducing gas (say H) to be injected into the vessel in order to avoid reoxidation of metals? Or could it do without it?

I think the elements should separate on their own without reoxidation because at a given temperature they have different thermal velocities (heavier ones move slower).

The purpose of the device is to be as simple as possible. It should make a good extraction means on other planets/asteroids, but even here on Earth.

 

[Bystander]

See:
https://en.wikipedia.org/wiki/Incongruent_melting

 

[Gigel]

Incongruent vaporisation may be of help here.

But I'm looking for something else: firstly whether the different thermal velocities can help with separation, and secondly whether the contact between the hot atomic gas and the cold surface can ensure condensation of metals on the surface without (at least complete) recombination with light elements. I assume that close to the solid surface of the rock vaporised gases have the same atomic composition as the rock, and any separation appears either during gas expansion or during condensation on the cold surface in front of the rock.

Useful temperatures would be 3000-5000 K, which would generate atomic gas and even plasma. Solar energy can give about 3000 K, with very good design maybe up to 5000 K (but it's hard). The limit is 5772 K, the temperature of the solar radiation, but that can't be achieved practically; beyond that a laser can be useful, but I don't plan that for now.

 

[Charles Kottler]

I recall watching a video a few years ago about a laser drilling project. Due to the differing thermal properties of the material in the rock, a stream of small fragments of rock was continually ejected from the contact point as the surface shattered. I think this is a more likely outcome than the vaporisation you are hoping for.