Metallic Oxides--->Oxygen+Metal?

[_The_Burn_]

I was thinking about native sourcing of materials for colonies and such, and my mind went to the iron oxides present on mars. I figured that the rust could be decomposed into iron and 02, most likely using energy from solar panels. Does anybody know how much energy would be required for this reaction?

[Kryten]

You'd need a reducing agent of some kind.

[KerikBalm]

I don't think you would, just an energy source.

For example, this was pointed out on the thread about greenhouses on mars and O2 concentrations getting too high (go look at that thread if you want more context).

http://en.wikipedia.org/wiki/Magnesium_injection_cycle

" The only by-products of this reaction are water and magnesium oxide. The magnesium (a common metallic element) is separated from the oxygen through a solar-powered laser process (the development of which is already well advanced) and is reused over and over again as fuel."

Edited October 21, 2014 by KerikBalm

[_The_Burn_]

You'd need a reducing agent of some kind.

Example chemical formula? (With energy required)

- - - Updated - - -

I'm starting to realize how much I've forgotten since I took chemistry 2 years ago...

[InfinityArch]

Example chemical formula? (With energy required)

- - - Updated - - -

I'm starting to realize how much I've forgotten since I took chemistry 2 years ago...

If you're looking for a purely spontaneous chemical process, I don't believe what you're asking for is possible, but you can use electrolysis to split oxides into the metal and oxygen gas.

2 Al₂³⁺O₃²⁺ (l)--> 4Al (l)+ 3O² (g)

which can be broken down into

Al³⁺+3e- --> Al

and

2O^2--4e- --> O₂

Note that the Alumina must be in the liquid phase for this electrolysis to be possible, and the melting point of Alumina at atmospheric pressures is 2,072ºC, meaning this process will be taking place in a high temperature furnace. You'd be using graphite electrodes in a steel container in the setup I saw, and the free oxygen at that temperature would readily react with the graphite to produce carbon dioxide, meaning you'd need at least one addition step to extract the oxygen.

Iron (II) Oxide melts at a "mere" 1,377ºC however, and searching around, I've found an MIT article on a process that uses and iridium-molybdenum electrode combination and various oxide slags as electrolytes to extract pure iron and pure oxygen from molten iron oxide. You'd need to be operating above the melting point of iron for this to work, which is 1,538ºC, and your options for electrodes becomes somewhat limited there. Which is where the Iridium comes in, serving as a high temperature anode in this process.

2 Fe₂³⁺O₃²⁺ (l)--> 4 Fe (l)+ 3O² (g)

Source: http://web.mit.edu/dsadoway/www/137.pdf

Now, as far as the energy requirements for this go, a big energy cost is going to come from heating the entire system to the necessary temperature, and I honestly don't know how to calculate the relative masses of the Iron (II) Oxide, the Silicon Dioxide, and the electrodes that would be required for this.

Edited October 21, 2014 by InfinityArch

[KSK]

If you're looking for a purely spontaneous chemical process, I don't believe what you're asking for is possible, but you can use electrolysis to split oxides into the metal and oxygen gas.

2 Al₂³⁺O₃²⁺ (l)--> 4Al (l)+ 3O² (g)

You could use a more reactive metal (as your reducing agent, as per Kryten's post). For example, thermite (or a thermite at any rate) is a mixture of iron oxide and aluminium. It needs energy to get started but once it has started, it's extremely exothermic. Lugging enough magnesium to wherever you're colonising is a different matter of course.

So lets think. Direct iron reduction looks promising. Take some synthesis gas (carbon monoxide and hydrogen) heat it up with iron oxide and you get iron, CO2 and water. Synthesis gas is most commonly produced by steam reforming methane (natural gas) which you could make in-situ using the Sabatier reaction:

CO2 + 4 H2 → CH4 + 2 H2O + energy

Mars has CO2 and you could obtain hydrogen from water hydrolysis. Alternatively (and probably more usefully), you could use the reverse water-gas-shift reaction to make your carbon monoxide directly without bothering to make methane first. Hydrogen from electrolysis again.

CO2 + H2 <====> CO + H2O. (to any chemists reading this - apologies for the dodgy arrows)

So yeah, making iron in-situ is quite feasible on paper. I'm not sure how much energy it would take though, and building a nice reliable set of reactors to make it work would be the real trick. Not to mention getting those reactors to Mars.

[InfinityArch]

You could use a more reactive metal (as your reducing agent, as per Kryten's post). For example, thermite (or a thermite at any rate) is a mixture of iron oxide and aluminium. It needs energy to get started but once it has started, it's extremely exothermic. Lugging enough magnesium to wherever you're colonising is a different matter of course.

So lets think. Direct iron reduction looks promising. Take some synthesis gas (carbon monoxide and hydrogen) heat it up with iron oxide and you get iron, CO2 and water. Synthesis gas is most commonly produced by steam reforming methane (natural gas) which you could make in-situ using the Sabatier reaction:

CO2 + 4 H2 → CH4 + 2 H2O + energy

Mars has CO2 and you could obtain hydrogen from water hydrolysis. Alternatively (and probably more usefully), you could use the reverse water-gas-shift reaction to make your carbon monoxide directly without bothering to make methane first. Hydrogen from electrolysis again.

CO2 + H2 <====> CO + H2O. (to any chemists reading this - apologies for the dodgy arrows)

So yeah, making iron in-situ is quite feasible on paper. I'm not sure how much energy it would take though, and building a nice reliable set of reactors to make it work would be the real trick. Not to mention getting those reactors to Mars.

From what I gathered, he was talking about going straight from Iron Oxide to usable iron and free oxygen however, and electrolysis would be the only way to do that in a single step, and it also has the advantage of outputting molten iron, which is separated from the electrolytes by its greater density. Given that you'd need to melt the resulting iron precipitate to its melting point to process it into steel or otherwise make it useful (for most purposes), electrolysis cuts out the middleman here.

Now that said, the fact that the system I proposed uses rare-earth electrodes means that purely chemical extraction of iron might be more economical.

Reading further, you have the "third option" of heating the oxide in the presence of hydrogen gas, which only requires temperatures of ~500ºC, though that's a "laboratory" method of producing metallic iron, and thus probably doesn't have the required yield to be useful on an industrial scale.

Edited October 21, 2014 by InfinityArch

[Raukk]

I'm curious of the intent behind this question. If you are thinking industry on Mars then I'd ignore getting any oxygen out. If you are thinking of getting breathable air, then plain Co2 (or maybe water) is your best source.

As for how much energy is used, I think the Wiki page for different metals or oxides would have that, I believe that Aluminum is around 50 Mega Joules per Kg. If I was going to Mars I'd want to bring a method of refining Aluminum, someone already mentioned you can make thermite and reduce iron with aluminum, and thereby getting 2 refined metals for the price of one.

[lajoswinkler]

I'm curious of the intent behind this question. If you are thinking industry on Mars then I'd ignore getting any oxygen out. If you are thinking of getting breathable air, then plain Co2 (or maybe water) is your best source.

As for how much energy is used, I think the Wiki page for different metals or oxides would have that, I believe that Aluminum is around 50 Mega Joules per Kg. If I was going to Mars I'd want to bring a method of refining Aluminum, someone already mentioned you can make thermite and reduce iron with aluminum, and thereby getting 2 refined metals for the price of one.

You do realize that aluminium, when it reduces iron from its oxide, is oxidized into aluminium oxide? You don't get 2 refined metals. You get zero. Iron made by such reaction is very dirty.

[_The_Burn_]

I was thinking that someone could get iron for construction and oxygen to breath using one process, instead of having multiple systems running which would require more infrastructure.

[linkxsc]

Sorry to butt in so randomly. But there was mention of the melting points for iron oxide and aluminum oxide (mars and lunar surface materials)

They mentioned the temps at atmospheric pressure. And a problem would be the new pure metal reacting with the atmosphere...

Well, if your doing this on mars. The atmosphere is mostly CO2, and is less than 1% the pressure on earth. So how would those factor into the melting, and electrolysis of metal? Sorry Id know but material science 1 the 1 class I havent taken out of my degree yet (money problems)

[_The_Burn_]

I assume the process would be done in a pressurized environment.

[lajoswinkler]

Sorry to butt in so randomly. But there was mention of the melting points for iron oxide and aluminum oxide (mars and lunar surface materials)

They mentioned the temps at atmospheric pressure. And a problem would be the new pure metal reacting with the atmosphere...

Well, if your doing this on mars. The atmosphere is mostly CO2, and is less than 1% the pressure on earth. So how would those factor into the melting, and electrolysis of metal? Sorry Id know but material science 1 the 1 class I havent taken out of my degree yet (money problems)

Air oxidizes hot metals. In vacuum, there'd be no need for covering the molten metal with dross all the time. That's the good part. The bad part is that lots of energy during electrolysis is spent on heating, and while that waste heat is easily vented on Earth by convection or air and conduction (actually, sometimes the problem is to save the heat, hence refractory material to insulate the reaction), in space it can conduct to the regolith poorly. The main path is radiative, but that's very inefficient, as we all know.

Look at how many radiators ISS has, and it deals with a lot less heat.

It would require serious chem-enginnering study to figure this out for a particular problem, but on the top of my mind, I'd say it would be very difficult to make such plant.

[Raukk]

You do realize that aluminium, when it reduces iron from its oxide, is oxidized into aluminium oxide? You don't get 2 refined metals. You get zero. Iron made by such reaction is very dirty.

If I was going to Mars I'd want to bring a method of refining Aluminum

I was assuming that if Iron was needed (Ferrous metals are useful) it would be easier to mostly refine the Iron oxide with excess aluminum for the refinery, then to purify the dirty Iron, being that iron melts at a lower temperature than is needed to refine it, I assume that would be easier to achieve.

I was thinking that someone could get iron for construction and oxygen to breath using one process, instead of having multiple systems running which would require more infrastructure.

I understand the thought, but I assume this is for a theoretical mars base. Because you need food to eat then you should just get your Ox from plants, Mars One has been getting flack because it would have too much Ox, not too little. If it was on the moon then there would be other problems but I think getting it from Metal is about the most energy intensive way to get Ox.

[InfinityArch]

Sorry to butt in so randomly. But there was mention of the melting points for iron oxide and aluminum oxide (mars and lunar surface materials)

They mentioned the temps at atmospheric pressure. And a problem would be the new pure metal reacting with the atmosphere...

Well, if your doing this on mars. The atmosphere is mostly CO2, and is less than 1% the pressure on earth. So how would those factor into the melting, and electrolysis of metal? Sorry Id know but material science 1 the 1 class I havent taken out of my degree yet (money problems)

Obviously the reaction would be occurring in a strictly controlled environment; but the free oxygen you're producing could potentially react with the purified metal, or the electrodes at the temperatures these systems would operate at.

I must reiterate that inorganic chemistry and the material sciences are not my area of expertise, but my understanding is that the melting point of metals and ionic compounds aren't particularly sensitive to reduced pressure; it certainly wouldn't reduce the heating requirements that much.

[InfinityArch]

Air oxidizes hot metals. In vacuum, there'd be no need for covering the molten metal with dross all the time. That's the good part. The bad part is that lots of energy during electrolysis is spent on heating, and while that waste heat is easily vented on Earth by convection or air and conduction (actually, sometimes the problem is to save the heat, hence refractory material to insulate the reaction), in space it can conduct to the regolith poorly. The main path is radiative, but that's very inefficient, as we all know.

Look at how many radiators ISS has, and it deals with a lot less heat.

It would require serious chem-enginnering study to figure this out for a particular problem, but on the top of my mind, I'd say it would be very difficult to make such plant.

The link I posted earlier in the thread proposed using an iridium-molybdenum electrode combination with a molten Silicon Dioxide electrolyte, and given that this plant would be designed to operate on the surface of Mars, you could potentially pump excess heat into subsurface (manmade) reservoirs of water, which could in turn conduct heat into the Martian crust.

[_The_Burn_]

Air oxidizes hot metals. In vacuum, there'd be no need for covering the molten metal with dross all the time. That's the good part. The bad part is that lots of energy during electrolysis is spent on heating, and while that waste heat is easily vented on Earth by convection or air and conduction (actually, sometimes the problem is to save the heat, hence refractory material to insulate the reaction), in space it can conduct to the regolith poorly. The main path is radiative, but that's very inefficient, as we all know.

Look at how many radiators ISS has, and it deals with a lot less heat.

It would require serious chem-enginnering study to figure this out for a particular problem, but on the top of my mind, I'd say it would be very difficult to make such plant.

Maybe the process could be done in a inert gas (like helium) so that the metal doesn't oxidize and the hot gas could be run through a heat exchanger immersed in a good coolant, like water. Better yet, the warm water could be used for powering the station.

[_The_Burn_]

What is the best oxygen output per pound rate for plants (disregarding the systems required for growing the plants)?

[_The_Burn_]

Actually helium probably isn't the best inert conductor of heat, and that would raise problems like extracting the oxygen or whatever reactant produced. I guess the oxygen could be distilled out but that would require lowering the temperature very low and would be hard to do on a industrial scale.